yamaha preamp
Hi Chris,
Eventually I got most parts for my Yamaha c-65 and began working on it on Sunday. So far I have replaced all electro-caps except for the main 4700uFs, which I haven't got yet.
I decided to do this without checking, which caps are still ok and which are gone to save time. I know for sure that some caps in the Tone Control and Loudness sections are bad as treble section and loudness did not work. Hope only electro-caps were gone. Doing the job I also have spotted four transistors with problems. Basically some of the tracks cracked around their soldering so they lost connection with the board.
Have you noticed any track cracks around factory soldering in your Yamaha? I have noticed that cracking of tracks appears only around some bigger solder joints. Good thing is that tracks in these models are wide. It would be a nightmare if they were narrow. Anyway, if cracking continue it might be a problem.
Tomorrow I'll install pots (after washing and track polishing they tested OK), replace eight rectifying diodes with fast ones and plug the preamp in. Hope it will work.
Main filtering caps will go when I get replacements. Two of these adjacent to the transformer are swallen with their tops touching the case. Still, I do not intend to put the transformer out. I hope drilling the case will do as c-65's circuits are less complex than the c-85's and therefore are less current hungry.
How is your preamp working now? Have you noticed any improvement in sound as well?
cheers,
Hi Chris,
Eventually I got most parts for my Yamaha c-65 and began working on it on Sunday. So far I have replaced all electro-caps except for the main 4700uFs, which I haven't got yet.
I decided to do this without checking, which caps are still ok and which are gone to save time. I know for sure that some caps in the Tone Control and Loudness sections are bad as treble section and loudness did not work. Hope only electro-caps were gone. Doing the job I also have spotted four transistors with problems. Basically some of the tracks cracked around their soldering so they lost connection with the board.
Have you noticed any track cracks around factory soldering in your Yamaha? I have noticed that cracking of tracks appears only around some bigger solder joints. Good thing is that tracks in these models are wide. It would be a nightmare if they were narrow. Anyway, if cracking continue it might be a problem.
Tomorrow I'll install pots (after washing and track polishing they tested OK), replace eight rectifying diodes with fast ones and plug the preamp in. Hope it will work.
Main filtering caps will go when I get replacements. Two of these adjacent to the transformer are swallen with their tops touching the case. Still, I do not intend to put the transformer out. I hope drilling the case will do as c-65's circuits are less complex than the c-85's and therefore are less current hungry.
How is your preamp working now? Have you noticed any improvement in sound as well?
cheers,
yamaha preamp
Hi,
Having replaced all electros with cleaned up pots (including polishing of tracks) soldered in the preamp works fine. I do not know how much life span is left in these pots but a number of caps died out / started to act as funny AC resistors with increased DC leakage. 1000uF filtering caps next to the main 4700uF caps appeared to have almost completely dried out and were adding noise.
As the preamp, even with drilled case, becomes quite hot inside life span of electros is shortened considerably. Anyway, after 20 years it is usually necessary to replace all electros except for the truly long life/high quality ones.
If I like the preamp and pots will not get noisy within a couple of years I will replace most op-amps.
cheers,
Hi,
Having replaced all electros with cleaned up pots (including polishing of tracks) soldered in the preamp works fine. I do not know how much life span is left in these pots but a number of caps died out / started to act as funny AC resistors with increased DC leakage. 1000uF filtering caps next to the main 4700uF caps appeared to have almost completely dried out and were adding noise.
As the preamp, even with drilled case, becomes quite hot inside life span of electros is shortened considerably. Anyway, after 20 years it is usually necessary to replace all electros except for the truly long life/high quality ones.
If I like the preamp and pots will not get noisy within a couple of years I will replace most op-amps.
cheers,
C-85 Still working
Sorry, it has been a while but I've been busy with my step-daughter's
Senior Project for High School. She performed two vocal concerts for
the local Senior Centers. I used all my equipment including the C-85
at the center of it all. Worked flawlessly. What a mistake putting
the transformer inside the case. . .it generated close to 75% of all
the heat! I probably didn't even need the fan! With the transformer
outside the case I could have used the void to put the big caps in.
Just an afterthought. I'm still willing to drill the top to allow the
protrusion of tall caps. I will replace all the electros when $$ is available. Sounds like janusz had good luck with the replacement;
it also looks like his boards are in poor shape from the heat. But
thanks to bigger solder traces. . .repairable. Would like to see
pictures some day.
Chris
Sorry, it has been a while but I've been busy with my step-daughter's
Senior Project for High School. She performed two vocal concerts for
the local Senior Centers. I used all my equipment including the C-85
at the center of it all. Worked flawlessly. What a mistake putting
the transformer inside the case. . .it generated close to 75% of all
the heat! I probably didn't even need the fan! With the transformer
outside the case I could have used the void to put the big caps in.
Just an afterthought. I'm still willing to drill the top to allow the
protrusion of tall caps. I will replace all the electros when $$ is available. Sounds like janusz had good luck with the replacement;
it also looks like his boards are in poor shape from the heat. But
thanks to bigger solder traces. . .repairable. Would like to see
pictures some day.
Chris
yamaha c-65
Congratulations on the work so far. Supporting kids performance was a good test for the preamp. My daughter does not sing. She only dances in a folk group but she likes acting and does some taping of her inventions.
Yesterday, finally!!! I hope, I managed to fix the last of the main problems C-65 was exhibitng (intermitent problem cap related which was annoying me for quite a while). I still have to test it with a few LPs for a few hours to see if truly all the phono section problems disappeared.
C-65 does not run that hot so I have only drilled the case - top and bottom. If it is not enough I'll screen internally the transformer to minimize heat transfer to the rest of the case. As I do not run it for hours it should not be so bad.
Pot tracks required some polishing on top of cleanning to work quietly. Changing all the elctros was not so expensive except for the main four filtering power supplies. These four alone cost me almost A$100. I got BH aerovox caps 4700uF/63V ALP22 long life series (10,000 hours at 85 degrees C) so heat should be no problem as two of the originals were already fried. Aerovox caps have different pin layout so some drilling was necessary.
All the other caps cost me probably close to A$100 but I did not count every dollar spent. I used Nichicon caps mainly: KZ Muse, ES bipolars and other low ESR and impedance plus some ELNA and other. Also used 500V silvered mica in the phono stage insted of ceramics. Actually there are only two more ceramics still left in the c-65 in the tone control circuit.
If I like the preamp I can replace all ICs outside the initial phono stage and get rid of the last ceramics. I will ned 6 more Brown Dog (Cimmaron Technology now) adaptors to do this but I already have all the the other bits.
Now I have to finish my new PAs and attend my pioneer rt-909 open reel. It needs all its electros and ceramics replaced as well heads. The old heads will be relaped. Hope the motors will not fail. I already have a new head set and MRL test tape. RT-909, however, is much more complicated than c-65 so it will take me many weekends and evenings before it will be like new.
cheers,
Congratulations on the work so far. Supporting kids performance was a good test for the preamp. My daughter does not sing. She only dances in a folk group but she likes acting and does some taping of her inventions.
Yesterday, finally!!! I hope, I managed to fix the last of the main problems C-65 was exhibitng (intermitent problem cap related which was annoying me for quite a while). I still have to test it with a few LPs for a few hours to see if truly all the phono section problems disappeared.
C-65 does not run that hot so I have only drilled the case - top and bottom. If it is not enough I'll screen internally the transformer to minimize heat transfer to the rest of the case. As I do not run it for hours it should not be so bad.
Pot tracks required some polishing on top of cleanning to work quietly. Changing all the elctros was not so expensive except for the main four filtering power supplies. These four alone cost me almost A$100. I got BH aerovox caps 4700uF/63V ALP22 long life series (10,000 hours at 85 degrees C) so heat should be no problem as two of the originals were already fried. Aerovox caps have different pin layout so some drilling was necessary.
All the other caps cost me probably close to A$100 but I did not count every dollar spent. I used Nichicon caps mainly: KZ Muse, ES bipolars and other low ESR and impedance plus some ELNA and other. Also used 500V silvered mica in the phono stage insted of ceramics. Actually there are only two more ceramics still left in the c-65 in the tone control circuit.
If I like the preamp I can replace all ICs outside the initial phono stage and get rid of the last ceramics. I will ned 6 more Brown Dog (Cimmaron Technology now) adaptors to do this but I already have all the the other bits.
Now I have to finish my new PAs and attend my pioneer rt-909 open reel. It needs all its electros and ceramics replaced as well heads. The old heads will be relaped. Hope the motors will not fail. I already have a new head set and MRL test tape. RT-909, however, is much more complicated than c-65 so it will take me many weekends and evenings before it will be like new.
cheers,
That is an incredible amount of work. . .but the payoff is worth it?
I didn't realize that it would be close to $200 to replace all the caps.
They are so darn expensive. . . .seems like the $ isn't going quite as
far as it used to. I guess I will start combing the used parts stores
for the caps. . . it might take a while.
Chris
I didn't realize that it would be close to $200 to replace all the caps.
They are so darn expensive. . . .seems like the $ isn't going quite as
far as it used to. I guess I will start combing the used parts stores
for the caps. . . it might take a while.
Chris
yamaha c-65
Hi Chris,
These are Australian dollars and include mailing costs so it should be no more than US$150 or less. I had to replace a number of cpas anyway as they were gone - dry and leaking badly or open. All in PS, phono and tone control circuits. I have decided to replace all electros as a quicker way to fix faulty circuits. I checked all the caps afterwards. Two of the main PS caps were not original anyway. Besides, the remaining 20 year old electros in a closed box with a hot transformer could not have much life left in them anyway.
Was it worth doing it? In my case I had to replace at least some of them plus cleanning and polishing pot tracks and switches. With the remaining caps I could wait until they expired. That is potentially asking for more problems. I have also bypassed all electros in audio circuits with polypropylene caps. With new caps the difference is enormous as I am comparing a faulty preamp with a working one.
The only circuit which worked when I bought this preamp is the line high input level circuit. Well there is almost half a year between the first days and now so my memory is not fresh. Nevertheless, I can say with certainty that the sound is much more clearer and very quiet. That I remember well. Half a year ago when I switched the preamp for the first time I was very disappointed.
Now, after repairs being completed, it is a completely different preamp. It is quite transparent and QUIET including phono. It is not a top preamp and will never be even if I upgraded all the op-amps. But with op-amps upgraded it will be a touch better again.
I have also replaced rectifying diodes with fast ones. I do not think their contribution is enormous but I had about a hundred of these then so that mod could be seen a s a bonus.
If you decided to replace all the remaining electros use only high quality caps and bypass all audio circuit caps with polypropylene. It really makes a difference. I have also bypassed main PS caps with 1.5uF polypropylene caps.
cheers,
Hi Chris,
These are Australian dollars and include mailing costs so it should be no more than US$150 or less. I had to replace a number of cpas anyway as they were gone - dry and leaking badly or open. All in PS, phono and tone control circuits. I have decided to replace all electros as a quicker way to fix faulty circuits. I checked all the caps afterwards. Two of the main PS caps were not original anyway. Besides, the remaining 20 year old electros in a closed box with a hot transformer could not have much life left in them anyway.
Was it worth doing it? In my case I had to replace at least some of them plus cleanning and polishing pot tracks and switches. With the remaining caps I could wait until they expired. That is potentially asking for more problems. I have also bypassed all electros in audio circuits with polypropylene caps. With new caps the difference is enormous as I am comparing a faulty preamp with a working one.
The only circuit which worked when I bought this preamp is the line high input level circuit. Well there is almost half a year between the first days and now so my memory is not fresh. Nevertheless, I can say with certainty that the sound is much more clearer and very quiet. That I remember well. Half a year ago when I switched the preamp for the first time I was very disappointed.
Now, after repairs being completed, it is a completely different preamp. It is quite transparent and QUIET including phono. It is not a top preamp and will never be even if I upgraded all the op-amps. But with op-amps upgraded it will be a touch better again.
I have also replaced rectifying diodes with fast ones. I do not think their contribution is enormous but I had about a hundred of these then so that mod could be seen a s a bonus.
If you decided to replace all the remaining electros use only high quality caps and bypass all audio circuit caps with polypropylene. It really makes a difference. I have also bypassed main PS caps with 1.5uF polypropylene caps.
cheers,
Hi Chris,
I have an C80 , similar or equal to c85, it is very silent, over -90 dB input Phono.
Therefore it is not a good idea to move out some houses the transformer, however not necessary.
the warm is produced by the transistors stabilizers that have to dissipate a great jump of voltage having a too small squanderer.
If you want to improve your c85 I recommend you to eliminate all the connectors (oxidized) at least on an only input, what uses more frequently
and it eliminates the four resistances in series to the supply, immediately before the four big condensers, 2,2 ohm and 4,7 ohm.
Ciao from Italy
I have an C80 , similar or equal to c85, it is very silent, over -90 dB input Phono.
Therefore it is not a good idea to move out some houses the transformer, however not necessary.
the warm is produced by the transistors stabilizers that have to dissipate a great jump of voltage having a too small squanderer.
If you want to improve your c85 I recommend you to eliminate all the connectors (oxidized) at least on an only input, what uses more frequently
and it eliminates the four resistances in series to the supply, immediately before the four big condensers, 2,2 ohm and 4,7 ohm.
Ciao from Italy
I've already move the transformer externally; mounted a fan
where the transformer was. . .there is a class A circuit near the
middle of the preamp that produces a good amount of heat. . .second
to the potted transformer. . .that keeps the box warm.. .I've only
used the fan a couple of times during the summer when I was using
the unit for all day events.
Great unit. . .had it 20 years this fall.
where the transformer was. . .there is a class A circuit near the
middle of the preamp that produces a good amount of heat. . .second
to the potted transformer. . .that keeps the box warm.. .I've only
used the fan a couple of times during the summer when I was using
the unit for all day events.
Great unit. . .had it 20 years this fall.
yamaha c series preamp
Hi,
In C-65, the transformer is by far the main heat generator. The phono and equalizer section PS generates much less heat.
The transformer generates so much heat (and in C-85 even more) as it is terribly undersized. I'm still hesitating what to do with my c-65 but I'm getting closer to accepting it. That means I'll put sockets under all op-amps in the audio section and replace them with new op-amps (lm4562 where low noise is important and opa2132) on Brown Dog adaptors.
If I go for the above then I'll also replace the original transformer with two 30VA 2x15V toroids. They will deliver plenty of power with very little heat. In Australia Altronics sells them for $23 each so this transplantation will cost well below the price of all the BD adaptors (US$3 each - 13 are needed - plus mailing cost to Australia) needed in the audio section.
The middle section PS power transistors may be replaced with more powerful ones on much bigger heatsinks or at least the original PS power transistors may be put on bigger heatsinks. A few holes I drilled above improved ventilation - I'd say sufficiently .
cheers,
Hi,
In C-65, the transformer is by far the main heat generator. The phono and equalizer section PS generates much less heat.
The transformer generates so much heat (and in C-85 even more) as it is terribly undersized. I'm still hesitating what to do with my c-65 but I'm getting closer to accepting it. That means I'll put sockets under all op-amps in the audio section and replace them with new op-amps (lm4562 where low noise is important and opa2132) on Brown Dog adaptors.
If I go for the above then I'll also replace the original transformer with two 30VA 2x15V toroids. They will deliver plenty of power with very little heat. In Australia Altronics sells them for $23 each so this transplantation will cost well below the price of all the BD adaptors (US$3 each - 13 are needed - plus mailing cost to Australia) needed in the audio section.
The middle section PS power transistors may be replaced with more powerful ones on much bigger heatsinks or at least the original PS power transistors may be put on bigger heatsinks. A few holes I drilled above improved ventilation - I'd say sufficiently .
cheers,
Sounds great. . .let's see some pictures when you get closer to
being done. I loaned my C-85 to an older woman who wanted
to listen to her opera LPs again. . . working like charm. . . The idea
of replacing the transformer with two toroids is an idea worth
looking into. . . but if I remember correctly. . .the two different
secondaries are not both 30VAC CT; one seemed higher voltage
than the other. . .I would have to go back and review my notes.
being done. I loaned my C-85 to an older woman who wanted
to listen to her opera LPs again. . . working like charm. . . The idea
of replacing the transformer with two toroids is an idea worth
looking into. . . but if I remember correctly. . .the two different
secondaries are not both 30VAC CT; one seemed higher voltage
than the other. . .I would have to go back and review my notes.
c series mods
Ideally one could use one 2x18V transformer and one 2x15V transformer. Maybe I'll go for that solution. No difference in costs. I've just checked - $22.50 each. That would allow for no changes of resistors controlling the value of DC voltage.
I do not know if c-85 and c-65 are exactly the same in this respect but the rectified voltage of 2x15V AC at 2x30VA is good enough for both sections and allows to keep rectified voltage well below the 35V caps limit. Important as I have recently changed these main caps from a touch too long for the case 4700uF/63V to 3300uF/35V 105deg caps and used two of these in place of each 4700uF. This way i get 6600uF instead of 4700uF, lower impedance and possibly better speed.
Alternatively one can use two 2x18V transformers. That would give somewhat better headroom in the line section and again no need for DC voltage control resistor changes.
As yamaha used an undersized dual cheapo transformer they had to keep its AC voltages much higher than necessary (that is what I believe).
The series resistors before the main caps should go. I have to check if they are in c-65 as I must admit I did not notice them.
cheers,
Ideally one could use one 2x18V transformer and one 2x15V transformer. Maybe I'll go for that solution. No difference in costs. I've just checked - $22.50 each. That would allow for no changes of resistors controlling the value of DC voltage.
I do not know if c-85 and c-65 are exactly the same in this respect but the rectified voltage of 2x15V AC at 2x30VA is good enough for both sections and allows to keep rectified voltage well below the 35V caps limit. Important as I have recently changed these main caps from a touch too long for the case 4700uF/63V to 3300uF/35V 105deg caps and used two of these in place of each 4700uF. This way i get 6600uF instead of 4700uF, lower impedance and possibly better speed.
Alternatively one can use two 2x18V transformers. That would give somewhat better headroom in the line section and again no need for DC voltage control resistor changes.
As yamaha used an undersized dual cheapo transformer they had to keep its AC voltages much higher than necessary (that is what I believe).
The series resistors before the main caps should go. I have to check if they are in c-65 as I must admit I did not notice them.
cheers,
So that will run the preamp a little cooler also. . .less heat from
the new transformers and less heat do to the reduced voltage?
Now I want to try. . .
the new transformers and less heat do to the reduced voltage?
Now I want to try. . .
Saying that there's no need to change DC value resistors I'm guessing from memory that departure from the final DC supply voltage will be acceptable with 15V and 18V toroids. Two times 30VA should be well below what is needed but one can go for an overkill 50VA 2x18V toroid for the phono section as this one takes more current.
The 50VA toroid is only a touch bigger than the 30VA and only a few dollars more expensive. As a matter of fact I think I have one such toroid in my old discarded preamp. I have only to check whether it will fit without problems so $22.50 will be saved. Sometimes a few mm more is too much like with my previous caps. With the case on they were pushing down PCBs strainning tracks and joints. So they had to go and it was only a couple of mm too much!
As a matter of fact I tried to remove these tiny heatsinks from the middle section PS transistors but could not undo the nuts. They are like welded to their bolts. Probably will find replacement transistors and desolder the olod ones. Certainly their heatsink paste is long gone. But anyway the idea is to get rid of the transformer heat.
The replacement of op-amps should really make a difference as those used are quite below a present day preamp norm. OPA2132P (or even PAs) for tone and loudness controls and LM4562s in other sections will be as good as their low price.
cheers,
The 50VA toroid is only a touch bigger than the 30VA and only a few dollars more expensive. As a matter of fact I think I have one such toroid in my old discarded preamp. I have only to check whether it will fit without problems so $22.50 will be saved. Sometimes a few mm more is too much like with my previous caps. With the case on they were pushing down PCBs strainning tracks and joints. So they had to go and it was only a couple of mm too much!
As a matter of fact I tried to remove these tiny heatsinks from the middle section PS transistors but could not undo the nuts. They are like welded to their bolts. Probably will find replacement transistors and desolder the olod ones. Certainly their heatsink paste is long gone. But anyway the idea is to get rid of the transformer heat.
The replacement of op-amps should really make a difference as those used are quite below a present day preamp norm. OPA2132P (or even PAs) for tone and loudness controls and LM4562s in other sections will be as good as their low price.
cheers,
Hi,dear friends,
I don't believe that the transformer is too much small.
I believe that the problem of the preamplificatoris is the output section and muting.
the scheme that attach show an output line with transistors. 2n2878. of muting in series!!
The signal crosses the transistors of muting with serious degrade of sound.
I don't believe that the transformer is too much small.
I believe that the problem of the preamplificatoris is the output section and muting.
the scheme that attach show an output line with transistors. 2n2878. of muting in series!!
The signal crosses the transistors of muting with serious degrade of sound.
Hi,dear friends,
I don't believe that the transformer is too much small.
I believe that the problem of the preamplificatoris is the output section and muting.
the scheme that attach show an output line with transistors. 2n2878. of muting in series!!
The signal crosses the transistors of muting with serious degrade of sound.
I don't believe that the transformer is too much small.
I believe that the problem of the preamplificatoris is the output section and muting.
the scheme that attach show an output line with transistors. 2n2878. of muting in series!!
The signal crosses the transistors of muting with serious degrade of sound.
I think I understand what is being stated. You don't like the fact
that the C-80 uses transistors in the muting circuit?
Hi,
the transistor of muting is not normally crossed by the signal (series)
IN other pre-amplifier it normally short-circuits the exit during the power-up ( parallel ).
In this case ( C80) to the exit of the stadium, the signal coming from two strong end transistors ( 2SB580/2SD438) of medium power, is subsequently forced to cross two small transistors (2n2878) of muting.
This produces a serious I degrade some sound.
Yamaha no you has planned anymore in this way.
To remove the two transistors of muting is possible, they goes substitutes from a piece of wire among Base and Emitter of 2n2878 , however in this way it is had to turn on the pre-amplifier for first then the end- amplifier, otherwise ago a big noise in the loudspeker,
the transistor of muting is not normally crossed by the signal (series)
IN other pre-amplifier it normally short-circuits the exit during the power-up ( parallel ).
In this case ( C80) to the exit of the stadium, the signal coming from two strong end transistors ( 2SB580/2SD438) of medium power, is subsequently forced to cross two small transistors (2n2878) of muting.
This produces a serious I degrade some sound.
Yamaha no you has planned anymore in this way.
To remove the two transistors of muting is possible, they goes substitutes from a piece of wire among Base and Emitter of 2n2878 , however in this way it is had to turn on the pre-amplifier for first then the end- amplifier, otherwise ago a big noise in the loudspeker,
That is very interesting to know. . .I hadn't studied that part of the
circuit. . . that could be an interesting mod. . .but with the side effects
that you pointed out.
Might open up the sound. . .
circuit. . . that could be an interesting mod. . .but with the side effects
that you pointed out.
Might open up the sound. . .
I have found this change after having compared my c80 with a spectral dmc20,
the yamaha was clearly defeated in the comparison.
The c80 in a hi-fi chain of high-level to the place of the spectral, made the mixed sound and confused.
Then I have thought about eliminating the transistors of muting and the sound it is very improved.
it has almost reached the dmc20, however it is very well
the pre could stay always turned power-on as also the dmc20, that never extinguishes him second SPECTRAL.
the yamaha was clearly defeated in the comparison.
The c80 in a hi-fi chain of high-level to the place of the spectral, made the mixed sound and confused.
Then I have thought about eliminating the transistors of muting and the sound it is very improved.
it has almost reached the dmc20, however it is very well
the pre could stay always turned power-on as also the dmc20, that never extinguishes him second SPECTRAL.
- Status
- Not open for further replies.