Peavey Vypyr Tube 120 Headphone Socket Problem

[nickb]

I'd happily pack the chassis up and ship it to wherever if there was a chance that an amp tech could fix the problem. However, I can't see how they'd have more success than I've had in obtaining correct sockets or PCB's for this amp. Unless the problem lies elsewhere and the correct tests could provide an accurate diagnosis.

I think there is an error somewhere in the tests. The fact that the brand new board does the same thing tells us so. I'd be happy to look at it if you want to ship it here. Or drive down with it.

[MarkusBass]

I could also fix it but sending the amp to Poland would cost a fortune. Take it to Nick. This is actually quite simple problem because it can be easily reproduced. It looks like headphones are shorted to AUX inputs (that's why the amp becomes microphonic) - but they shouldn't be. Maybe solving this problem will help to solve the muting issue. It seems to me that the problem is not related to the board.

Mark

[Enzo]

Nick sounds like a good bet. But otherwise, doesn't Peavey have a service center in the UK?


Don't assume because you can't find the solution that no one else can either. I am a very experienced tech, but now and then something evades my solution, I send it to someone else, and more times than not, it is something simple I managed to overlook or make faulty assumptions about. And I was also in the position of being the place other shops sent things when they couldn't figure them out. Sometimes I found it simply, other times I pulled hair until I got it. But everything is solvable.

One novice error is to assume problems are all bad parts. I don't know your circuit, but I can imagine two unrelated circuits near to each other, each needing a ground reference, and that ground connection is missing. Now they are in series instead of unrelated. Zaniness ensues.


And when it comes to parts, a guy in my position knows a lot more places to look for them.

[Kidderman]

Thanks Mark and Enzo. I've accepted that my limited experience and knowledge aren't going to get this issue sorted and that simply making assumptions about parts being bad can waste a lot of time, effort and money. Having exhausted the possibility of obtaining the 'correct' parts from Peavey U.S. and U.K. (Barnes & Mullins), as well as the doubt which has now been cast on whether the problem lies with the phones/aux PCB, I've decided to ship the amp to Nick for further testing which I hope will identify and rectify the problem once and for all. I'll post the outcome soon, hopefully.

[nickb]

I took a look at this today. I started by looking athe aux/headphone PCB before even turning on. This is how the 8 pin connecter is wired

PIN	SCHEMATIC	PCB
1	PHONES PULLUP	AUX TIP SWITCH
2	GND	GND
3	GND	GND
4	AUX TIP	HEADP TIP
5	PHONES TIP	AUX TIP
6	AUX SLEEVE	PHONES SLEEVE
7	PHONES SLEEVE	AUX SLEEVE (TRACK WAS DAMAGED- OPEN)
8	N/C	N/C

So the board does not correspond to the schematic. I bussed out the DSP PCB end and it matches the schematic. So back on the aux/phones PCB I cut tracks to the jacks and rewired it in the correct order. We now have aux in and headphone out working. But wait, there is more. The mute does not work. The phones inserted signal makes it all the way to the DSP and it does mute the signal a little and in a distored kind of way. Could be fimware but I need to check the mute circuit first.



There's more...
There is a really ugly mod on the main board. It corresponds to the 30V supply. I note the board is Rev A. I also note the front panel overly does not quite line up with the LEDS. Further it's clearly been in a fire. It has that distinct smell. IMHO this is a very early version that was released for demo only. A fire happend and this got sold off and so escaped it's confines.





And finally...

There is oscillation somwhere. As you turn up the master and listen through the headphone it's like listening to a short wave radio. Oh dear...

Update 1: The oscillation was crosstalk in th aux/phone ribbon cable. Fixed
Update 2: The mute FET had been removed and replaced with a bypass resistor (due to non-functional phone insert signal ). Fitted new FET. Fixed.

[MarkusBass]

Does it mean that Peavey released the amp with incorrect AUX board and they didn't notice that? Meaning: an inexperienced user wouldn't be able to fix it because the amp was already manufactured incorrectly.

Update 2: The mute FET had been removed and replaced with a bypass resistor (due to non-functional phone insert signal ). Fitted FET.

What do you mean by "FET had been removed" and "Fitted FET"?
I assume that that the "processor" part is working correctly but the JFET muting circuit was not correct, right? There should be a resistor in series and another JFET to the ground. Otherwise, even though the JFET is switched off, the signal is passed to the following stage due to the high input resistance of the following circuit. Is it a possible explanation of the problem?

Mark

[nickb]

Does it mean that Peavey released the amp with incorrect AUX board and they didn't notice that? Meaning: an inexperienced user wouldn't be able to fix it because the amp was already manufactured incorrectly.

The knew about it and that is why they yanked the JFET and bypassed it. That is also why I think this was an early demo-only model and eventually got sold off .

What do you mean by "FET had been removed" and "Fitted FET"?

Hmm, that wasn't too clear was it? My brevity got lost in translation. The PA mute JFET Q7 was missing and replaced with a small value resistor so defeating the mute function. I removed the resistor and fitted the JEFT.

I assume that that the "processor" part is working correctly but the JFET muting circuit was not correct, right? There should be a resistor in series and another JFET to the ground. Otherwise, even though the JFET is switched off, the signal is passed to the following stage due to the high input resistance of the following circuit. Is it a possible explanation of the problem?

Mark

Yes the processor part was working.

[Kidderman]

The knew about it and that is why they yanked the JFET and bypassed it. That is also why I think this was an early demo-only model and eventually got sold off .



Hmm, that wasn't too clear was it? My brevity got lost in translation. The PA mute JFET Q7 was missing and replaced with a small value resistor so defeating the mute function. I removed the resistor and fitted the JEFT.



Yes the processor part was working.

The amp was in Nickb's hands for a day. As the day unfolded, he kept me updated with one discovery after another. To say I was getting worried is an understatement. I had no idea that the issues he was describing existed. I don't believe the guy who I bought the amp from would have known either. Can't get my head around the theory that the amp would have been modded/repaired prior to it originally being released for sale. What began as a search for replacement sockets (and later a PCB) ended up as being a repair needed to put right a botched attempt to conceal and rectify an early problem resulting from damage (a possible fire). As can be seen from Nick's posts above, he was able to work through and fix each of the problems as they became apparent. This is a guy who clearly knows what he's doing and who takes great pride in his work. With hindsight (aint that a great thing?), I should have shipped the amp to him as soon as I noticed the problem with the headphones/aux/muting. Would have saved a lot of time and effort from the numerous people (Peavey U.S., Barnes & Mullins, forum members-I thank you all) who tried to help me with that particular problem. Should the need for amp-related work arise in future, I'll be doing exactly what I should have done in this case. I should have the amp back in a couple of days. It'll be great to have it functioning at 100%. I paid £130.00 for the amp and a Sampera ll unit. Together with the extremely reasonable cost of the repair, that's a bargain in anybody's book. When the amp gets back to me, I'll post one final message. Thanks again for all the help and to nickb for doing such a great job.

[Enzo]

As I read the earlier discussion, the amp was never released for sale. I read it to mean the amp was some sort of prototype or work in progress that escaped somehow. I have in my possession a few amps that were never meant to be sold. They were to be destroyed, but I hid them and fixed them up for my use. Someday, someone will probably wind up with them, I certainly won;t have instructions in my will to destroy anything.

Who knows, the amp may be in circulation due to someone diving into the rubbish bin.

[Kidderman]

As I read the earlier discussion, the amp was never released for sale. I read it to mean the amp was some sort of prototype or work in progress that escaped somehow. I have in my possession a few amps that were never meant to be sold. They were to be destroyed, but I hid them and fixed them up for my use. Someday, someone will probably wind up with them, I certainly won;t have instructions in my will to destroy anything.

Who knows, the amp may be in circulation due to someone diving into the rubbish bin.

One of the attractions when I first looked at buying the amp was its pristine-looking cosmetic condition and the fact that it was demo'd and sounded great. I'd really like to have a blow by blow history of the amp from day one-just out of curiousity-but it seems from what you say, Enzo that strange, unexplained things happen in the wonderful world of guitar amplifiers. Had I thought to look under the hood, I'd have been totally unaware of any work or mods which had been carried out at whatever point in the amp's life. I'm confident that it'll now be fine for a long time to come, and that there's a source of expertise out there which I could trust in the event of future work becoming necessary.

[Kidderman]

I just got the amp back from nickb. Hooked everything up and it's perfect. Speakers mute, headphone output and aux input work fine. Couldn't be happier. Thanks to all who offered advice during the course of this thread.