Converted Peavey Deuce issues

[cbass]

Did we ever determine if the NFB is phased correctly?
You may want to disconect it for now or try swapping it again.

That chassis is huge you should be able to find a better place for the Imp switch

[beasleybodyshop]

Cbass, I went ahead and removed the imp. Switch entirely and hooked up the one OT wire to the output jacks.

[Leo_Gnardo]

How 'bout those output jacks, are they still jam up next to the pre tubes? Whatever you can do to keep output wiring from seeing input, distance, shielding, it all helps.

Sounds like we're sneaking up on a solution.

When you put an ohmmeter on your feedback R, it's also seeing the circuit to ground - thru the presence control, and a near short to ground thru the OT secondary. So 4K7 seems about right.

You might try increasing or decreasing the feedback R, might find a sweet spot where the 13 kHz chatter goes away. I've had to do this in authentic Marshalls, before during and after the plexi era.

Forgot to say - the board looks terrific, nice job!

[beasleybodyshop]

How 'bout those output jacks, are they still jam up next to the pre tubes? Whatever you can do to keep output wiring from seeing input, distance, shielding, it all helps.

Sounds like we're sneaking up on a solution.

When you put an ohmmeter on your feedback R, it's also seeing the circuit to ground - thru the presence control, and a near short to ground thru the OT secondary. So 4K7 seems about right.

You might try increasing or decreasing the feedback R, might find a sweet spot where the 13 kHz chatter goes away. I've had to do this in authentic Marshalls, before during and after the plexi era.

Forgot to say - the board looks terrific, nice job!

Thanks Leo, although I feel like i did a "good enough for government work" job, I have learned tremendously for my next build.

When I get home I will play around with resistor values, maybe attempt to replace the input wires with another double conductor shielded one. Still pretty sure my CH2 volume pot is bad - ordered another one, we will see where that goes when it gets in. Fun fact - I have discovered that I can't hear anything over 13Khz very well lol. I had my RTA out when I was troubleshooting, and noticed big spikes past 13K that should have been painfully loud, but I couldn't hear them. lol.

[JazzGuitarGimp]

Fun fact - I have discovered that I can't hear anything over 13Khz very well lol. I had my RTA out when I was troubleshooting, and noticed big spikes past 13K that should have been painfully loud, but I couldn't hear them. lol.

If you were listening through a typical guitar speaker, you may not be as bad-off as you think. Guitar speakers' frequency response typically dive bombs at about 5KHz. At 13KHz, they are all but petered out.

[Leo_Gnardo]

Thanks Leo, although I feel like i did a "good enough for government work" job, I have learned tremendously for my next build.

When I get home I will play around with resistor values, maybe attempt to replace the input wires with another double conductor shielded one. Still pretty sure my CH2 volume pot is bad - ordered another one, we will see where that goes when it gets in. Fun fact - I have discovered that I can't hear anything over 13Khz very well lol. I had my RTA out when I was troubleshooting, and noticed big spikes past 13K that should have been painfully loud, but I couldn't hear them. lol.

There's something to be noted about the typical geography of a successful amp's interior layout - the input's kept well away from the output. In some small chassis that can't be accomplished. In the case of Mesa/Boogies that are kicking up an awful fuss in the 12KHz+ ultrasonic feedback region, I've even put a copper "dam" between the OT leads and input circuit, that seems to help. In your case I don't think it's the input leads from jacks to board, but the leads from board to tube sockets that are dangerously close to the output jacks.

And 100% agree with JGG. JBL's have a 6K 'spike', and Altec 417 to a lesser extent, due to their aluminum dust domes acting as tweeters, but just about all other guitar speaker def. roll off quite a lot past 5KHz.

FWIW I used to hear up to 19K no problem but now 14K is the limit, and that will decrease with age, with anybody, listening to loud music or not. The fancy name is presbycusis.

[beasleybodyshop]

Thanks Leo, although I feel like i did a "good enough for government work" job, I have learned tremendously for my next build.

When I get home I will play around with resistor values, maybe attempt to replace the input wires with another double conductor shielded one. Still pretty sure my CH2 volume pot is bad - ordered another one, we will see where that goes when it gets in. Fun fact - I have discovered that I can't hear anything over 13Khz very well lol. I had my RTA out when I was troubleshooting, and noticed big spikes past 13K that should have been painfully loud, but I couldn't hear them. lol.

There's something to be noted about the typical geography of a successful amp's interior layout - the input's kept well away from the output. In some small chassis that can't be accomplished. In the case of Mesa/Boogies that are kicking up an awful fuss in the 12KHz+ ultrasonic feedback region, I've even put a copper "dam" between the OT leads and input circuit, that seems to help. In your case I don't think it's the input leads from jacks to board, but the leads from board to tube sockets that are dangerously close to the output jacks.

And 100% agree with JGG. JBL's have a 6K 'spike', and Altec 417 to a lesser extent, due to their aluminum dust domes acting as tweeters, but just about all other guitar speaker def. roll off quite a lot past 5KHz.

FWIW I used to hear up to 19K no problem but now 14K is the limit, and that will decrease with age, with anybody, listening to loud music or not. The fancy name is presbycusis.

Presbycusis? That deserves some after dinner reading. As far as wires being too close, are you referring to my signal wires being too close to the output jacks? what about wrapping them in conductive adhesive copper tape? if they are taped to the chassis, that would serve to shield them no?

Edit: Or possibly build a little shielded box out off copper foil around the output jacks?

[cbass]

ALso move/shorten the input jack wires on ch2 away from the volume and tone stack controls

[Leo_Gnardo]

Presbycusis? That deserves some after dinner reading. As far as wires being too close, are you referring to my signal wires being too close to the output jacks? what about wrapping them in conductive adhesive copper tape? if they are taped to the chassis, that would serve to shield them no?

Edit: Or possibly build a little shielded box out off copper foil around the output jacks?

Best would be to get the output wires at some distance say 4 inches or more from the pre circuitry. I think any other solution would be a second-best. If you cover with shield tape, don't forget to run a ground wire to it. Don't depend on its adhesive to be conductive.

- - - - - - - - -

Loss of visual acuity with age is presbyopia. If you're a presbyterian, you win the hat trick!

I first ran across mention of presbycusis in Don & Carolyn Davis' "Sound System Engineering". What's remarkable about the loss of high frequency acuity, is turning up the treble just annoys the listener. When my living room speakers started sounding harsh & brittle to me, I just re voiced 'em by modifying the crossover, padded down the tweeters. Maybe they're not "flat" but I like the way they sound now, and so does everyone else.

What I read about in my early 20's, is coming true. Drat! Well, at least I knew it was coming up. What hearing I have left, I try to save by giving my ears lots of rest, and using ear plugs or shooters muffs when running any kind of loud equipment, vacuum cleaners, drills, dremels, lawn mowers, like that. My neighbors used to look at me like I just landed from Mars. What a NUT! Now - many of them are seen running their lawnmowers with muffs on.

[beasleybodyshop]

Well, It has come a long way. After hours of madness, two six packs of Woodchuck, and lots of help I finally finished it.Final solution was re-wiring the input jacks with shielded cable, plus taping down the OT wires and signal wires with copper tape finally done did it. lol. I can crank the presence up to almost 4 o'clock before getting faint squeal, and thats with the treble maxed. I think ive come as far as I can. Tomorrow i am going to take 'er up to work (I work at the Perot Museum of Nature and Science) and after all the little kids and parents leave i'm going to turn it all the way up in the Dinosaur hall (i think the T-Rex and Alamosaurus will really dig it)!!!

Thanks everyone. Big shout out goes to Leo, M Fowler, cbass, Martin Manning, and everyone else in the TAG community. Now when I look at an amp from the inside, things make a little more sense than they did a month ago, and if it wasn't for you guys I wouldn't be here. Now, on to the next project! I was bored at work today and found a piece of 14 ga aluminum that is just big enough to brake into an Express chassis...

[Leo_Gnardo]

A little shakedown run, good! Yes the dino's and the kids will love it.

Here's a couple more ideas.

The traditional Marshall way of running inputs to 68K resistors on the board then leads to the preamp tubes' grids, that last jump is a magnet for noisemaking. You could either go 2-input not 4, run a shielded lead to each grid and put your 68K stopper right there at the tube socket. Or if you insist on 4-input, 2 68K's at each input grid.

I see there's already a mica 'quench' cap on the output drive, between the 100K and 82K. You can increase the size of this cap as necessary to stay out of the squeek & squeal zone. I've used up to 470pF and in extreme cases .001 uF (1 nF Martin!). This rolls off the extreme hi frequencies. The trick is to use the smallest cap you can to stay out of the squeek zone.

One of these days it would be good to put that amp on a scope & see what it's really turning out. You're going to continue building, treat yourself to a scope and signal generator. Used gear is available very cheap compared to new. Sure beats thrashing around "in the dark." Ya done well, you deserve it.

Perot Museum eh? Well I had a lot of respect for that ol' fossil. Sounds like a good gig.