Sony c800(non G) noise issue help!

[ktziavos]

Hello,
i am experiencing a noise issue at low frequencies something like ocean noise. I am tring to first troubleshoot the power supply by changing some capacitors and hear if anything changes. I've change tubes but the noise is exactly the same. i was trying to measure the very big cap (10000uF 35V) after a half an hour turned on with multimeter and the cap off the curcuit and i couldn't measure anything but a few nF. It seems that the capacitor is dead. With the ps turned on i measured the Volts and they are ok except the 142V at the C103-C104&C105 that is 8 Volts lower(around 133V-135V). is there any point to change all the capacitors? or start from the 10000uF one? The most important question is that the capacitor is a three pin capacitor and at the schem is C102 10000uF 35V x2. can i use a single two pin capacitor 10000uF? or it is a dual capacitor and i have to use two? i can't find anything with the service code from the Sony manual.

 

[Tubetec]

You will need 2x10000uf caps to replace the original , although a single dual element cap might be found somewhere , it might not be the best quality .
Id check closely the integrity of all the caps , anything with the seals bulging or starting to leak ,definately replace .

The small difference between what the manual states the HT should be and what you read wont matter much .
Is it possible the mic itself is making the noise ?

 

[RuudNL]

'Ocean noise' could also be caused by a contaminated microphone capsule.

 

[ktziavos]

You will need 2x10000uf caps to replace the original , although a single dual element cap might be found somewhere , it might not be the best quality .
Id check closely the integrity of all the caps , anything with the seals bulging or starting to leak ,definately replace .

The small difference between what the manual states the HT should be and what you read wont matter much .
Is it possible the mic itself is making the noise ?

Thanks for the answer.
The mic used to be very quiet. Everything seems very clean and no leaks or bulking seals. I will start from the power supply changing the less expensive components and hear if anything changes.... It is really annoying...

 

[ktziavos]

'Ocean noise' could also be caused by a contaminated microphone capsule.

Thanks for the reply! Contaminated means that it is damaged or just dirty?

 

[rock soderstrom]

Thanks for the reply! Contaminated means that it is damaged or just dirty?

Means dust dirty and especially moist by breathing air. This can cause the symptoms you describe. Here I agree with Ruud.
Try drying the microphone capsule at a warm and dry place and see if it gets better. Capsules can also be cleaned, but this should be done by someone with experience.

I don't think your capacitors are defective, especially the thick ones. BTW you can't measure a 10000uf cap with a multimeter in circuit. At least not with the multimeters I have....

 

[RuudNL]

What you could do to check if it is a capsule problem, is replace the capsule with a fixed capacitor (68 or 82 pF).
The polarisation voltage in the C800 is high, so use a type that is at least rated 150 V.

 

[Tubetec]

Ive seen where capacitor mics dont perform until placed a few days in a dry warm environment , second Rockys suggestion there , before touching anything else in the circuit . Do also examine the capsule surface for any signs of contamination ,a layer of dust and particals in conjunction with a cold capsule can cause moisture from the performers voice to condense and cause leakage and its associated spurious noises . An extended period of power up in a tube mic is usually enough to drive off any moisture from the capsule , My advice is dont change a thing until you have discounted whats been said in the last few parragraphs .

 

[Moby]

Yes, RuudNl is right, it sounds like the contamined (moisture) capsule. You can just disconnect it from the circuit and listen if ocean noise is gone. If not, then proceed with capacitors.

 

[ktziavos]

Hello to everyone! thanks for your replies and your help! i've done the trick with the capacitor instead of the capsule. and the results are that the noise resists. is pretty much the same without the enviromental noise. i uploaded the files to hear it yourself. I don't know if i am accurate with the label "ocean noise". Any further suggestions?

 

[rock soderstrom]

Hello to everyone! thanks for your replies and your help! i've done the trick with the capacitor instead of the capsule. and the results are that the noise resists. is pretty much the same without the enviromental noise. i uploaded the files to hear it yourself. I don't know if i am accurate with the label "ocean noise". Any further suggestions?

Ocean noise sums it up quite well. Are you sure the replacement tube is OK? How loud is the noise, how much gain from which preamp do we hear? Since the capsule is no longer part of the equation, besides the tube, the following suspects come into play.

Contamination/moisture in the high impedance area of the microphone. Clean it with isopropanol.
Maybe we also hear a noisy anode resistor?

Can you please post the schematic?

PS: I still don't believe that the filter caps have anything to do with it.

 

[ktziavos]

Ocean noise sums it up quite well. Are you sure the replacement tube is OK? How loud is the noise, how much gain from which preamp do we hear? Since the capsule is no longer part of the equation, besides the tube, the following suspects come into play.

Contamination/moisture in the high impedance area of the microphone. Clean it with isopropanol.
Maybe we also hear a noisy anode resistor?

Can you please post the schematic?

PS: I still don't believe that the filter caps have anything to do with it.

Hello rock!
Thanks for the reply and for your help! I've changed many tubes new old etc and the noise was exactly the same ,so i realized that the tubes are not the problem as soon as different combination doesn't change anything. I am using a UAD default interface preamp and i have a limiter plugin to just get the issue front.
Post in thread 'Sony' https://groupdiy.com/threads/sony.44790/post-1034894

Here's the schematic of the ps and the mic.

Thnx again
Konstantinos

 

[ktziavos]

Ocean noise sums it up quite well. Are you sure the replacement tube is OK? How loud is the noise, how much gain from which preamp do we hear? Since the capsule is no longer part of the equation, besides the tube, the following suspects come into play.

Contamination/moisture in the high impedance area of the microphone. Clean it with isopropanol.
Maybe we also hear a noisy anode resistor?

Can you please post the schematic?

PS: I still don't believe that the filter caps have anything to do with it.

Anode resistor is the R101?

 

[rock soderstrom]

Anode resistor is the R101?

Forget the anode/plate resistor, your mic is based on a cathode follower, there is no plate resistor. Now with the schematics in hand I see that your mic has tube rectification in the PSU. I assume that you have already replaced them, too?

Do you have the possibility to test the mic with a second, known good PSU?

 

[ktziavos]

Forget the anode/plate resistor, your mic is based on a cathode follower, there is no plate resistor. Now with the schematics in hand I see that your mic has tube rectification in the PSU. I assume that you have already replaced them, too?

Do you have the possibility to test the mic with a second, known good PSU?

Yes already replaced the tubes in the ps with new ones. Nobody around has the non G version so i can't find PS for test.
Is there any possibility that the transformer is making that noise?

 

[rock soderstrom]

Is there any possibility that the transformer is making that noise?

I don't think so. I have not had any hissing transformers yet.

 

[Tubetec]

Might be a stupid question but did you try replacing the tube in the mic itself?
If youve discounted the capsule being the issue that would be the logical next thing to check .
You may need a selected 6AU6 to work properly in the mic , I note that in the C800g manual the tubes used in the HT rectifier even though there 6AU6's are a different part number , maybe Sony used the tubes that didnt measure up good enough for usage in the mic for the PSU to save having to dump loads and loads of tubes ,
I wonder what the hit rate for low noise 6AU6's suitable for microphones is out of a pile , I got a box of 100 mil spec 6au6 for 50 euros a few years ago . I'm planning on building a 6AU6 based tube microphone soon using a T.bone SCT700 body and PSU.

I'm interested to hear if anyone has tried a 6AU6 based tube mic before , not nessesairily a Sony clone .

Another thing that might be worth a try is cleaning inside the mic ,on the pcbs etc especially the high Z areas , it might have become contaminated through touch, which leaves a residue behind that dust and dirt will cling too
I'd go in there with dry cotton buds first ,take away any residual crud , then use a clean cotton bud dampened with isopropyl alcohol to wipe things down . Avoid pools of iso inside the mic

I found this comment on a another site ,
'About 2 years ago I tested a bunch (100 +) 6AU6's in triode mode. I found good ones and bad ones in every flavor. I can't find my notes from that testing. The main difference between good ones and bad ones is noise, microphonics, hum and distortion (in that order). Most of my tubes are either pulled from military spares, or NOS military bulk pack. The tube to tube variations were pretty wide. I would think that you should be able to find some good ones in a big collection of any vendors tubes (except maybe some of the early Japanese tubes)'

 

[Gus]

Tubetec's post makes sense to me try different tubes.

You might need to try a number of tubes and they should be the tube Sony used because of the way Sony runs the tube in the C800 and C800G circuit

A search of this forum should help.

FWIW when I built a C800G like circuit with the 6AU6 tube operating points I found I needed to find a low noise tube and use super caps in the heater supply. I did not have any luck with real 6AU6s even ones built by Mullard etc.

I think part of this is due to the bigger envelope with possibly better vacuum or the alloy and/or oxides and/or process used at the cathode section of the tube

I bought over 10 tubes of the type that are used in the microphone.
I also needed to burn in the tubes. I made a setup that could run the tubes I changed things at 4 hour intervals and IIRC ran the tubes for two day and then selected the tubes for noise by trying them in a microphone.

FWIW look for Schoeps tube microphone they use a real 6AU6 however they are run a little different

 

[ktziavos]

Might be a stupid question but did you try replacing the tube in the mic itself?
If youve discounted the capsule being the issue that would be the logical next thing to check .
You may need a selected 6AU6 to work properly in the mic , I note that in the C800g manual the tubes used in the HT rectifier even though there 6AU6's are a different part number , maybe Sony used the tubes that didnt measure up good enough for usage in the mic for the PSU to save having to dump loads and loads of tubes ,
I wonder what the hit rate for low noise 6AU6's suitable for microphones is out of a pile , I got a box of 100 mil spec 6au6 for 50 euros a few years ago . I'm planning on building a 6AU6 based tube microphone soon using a T.bone SCT700 body and PSU.

I'm interested to hear if anyone has tried a 6AU6 based tube mic before , not nessesairily a Sony clone .

Another thing that might be worth a try is cleaning inside the mic ,on the pcbs etc especially the high Z areas , it might have become contaminated through touch, which leaves a residue behind that dust and dirt will cling too
I'd go in there with dry cotton buds first ,take away any residual crud , then use a clean cotton bud dampened with isopropyl alcohol to wipe things down . Avoid pools of iso inside the mic

I found this comment on a another site ,
'About 2 years ago I tested a bunch (100 +) 6AU6's in triode mode. I found good ones and bad ones in every flavor. I can't find my notes from that testing. The main difference between good ones and bad ones is noise, microphonics, hum and distortion (in that order). Most of my tubes are either pulled from military spares, or NOS military bulk pack. The tube to tube variations were pretty wide. I would think that you should be able to find some good ones in a big collection of any vendors tubes (except maybe some of the early Japanese tubes)'

Hey tubetec! Thnx for your reply. I changed all the tubes with new ones and a combination of two new in psu and the original in the mic and i realized that the noise is exactly the same. So i don't think is a tube problem.

 

[Gus]

How many tubes did you try?
Are you using a Sony selected tube?
Are you using the same tube that Sony used?

You might need to try 10 or more non-selected tubes to find one that works with low noise.

If you are using real 6AU6s good luck finding one that works with low noise in the Sony 800 microphones.