Supercharging a V8

[Wayne2]

 

it would be the better choice if your gigging. For studio work the V8 is a monster.

 

 

I guess I'm a little gunshy because my first amp had the clean channel destroyed when someone plugged a microphone into it.

[Verne Andru]

Typically the preamp section will provide an initial signal boost [first 1/2 of 12A?7], run the signal through whatever tone stack is provided, then another boost [second 1/2 of 12A?7] prior to going into the power section. The signal coming out of the preamp tends to be pretty hot.

 

What Saint Lois Music did was kinda tricky, and pretty neat once you get your head around it. The first boost comes from the first 1/2 of the opamp, not the preamp tube. Then they run the signal through a pot [Gain] which lets you vary how much you want to push the second 1/2 of the opamp which drives the first 1/2 of 12A?7. This is what gives the amp so much gain [preamp distortion]. It's like having a built-in clean boost instead of using a pedal. The higher quality opamp I suggest lets you keep the signal as clean as possible so you can really drive it with less opamp distortion.

 

The signal then goes through the tone stack, which causes the signal level to drop due to component resistances. At this point there's usually a makeup gain stage but if they put that before the FX loop the signal would be too hot to run through pedals. Other amp designs have to specifically force a drop in signal level before the FX send - in this design they [cleverly] use the already attenuated post tonestack signal. The Volume control can be thought of as an FX send level control as it performs that function when using the FX loop.

 

Without using the FX loop it controls the signal level that passes from the preamp to the poweramp. Without the FX loop you could do away with the Volume control and just use the Gain. In fact, this is exactly what they did with the last V5 [Chinese made one] that doesn't have the FX loop. They simply relabeled the Gain control to Volume. Everything else is pretty much the same.

 

When the signal returns from the FX loop it needs to get boosted so it can properly drive the poweramp section [tonestack gain makeup stage described above]. They use the second 1/2 of the preamp tube for this, then on to the EL84 and out the speaker.

 

So in effect you're correct - we can't be sure how much of the "power amp" distortion is coming from the preamp tube and how much is coming from the EL84. Using a lower gain tube - like the 12AT7 I suggest - helps to keep distortion from that tube to a minimum. If you keep the 12AX7 in there, you're most surely hearing more breakup from that tube than the other.

 

As with all designs, there have been trade-offs made. But I think, for what it is, it's a pretty smartly designed amp with features you're not going to find until you get up into the boutique market - and even then the pickings are pretty scarce.

 

Experiment and enjoy. It's a fun little amp with tons of tone in it.

[Wayne2]

 

. They use the second 1/2 of the preamp tube for this, then on to the EL84 and out the speaker. So in effect you're correct - we can't be sure how much of the "power amp" distortion is coming from the preamp tube and how much is coming from the EL84. Using a lower gain tube - like the 12AT7 I suggest - helps to keep distortion from that tube to a minimum. If you keep the 12AX7 in there, you're most surely hearing more breakup from that tube than the other. As with all designs, there have been trade-offs made. But I think, for what it is, it's a pretty smartly designed amp with features you're not going to find until you get up into the boutique market - and even then the pickings are pretty scarce. Experiment and enjoy. It's a fun little amp with tons of tone in it.

 

 

I agree. I love this amp. I'm eagerly waiting for the clean boost pedal to come in the mail.

 

In the meantime I've been cranking the volume section and I'm beginning to hear what you're talking about. Even with the gain way low, as volume approaches the top the tone improves, and it seems like it's on the verge of getting really good.

 

I actually found the manual, and it has a block diagram of the signal path. Maybe one of these days I'll scan it in.

[TechFan2010]

I want to thank everyone who has posted on this thread. I removed c9 and c12 last night and added the 1k ohm resisters to r10 and r15. The piercing highs and obnoxious mid-ranges are gone, and I am still using a JJ 12ax7 preamp tube. My 12at7 tube will arrive tomorrow, but I don't know how my little v58 could sound any better than it does now. Thanks again.

[Verne Andru]

Here's a neat little mod/trick I just came up with. I have my 2 V8 cabinets on the floor and was pondering how I could do a non-destructive tilt-back mechanism so the speakers would aim the sound up a bit, away from my ankles. While cleaning out some junk I found a bunch of these old plastic 35mm film containers I had squirreled away that look like this:

 

 

I tried a couple under the front feet [take the top off and put the foot inside] and they were pretty near the perfect fit, albeit a bit floppy. Then I came across the idea of putting the lid between the foot and the cabinet so the canister part could pop on/off as I needed. After looking at a bunch I found some black lids that the feet fit in perfectly [on the inside] - punched some holes for the screw and - voila - instant kick-back.

 

The come in various colours and from slightly different molds. If you have a shop that still does 35mm film processing chances are they'll have boxes of them and be more than willing for you to take a few off their hands [at least one close to me was like that].

 

Hope somebody else can put this idea to good use.

 

This little amp seriously rocks!

[TechFan2010]

I have auditioned several tubes with my V58. My tele sounded great with all of them, but my ES-335 was harsh with everything except a JJ 12at7. I tried an EH 12ax7eh, a JJ ECC83S, a Jan Phillips 5751 and the JJ 12at7. The lower gain tubes need a clean boost to drive the EL84. I am using an eq pedal, and the sound is thin without it. Finally, the only mods that I have made are removal of the two capacitors from the tone section and addition of the cathode bias resistors for the preamp tube. I'm not brave enough to try the op-amp. Even so, the sound is now many times better than the original. It really makes me wonder why Crate didn't ship it like this from the factory.

[Wayne2]

The clean boost has arrived and I finally got a chance to use it. It's producing some interesting tones but kind of flattens everything out, so it seems loud but not as dynamic as without it. Sort of greasier and less responsive to picking. I'm also starting to realize what's meant by "harshness" in the mids.

I think I might try changing the tube next.

Interesting post at tdpri.

[Wayne2]

Does anyone know if the VOX AC4TV is related to the Crate Palomino V8? The reason I ask is that I noticed that they're being made in Vietnam, have a 10" Celestion speaker, similar size and layout, Russian 12AX7 and EL84 tubes, and are sold through Guitar Center. I wonder if they're rolling off the old V8 assembly line.

[gnolivos]

That's interesting. I never heard this was the case, but who knows. I'd like to know more if anyone finds add'l info supporting this.

Originally Posted by Wayne2

Does anyone know if the VOX AC4TV is related to the Crate Palomino V8? The reason I ask is that I noticed that they're being made in Vietnam, have a 10" Celestion speaker, similar size and layout, Russian 12AX7 and EL84 tubes, and are sold through Guitar Center. I wonder if they're rolling off the old V8 assembly line.

[vaughandy]

Hey all,

I wonder if anyone will see this as the thread is pretty old... Here's hoping! Anyway, I recently got a used V8 off craigslist and have started modding it as per this thread. I've installed a 12at7 and an L-Pad after the power tube. I also wired in a speaker out TRS jack. So far so good; amp sounds great. I'm planning on doing the tone knob mods and replacing the op-amp in the near future.

That said, there's a couple questions I have as a newby. First, I've tried using an EHX LPB-1 in the fx loop to drive the power tube. This works, but I've found that it makes me extremely susceptible to EMI / RFI interference (I can hear NPR quite well). Do you guys think that's a product of that particular clean boost pedal? Other recommendations?

Second, I'm considering going from the 12at7 to an even lower gain tube in order to get more clean headroom. If I do this, will I be lowering the overall volume output potential of the amp? I know this is a silly question, but I'm new to the whole tube amps thing.

Finally, any suggestions for an external cab? Since the speaker out is really 8 ohm but the stock speaker is 4, I presume I could use any combination of speakers with a total z of either 4 or 8 without having to worry too much? And finally, dumb question of the day, can I expect significantly more clean headroom by driving, say, 2 x 10" than the current 1 x 10?

Thanks!

[Verne Andru]

Originally Posted by vaughandy

I've tried using an EHX LPB-1 in the fx loop to drive the power tube. This works, but I've found that it makes me extremely susceptible to EMI / RFI interference (I can hear NPR quite well). Do you guys think that's a product of that particular clean boost pedal? Other recommendations?

Welcome to the forum. The thing to note about the V8 is on the FX return the first thing the signal hits is the 2nd half of the 12A?7 which is used for gain makeup prior to hitting the power tube. I've tried various types of "boosts" in the loop and have had mixed results. Perhaps the best I've tried is a home-made clean booster. After tons of experimentation I've concluded the amp sounds best without a boost at all. I set the gain to the level of crunch I want and use my guitars volume knob to dial it in/out. YMMV of course.

Originally Posted by vaughandy

I'm considering going from the 12at7 to an even lower gain tube in order to get more clean headroom. If I do this, will I be lowering the overall volume output potential of the amp?

Simple answer is "yes." I don't think you'll be gaining anything with a lower gain tube.

Originally Posted by vaughandy

Finally, any suggestions for an external cab? Since the speaker out is really 8 ohm but the stock speaker is 4, I presume I could use any combination of speakers with a total z of either 4 or 8 without having to worry too much? And finally, dumb question of the day, can I expect significantly more clean headroom by driving, say, 2 x 10" than the current 1 x 10?

I've found the V8 is happy driving either a 4 or 8 ohm load. Mine has an 8 ohm Weber Alnico Silver Bell in it and I have another V8 cabinet with an Eminence Lil Buddy Hemp cone speaker that's also 8 ohm. Together they put a 4 ohm load on the amp. This combination sounds great, but the amp also sounds great with one or the other at 8 ohms. I've also used the V8 to drive my Genz-Benz G-Flex 2-12 with fabulous results but I don't find it sounds much better/different than driving the 2x10's. A little, but not much.

Best - V

[vaughandy]

Thanks Verne! I really appreciate the advice!

Originally Posted by Verne Andru

Welcome to the forum. The thing to note about the V8 is on the FX return the first thing the signal hits is the 2nd half of the 12A?7 which is used for gain makeup prior to hitting the power tube. I've tried various types of "boosts" in the loop and have had mixed results. Perhaps the best I've tried is a home-made clean booster. After tons of experimentation I've concluded the amp sounds best without a boost at all. I set the gain to the level of crunch I want and use my guitars volume knob to dial it in/out. YMMV of course.



Simple answer is "yes." I don't think you'll be gaining anything with a lower gain tube.



I've found the V8 is happy driving either a 4 or 8 ohm load. Mine has an 8 ohm Weber Alnico Silver Bell in it and I have another V8 cabinet with an Eminence Lil Buddy Hemp cone speaker that's also 8 ohm. Together they put a 4 ohm load on the amp. This combination sounds great, but the amp also sounds great with one or the other at 8 ohms. I've also used the V8 to drive my Genz-Benz G-Flex 2-12 with fabulous results but I don't find it sounds much better/different than driving the 2x10's. A little, but not much.

Best - V

[Wayne2]

Originally Posted by vaughandy

Hey all,
That said, there's a couple questions I have as a newby. First, I've tried using an EHX LPB-1 in the fx loop to drive the power tube. This works, but I've found that it makes me extremely susceptible to EMI / RFI interference (I can hear NPR quite well). Do you guys think that's a product of that particular clean boost pedal? Other recommendations?

It might be your pedal. I've been using the ModTone Clean Boost without any interference.

I did have a problem a few weeks ago where my TRS cable failed. It was a Monster Cable that I had lightly used for about three years. I have no idea why it failed, but all I could hear was a weak staticky signal and I was worried I somehow broke the amp. I took it back to Guitar Center and they gave me a new one no questions asked.

[fivefingers]

Originally Posted by nreidt

ok well I just hooked up the L-Pad and tested it out briefly. nothing blew up, so I must have hooked it up right.
it definitely sounds better, crank the volume all the way up and put gain at about 2 o'clock and it sounds great, and this is while sitting in the living room with my wife watching tv and not getting TOO annoyed with me . I need more time with it, and I still need to test it out with the clean boost in the fx loop but I don't have my pedal with me at the moment.

I notice though, and wonder if yours is the same way, but the L-Pad seems very touchy at low volumes. it only really seems to be effective from around 0-3 (if there were numbers on it). and it has quite a jump from no sound to the lowest possible volume.
is your setup similar? maybe I have a bad ground or something...

I definitely need to do something about the preamp hum now, so I think I'll switch out the opamp and switch to a 12AT7 next, and maybe try the tone control mod as well.

thanks again for the information Verne. I'll report back later as I do more and test everything out better.

Every time I see these things

I will be very nostalgia time

[vaughandy]

Man alive, Verne Andru is the best! I've implemented most of your mods, although I haven't installed the new op-amp yet. Gonna do so tonight.

I've built an external 2 x 10" cab with AlNiCo Silver Tens and it sounds just awesome. HUGE sound for a 5 watt amp! I've also found that using an MXR 10-band EQ in the signal loop is the way to go for me. It has a ton of clean boost potential alongside the EQ, and most importantly is much less susceptible to EMI/RFI that my LPB-1 was picking up.

Anyway, just wanted to say thanks again. This has been a hell of a fun and rewarding project. I'll post pics of my cab sometime soon.

[Verne Andru]

Wow, thanks for the kind words vaughandy. You're the first person who's chimed in that they actually did the mods.

I take it you've experienced a bit of a sonic shift in the tonz coming from your humble, little V8? Care to share?

As a bit of an update on my on-going experiments, I recently installed some Seymour Duncan Mick Thompson Blackouts [i think they're the hottest active pups available ATM] in one of my guitars. The Blackouts are so clean I can crank the gain all the way up on my V8 without any oscillation or unwanted noise. They push the V8 straight into metal territory with great low end "chug" and searing top-end. Nice having an adjustable midrange to really dial in a sweet spot! Roll the Blackouts down with my guitar's volume and I get a great jazz tone on the neck and even country spanky on the bridge. Great pickups what work especially well with the V8 mods.

[vaughandy]

Hey Verne (or anyone else),

So like someone else on this thread, I made the mistake of putting in a TLE2072CP instead of the ACP you recommended. I'm wondering how much of a difference this could make. Do you think it'd be significant? I soldered in a new socket in addition to the chip, so replacing it wouldn't really be difficult this time around. Worth it?

- Andy

[Verne Andru]

I've not a/b'd them, so I can't say.

The Excalibur series is the best-of-the-best and will give you the lowest noise-floor, which is handy when you're really driving the amp, but if you like the sound from what you've already got, it's no biggie. Since you've done the socket you can always swap them out later without much trouble.

[vaughandy]

hey again,

so, just for the hell of it, I decided I might want to have a way to safely hook up both an external speaker cab and the internal speaker, for a total of 3 speakers. the external cab is a 2 x 8 ohm parallel setup, for a total of 4 ohms. the internal speaker is also a 4 ohm speaker. I could obviously hook them in series for a total 8 ohm, but the wiring of that seemed a bit crappy to me, in that it would require unhooking one of the wires from the internal speaker ever time I wanted to do this.

I reasoned that if I could make a little switch that would add a dummy load impedance in series to the internal speaker, I could make a parallel connection to the external cab much easier. Using a little dpdt switch and 2 x 10 ohm resistors, I designed a switch that would essentially increase the impedance of the internal speaker to 24 ohms. Hooked up in parallel with the external cab, I should have a total impedance of 3.43, which I guessed would be close enough to 4 to be safe.

I did this and everything *seems* to work fine, but the sound is pretty crappy. it's like there's some sort of added distortion and smallness to everything. I'm sure there's a very obvious reason for this, but being a total newbie to electrical work, I don't know what it is. Anyone have any insight to share? Do you suppose if I skipped the resistors and just hooked up things in series it would sound better?

Thanks!

[Verne Andru]

Your ears are telling you there is an impedance mismatch happening. When you shift the load up/down there will be a tonal shift. I forget what it is ATM. You can safely increase the load - i.e. go from 4 to 8 to 18 - without damaging the amp, but the closer you get to unity gain - i.e. 0 - the more current gets drawn through the transformer causing it to run hotter which eventually can lead to the internal wiring overheating and breaking resulting in a dead transformer.

I wouldn't run it as is. Try it - albeit briefly - in series. If it sounds the same as before [i.e. in 4/8 ohm load], you should be good, but if you're noticing the same tonal shifting issues and continue running it, you're put your amp at risk.

[BlackSpeed66]

Oh wow, I can't believe this thread is still going almost four years later. I found this shortly after I picked up my V8 in '07 and did the op-amp switch (which I may convert to the 'ACP' chip now). My curiousity got the better of me so I've gone and removed some of the caps and resistors. And, thanks to you Verne I went through the trouble of routing out the front of the amp for a speaker swap last weekend. Just got a confirmation Email from Weber that my Silver Ten is shipping! Tube-wise I'm running an 'early distortion' JJ EL84 from Doug's Tubes and a blackplate JAN Philips 12AT7. I also have a grey-plate version around somewhere but don't quite know what the difference would be. It's all sounding pretty good now, can't wait for the new speaker :-)

[vaughandy]

quick question: I skipped jumping C8 because it appears to be this massive yellow box and I was unsure how to safely get it out of there. Do I need to flip the board or something? Aside from getting the ACP vs CP op-amp in there, it's the only mod I haven't done. well, minus the tone stack.

PS, i'm not 100% sure it was c8, as I don't have the schematic in front of me and your schematic link is broken at the moment.

[Verne Andru]

Funny, I just checked my sites and they were down for a bit but are back up now.

In answer to your question, I honestly can't remember which is which, but I do recall spending quite a bit of time flipping the board, changing things, flipping it back, testing, flipping again, etc., so it's very likely. If C8 is a big yellow box cap [i honestly can't remember], then the only way to get it out is unsoldering it from the underside of the board.

[vaughandy]

yep, flipped the board and desoldered it from below. thanks!

oh, and I also hooked the speakers up in series and it sounds about a billion times better than when I was trying to add the resistors in there. I also realized I could make a DPDT switch that could allow for much easier hookup of the external cab in series without having to unplug the internal speaker, so mission accomplished.

By the way, did you ever build that reverb tank you were talking about? I think that'll be my next project with this amp.

[Verne Andru]

Glad to hear you got sorted.

On the reverb - I made the PCB but haven't gotten the parts to populate it yet. I was waiting on the CDN$ to rise before I got an Accutronics tank and in the interim I've heard Accutronics is now getting their tanks made in China, so I've not been real motivated to spend the coin. I use a delay pedal that tends to accomplish much of the sound filling I get from a reverb. It'll happen, it just hasn't made it to the top of the list yet.