Supercharging a V8

[vaughandy]

This is a re-post of mine from another thread. Thought I'd post it here as well if since it pertains to this amp. If this is bad forum etiquette, my bad!

effects loop "buffering"

Hey out there,

I'm curious if anyone has any ideas about mod'ing an effects loop to reduce the introduction of emi / RFI noise. Im working on Verne Andru's series of mods for a crate v8.

More background: I find that there is significant noise introduced simply by plugging in an insert cable. This diminishes greatly when the leads are hooked up to a pedal. If I was using a single pedal in this fashion I would be pretty okay, but I've found that the more pedals I introduce into the signal loop, the more noise is generated. This is the case even if all the pedals are set to bypass (all of them have true bypass).

Anyway, it totally makes sense that I would hear more noise with more pedals, as I am essentially building a longer antenna with each pedal. So I think I understand the problem, but don't know the best way to address it.

One thing I'm considering is adding a grid resistor on the second half of the preamp tube. The effects return goes into the second half of the tube, so I think this might be a good idea. Any thoughts? Would this do the trick?

I'm worried that this approach might work, but could also suck additional tone and volume. I've already noticed a drop in volume when using the effects loop at all. I'd love to fix that as well, but nothing obvious comes to mind. Suggestion? Any way I might be able to have my cake (lose the noise) and eat it too ( maintain volume and tone)?

[Verne Andru]

I don't any RFI noise issues with my V8 and I use quite a few pedals in my fx loop. My foggy memory seems to be saying that while I was working out the mods - wiring the backpack I think - I was picking up some radio interference but that was traced back to some bad grounding.

Generally speaking, when you encounter radio interference, it indicates a grounding problem and that's where I would look first.

[Wayne2]

 

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.

 

Alright, I took your word for it and finally took out C9 and C12 this morning. It's definitely a dramatic change. I think I like it so far. Thanks.

For anyone hesitating because you think it will be difficult, it's really not. All you need are a phillips head screwdriver, a wire cutters, and a forceps/tweezers is helpful. The component board is right there as soon as you remove the back plate, and C9 and C12 are clearly labeled. It's actually way easier than changing a tube in this amp.

I also put some weatherstripping along the edges of the back plate and got rid of the rattle that was there at high volume.

As far as the sound goes, I think the amp is a little quieter now that the caps are gone, but that's possibly because the upper mids/highs are a little less aggressive. At any rate, it seems to want to be turned up more. I didn't get to play too long... maybe later I'll attempt to describe it again.

[Verne Andru]

Just a heads-up - based on a suggestion by Wayne2 and since others have had some confusion, I've updated the schematic clarifying the OPAMP should be the ACP Excalibur.

I've taken a look at the schematic for the last [Chinese] V5 - the black one in the new design. The circuit is basically identical except they removed the "Volume" pot and effects loop. I've not tried my mods on one of those [yet] but am pretty confident they will work. Since those amps sound so bad, one could pick one up for a song and a few mods and speaker change later have a pretty smokin' little amp.

[Wayne2]

I changed speakers yesterday. Stock is a Celestion Tube 10 4 ohm in there, as we know (I confirmed with Celestion). I think they might have gone 4 ohm to make it sound louder in the store, to be honest. Worked on me... I really liked it and the Epiphone Valve Jr. seemed dark and muddy in comparison.

Yesterday I put in a Jensen MOD 10-70 speaker. I read somewhere that Jensens have scooped mids and thought it might complement the excessive mids of the amp. Also the depth is about the same as the stock speaker (otherwise I would have put in an Eminence). I went with the 10-70 over the 10-50 or 10-35 because I have a Lil' Buddy that I really like and it has a large magnet and voice coil too. Based on the graph, the 10-70 has a nice bulge in the low frequencies that I was hoping will give the amp better bass without me having to use a soldering iron. Additionally the MOD is described as having a hint of Celestion sound so I thought why not leave a little of the original sound.

Anyway, mission accomplished. I think I have finally tamed the mids. The highs kind of jump a little in a nice way and the bass, though not overwhelming, is enough that you can feel it in your feet when you stand next to the amp at moderate volume. The shrill ear-piercing sounds are under control now and the distortion is much smoother.

This should hold me for a few days until I decide to mod the amp again. I have a JJ 12AT7 and a JJ 12AX7 on deck, but I wanted to give the existing tube a chance with the new speaker. (RCA 12AX7A, gray plate. I like it). I really wish the tubes were easier to get to.

If I had to redesign this amp for Crate I'd make it slightly bigger to accomodate deeper speakers (like any alnico) and also so the tubes would be easier to get to. It's marketed as an affordable tube amp but why not let it be a tube rolling/ mod platform as well?

I also finally solved the mystery of the loose screw inside the amp. Apparently two of the speaker mounting screws fell out before I bought the amp. The other one is gone. It is USA-built.

[Wayne2]

I got to crank the amp this morning and was not happy. It was better, but still harsh at moderate to high volume. Tonight I yet again disassembled it and replaced the 12AX7 with a JJ 12AT7 (ECC81). I was able to try it at quiet volume. I like it. It's definitely less gain, and the distortion sounds tighter and bouncier, more like Verne's second demo.

Beginner mods as done by me:

1) Replace 12AX7 with JJ 12AT7

2) Replace EL84 with JJ EL84 ("early distortion" option from Doug's Tubes)

3) Remove C9 and C12 capacitors

4) Replace speaker with Jensen MOD10-70

The cost was around $75 and the required tools are a philips screwdriver, wire cutters, and forceps.

I got the 12AT7 and the speaker from Amplified Parts (adding the tube gets you over the free shipping threshold).

I also blew another $100 on RCA NOS tubes but I don't think I would do that again.

Who knows how I'll feel about this in a few days. If I want to go any further I'm going to have to dust off the soldering iron and/or power tools, and learn how to drain a capacitor.

[kevinfelixlee]

it looks complex, How was that done, though?

[Wayne2]

I'm having as much fun messing with this amp as I am playing it.

I opened it up yet again and tried a JJ 12AX7 in place of the JJ 12AT7.

It's a little darker sounding, with a little more compression, which I like (part of the reason I bought a tube amp was for the natural compression). Articulation, string definition, and dynamics are all a little less pronounced than with the 12AT7.

I think the 12AX7 suits my sloppy playing style a little better, but I still think either is a valid choice and I imagine I'll keep trying different tubes as long as I have this amp.

[antipole]

This thread is very informative. I might consider this project in the future. I am very in need of a low-wattage with a limited budget. This V8 could be the solution to my problem.

[Verne Andru]

FYI - There is a V8 on Guitar Center's used site for $99.

USED CRATE V8 PALOMINO 8.5 022111

Guitar Center Manchester - Manchester, Connecticut 06040 - 860-648-3900

[fatusstratus]

neat - that's very kind of you to give the heads up.

I noticed the thread is a few years old.

How do you like the little guy over the longer haul?

[Verne Andru]

Since I couldn't find an off-the-shelf amp like I wanted, I made one out of the V8, which was as close as I could find.

It's great. Use it all the time. Couldn't live without it.

[jrcorp]

I just spent a good hour or so reading this start to finish. I need that popcorn emote, haha. Nice work, it's very encouraging to see you take this amp further and further. I appreciate your in-depth explanations, included schematics, and your concern for safety in tinkering.

As you know, I just picked up a V5. I'm sure the amp isn't of the same quality for multiple reasons, but I aspire to do the best I can and I'm inspired by this thread. Here's hoping I can adapt any of these mods.

Thanks so much, I'm sure that I'm not the only noob to amp technology that you've inspired to get to work. My only complaint is that I didn't realize there was a V8 for sale so close to me for little more than what I paid for my V5! Please be patient with me if I start asking all kinds of simple questions.

[Verne Andru]

It's really a 6 of one and half a dozen of another when comparing the new V5 to the V8.

The V5 is in a plywood case while the V8 is particle board [except for the baffle]. This makes the V5 lighter and less prone to damage if dropped. With black tolex the V5 will be easier to keep clean [or kept to look clean]. As I understand it the tube sockets are mounted to the chassis whereas they are mounted on the PCB in the V8. Chassis mount is always the better way to go.

Because the V5 sounds so bad stock, they can be picked up dirt cheap. V8's still tend to command a fairly descent resale price.

OTOH the V8 does look really slick in it's cream tolex with gold accents. Comes with a much better stock speaker [Celestion] and has the EFX loop and master volume. Since the circuits are pretty much identical except for those 2 features, you could easily add both to the V5 if you want. V8's are MIA while the V5's are MIC.

I'd say you make a good score and I'm looking forward to you getting that puppy up and running.

[SciHi]

 

Originally Posted by jrcorp

...As you know, I just picked up a V5. I'm sure the amp isn't of the same quality for multiple reasons, but I aspire to do the best I can and I'm inspired by this thread. Here's hoping I can adapt any of these mods...

 

We found the v5 although better constructed, the circuit was much worse. For modding the v5 I would go check out this thread, http://www.thefret.net/showthread.ph...mods...-anyone .

EDIT: Moved to jrcorps v5 thread....

[jrcorp]

Thanks for the link and info, I'll be sure to look into it. I'm curious about how the circuit compares; I plan to look at some wiring diagrams but I'm sure to have all kinds of questions.

In any case, I don't want to jack Verne's thread. Here is my thread.

[Verne Andru]

That's good to know SciHi - thanks. I don't have a problem with V5 stuff happening here - it's all in the family.

[Wayne2]

Am I crazy or does plugging something, anything, into the effects loop change the tone? I've tried it with buffered bypass and true bypass pedals, both of them off, and in both cases the attack seemed to be softened a little bit and a little more pleasing, with maybe a very very subtle roll off of highs. Is this because of the twelve feet of cable plus the pedal?

BTW, I just got a Boss FRV-1 Fender '63 Reverb. I've tried it in front of the amp and in the effects loop. I like it a little but I'm not sure I won't return it. I wanted to sound like the Trashmen.

[Verne Andru]

Not crazy. Anytime you plug something into the FX loop you'll be modifying the signal path which can cause a tonal change. As long as it's good, it's good.

[Wayne2]

I agree. I'm speculating but I think the designers might have left the tone a little aggressive coming out of the tone stack in order to account for some of the suck that it would experience in the effects loop. Right now I'm still running the 12AX7 and I have the tone at about 2:30 with the monster cable plugged into the effects loop and the clean boost not turned on and basically just serving as a connector. With the guitar volume at about 6-7 it sounds good to me.

Amazon's selling the little MXR eq for $61 now, and the 10 band one for $101. I'm tempted to drop one of them into there... kind of kicking myself that I didn't just get that instead of the clean boost. I returned the reverb.

[Knutsaq]

Hello all, this is my first post in the DYI forum - actually, my first post on HC in quite some time. I stumbled upon this thread and I was intrigued; I have a V8 that I bought as a "practice" amp back when they were brand new, so I guess about 6 years ago or so.

Overall, I liked the tone of the amp, but I always found the gain to be a bit "hairy" and the tone control to do little good and I mostly have used the amp by plugging directly into the effects loop return and using an overdrive pedal as a "preamp" to get the sound I want out of it.

I started messing with it a while back and ended up defeating the tone control and removed several of the C's and R's (can't remember which ones - wish I had seen this thread before I started tinkering). It took care of the crazy midrange and gave me a lot more volume, but it the amp still seems a bit shrill, and I continue to just plug into the loop for the most part to get the tone that I want. And it does get a really nice, greasy grind when you wind it up this way - and there is a lot of bass that is simply not present when plugging into the regular input and using the gain control.

Question is, do you guys think the gains are worth it to keep tinkering, or should I just keep using it as I have been since I dig the sound this way for its purpose? Keep in mind, this is not my main amp, just something I mess with when I don't want the volume too high.

[Verne Andru]

I'll let others chime in here, but wanted to say the 99% of my mods are for the pre-amp section. Since you don't normally use that part anyway, if you don't like the results all you're out is a bit of time. OTOH, I did spend a great deal of time fine-tuning the mods to get rid of the high's and get a good, solid tone out of it, so you might actually find you like the results.

[jrcorp]

Hope this isn't off-topic, but could anyone generally explain what an effects loop does? My Fender has one, but I haven't used it properly I think. I believe I understand the concept, but I want to know how it fits in the whole signal chain or whatever. My guess would be pre-amp => effects loop => power => out?! Always wondered what the ins and outs were there, so I could tinker with how to get the best possible sound. Thanks!

[Verne Andru]

That's about it:

pre-amp => effects loop => power => out

Generally speaking you'll be getting your overdrive/distortion from the pre-amp section. Modulation effects like phasers, delays and reverbs sound "different" [some argue better, others just argue] after the distortion. The effects loop simply gives you the ability to place effects between the 2 amp sections.

Again, generally speaking, some argue an effects loop "sucks tone." There is no arguing that it has an effect on the tone of the amp [when done properly it should be tone neutral when not used]. Whether it's good or bad is a subjective thing.

I like it and use it all the time.

[Knutsaq]

Good point, Verne. I think I will try some of your mods to see if I can tame the shrillness and hopefully reduce some of the overall gain. It would be nice to be able to use the amp without having to also plug into a stompbox.

What I have liked most about using the effects return is that I can hit the power amp with a clean boost and get a really nice organic distortion from the output tube at reasonable volumes, and it is super simple to modulate with the guitar volume control. I just never seem to get the same amount of interactivity going through the amp's preamp section - it's too wooly and adds too much distortion before you get the power amp into play, and IMO just doesn't sound as nice nor is it as touch-sensitive as driving the power amp directly.