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Marantz Model 33 restoration
- Thread starter MrJackson
- Start date
I finally got to working on this, due to huge delays on part deliveries. Thanks global pandemic!
Anyways, I redid the power supply board and it all seemed to work smoothly (got +/1 15V after a quick adjustment of the trimpots). I was just about to start working on another board, but I decided to connect the power supply and see how it sounds... here things seem to have gone downhill, since I noticed a very annoying 100hz hum on the headphones out (I don't remember having this hum initially, but I didn't give it much of a listen as the headphone out didn't sound like much out of the box). I then connected the preamp to my 1060 power section (like I previously used it for about a month) to see how it behaves and honestly I don't think it has more hum than the 1060 on it's own, but it's still a bit too much.
I looked for an imbalance in the bipolar supply, but found none. Connected my scope to the outputs and noted a 2.5mV ripple (50hz) on each output - it's not a lot, but it's still something. Wish I did that before I rebuilt the board to have a baseline...
Any suggestions would be welcomed. I'm positive that hum wasn't there initially and I can't really figure out what could cause it, especially since how I'm using bigger caps (upgraded the 4 of the 6 reservoir caps from 470uF to 680uF). BJTs are now BC550 / BC559, JFETS are a complement of J111 and J175, while the metal can BJTs are 2N2219A and 2N2905A.
Before:
After:
Anyways, I redid the power supply board and it all seemed to work smoothly (got +/1 15V after a quick adjustment of the trimpots). I was just about to start working on another board, but I decided to connect the power supply and see how it sounds... here things seem to have gone downhill, since I noticed a very annoying 100hz hum on the headphones out (I don't remember having this hum initially, but I didn't give it much of a listen as the headphone out didn't sound like much out of the box). I then connected the preamp to my 1060 power section (like I previously used it for about a month) to see how it behaves and honestly I don't think it has more hum than the 1060 on it's own, but it's still a bit too much.
I looked for an imbalance in the bipolar supply, but found none. Connected my scope to the outputs and noted a 2.5mV ripple (50hz) on each output - it's not a lot, but it's still something. Wish I did that before I rebuilt the board to have a baseline...
Any suggestions would be welcomed. I'm positive that hum wasn't there initially and I can't really figure out what could cause it, especially since how I'm using bigger caps (upgraded the 4 of the 6 reservoir caps from 470uF to 680uF). BJTs are now BC550 / BC559, JFETS are a complement of J111 and J175, while the metal can BJTs are 2N2219A and 2N2905A.
Before:
After:
That's one keen eye you got there. Fortunately, I noticed the same thing before I plugged it in, so I changed them before testing, but I didn't snap another picture - they are mounted correctly at this time, so that's not the cause of the issue.
One thing that struck me as odd since the beginning is that whoever did the 220V conversion did it wrong (tied together the white and brown wires of the trafo's primary, instead of the black and gray. I don't think this affects it negatively, but I will investigate further.
@ocdecio, if you have a change, could you do a headphones test with yours?
If the hum wasn't there it can't be because of the transformer wiring. I tested mine with headphones and it works OK, this model has a separate amplifier for them but it bypasses all tone controls. I wonder if you got a cold joint somewhere. These issues are the hardest to track...
These are the notes in the manual that I found insteresting:
The manual also asks to look for the very caps you swapped to troubleshoot hum and noise so therec ould be something there:
These are the notes in the manual that I found insteresting:
The manual also asks to look for the very caps you swapped to troubleshoot hum and noise so therec ould be something there:
I'll have a look... maybe there's a bad solder joint somewhere indeed. I'll check those caps once again, maybe take out a pair - that should increase the AC ripple at the output. Either way it's strange that with "better" parts it seems to behave worse.
Okay, so pardon my ignorance, but how the heck do you get access to the filter/center channel board? I'm having some weird readings there and haven't figured a good way to get to the bottom
You can access the bottom by removing the bottom panel; when I recapped I had to disconnect the switches/pots so I could wiggle it out enough. Everything is very tight in there and in my case I had the center channel wires breaking off the board so I had to reconnect them.
Out of curiosity, what weird readings did you get? Maybe we can help each other out.
I haven't had time to work on my unit lately, but I want to get back at it soon.
So I finally managed to get one of the preamp boards done, hooked it up today and… it’s partially working. Headphone amp works just fine, a bit more silent and less shouty than before.
However, I can get a proper output from the preamp outs. I’ve tried to narrow it down and I noticed the low level amplifier is working (didn’t have a TT at hand so I tested it with regular line level signal… distorted like crazy, as expected, but had output on both headphone channels. No dice on the preamp outs, so I’m guessing it’s either a bad connection or some part not connected properly. Also, the tone amplifier seems to be working, since I can get a faint signal when engaging it.
I’ll try to go at it again tomorrow, but it’s a real pain to connect these boards. I’m considering testing it outside of the preamp, wiring up just the power supply and some loose wires from a signal source.
However, I can get a proper output from the preamp outs. I’ve tried to narrow it down and I noticed the low level amplifier is working (didn’t have a TT at hand so I tested it with regular line level signal… distorted like crazy, as expected, but had output on both headphone channels. No dice on the preamp outs, so I’m guessing it’s either a bad connection or some part not connected properly. Also, the tone amplifier seems to be working, since I can get a faint signal when engaging it.
I’ll try to go at it again tomorrow, but it’s a real pain to connect these boards. I’m considering testing it outside of the preamp, wiring up just the power supply and some loose wires from a signal source.
I find it odd that both channels are equally not working - it sounds like a missing or bad connection. And yes it is a pain to connect the boards, when I recapped mine I disconnected the bare minimum wires and worked with the board slightly raised.
Lavane
Lunatic Member
I restored a 33 about ten years ago. Luckily all the transistors were good. No leaks or noise. It was a later version that had all the service bulletin updates.
The 33 is a bit of a pain to get to all the boards for sure. I didn't notice reading through your thread, did you have any noise or problems with the phono board?
I didn't whole sale replace resistors in mine since tight tolerance resistors were used originally. I really didn't want to change the sound of this one, so pretty much replaced caps and other parts with same type except for the tantalums.
I used audio grade low ESR electrolytics to replace them. I have used Wima caps in a lot of other Marantz seperates, but with the 33 preamp and matching model 16 power amp I wanted to restore them as stock as possible.
Nice work on yours so far, its looking good.
The 33 is a bit of a pain to get to all the boards for sure. I didn't notice reading through your thread, did you have any noise or problems with the phono board?
I didn't whole sale replace resistors in mine since tight tolerance resistors were used originally. I really didn't want to change the sound of this one, so pretty much replaced caps and other parts with same type except for the tantalums.
I used audio grade low ESR electrolytics to replace them. I have used Wima caps in a lot of other Marantz seperates, but with the 33 preamp and matching model 16 power amp I wanted to restore them as stock as possible.
Nice work on yours so far, its looking good.
Oh, no, just the one I restored isn’t working properly. Thought I’d do one board at a time, to have a working one as reference.
@Lavane mine had an annoying hiss, so I decided to replace all transistors. I looked at the schematic and figured out which ones needed matching and which could go without. I don’t feel any of these changes really make that much of a difference in the overall character. Right now I can only compare the headphone amplifier stage (which has one vintage channel and one restored channel). Not much of a difference between the two, minus the noise and the slightly more laid back sound of the new one.
Lavane
Lunatic Member
Did yours have transistor sockets on the line stage boards? Mine did, and that can be a cause for hiss as corrosion and carbon can build up on the legs of the transistors. I had a bit of hiss in one channel, but a good cleaning of the transistor legs and sockets cured it. Once restored, the 33's and 3300's do sound very nice. The 33 mated very nicely with my tube amplifiers as well.
Mine is the first revision and it doesn't have transistor sockets. I replaced all electrolytics and tantalums with Elna Silmic IIs and one Vishay.
I wonder if the mylars are worth replacing. It is sounding good, but I think it still has potential to be better.
@Lavane Had sockets only on the Q101 & Q102, the differential pair at the front of the phono stage, but the hiss that annoyed me was on the regular line inputs and was equal on both channels. My thinking is that it’s a sum of noise from all those transistors in the path.
@ocdecio mylars? I think those are silver micas. Haven’t replaced mine.
ps: you’re on the Vintage Marantz Fb group too, right?
@ocdecio mylars? I think those are silver micas. Haven’t replaced mine.
ps: you’re on the Vintage Marantz Fb group too, right?
I believe the two yellow blocks in the middle are Mylar, the brown drops are silver mica and I don't touch those.
Yes, I am on the Marantz FB too! Good group of people there!
Ah. The yellow ones might have been mylar, yes. However they were kinda crumbling when I touched them, so I decided to change them with WIMAs just to be safe. Wouldn’t want to open it again for repairs anytime soon.
So I did replace the yellow blocks - the one right at the input (C109) which seems to be a monolytic I replaced with a Solen "fast cap". The other which is part of the loudness circuit I replaced with a Vishay.
It made the preamp sound clearer for sure. What I read is that the Solen may need some 100 hours to get really good. We shall see.
It made the preamp sound clearer for sure. What I read is that the Solen may need some 100 hours to get really good. We shall see.
Wow… I can’t believe what a stupid issue I had.
I finally found a bit of time to debug my faulty board, so I took out my DMM and my toy scope to try and trace the signal throught the X10 amp. Relatively quickly, I noticed signal wasn’t coming out of Q110 and when I measures its collector I noticed it wasn’t at 0V as the schematic says, but at -6V. Definitely wasn’t biased properly, but it was weird since all there was on the collector side was a resistor network that should’ve been almost perfectly balanced. So then I look over the layout and I noticed I didn’t install two straps around Q111 and Q113. Gee… I also missed out C115 due to a clerical error, but it seems like that’s just a power supply bypass. Added all of them and it now works as it should.
Funny thing, I also managed to reduce the headphone hum almost compeletely, by decreasing the power supply voltage. Not sure how this works, since I started toying around with the adjustment pots, trying to balance the thing out (there was this small 0.07V difference between positive and negative rails). I was doing this with my headphones on so I noticed that reducing the voltage to just over -15V also decreased the hum. What’s really interesting is that playing with the adjustment pot not only did influence the hum amplitude, but also the its frequency. Moreover, it played just fine with -8V on the negativ rail (and 15V on the positive), but this was just in headphone mode where I suspect balancing is not important. In the end I ended up with +/-14.20V which seems to sound fine on all outputs. Still, I wish someone could explain the logic to me.
I finally found a bit of time to debug my faulty board, so I took out my DMM and my toy scope to try and trace the signal throught the X10 amp. Relatively quickly, I noticed signal wasn’t coming out of Q110 and when I measures its collector I noticed it wasn’t at 0V as the schematic says, but at -6V. Definitely wasn’t biased properly, but it was weird since all there was on the collector side was a resistor network that should’ve been almost perfectly balanced. So then I look over the layout and I noticed I didn’t install two straps around Q111 and Q113. Gee… I also missed out C115 due to a clerical error, but it seems like that’s just a power supply bypass. Added all of them and it now works as it should.
Funny thing, I also managed to reduce the headphone hum almost compeletely, by decreasing the power supply voltage. Not sure how this works, since I started toying around with the adjustment pots, trying to balance the thing out (there was this small 0.07V difference between positive and negative rails). I was doing this with my headphones on so I noticed that reducing the voltage to just over -15V also decreased the hum. What’s really interesting is that playing with the adjustment pot not only did influence the hum amplitude, but also the its frequency. Moreover, it played just fine with -8V on the negativ rail (and 15V on the positive), but this was just in headphone mode where I suspect balancing is not important. In the end I ended up with +/-14.20V which seems to sound fine on all outputs. Still, I wish someone could explain the logic to me.