modifying peavey valveking

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vodka
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modifying peavey valveking

Post by vodka » Mon Nov 15, 2021 5:28 am

Hello everyone, 6 months ago i got my peavey valveking 100 head and about 2 months after the purchase i started modding it and now it sounds really good. However, i wanted to do some more things. I noticed at the schematic, at the preamp section, there is the Q103 transistor, the Q102 and the Q101. I was wondering, what is their purpose? Also, when i opened up the amp i saw there was an ic. Last thing is that whenever i put a boost in fromnt of the amp, in the clean channel there is a significant volume boost as well along with a tad more gain. Is the lead channel supposed to not have the volume boost? if not how can i make it have that volume boost? In the lead channel though, whenever i boost it, there is no volume boost, just more gain. I have removed the diodes d101, d102 and bypassed the r100, removed the r171, changed r101, r104, r103 to 100k, removed c149.
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Enzo
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Re: modifying peavey valveking

Post by Enzo » Thu Nov 18, 2021 4:45 pm

Volume boost on clean but not dirt channel? Means the clean channel has headroom you can use, the dirt channel does not, it is already using a ton of gain to give it the dirt. And when you say all you get is more gain, by gain, do you mean distortion?

Q103? Look at your schematic, it enables C115 or not. That increases gain of stage for dirt channel.

Q102? A simple emitter follower to drive the FX send. Works same way a cathode follower works, but doesn't require a whole extra tube.

Q101? It acts as a mute. When channels switch, all the relays moving and other stuff can cause pops or noises. Q101 very briefly mutes the amp to prevent noises then. Note that Q101 is controlled by stuff in the switching circuits.

IC? Look at your schematic, the IC is the whole reverb circuit. Very common circuit, used in a zillion amp models.

D101, D102. Not sure I would have removed them. They are not "Clipping diodes" as is so often said. They are noise reduction diodes. The circuit only uses them on dirt channel ,not clean. You might hear a small difference without them, usually at the expense of noise. Mostly that difference is noted at lower levels. If you short R101, it is in parallel with them, so removing them is pointless.

C149? If you like it better, fine. It should only affect the dirt channel. It was there to roll off some of the fizziness.

R171? Huh? Why would you remove that resistor? Could 171 be a typo? It affects when Q103 turns off or on.

vodka
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Re: modifying peavey valveking

Post by vodka » Mon Jan 03, 2022 2:39 pm

Some more info on the boost: i changed r120 to 2.7k, c114 to 680n, and when i use the boost pedal, there is a slight, very slight volume boost. To clarify, im not talking about the volume boost switch on the lead channel, just a clean boost pedal with about +10db boost.

As for the r171, not a typo. I heard that removing it would allow to enable gain boost switch even when using the clean channel, and it does. give a slight gain boost, a bit of volume and some highs.

Thanks for the info on the transistors and the ic.

What woudl change if stage v2b (the one with pins 6,7,8) was supplied with b+ voltage instead of b++? I assume more headroom and a tad more clarity, but i am really curious.

vodka
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Re: modifying peavey valveking

Post by vodka » Sat Jan 08, 2022 12:47 pm

update:
Removed c108 and put wire in its position, r114 to 1meg. Result was better response, and tone not as bassy as it was. Feels more real.
c116? What is its purpose?
r107? Should i bypass it? Would this bring more clarity? Maybe was r107 filters some noise?
Im just brainstorming.

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Enzo
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Re: modifying peavey valveking

Post by Enzo » Mon Jan 10, 2022 9:02 pm

V2b? It is powered by B++, which appears to be considerably higher voltage that B+, isn't it? Not sure how that would increase headroom. Also note clipping in the stage is more likely against the cathode voltage than the plate voltage. Also consider the filter caps in the preamps of amps are less about smoothing than they are decoupling. If you move that gain stage to another B+ node, you risk causing instability or motorboating.

Just a suggestion, in a complex circuit like this, it is difficult to look high and low to find a part just by its number. I found C116 and R114, but really it would have been easier if it was called C116 at the input or R114 V1 grid return.

C116 is a tiny cap, it is there to shunt off any RF that gets into the input - ever pick up radio stations? You probably have guitar cords with higher capacitance.

R107. Filters? Hold the schematic farther from your eyes, so you can see the larger picture. The hot signal from V2a comes to R107 and R111. They form a voltage divider to reduce signal level going into V2b. That helps control overloading the tube. You will find the same thing happening at R143 and R146. A 5150 and others of that family has level control stuff like that all through it.

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