Yorkville-Traynor YCV40 preamp noise troubleshooting (2nd try)

[scopetrace]

First off, here is the service manual of the amp in question.

http://traynoramps.com/downloads/servman/smycv40.pdf

I have this Traynor amp since a few years now and it always made the same noise.

Description of the noise problem.

On the clean channel, when the volume is rolled down (no master volume on the clean channel) and when the amp has been warming up for half an hour the noise starts.
It will start with a sound that is like drops of water falling down on a cardboard box. If the volume is increased with or without guitar plugged in, the noise will still be there.
The toc-toc-toc is neither regular neither random. It can start accelerate or cease. So I would call it semi-random.

If the amp is opened or played for a long while, the toc-toc-toc sound can accelerate and transform itself to a sch-schhhh-sh---schhhhh. A soud similar to a flag waving in the wind. Or a snake slowly moving on the cone of the speaker. Then it can even make a noise like someone tearing down a rag or drapes. Then it can stop suddently or making toc-tocs again.

When the lead channel is played loud, the guitar sound completely drown down the noise. So the noise will not go up or down with turning up or down the volume knob.

Now for the lead-distorted channel.
If the amp is switched to the lead channel (the lead channel have gain volume and master volume):
1) Gain and volume knob turned down: no noise.
2) Gain completely cranked and master volume turned down: no noise.
3) Gain completely turned down and volume cranked: the noise will behave exactly the same as in the clean channel.
4) Gain up and master up: hi pitched whine-oscillation.


Since the lead channel is played with the master volume turned to low, the noise will usually be very less noticeable.

---------------------------------------------------
My guesses:

1) There is something affecting both lead and clean channel.
2) The problem is not in the power amp since, when the lead channel master volume is turned down, no noise is heard.
3) Does not seem to be a tube problem, since swapping all the tubes does not change the problem much.
4) Lead and clean channel does not use the same (half) of the 12ax7 except for the front end of the amp (first half). But it would not seem to be the problem since augmenting the volumes of both channel does not increase the noise volume amplitude.
5) does not seem to be the autobias of the power amp since the noise can be cutted with the master volume of the dirty channel.

This leave me with a power section problem ? Am I right ?
And only the power section feeding the preamp tubes ?

What do you guys think the problem might be worth investigating ? What kind of (failing ?) parts can make those sounds ?

Thanks !

PS: Ignore the topic with the same message I had problems with it.

[Prairie Dawg]

Have you tried contacting their product support people? They're pretty knowledgeable and walked me through a standby switch problem with a YCV40 without a lot of prodding. Worth an email or phone call.

[scopetrace]

Ok, thanks, that is a good idea Prairie Dwag. I'll try also to gather the most info I can, wherever the advices come from.

I've seen an other member posting a similar topic at the same time than me.

[Jazz P Bass]

The very first item on the check list should always be the power supply.
Check all of the main voltages that the amp needs to work properly.
Check each node along the preamp stages for stability & lack of gross ripple.
If you honestly feel that the problem is in both channels & not the power amp, that pretty much narrows it down to V1. (a signal in to 'amplifier in' will preclude the preamp)
Take a look at the block diagram.
V1 is before the channel switching relay.
Pulling V1 & observing how it affects the noise would be a good thing to try.

[scopetrace]

The very first item on the check list should always be the power supply.
Check all of the main voltages that the amp needs to work properly.
Check each node along the preamp stages for stability & lack of gross ripple.
If you honestly feel that the problem is in both channels & not the power amp, that pretty much narrows it down to V1. (a signal in to 'amplifier in' will preclude the preamp)
Take a look at the block diagram.
V1 is before the channel switching relay.
Pulling V1 & observing how it affects the noise would be a good thing to try.

Thanks for the block schematic Jazz Bass

What you say is exactly what I think at the moment. But I had decided to weed out the V1 problem out since turning up any of the volumes don't have an effect on the noise's volume amplitude. So my thinking is that the problem can not be something in the signal path. Either it is fluctuations in the power supply that feed the preamp tube, either it is something like hi voltage leaking from trace to trace on the pcb (???) I am thinking about audio probing the bias pins of the preamp, not scoping it, because I am not sure that given the random nature of the glitch, that I could see something (I mean nothing...) on my analog scope.

[nickb]

You might try a low noise tube for V1. Rumor has it that Ruby 12AX7AC5 is a suitable candidate. If you try one let us know how it went.

[scopetrace]

You might try a low noise tube for V1. Rumor has it that Ruby 12AX7AC5 is a suitable candidate. If you try one let us know how it went.

Good advice. Thanks. It's on my list.

[scopetrace]

Woops! double post.

[olddawg]

Run an iPod into the effects return or power amp in. Got noise? Run the effects send into another amp with an iPod on the input. Got noise? Cycle the rear panel patch jacks anyway. Scratchy jacks may cause your problem.

[scopetrace]

double post again...

[scopetrace]

Run an iPod into the effects return or power amp in. Got noise? Run the effects send into another amp with an iPod on the input. Got noise? Cycle the rear panel patch jacks anyway. Scratchy jacks may cause your problem.

I'll report what will happen with that strategy.
Thank you.
I already tested with a patch cable in the effect loop with no discernible difference.

[olddawg]

Is the amp under warranty or near warranty? If it is within a year of the warranty being over you might want to call them and bitch like hell. Believe it or not, most manufactures are concerned with their reputations and they may give you a one time repair/ evaluation at no cost or a discount flat rate at an authorized service center. I used to regularly repair things years out of warranty with these type of authorizations for many different brands. Squeaky wheel and all that.

[bsco]

I had one of those amps awhile back...Didn't make all the noises that yours is making but when I turned the master up and tried to increase the gain, I kept getting feedback...or a high pitched oscillation as you will on one of the channels........I found two 10uf/450 volt electrolytic capacitors that were bad..well actually one was bad but I replaced both of them...I think they were C39 and C40. They are in the power supply...there are two more there as well..C41 and C50....same values....when I replaced C39 and C40, my problem went away....so for what it's worth, you might want to check those...they could be causing your problem or at least some of it...hope this is of some help to you....
Cheers,
Bernie

[scopetrace]

Run an iPod into the effects return or power amp in. Got noise? Run the effects send into another amp with an iPod on the input. Got noise? Cycle the rear panel patch jacks anyway. Scratchy jacks may cause your problem.

I tried to plug an external preamp in the effect loop and the noise is not there. Very silent. So the problem In the front end (or might I say, the front end of the power supply...)

Is the amp under warranty or near warranty? If it is within a year of the warranty being over you might want to call them and bitch like hell. Believe it or not, most manufactures are concerned with their reputations and they may give you a one time repair/ evaluation at no cost or a discount flat rate at an authorized service center. I used to regularly repair things years out of warranty with these type of authorizations for many different brands. Squeaky wheel and all that.

I bought it used and it's been a while... So no garanty.
And I am not in the mood to get angry. LOL

[scopetrace]

I had one of those amps awhile back...Didn't make all the noises that yours is making but when I turned the master up and tried to increase the gain, I kept getting feedback...or a high pitched oscillation as you will on one of the channels........I found two 10uf/450 volt electrolytic capacitors that were bad..well actually one was bad but I replaced both of them...I think they were C39 and C40. They are in the power supply...there are two more there as well..C41 and C50....same values....when I replaced C39 and C40, my problem went away....so for what it's worth, you might want to check those...they could be causing your problem or at least some of it...hope this is of some help to you....
Cheers,
Bernie

So...
I talked to a tech here where I live and he think that it might be the power filter capacitor for the preamp.
OK: C39 and C40 and most probably C41 also since it's the one for the preamp.

Good !