Supercharging a V8

[Verne Andru]

No different than between a 50 watt and a 100 watt speaker.

I found there was no change in tone on mine with the exception that I obviously wasn't pushing the speaker as hard Distortion tends to be a combination of pickup breakup, pre-amp breakup, power-am breakup and speaker breakup. Change or eliminate any of those - say a lower power pickup - and your tone will change accordingly.

[larryguitar]

Verne-
Excellent post. I tried both a V8 and V16 at GC the other day, and was thinking of going back to check (buy?) again.

I'm curious about one thing you mentioned, though-is the op-amp in the input simply used as a buffer, or is it used to add clipping, ala the JCM900?

Thanks,

Larry

[Verne Andru]

Hey Larry - if the V8 is the same, more or less, as the V508, then the op-amp is used as the first stage of preamplification. Since it is a noisy chip, it may also be in there for some added clipping, but it certainly isn't needed.

If you really want to check out what the V8 is capable of, hook up your fave type of guitar and dial in the gain just before it starts distorting. On a stock V8 this should be around 9 o'clock - on a modded one it moves to around 1 o'clock. Crank the volume all the way - you should have a pretty loud, albeit noisy, clean tone. Then put a clean booster in the FX loop and dime it. This will push the power section into distortion and should shake the house.

The neat part of the V8 is you can set it so the preamp distorts, then roll back your guitars volume for a clean tone, plus put a booster in the FX loop and switch distortion between preamp, poweramp or both on the fly. It's got tone for days. If the V16 had an FX loop [i hear some people have theirs modded after the fact for $75] it would be the better choice if your gigging. For studio work the V8 is a monster.

[jjpistols]

Originally Posted by yaz75

Sounds like all you need to do now is put it in a bigger cabinet to utilize a 12" speaker.








Nice thread.

fknawesome!!!

[gnoj_LL]

ey guys! jUst a quick question to all of you. is there a big difference form the plaomino V8's that are made in the US compared to the vietnam ones?

[jrockbridge]

Great thread!

[SLEEPER 86]

Originally Posted by gnoj_LL

ey guys! jUst a quick question to all of you. is there a big difference form the plaomino V8's that are made in the US compared to the vietnam ones?

i am also very interested in this, has anyone had a chance to back to back the older vs. newer ones?
great post!
Eric B

[SLEEPER 86]

anyone know if the op amp in the v16 is the same as the v8?

[dcindc]

It's the same op amp in the V1512 that I just took apart, so I'd feel comfortable saying, yes.

There's lots of op amp choices. We could fill pages with discussion about them. But we have Verne's relayed experience, which is pretty damned helpful!


edit: found a V16 schematic. That op amp is only for the reverb. The main signal path is all tubes.

[Verne Andru]

I've added the following notations to the first few posts, but thought I'd copy them here for those following the thread.

Update:

0 - When I did the Opamp swap, I used a cheap chip socket. Under use, the chip has a tendency to wiggle around and not make proper contact, audible by an annoying hum. Use of a high-quality socket or, even better, soldering the chip to the board/old chip legs are better options.

1 - Somewhere in this thread I mention that I used a plastic enclosure for the Backpack but should have used a metal one. As it turns out, plastic is the better choice. Because of the different circuits - some input, some output, some FX - using a metal enclosure would have forced everything to the same ground. I lined the plastic box with copper foil and simply cut out what was needed to isolate the various circuits and their accompanying grounds.

2 - Add more bottom-end thump and remove shrillness - Amp techs love to screw with some specific capacitor and resistor values to tweak an amps voice. On the V8, changing capacitor values involves taking the whole amp apart, but you can effect most of these changes by adding a couple of resistors to the component sided of the PCB. First, download the schematic:

http://www.guitarnuts.com/amps/vc508..._schematic.pdf

Second, get 2 x 1K 1/2 watt resistors. Cost - under 50 cents.

Now, locate and remove C9. This involves clipping one of it's legs to debilitate it, both to remove it. This is similar to the Fender top-boost circuit that nobody uses. It just adds the shrillness to the amp. Cost - nothing.

Now for the resistor changes. We can change the values of R10 and R15 to the same as replacing them with 560 to 830 ohmer's by putting a 1K 1/2 watt resistor in piggy-back fashion across each. This lets more current/frequency through providing a sweater mid range.

The corresponding caps at C7 and C13 can be changed as well [board flip required] but my amp tech claims the bigger changes come with the resistors. These changes cost pennies and don't take long once you're inside the amp. If you do decide to flip the board, changing C8 to .068 uF 400 volt MTLPOLY would also be worth your while.

[Oblivionaut]

sorry to bring back such an old thread but i have a question...

I have a Palomino V8 would actually like to remove the tone control completely. I have been using the amp by pluggin directly in to the line out wqith a stereo plug, bypassing boththe preamp as well as the tone control and it sounds killer. But it also only runs at full volume, so i would like to use the preamp minus the tone control...
To do this which caps and resistors are the correct to remove or jumper...

TO me it looks like R12,R13, C10, C11, C9, then jumper r11 to r16 as well as remove the tone pot.... is this correct???

Thanks a million...

[dcindc]

Lift one end of C12 and the wiper of P2. That should do it.

[Matter-Eater Lad]

What about speaker change? I have the V58 w/ 8" speaker & man it is bright. I just noticed an 8" Jensen MOD 8-20 is only $14 (+$9 ship.) from tubedepot.com, anybody know about these speakers?

[Verne Andru]

September 28, 2008 update:

I just picked up a new Crate V33H

[Verne Andru]

Another quick tweak.

I've been contemplating tone stacks and it appears the V8 is very similar to the Marshall 18 watt [http://amps.zugster.net/articles/tone-stacks#18Watt]. The resistor values on the V8 are higher - I'm assuming that's to cut the signal strength to allow for the effects loop, which the Marshall doesn't have. The V8 also has a .0022 uF 100v capacitor [C12] the Marshall doesn't have.

I decided to pop the leg on one side of the cap to see what effect it has on the tone. Surprise, surprise - that little bugger is the cause of some major nastiness. The tone control on the V8 works so in the middle you get full treble, turn left and you add bass and turn right and you alter the mid-range [in a good way] but muddy up the signal at the same time.

It turns out the "honky" mid-range that adds a "boxiness" to the tone is coming from C12! By simply removing that cap you re-voice the amp in a very good way. The tone pot now does the same thing turning right or left, except it isn't affecting the mid-range because the cause of the midrange problem, C12, is no longer in the circuit.

If you do nothing else to your V8, remove C12 and C9. These can be easily snipped off without taking the amp apart. Thank me later.

[dcindc]

Originally Posted by dcindc

Lift one end of C12 and the wiper of P2. That should do it.

I know it's not the same, but I found it funny.

That's a unique tone control circuit.

I was gona say that I've had good luck snipping bright caps in a lot of SS newer amps, but that's not really a bright cap, C9 is.

Anyway, good find!

[Verne Andru]

Originally Posted by dcindc

I know it's not the same, but I found it funny.

That's a unique tone control circuit.

I was gona say that I've had good luck snipping bright caps in a lot of SS newer amps, but that's not really a bright cap, C9 is.

Anyway, good find!

Right you are - I never even noticed that. I kept ignoring C12 until it dawned on me it was like the proverbial elephant in the living room.

Here's one for you. I'm thinking of re-wiring the tone stack into a 2-knob similar to this -> http://amps.zugster.net/articles/tone-stacks#Brownface

I figure I could use a 250K concentric stacked pot [http://www.allparts.com/store/ep4485-000,Product.asp], tap into the signal at R12, remove the existing pot and come back in at the existing tone wiper terminal.

Thoughts?

[dcindc]

No, I think this is the way to do it:
remove C9, 10, 11, 12.
remove at least R12, but possibly R13 too.
and of course P2 the original pot.

so IN is at R11 out.
OUT is at R6 in.


I'm real interested in how that turns out. Would make for a very versatile little amp!

[Verne Andru]

That would be taking 2 x 221K resistors out of the path to FX send. You sure that wouldn't be driving that line too hot?

[dcindc]

I'm betting on there being a lot of loss in that new double tone stack.

The stock one didn't have much loss.

Which is why I believe the resistors are there, along with creating the split for the tone stack to work against.

If I'm utterly wrong, just take the in from the out of the first resistor, and the out to the in of the second resistor. Remove all those other caps.

[Verne Andru]

Worth a shot. I'll keep you posted.

FYI - with all the other mods I've done to this thing it sounds almost exactly the same as the V33 gain channel [which is heavily modded as per the other thread]. I'm going to try changing C14 to a 1.2uF and dropping R10 & R15 to 510K's [they're currently around 600]. I'm figuring that should open up a bit more low-end thump. It sounds fantastic now as is, but I'm seeking perfection here!

[datru]

Originally Posted by Verne Andru

If you do nothing else to your V8, remove C12 and C9. These can be easily snipped off without taking the amp apart. Thank me later.

I have a V8 with a 12AT7 installed and an L-pad. No other mods.

Are you saying that I should just go in and clip off C12 and C9, no jumping, no soldering, etc? Exactly what will the change be?

Just curious, why does the factory put them in if it's better without them?

Great thread.

[Verne Andru]

Originally Posted by datru

I have a V8 with a 12AT7 installed and an L-pad. No other mods.

Are you saying that I should just go in and clip off C12 and C9, no jumping, no soldering, etc? Exactly what will the change be?

Just curious, why does the factory put them in if it's better without them?

Great thread.

If you want to be "safe" use a soldering iron, slip something under the capacitor in question [i find a letter opener works well], heat one side and pop one leg up from the circuit board. Do that to both and see how you like it. If it's not to your taste, you can quickly solder them back in place.

If you feel "randy" just go in with snippers and snip them out of there.

Removing C9 will take some of the harshness out of the amp - particularly with gain.

Removing C12 should [i say "should" because I've done this after numerous other mods, but I'm fairly confident it will] remove most of the midrange that makes the amp sound "boxy" and "honky," for lack of a better term.

I'm not sure what the Crate engineers are smokin', but I don't want any. They seem to get 90% there on a great design then it seems they head off for munchies and leave the janitorial staff to finish the job.

Seriously - I think C12 was put in there as somebodies "bright idea" to add mid-range as well as bass and treble to a single knob tone stack. Probably worked on paper but it ended up introducing a whole bunch of unwanted midrange that you can only dial out by making the signal muddy.

Good luck!

[datru]

Is it necessary to drain the caps prior to cutting out C9 and C12?

[Verne Andru]

My legal department tells me I can't answer that question. I don't want to be held responsible for anybody that touches the wrong thing and gets electrocuted.

Draining the caps is relatively easy on the V8. Wear rubber soled shoes. I use a multimeter to test the voltage from pin 1 on v1 [the preamp tube]. IME the V8 maintains a charge of around 60 volts. I run a wire from pin 1 on v1 to ground [chassis] for around a minute then test again just to make sure. Might have to do it a couple of times to make sure everything is completely drained.

That said, and I'm not recommending this to anybody, I only do the above when removing the circuit board from the chassis. Being very careful, I can do simple mods to the component side of the board without draining the caps - but that's me.