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Supercharging a V8


Verne Andru

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Quote Originally Posted by dcindc View Post
If it's one tube, it's class A, otherwise it would have horrible distortion. No audio product with a single tube would be biased anything but Class A. It would sound like KaKa.
That's what I thought until I ran across this article - Is the Vox AC-30 Really Class A. The reason I'm leaning toward class A/B is that when I record DI out of the power section, the waveform looks clipped at the bottom like the purple and green waveforms here [from that link]

VoxAC30_1.gif

I would have to dust off my scope to really get to the bottom of this, but it really isn't that important to me. Makes for interesting reading though.
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Quote Originally Posted by guitarcapo

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Any thoughts on the V16?

 

I looked at the V16's and was interested, but I passed for a number of reasons. The reviews said the reverb is kinda meh. An amp tech had posted a review on either the GC or MF site [it's since been deleted] going to great pains to explain that it had a microphonic tube problem. He said he had been working with SLM but nobody could come up with a fix. The FX loop was the biggie for me though. While the V8 isn't enough to gig with unaided, the DI I built into the backpack lets me jack into a PA, or my G100 2x10, giving me more than enough horsepower when needed. And, at only 18 lbs, it's a cinch to load in and out.
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Quote Originally Posted by Verne Andru View Post
That's what I thought until I ran across this article - Is the Vox AC-30 Really Class A. The reason I'm leaning toward class A/B is that when I record DI out of the power section, the waveform looks clipped at the bottom like the purple and green waveforms here [from that link]


I would have to dust off my scope to really get to the bottom of this, but it really isn't that important to me. Makes for interesting reading though.
ANY two ouput tube amp will be Class AB. Stupid to do otherwise.
ANY single tube amp will be Class A. REALLY stupid to do otherwise.

Check your grounds, sounds like you are floating.
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Quote Originally Posted by dcindc View Post
ANY two ouput tube amp will be Class AB. Stupid to do otherwise.
ANY single tube amp will be Class A. REALLY stupid to do otherwise.

Check your grounds, sounds like you are floating.
Gibson did make some dual tube - single ended amps. Those too are class A. Some lower power tube amps are biased class A, for no other reason than that is just what they did.
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Quote Originally Posted by dcindc View Post
ANY two ouput tube amp will be Class AB. Stupid to do otherwise.
ANY single tube amp will be Class A. REALLY stupid to do otherwise.

Check your grounds, sounds like you are floating.
Checked into and corrected. There was a floating ground on the L-Pad. I ran a lead from it to the chassis and the issue cleared up.
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Quote Originally Posted by dcindc View Post
ANY two ouput tube amp will be Class AB. Stupid to do otherwise.
ANY single tube amp will be Class A. REALLY stupid to do otherwise.

Check your grounds, sounds like you are floating.
I agree with your second statement but not your first.
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I got the following as a PM, but the new HC forum severely limits the amount of text you can send in a PM, so Im putting it here.

Quote Originally Posted by nreidt
hey dude, I've been reading all of your posts about the little palomino V8. very good stuff, thanks for posting. I have one of these and am glad someone is actually taking the time to figure out how to make it sing.

I'm going to start modding mine soon, following along with your advice and the guitarnuts stuff.
I'm very interested in your "L-Pad" mod, but you don't go into much detail about it. could you elaborate some on it? I also notice they have an impedence of 8 ohms, whereas the speaker in the palomino is 4 ohms. ideally, shouldn't you be trying to match those?

also, have you tried an alnico speaker with it by chance? I'm wondering how much of a difference it might make.

thanks again, and any more info you want to share about this amp would be great.
Thanks - glad it's helping. It's a bad-ass little amp that doesn't get near the respect it deserves. Not perfect, but getting pretty close.

You're right about the impedance on the V8. Matching the output from a tube amp isn't nearly as critical as transistors. As long as you don't load the amp to zero ohms [unity] you won't hurt it [much]. As you change from 4 to 8 to 16 ohms the sound gets darker with a bit of a volume drops and vice-versa. Don't stray too far from it's rating or you can cause long term wear and damage, but going up or down a bit won't break it.

I suspect the output from the V8 is 8 ohms - that's what the V508 schematic shows. The difference between the V8 and V508 is primarily the speaker - 10" and 8" respectively. A 10 will always be darker sounding than an 8 so my hunch is that they used a 4 ohm speaker to make it a bit brighter and louder when they changed speakers so they could keep the circuitry the same. If you know anyone with a V508 get them to check the speaker - I bet it's an 8 ohm rated around 10 watts or less. The V8 is 4 ohm rated at 15 watts. If you listen to just the power amp section soloed, it's actually quite a dark amp. The pre-amp, OTOH, is quite bright so they balance each other off nicely.

As far as speakers go, I've hooked the V8 up to the 2 10's in my Yamaha G100 [rated @ 75 watts each and wired for an 8 ohm load] and, quite frankly, I don't notice much of a difference in tone at all. The Yamaha is renowned for it's clean tone [Mike Stern has been using one forever], so I now these are premium speakers, but the V8 sounds pretty much the same regardless of the speakers I'm driving. Maybe going to a 12 will make a difference, but based on my testing, I don't see the need to change to a different 10 as the stock Celestion is more than adequate.

I didn't go into the L-Pad much because there really isn't that much to say. I used a shielded stereo cable and some spade connectors to connect to the output of the amp and speaker terminals. I run the cable out of the back of the amp to a TRS [Tip, Ring, Sleeve] jack that plugs into the backpack. I kept to the same wiring scheme as they used for the FX loop on the V8, i.e.: Sleeve is ground/common - Tip/Sleeve is for the Send and Ring/Sleeve for Return.

The L-pad only has 3 terminals. The center is what's called the wiper. Inside the backpack I run the Tip [send] to one side, Sleeve [ground] to the opposite side and Ring [return] in the middle. It's early in the morning and I'm still working on my first pot of coffee, so double-check this before you run it to be sure. I don't want to be responsible for someones amp blowing.

For the backpack I used a plastic case, which is what's causing the floating ground issue discussed above. When I get around to it I'm going to pull it apart and line the inside with copper tape and run a ground cable back to the amp chassis. Metal boxes are a bit more expensive, but would be the preferred way to go if I was to do it again.

Best of luck and let me know how you make out.

V
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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 smile.gif . 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.

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Great - thanks for the update. My L-pad, and it sounds like yours as well, is audio taper. This means it has more variance on one end of the windings than the other - hence most of the volume comes within the first 1/4 of its range. It sounds like mine is more toward a custom taper though, as it does vary the volume all the way through to 10 - its just that most of it happens early.

The op-amp makes a huge difference to the hum and hiss - especially if you're cranking the gain to 2 o'clock and have the volume wide open. Sure makes a world of difference, doesn't it?

I keep my gain around 10 for humbuckers and noon for the strat - that gives me a good clean tone - then push the power section with a clean booster. You can do the same thing without all the backpack stuff - just get a stereo to 2 mono [make sure they are left and right split] cable and wire your FX up from there. But since you have to mount your L-pad in something, you're probably already moving down the backpack road anyway.

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Nicely done 12" cab. If I can snag another V8 [V58 or V508] cheap enough I'd like to rehouse it as a head and get an external closed-back 12.

I just finished changing pre-amp tubes - I put in a NOS GE 12AT7. I was looking for JJ's, but when the guy mentioned he had some NOS I couldn't resist.

As suspected I gained between 25 and 30% clean headroom. Added bonus is the amp has got a really nice, smoky tone to it now and all the boxiness is gone. I was using a bit of delay and reverb to round out the tone and take the bite out of the 12ax7, but it sounds great by itself now. The pedals are a bonus!

With humbuckers [Ric 650] I can push the gain to noon and it stays clean. Gets some nice hair on it around 12:30 and after that it's crunch city. With my strat [fat strat with Dano lipsticks in the neck and mid] it stays clean to around 2:30 then we're into serious SRV territory. I can crank the gain wide open with the strat and it still sounds great. The hotter buckers in the 650 start getting a bit nasty close to wide-open, but still nothing like before. The 12at7 lets a bit more of the darker el84 tone to get through, which I think is a good thing.

My only complaint with it now is it just isn't loud enough! But, what do you want for 5 watts? Besides, that's what I built the DI and extension speaker jack into the backpack for. When I gig I'm going to plug the DI into my 100 watt G100 210 - that should give me plenty of volume me thinks!

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What would you think about l-pads on a little bit bigger amp? i have a Gibson(Trace Elliot) Goldtone GA30rvs that is actually two 15w class A amps in the same box meant to run stereo, thus they dubbed it a 30-watter. i love the power tube overdrive on this thing but it's *ungodly* loud in most places, particularly at this power rating. i've tried attenuators but i don't get quite the hair out of that. i'm fairly certain there's no cone breakup because it's loaded with 16ohm vitage 30's which are rated @ 60w each so it's just amp-tone as best i can tell. Do you think the l-pad might be a good solution? It sounds like the amp would see it as a speaker, right?

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All the L-pad does is put a constant load/resistance on the output so it looks like a speaker is attached. Tube amps tend to peak higher than their rating - a 5 watt can peak up to 10, etc. - so I'm not sure I'd try a 100 watt L-Pad on a 100 watt tube amp, but anything 60 and below should be fine.

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