View Full Version : Godsent Revox A77. Questions.
Hi!
Great forum!
I registered a few months ago after purchasing a B77 MkII standard speed... I had question about it but then I figured things out after intense reading the service manual/googling. I found lots of info and hints here too.
In the meantime I managed to get ahold of another MkII, a high speed version that sounds quite a good notch better. It still doesn't have xlr jacks... which, after working with it for a while, became a tad annoying. Sounds great however. It's just not as convenient as I'd like it to be for what I do... I compose and produce music...recently started to mix down to tape as it does wonders to the music I make these days. www.myspace.com/thomasbelley).
A music store nearby is moving to a new location and I stopped as I saw they were emptying the basement. They let me steal this A77 Professional for 30 bucks. I feel like I was kissed by god... or at least like one lucky son of a b*. A few pics:
http://img245.imageshack.us/img245/8317/picture94mr2.jpg
http://img85.imageshack.us/img85/1056/picture89od7.jpg
XLR Jacks!!! YAY!
http://img222.imageshack.us/img222/4725/a77eraseaq5.jpg
http://img216.imageshack.us/img216/8407/a77recordheadmn8.jpg
http://img299.imageshack.us/img299/5635/a77replayheadjz0.jpg
While the heads have some wear, it doesn't seem to affect it much at all.
http://img216.imageshack.us/img216/4744/a77serialyy4.jpg
The serial number suggests that it was made around 1975, in the Mk IV "era".
It looks nothing like a mk III or IV though. Perhaps the "Pro" model always had that look.
It had about 2mm of gunk all over it. A sticker under it says "12/9/89"... I guess that's when it was serviced last time. I cleaned and degaussed it, loaded some Rmg SM900 and did a test. (Capstan didn't start at first, I'll get back to that.) It sounded so good and crisp that without realizing it I went back to work and started to mix down a track to it without further testing. I cannot think of any other machine half as complex that wouldn't completely go out of whack after twenty years of collecting dust... a car, bike, watch... you name it. I'm no engineer but I know this machine is just... wow. I raise my hat to Willi Studer.
I took some snapshots of the spectrogram... I used pink noise
Original signal:
http://img156.imageshack.us/img156/6990/digitalig8.png
And the output of the tape:
http://img172.imageshack.us/img172/7508/tapenn9.png
Note: the snaps were not taken simultaneously... the bumps move around a bit...
I thought that looked as good as it sounded. Unless my test is invalid for some reason, I'd say it's well up to specifications if not above. I'm let to assume it was calibrated for similar tape. I don't believe it can get much better than that. Unfortunately, for now, I can't hear how it sounds like when driving the tape hard as my console doesn't have enough output. I might crank the internal recording level and reduce the playback, so that my console can handle it... but I'd rather keep reading what I can before doing that.
At first, the capstan motor would not start at all, then a bit for a few seconds... on... off... etc. Then for a good hour it worked fine and I could verify that the speed is amazingly accurate. A little more so than my b77's. But then it started jerking again. Then less and less as I kept on messing with it and cleaning it further. Odd, I thought. Again, when it works, the speed is extremely accurate (on average, 2-4 ms drift in a four-minute song!!). I took it out of it's metal case and started to look for something wrong (lol). I did find something!!
See that variable resistor?
http://img249.imageshack.us/img249/1191/a77prof3cvresbentna0.jpg
Well, it sticks out a bit and it was bent when I took it apart. The reason? Inside the metal case there are, in the corners, four rubber cushions that separate the case from the aluminum frame of the machine by a few millimeters. These rubber things dried with time and got thinner. As a result the metal case got closer to circuits and eventually was resting on the resistor and it bent it. I carefully bend it back to it's original position, added pads inside the case and put it back on making sure the case didn't touch anything it shouldn't. I don't even know if the resistor affected is on a board that's related to the capstan speed/motor... I don't think it is. It still goes out from time to time. But last weekend it worked like a true soldier with no drops ever. Incredibly precise machine. But then it stopped yesterday while I was was listening to what I've done last weekend. Any hints? Erm... will it heal itself with time?:scratch2: ...it seems to be doing it progressively less and less. Hints?
There seems to be a lot of people who know Revoxes pretty well so here are a few extra questions
-Is there a reason why I should not replace the right aluminum spacer with a ball bearing roller like on the left? That would reduce friction and that's good no?
-Braking with the motors: once and for all, yay or nay?
-Can anyone confirm me that the electronics can handle the output of overdriven tape (in this case sm900 (equivalent to gp9))?
I will certainly have more questions as I go along...
Thanks in advance!
I'll start with the good news. The heads on the deck are shot!
Now, you may wonder - how can this be good? Well, it performs as it does with these heads. Throw in a set of new heads and you will be amazed.
And on we go with the ... better news. Yes, these machines are extremely tolerant to abuse, misuse and accidents. I once short circuited the capstan drive board and although I heard a spark and the machine shut down, I shut it off and on and it started again, no sweat.
It will not heal by itself necessarily, but with a little bit of help...
When you say it's dead - how dead? If you kick start the motor with your hand, will it roll or does the motor break the turn by hand?
The trimmer you show in the pictures is - I am almost sure - the capstan speed trimer. It was bent and you straigthened it. Is it perhaps broken? Does the rotating disk make good contact with the graphite part? Is perhaps the resistor / PCB soldering broken by the original event?
I would not recomment dismantling the capstan motor unless every other possible reason is eliminated. Too much work, lots of things can go wrong if you are not careful, and these motors don't seem to break.
A good place to collect some ammo is ftp://ftp.studer.ch/Public/Products/Revox/
where you can download op manual, service manuals, schematics AND modification technical bulettins.
Regarding your other questions:
Is there a reason why I should not replace the right aluminum spacer with a ball bearing roller like on the left? That would reduce friction and that's good no?
I think there is a reason. It is supposed to reduce flutter. I did replace that on my B77 and I'm not sure if it became worse or better, but I just received a Wow&Flutter meter and I am going to test both configurations for the right idler. Note that the PR99 has identical tape drive with the B77 but has the right spacer replaced by a tape motion/counter pulser idler wheel.
Braking with the motors: once and for all, yay or nay?
I think this is the most gentle way to break - rocking the wheels - switching from FF to REW, wait until the tape almost stops, then hit stop.
Andyman
03-11-2008, 02:38 PM
I'll start with the good news. The heads on the deck are shot!
Now, you may wonder - how can this be good? Well, it performs as it does with these heads. Throw in a set of new heads and you will be amazed.
From what I've read, he could probably get those lapped for a fraction of the cost, perhaps even do it himself. Mine look similar, but it still sounds great, so i'm not messing with it right away. I don't use my A77 that often, but I like the sound just fine. I probably will go the hand lap way eventually, but there's other fish to fry right now.
Nice score, BTW
Hey thanks a lot SaSi!
I'll start with the good news. The heads on the deck are shot!
Now, you may wonder - how can this be good? Well, it performs as it does with these heads. Throw in a set of new heads and you will be amazed.
Well... I just might do it. My standard speed B77 is new... litteraly. The heads have no flat surface. Only a hint that it has been used for a handful of hours. I'll have someone make the swap sometime. The heads on my HS B77 have quite less wear than that of the A77 and I did notice it replayed the A77 tapes a wee bit crispier... but it's not much. I thought it was possibly due to the "updated" electronics in the B77 Argh... I so wish my b77 had xlr jacks and more output level...
But yeah... the A77 sounds great as it is. It IS awesome news to hear it will sound even better with the other heads!:thmbsp: See, I'm not after exact reproduction... not with the music I'm making right now anyway. I won't mind shelfing up the high freqs a bit to compensate if there is a need for it.
I yet have to hear how the tape saturates... I have a feeling the head wear has much effect on the result.
When you say it's dead - how dead? If you kick start the motor with your hand, will it roll or does the motor break the turn by hand?
It will not kick start by hand... I'll usually let it alone for a while... then it goes erratically on and of for,say, a minute then it'll be good for another good while. FWIW(not much):I noticed telling it I love it sometimes worked. I swear to god.
The trimmer you show in the pictures is - I am almost sure - the capstan speed trimer. It was bent and you straigthened it. Is it perhaps broken? Does the rotating disk make good contact with the graphite part? Is perhaps the resistor / PCB soldering broken by the original event?
The soldering looked fine... but yeah it crossed my mind that, whether or not it is what's causing the prob, the rotating parts might have been warped and the contact affected.
I would not recomment dismantling the capstan motor unless every other possible reason is eliminated. Too much work, lots of things can go wrong if you are not careful, and these motors don't seem to break.
Yeah for now I'll keep telling her I love her and hope the problem keeps occurring less and less, although it will not likely go away all by itself. I like the idea of being able to work with it as much as I'd like while I get the money to get that problem fixed and the heads swapped on the machines. That means lots of labour cash I'm afraid.
Braking with the motors: once and for all, yay or nay?
I think this is the most gentle way to break - rocking the wheels - switching from FF to REW, wait until the tape almost stops, then hit stop.
Cool!
Oh... the erase depth seemed ok... will it likely be the same for a while? 'Cause I just read that the erase heads are not swappable between A's and B's
Oh... the erase depth seemed ok... will it likely be the same for a while? 'Cause I just read that the erase heads are not swappable between A's and B's
No they are not. As you might have already noticed, the A77/B77 heads, idlers and pinch rollers are identical. The erase head is totaly different between the two. However, for whatever reason, the erase heads on the Revoxes don't seem to suffer from wear. Harder ferrite perhaps.
Regarding general condition: I have a PR99 that I received in a condition similar to what you described. I had to soak the PCBs in hot tub water with washing machine detergent and then brush them with an old toothbrush (and then repeat it). Especially useful was this on the main audio board that had so much tar that the switches failed to make contact some times.
Regarding the capstan motor: It might be a failing motor. There are actually no contacts inside - the motors are I think inductive. I would say her I love her to get her started and then leave the deck running for hours on hours. IIRC the capsan motor starts as soon as power is applied. Not sure if it so in all versions of the A77. It is so in the B77s though.
If there is dirt to go, keeping the motor running will iron out that. If it is about to die, you will find out soon. A77 capstan motors aren't particularly expensive or hard to find on the German ebay. Have a look there, although a heavy box might cost about $40~50 to ship to the USA.
Regarding the heads: My PR99 had heads with exactly the same mirror wear. If I can see clearly, it's about 4-5mm (<0.2"). My PR99 sounded great, especially at 15ips. I did some measurements and realized that the highs were not stable. Recording at 0dB, produced a reproduction with a fluctuation of more than 2-3dB, increasing as frequency went up. I think this fluctuation is a good objective measurement of head wear. High frequency loss (>18~19kHz) starts once the heads are totally gone beyond relaping.
But of course, you should not be worried about the heads unless all other issues you know and a few you will probably discover down the road are resolved. Don't want to disappoint you, but breaks and pinch rollers will be a strange thing to work properly after almost 20 years of no action. They only seem to work now because these machines are indestructable.
KentTeffeteller
03-12-2008, 12:36 PM
Hi,
The pro version of the A and B 77 line is the PR 99 machines. They have balanced inputs/outputs. Your machine appears to be an original version or a MK II. You likely need to get that trimpot replaced that was bent. Yes, you do need heads. I would check with Jack Clark at J-M Technical Arts for parts and advice. He is at www.jmtecharts.com. Mr. Clark was the manager of the service department at Studer-ReVox America in Nashville, TN. He's expert on these machines. You might be able to find relapped heads reasonably. You could send yours to John French at JRF Magnetic Sciences. John does superb work and is worth it. He also has new heads for ReVoxes.
Nakdoc
03-12-2008, 01:00 PM
The B77 has significantly improved headroom over all the A77 versions, at least on line in. This is especially true at low speed 3 3/4. I always thought the heads were different based on the huge difference at low speed between the 2 models. A77 meters are just plain useless, so my beef with the A77 may simply be caused by the difficulty in getting record levels correct. You may loosen the cap on the idler and rotate to a fresh unworn surface. In theory as the aluminum wears the tape pack wind changes. I do not think a ball bearing would hurt things.
Regarding general condition: I have a PR99 that I received in a condition similar to what you described. I had to soak the PCBs in hot tub water with washing machine detergent...
Damn!
It was pretty clean inside, although a spider managed to build a web in there. it was only very dirty on the outside.
Regarding the capstan motor: It might be a failing motor. There are actually no contacts inside - the motors are I think inductive. I would say her I love her to get her started and then leave the deck running for hours on hours. IIRC the capsan motor starts as soon as power is applied. Not sure if it so in all versions of the A77. It is so in the B77s though.
If there is dirt to go, keeping the motor running will iron out that. If it is about to die, you will find out soon. A77 capstan motors aren't particularly expensive or hard to find on the German ebay. Have a look there, although a heavy box might cost about $40~50 to ship to the USA.
I turned it on when I got back from work yesterday... then sat down some hours later to make some music... it behaved perfectly the whole time...
It does seem to go on and off only during the first hour or so after powering on.
I'll see how things go as I gather the money to get the head swapping done.
You know, it's very possible that the capstan motor has done it's share of spinning. The heads don't show as much wear as the rest of the tape path does, If my judgment is correct. I assume they were probably replaced at some point.
http://img292.imageshack.us/img292/9185/picture97fr4.jpg
There's a mirror there too!
http://img292.imageshack.us/img292/5029/picture98al4.jpg
Regarding the heads: My PR99 had heads with exactly the same mirror wear. If I can see clearly, it's about 4-5mm (<0.2"). My PR99 sounded great, especially at 15ips. I did some measurements and realized that the highs were not stable. Recording at 0dB, produced a reproduction with a fluctuation of more than 2-3dB, increasing as frequency went up. I think this fluctuation is a good objective measurement of head wear. High frequency loss (>18~19kHz) starts once the heads are totally gone beyond relaping.
Hey that's interesting. Tell me one thing: Over the course of how much time would one of these fluctuations occur? Fraction of a second... a few seconds?
But of course, you should not be worried about the heads unless all other issues you know and a few you will probably discover down the road are resolved. Don't want to disappoint you, but breaks and pinch rollers will be a strange thing to work properly after almost 20 years of no action. They only seem to work now because these machines are indestructable.
I'm not worried at all! I dig how it sounds right now and it blows me away that it will get better. I already got my money's worth...That thing cost me 30 dollars and has already captured a mix I'm very, very happy with. (I have an ep coming out in a week or so:banana:) It's really great that it sounds satisfactorily as it is, despite the occasional capstan failures. It's not like that synth I'm waiting to get fixed and that produces no sound at all in the meantime. It hurts to look at it.
Hi,
The pro version of the A and B 77 line is the PR 99 machines. They have balanced inputs/outputs. Your machine appears to be an original version or a MK II. You likely need to get that trimpot replaced that was bent. Yes, you do need heads. I would check with Jack Clark at J-M Technical Arts for parts and advice. He is at www.jmtecharts.com. Mr. Clark was the manager of the service department at Studer-ReVox America in Nashville, TN. He's expert on these machines. You might be able to find relapped heads reasonably. You could send yours to John French at JRF Magnetic Sciences. John does superb work and is worth it. He also has new heads for ReVoxes.
I'm in Montreal. I actually found an old German tech that knows them inside out... but he's such a character... not the kind of guy I want to bother too much. Anyway... when I'm ready I'll bring him my A77 and the standard B77 for the head swap and that ill trimpot... and possibly whatever causes the capstan motor to behave. But thanks for the link!
The B77 has significantly improved headroom over all the A77 versions, at least on line in.
Hm... Before I have anything costly done on it, I think I am going to crank the recording levels a bit to see how things sound when the tape saturates.
It'd be nice to find a PR99... I already have two machines I could cannibalize to back it up. I'll have fun with what I have for now.
The heads don't show as much wear as the rest of the tape path does, If my judgment is correct. I assume they were probably replaced at some point.
It is not very easy to judge wear of the tape path vs wear of the tapes. The deck can work in two modes:
1. Normal play --> Heads into contact, Head Guards out of contact. Heads are worn.
2. FF/REW --> Heads out of contact, Head Guards into contact. Guards are worn, heads are safe.
(There is a third mode, CUE active, but that is equivalent to mode 1).
A deck's guards can become totaly worn if it is used for FF/REW of tapes over a week's time. OTOH, a deck that is used for PLAY and seldom used to FF/REW tapes, will have mint guards and worn out heads.
In normal mixed scenarios, both elements will be worn out.
Thanks SaSi.
Well... the capstan motor has been great this week. Less great was me when I pressed play on the remote then stopped, ffw'd then stopped again on the machine's transport with the play button still pushed in on the remote. Oh that noise... nasty... CLAKRUNCH!!
Ok... it seems I'll have to bring it to the tech after all. Capstan is fine. Now for some reason when I press play it stops immediately... the reel motors barely make a turn and the pinch roller doesn't get to rest on the capstan before it stops by itself... oh and using the remote does even less... nothing moves. It's like if the stop button was constantly pressed.
Sounds familiar?
Could it be anything I can fix myself? Anyone...
I was having such a good time... :(
Well, if the motors try to make a turn and stop, it looks like something is negating play.
You mention the remote control. Perhaps it conflicts with something. Tried disconnecting it?
More likely though I would suspect the tape end sensor found next to the ERASE head. If the deck senses no tape, it won't move. There is a light bulb and a sensor. Try blocking light to the sensor to see if the motors will engage.
Thanks SaSi.
Yeah... tried all of that but it wont change anything. I n fact the light bulb is slightly defective, by which when I push it back it lights up and when I push it up it turns off. Note that it will take a few seconds before pressing play again does something at all (If I press it repetitively it will do nothing)... and that nothing will happen at all if the bulb is lit up. I should have mentioned these observations before.
Sighhhh...It was working so well. *heartbroken*
Karma16
03-23-2008, 03:47 PM
HI,
With heads as worn as these you will not be able to adjust the azimuth or height in case you had that in mind. Even if the angle is changed, the tape will continue to follow the old path and there is nothing you can do about it. If you are happy with the frequency response performance, just leave the heads as they are.
If you are not happy then the only answer is replacing the heads. I really don't know if lapping Revox heads is possible. Some heads, like Ampex, have extra deep pole pieces and can stand lapping. I suspect the Revox heads have shallow pole pieces. I'm skeptical about lapping because of the required precision but if the heads are shot you have nothing to loose.
Nice machines. I hope you can fully bring them up to spec.
Sparky
Hi!
With heads as worn as these you will not be able to adjust the azimuth or height in case you had that in mind. Even if the angle is changed, the tape will continue to follow the old path and there is nothing you can do about it.
Yeah I'm 99% sure I've heard the cleanest sound that can come out of that thing... I was very happy before it went wrong. It sounds fabulous for my purposes and these heads will stay there for now it seems. Ah well...
I literally fell in love with the way this machine colours and "wraps", glues a mix together. It does it with quite more character than my B77 hs (and that makes me realize it might be pointless for me to look for a big, ultra transparent Studer or whatnot when what I look for is saturation and artifacts). That and the fact that it was nearly given to me just in time makes this failure one nasty party breaker. I really thought that I had found my machine...
I wouldn't freak out so much if I wasn't so dam broke. My 70ish german deck wizard will work it out. Quite a guy this guy. Here is his buisness card if you're in the Montreal area (he doesn't have a website... and never will):
http://img513.imageshack.us/img513/9933/cdmmtz7.jpg
Your wizzard appears German from the name. Perhaps he doesn't know of ebay, but perhaps he could help you identify the proper parts in the German ebay. It's full of parts for revox R2R machines.
Also, make sure you give the expert the service manuals for the A77 machine. Helps a lot when troubleshooting.
Hi!
Hey after closer inspection of the fuses (a friend advised I double check), I saw one of them is blown:
http://img174.imageshack.us/img174/6646/psuflechefi0.jpg
It really wasn't obvious... the little wire inside broke near one of the ends and there is only a tiny tiny mark of ... uh...burnt (my english...). I was supposed to bring it to Mr. Ungerleider tomorrow. I'll replace that fuse instead and see. :) I feel relieved already but I'll wait before I throw a paty. Maybe something is shorted inside, I fear.
I hope they have those at RadioShack... it has little ball in the middle...
Edit- I've been living in this flat for almost a year now and fuses blow a lot here.
Now, that's better...
Since you are going fuse shopping, I suggest you take a look at the fuses inside the deck and buy a box of each. They are dirt cheap but can be frustrating when you don't have the proper ones around.
Pay extra attention to the specs of each fuse, especially if some fuses are slow blow (sometimes denoted by a SB on the fuse edge). Slow blow fuses should be replaced with normal ones, as normal ones will tend to blow easily. Normal fuses again MUST NEVER be replaced with slow blow as the fuse won't blow fast enough and the damage will be done.
I strongly doubt there is anything fuses or shorted inside. These machines were built to last a lifetime and withstand serious abuse. That's why the Revox service centers still stock original spare parts for these machines. Many of those are still around and they don't break often to consume the spare parts inventory.
:banana::thmbsp::yes::D
It's alive!!!
:thmbsp:
Good for you. Is that your first score in troubleshooting?
On a tape deck?... well I can't call this troubleshooting... or I shot myself. I'm the incompetent that didn't see a fuse was blown. oh... I fixed my Tascam four track when I was 14 or so.
uhm...BUT... I'm a pro bike mechanic. I can feel what vibrations come from where... I can feel the bike. Also, with time it's like I've developed a sense for different metal's rigidity from touching it, especially when truing a wheel.
I once heard Bob Moog in a doc saying something similar about circuits...
I'd love to learn about electronics... In fact, I was able to spot the problem in my Yamaha CS-40m from looking at the schematics and googling. I needs a new capacitor I'm certain. I just need to trust myself for the simple unsoldering of the cap and soldering the new one. I will leave that to a pro still (I want that thing to sing again... and I don't want my noobness to cost me an oscillator that's as rare as pope poop)... I'd rather attempt building myself a nice mic preamp... ah... a tube compressor wouldn't be a luxury either.
I'm buying this off the provincial government :
http://img516.imageshack.us/img516/2713/42a320mb4.jpg
It's an actual picture of the one I'm getting.
They wanted 375$ for it. I asked if they could put it aside for me and the fine woman in charge asked "How much could you give for it now?" I replied "Dear god..200... and it would break me off pretty bad!" We spoke some more and she said "I"ll let you have it for 150. It's yours. Take your time."
I'm picking it up on Monday when my roomie is back from tour with his truck.
:banana:
Can't wait.
I'm going to put my good heads on this one. Then probably sell a deck or two. Or bring one in the living room and ditch the Akai...:scratch2:
What I like of the Pr 99 a lot is that I'll be able to smash the tape at the recording stage and turn the output level down to have a reasonable level for the soundcard/console. That is so cool. Yes yes.
I had to edit this post a million times because I'm so excited and make no sense.
Excellent find. And a bargain price for that.
I really hope you enjoy it.
I will certainly.
I don't even know how the heads are... All I know is that it was in use when taken out of service. Usually, the government looks after its stuff pretty well. If the heads are not shot, I'll just take that as a bonus.
I might get it tomorrow!
Got it!!
http://img169.imageshack.us/img169/1551/picture21pj8.jpg
Same head wear as on the a77... but the surface doesn't seem as flat... Sure enough, it sounds amazing.
I'm stoked.
Congratulations.
I notice in the photos that the unit appears to have a panel attached in the base. The normal Revox mounting system doesn't (IIRC). This panel is covering the set of trimmers designed to be accessible from the base to calibrate the unit for special tapes.
If that panel comes off without affecting the rest of the mount, I suggest you give that a try. It also would look cooler, IMO.
Yeah, you only have to take out four screws, the panel comes off and you have access to the calibration controls.
It has some problems... one of the vu's needle doesn't work, both lamps are out. The peaks leds work fine, and that's what matters most to me. I can live with one working vu. The input/repro switch isn't very clean, neither is the monitor selector (left, reverse, stereo, mono...), that one is pretty dead. These things need to be fixed. I wonder if normal parts could do. It needs calibration... of course. But new heads, really.
The recording settings are completely out of whack... so I can't work with it right now. The highs are rather harsh. It's calibrated for tape way different than the ones I'm using.
I'm thinking that I should maybe attempt "calibrating" it myself and have some fun with it while I put money together to get the heads installed etc. I will. I have nothing to lose.
I did it!
Btw, I found some good tips you posted around here Sasi. You rock.
I made myself a "reference tape" using my b77 that is perfectly tuned and I used an analyzer and a test tone generators on my computer. Of course I didn't touch the azimuth adjustment screws. I was able however to get both channels sounding very equal and the frequency response is flat. The bias was easy to adjust (the magic number was 4.5).
Question: The "repro treble" screws... are they there only to compensate for high frequency loss due worn heads? It seems they were set way too high... that's what playing back the pink noise on my "reference tape" showed....
Another question... I'd like to get more tape saturation. I'll have to recalibrate either the input level or the recording level. Wich one should I "supercharge"?
Thanks!
Treble controls: These actually are there to compensate for the playback. The idea in calibration is to make everything as flat as possible. While, in theory, you could boost rec equalization to compensate for playback loss, any tape recorded on that machine would be unusable on other machines.
In the same way, you should not over-saturate the tapes, but again, it's your game. I believe the best approach is to distribute the increase to both parts. At the same time increase the bias slightly (to control distortion) and also increase the treble settings for playback to compensate for highs loss due to increased bias and rec level.
Also, and while it is fun and educational to calibrate the deck with worn and un-adjusted heads, you should not expect top performance out of it.
Wow this is so much fun... and rewarding. I've been experimenting quite a bit between long minutes of thinking and looking at the block diagram. I ended up fine-adjusting the bias' and record eqs by listening and looking at the frequency analyser on the computer. The calibration screws happen to be at near-identical positions on both channels. Now it sounds very very good. The "head bump" is pretty heavy though, far more noticeable than on my B77 ... not that I hate it that much. For that matter, turning the tape speed up opened up a whole new can of worms. I had barely touched that knob so far. I think I'm going to put a sticker on top of "variable speed" so that it says "variable flavor". I'll experiment some more as mix a track to it but it seems that speed knob will have a use I didn't expect.
I sooo love that reproduce level knob!! It makes things much easier.
I spoke to my tech and swapping the heads will be costly... it's not for now.
stevevdb
05-03-2008, 02:11 PM
revox is always costly when it comes to spares.
when you order them directly from revox germany don't be surprised by the high prices.
you can find almost any part for the revox machines on ebay.de and mostly a lot cheaper.
I have several revox machines at home, mostly bargains but mostly a lot of work needed to be done.
European prices
a good B77: 250 us dollar
a good PR99: 600 US dollar
A77 mkIV: 150 us dollar
C270 (any condition): 2000 us dollar
C274: 2000 us dollar
C278: 3000 us dollar
If you can get them cheaper: go for it.
I spoke to my tech and swapping the heads will be costly... it's not for now.
How much? In the German ebay, you can find suitable heads in almost every possible condition, from worn out and useless to unused.
Prices seem to vary from 45 euro for a head-stack with heads in unknown condition to more than 150 euro for a single head unused.
I have replaced my deck's heads with unused Nortronics heads for a cost around $200 incl. shipping. The heads aren't identical to the huge Revox heads and the back cover in the headshells must be either removed or modified.
The new heads give a totally new level of performance and calibration and head alignment makes sence only with new heads.
stevevdb
05-04-2008, 02:27 AM
How much? In the German ebay, you can find suitable heads in almost every possible condition, from worn out and useless to unused.
Prices seem to vary from 45 euro for a head-stack with heads in unknown condition to more than 150 euro for a single head unused.
I have replaced my deck's heads with unused Nortronics heads for a cost around $200 incl. shipping. The heads aren't identical to the huge Revox heads and the back cover in the headshells must be either removed or modified.
The new heads give a totally new level of performance and calibration and head alignment makes sence only with new heads.
Buying new heads for a revox is indeed very pricy. When you buy them from revox you'll propably end up paying around 175 euro's for one head (2 track that is, the butterfly heads are around 500 to 600 euro).
KentTeffeteller
05-04-2008, 08:08 AM
Hi,
Typical USA prices for a complete A-77 headstack from ReVox USA (JM Technical Arts) is $500 plus. Not out of line for a semi-professional machine. The same headstack for an Otari is about $600. Reasonably priced indeed!
Yeah I think these prices are fair... considering the performance these machines provide.
But as I wrote earlier, I will most likely cannibalize my mint standard speed B77's heads to put them on the pr-99. It's the labor that will cost quite a bit.
I can't complain really... I already have the needed parts.
It might take a while before I have it done because when I actually sit down and make music, I use tape mainly as a process and go way in the red. While I'm very, very curious to hear how it sounds when in top form, as Sasi made me clearly understand :
Treble controls: These actually are there to compensate for the playback. The idea in calibration is to make everything as flat as possible. While, in theory, you could boost rec equalization to compensate for playback loss, any tape recorded on that machine would be unusable on other machines.
In the same way, you should not over-saturate the tapes, but again, it's your game. I believe the best approach is to distribute the increase to both parts. At the same time increase the bias slightly (to control distortion) and also increase the treble settings for playback to compensate for highs loss due to increased bias and rec level.
Also, and while it is fun and educational to calibrate the deck with worn and un-adjusted heads, you should not expect top performance out of it.
...going this far with the recording levels to get artifacts defeats the purpose of trying to obtain a remotely flat response at the nominal level. Let alone with worn heads; I find tape residue builds up quite fast on the edges of the heads' "mirrors" and even near-invisible amounts of residue will affect the high frequencies considerably, but not enough for 90% of the uses I make of it when I get to real work. Also, I don't really need the recordings made on the pr99 to be played back faithfully on the other machines at all so... "Custom calibration" is what I'll call my new hobby for a while. I even fantasized about a remote control with knobs for the calibration settings. That would kick serious ass.
Cleaning the heads very often does the trick...and that leads me to a question. My roommate noted that I use tons of q-tips and said "this is not very ecological dude". I had to agree. I wonder if there is a suitable, reusable lint-free material out there I could make myself cleaning thingies with. Ideas?
I am all into protecting the environment, but do you re-use your cotton swabs when you clean your ears?
However, since the Revox heads are "enormous" compared to others, you could use small pieces of cotton moist with alcohol to clean them by hand. This actually results in a better cleaning as the cotton mass goes everywhere inside the shell. Cotton by itself in the bin is environment friendly.
Regarding the head swap: I am also scheduled to do a head swap on my PR99. I have a set of full track heads to test, a set of Nortronics heads to re-install using optimized studs and also a set of quarter track heads to try. I am thinking of making this an illustrated thread. Would that be of interest?
I am all into protecting the environment, but do you re-use your cotton swabs when you clean your ears?
However, since the Revox heads are "enormous" compared to others, you could use small pieces of cotton moist with alcohol to clean them by hand. This actually results in a better cleaning as the cotton mass goes everywhere inside the shell. Cotton by itself in the bin is environment friendly.
Cool.
Regarding the head swap: I am also scheduled to do a head swap on my PR99. I have a set of full track heads to test, a set of Nortronics heads to re-install using optimized studs and also a set of quarter track heads to try. I am thinking of making this an illustrated thread. Would that be of interest?
Absolutely!!
I was just about to ask if you could post a picture of these Nortronics heads.:thmbsp:
This (http://www.pbase.com/sidiropoulos/pr99) is a gallery of the process of replacing the PR99 Revox heads with Nortronics heads. The photographic site allows for high resolution pics, but text and descriptions are limited. I may make a thread with lowres pics and have links to the high resolution ones. Some of the details are simply lost in the lores versions.
Hey hey!
The A77 has been great in he last months. No capstan problems except... It runs a wee bit slow (at 15ips at least) and needs a fine adjustment. It's been like that from the beginning. Not a problem until now.
I've been searching in the service manual that I have... trying to find the proper trimmer but my version sems to be a bit different (it's the ORF model). I'm not 100% certain but I believe it is this trimmer (it's the very same one that was bent when I got the machine):
http://img363.imageshack.us/img363/6966/dsc00079arrowsb3.jpg
Can someone confirm that it's the one? There is another board exactly like that one right behind it... one for each speed maybe?
It wasn't a problem until now... I have to playback tapes recorded on other machines.
Thanks :)
Edit:
It seems these two boards are actually the power amps. They are placed differently on the diagrams I found. The trimmer I'm looking for (P201) is on the horizontal board next to thecapstan motor...
Well I tried... tweaking that timmer (p201) didn't do anything. The sine tone on the tape was still a bit flat by 6hz. Hm. I didn't move it too much, seeing that it didn't do anything I set it back to where it was...approximately:sigh:
Looking at the pictures you posted makes me wonder what is in there. It doesn't resemble the diagrams in the service manual. And not having seen a single A77 from the inside, I am not sure what is what in there.
But, the service manual describes how speed is adjusted:
Switch to 7.5ips,
Load the test tape and press play,
measure the resulting frequency,
Adjust to core of discriminator coil T201
Then switch to 3.75ips (after having adjusted 7.5ips),
Adjust trimpot P201.
I have no idea where these are located (the service manual isn't really helpful without a machine) and you point that you adjusted P201 on a board that isn't really described in the manual. And you say there are two such identical boards?
I don't know, I am a bit lost, but it might be that your machine is newer and different than the single service manual I have for the entire range (MkI ~ MkIV) without any reference to Mk versions.
It might be that your machine has different capstan speed control and each board controls one speed. You might have adjusted the trimpot for the wrong speed?
Sorry I cannot be more helpful...
vBulletin® v3.7.4, Copyright ©2000-2009, Jelsoft Enterprises Ltd.