Bias Adjustment on Cassette Deck, Dolby S...

[CChase]

Hello all,

I have a Sony TC-KE500S cassette deck which I am sure is not the greatest (at least going by what it seems many on here have), but I am having an issue with it and don't know too much about cassette decks and would like some insight.

To make it brief, it has a manual bias adjustment and you're supposed to turn the bias adjustment knob clockwise or counterclockwise through about 270 degrees to get what I assume to be a high and a low to match up.

However, when I throw a new tape in there (Type I or Type II), I have to turn it almost the whole way counter-clockwise before the H and L line up properly. This doesn't seem right to me, and I am wondering if something needs to be fixed, maintained, cleaned, adjusted, etc.

I've cleaned the heads with isopropyl alcohol and they seem clean. When I get the bias adjusted properly (with the knob way down), the recordings sound perfect.



My other issue is probably from just not knowing enough, but basically the deck has Dolby S, and I spent a while researching at the time to make sure I found a deck with Dolby S as it seems like it's supposed to be the greatest thing ever...

However, when I play a tape with Dolby S, it just seems horrifically muddy to me, to the point where I can't deal with it. With no Dolby on at all, the sound is great... and I don't hear any hiss. I would call it pretty close to CD quality to my un-tuned ears (I can't tell the difference between source and cassette)...

Is this just how Dolby S is or is there more at hand?

Thanks in advance for any/all insight and assistance.
Also, don't let the fact that this is my first post dissuade anyone from helping, I promise I'll be checking on this often.

[goldear]

Were the tapes that you are playing back with Dolby S recorded using Dolby S? Dolby is an encode/decode system. It you don't have both haves of the process, the results will be horrible.

It sounds like you are adjusting your bias appropriately under the circumstances. But your deck might be significantly out of allignment, which could also explain your problems.

[AnalogDigit]

Have you also tried recording and playing back with Dolby B or C?

[CChase]

Were the tapes that you are playing back with Dolby S recorded using Dolby S? Dolby is an encode/decode system. It you don't have both haves of the process, the results will be horrible.

It sounds like you are adjusting your bias appropriately under the circumstances. But your deck might be significantly out of allignment, which could also explain your problems.

Initially, I tried recording with Dolby S on and had the deck set to monitor so I could hear what the recording was like with Dolby S on, and it sounded very muddy even just as the recording was being made. I have read what you say though, about both recording and playback having the same process in order to get the best results.

In terms of the bias, is there any way to align the head myself or is this something that's pretty much impossible?

[braxus]

I think your deck may need servicing. Only on really bad tapes, usually worn out ones, the bias is all the way to 7 oclock. Most of my tapes are between 12 oclock and 2 oclock. And I also have a Sony deck. Dolby S sounds great on my deck to the point I don't ever turn it off. So something is amiss in your Sony. The heads could need alignment or may even be worn out.

[CChase]

Have you also tried recording and playing back with Dolby B or C?

I know I tried Dolby B and Dolby C with tapes that had been recorded with B and C, and had similar results. In general, it was like if I took a tape recorded with B and had no Dolby on, it sounded great. If I turned Dolby B on, it got muddy, then progressively muddier when I went to C and then S.

I had remembered reading that Dolby S was supposed to be "backwards-compatible" with C and S... if I remember correctly it was that you could record with Dolby S and play back with a Dolby B or C deck and have good results, and that you could play back a tape that had been recorded with no Dolby with any of the 3 and get improved s/n ratios... perhaps I am misinformed (very possible).

[braxus]

Dolby S is best played back on S of course, but Dolby B or C will work. B is the closest to S. No Dolby when recorded will give you a very compressed bad sounding signal when Dolby is turned on on playback.

[CChase]

Dolby S is best played back on S of course, but Dolby B or C will work. B is the closest to S. No Dolby when recorded will give you a very compressed bad sounding signal when Dolby is turned on on playback.

If the head was mis-aligned, would this also cause the sound to be muddy when Dolby was on? The only reason it seems odd to me is because without any Dolby on while recording, when I monitor the recording the sound quality seems to be stellar.

In addition, when I played a cassette I recorded with the deck in my trucks stereo, the sound quality sounded equally great.

Would the head being magnetized or something cause the bias to be out of whack, or is this solely a function of the alignment of the head?

Is aligning the heads even possible with this deck? Where could I bring it to if this is something I can't do myself? Any ideas on cost?

[goldear]

If the head was mis-aligned, would this also cause the sound to be muddy when Dolby was on? The only reason it seems odd to me is because without any Dolby on while recording, when I monitor the recording the sound quality seems to be stellar.

In addition, when I played a cassette I recorded with the deck in my trucks stereo, the sound quality sounded equally great.

Would the head being magnetized or something cause the bias to be out of whack, or is this solely a function of the alignment of the head?

Is aligning the heads even possible with this deck? Where could I bring it to if this is something I can't do myself? Any ideas on cost?

Your problems sound much more serious than dolby mis-allignment. It sounds to me like your heads may be worn-out. Often to achieve resonably flat frequency response on a machine with an ailing head, one needs to back the bias way off. While this works to some degree, it has other unintended side effects, such as lower your tapes sensititivity.

It sounds to me like this machine has at least two problems. The first really sounds like a worn-out head. The other is probably either a bad dolby encoding IC in your machine, or is a severely mis-calebrated dolby circuit.

[braxus]

http://futureshop.partsearch.com/Part/Sony/Sony/TCKE500S/Sony/Sony/154373311/New.aspx

http://futureshop.partsearch.com/Part/Sony/Sony/TCKE500S/Sony/Sony/393733201/New.aspx

Here is the head part for your deck. Its still available. While your at it get it some new belt(s).

[CChase]

http://futureshop.partsearch.com/Part/Sony/Sony/TCKE500S/Sony/Sony/154373311/New.aspx

http://futureshop.partsearch.com/Part/Sony/Sony/TCKE500S/Sony/Sony/393733201/New.aspx

Here is the head part for your deck. Its still available. While your at it get it some new belt(s).

Is it worth it to drop $120 on this deck (in your opinion)? And how hard is it to change out the head? ie., am I going to be working on things that aren't really meant to be tampered with? I've got plenty of experience soldering and am on my last semester of an Electrical Engineering degree, so I have some knowledge, but not much.

Is there a chance that the head isn't worn, but just mis-aligned? Not trying to avoid the inevitable, just trying to be cheap...

Like I said, I don't know much about this stuff, feel free to educate me on anything and everything.

[CChase]

In addition, thanks so far to braxus, goldear, and AnalogDigit...

[CChase]

Also, I found this:

http://www.partstore.com/Part/Sony/Sony/154373311/New.aspx

http://www.nexttronics.com/catalog/sony/1/154373311.htm

which appears to be the same part for $20 less. Has anyone used these sites or have any idea about them?

[goldear]

Without having a good tech first look at your machine, its going to be difficult, if not impossible, to be 100% certain of the fix. Here are some reasons why I do not think that it would be wise to just buy a new head blindly:
1) I'm not certain that this is a head problem. It just sounds like a good possibility, but not the only one.
2) I think that there is an equali possibility that this is a bad Dolby IC.
3) I think that there is still a slight possibility that this is simply very extreme case of Dolby misallignment.
4) Installing heads involves allignment, which requires an expensive test tape, some test equipment, and understanding of the procedure.

Unfortunately I can't tell any better without testing it myself. Buying random parts and hoping that they fix your problem is a sure way to failure.

Frankly, if I were you, I'd be more inclined to try to find a good 3 head Nakamichi. They are very pleantiful, and the prices of all but the most notable models is dirt cheap these days. Virtually any Nak will outlive (and probably outperform) your Sony by a significant margin.

[CChase]

Thanks for taking the time to respond.

I am inclined to agree with your assessment concerning buying a new head. As the unit seems to record well with Dolby turned off and the playback quality is excellent with Dolby off, I think my best option should be to just enjoy it while it works and when I have some spare cash laying around just go out and spring for another unit.

Concerning having someone at least look at it, are there directories for where I might be able to bring it to have someone look at it? Are there good or bad places, etc? I don't know what kind of a business would actually be technically proficient on what is a fairly stagnant if not dead industry.

I would take a picture of the heads to have someone look at them, but I'm not sure what a picture shows. Usually very little, in my experience.

Are the Dolby circuits adjustable at all? I can't imagine what would go out, but then again I don't know what the circuitry actually looks like. Are they discrete components like caps, inductors, and resistors or is it entirely chip-based? Are there places out there to look at what the specs of them should be, anything I can test myself? I do have access to plenty of test equipment....

[CChase]

As a sidenote, I'm less concerned about Dolby being messed up, and more concerned with the bias issue... so don't get the idea I'm tied up on Dolby. I'd really prefer to get to the bottom of the bias issue...

[goldear]

I would take a picture of the heads to have someone look at them, but I'm not sure what a picture shows. Usually very little, in my experience.

Are the Dolby circuits adjustable at all? I can't imagine what would go out, but then again I don't know what the circuitry actually looks like. Are they discrete components like caps, inductors, and resistors or is it entirely chip-based? Are there places out there to look at what the specs of them should be, anything I can test myself? I do have access to plenty of test equipment....
Its often difficult to tell the condition of heads from picutres in my experience.

The Dolby circuit in this deck will be ICs. Discrete Dolby was only a reality in the early 70s. It is the input and output levels to the Dolby ICs that need to be callibrated to get proper Dolby tracking.

[CChase]

Its often difficult to tell the condition of heads from picutres in my experience.

The Dolby circuit in this deck will be ICs. Discrete Dolby was only a reality in the early 70s. It is the input and output levels to the Dolby ICs that need to be calebrated to get proper Dolby tracking.

Is this something I can look into doing myself (are there any pots or anything to adjust), or once they lose their calibration is that it?

Do you have any further insight as far as the bias adjustment goes?

[SaSi]

As you say, playback is fine with pre-recorded tapes, so I would rule out PB head wear. The REC head is probably the same age and condition. Based on the symptoms you describe, everything seems to point to extreme bias current.

I have worked only on very few cassette decks, so my experience is lacking. But it might be that the bias switches drive the circuits through trimmers on the PCB that actually tune the bias current. There might be a single trimmer with the switches selecting different smaller resistors to fine tune, or that separate trimmers exist for each level. The bias fine pot on the deck actually does very little tuning. It might be that a main bias trimmer (if it exists) is totaly out of calibration.

Some decks (Technics and Nakamichi come to mind) some times have legends alongside trimmers as to their function. A schematic would be a great help. I would be looking for a trimmer turned almost completely to one extreme end. A well designed circuit doesn't need that - trimmers generally get aligned towards the middle or a small angle from there.

I would recommend that you don't touch anything unless you are sure you are messing with the proper trimmer. And I would not alter more than one trimmer at a time, not before I took a good picture of it's original position.

The location of the bias oscilator should be close to the sockets holding the head leads.

[goldear]

Is this something I can look into doing myself (are there any pots or anything to adjust), or once they lose their calibration is that it?

Do you have any further insight as far as the bias adjustment goes?
Yes, there are callibration pots inside of most machines to adjust the dolby levels, and also the bias. But you really need to find a copy of the service manual, and also a callibration tape before approaching these tasks because twisting random post is on of the quickest way to really mess-up a machine.

[CChase]

Point taken... I won't go screwing around with this stuff.

Is there someplace I could bring the deck to and have them see how it is? How does one find a place like that?

Where are service manuals available (out of curiosity)?

Thanks for all the help so far, I have learned quite a bit in the past few days.

[wualta]

One more test: record the tape with S turned on, then play it back with all Dolby circuits switched off. The tape should sound very bright, almost unlistenably so.

I suggest this because it sounds as if the tapes were being recorded with Dolby off, then played with Dolby on. It's possible that there's a bad (dirty) switch somewhere.

This is a 3-head deck, right? So you set bias by recording two tones and adjusting a knob so the H and L meters indicate the same, right? If you do this with S turned on, can you get the H and L to line up? If you run this bias check with S turned off, does the bias knob end up in the same position?

[CChase]

wualta -

I was playing non-Dolby tapes with Dolby on. The problem I think, is centered more around the fact that when I am recording a tape, if I turn Dolby on, I can hear the sound become muddy (by monitoring the recording). The other part of this is just that with no Dolby on, I don't hear any hiss or excessive treble to start with... it just seems that every Dolby I turn on lose half the clarity of the treble and makes the bass a little deeper... maybe the tapes I am using just don't have a lot of hiss to begin with?

As a general rule, it seems to me that Dolby S is muddier than Dolby C, and Dolby C is muddier than Dolby B, and all of them are a lot mudder than Dolby off.

With no Dolby on, the deck sounds amazing. My uneducated ears can't tell the difference between the source (CD) and the tape when I switch between source and monitor.

You are correct that it is a 3-head deck, and about how the bias is adjusted (I think I read that it was a 400Hz tone that is recorded). I have not tried lining them up with Dolby S on vs. off. However, I will note this:

The procedure is to hit Calibration, then Hit Record... hit Pause to begin recording. Once the tape begins (off the end-piece), the 2 meters come up, one of the far less than the other. However, as the tape progresses (after about 30 seconds), the lower knob does begin to come up, just not very much. By turning the knob counter-clockwise between 90 and 120 degrees, I can get the meters to match up.

I will try your test by running the Calibration, matching them up, and then turning Dolby S on and seeing if the bias moves at all.