Members Verne Andru Posted April 13, 2011 Author Members Share Posted April 13, 2011 Tube amps are generally pretty dark sounding. That's why they used to use things like treble boosters back in the day. Vox got around it with their Top Boost circuit. Modern circuits have tried to compensate with varying degrees of success. On the V8 they threw a bunch of circuitry in there to try and make their Tone Shape control "work." Once you remove that you're left with some pretty strident high-end. I traced everything right back to the input jack and got it working pretty well. I still think it could be tweaked a bit more, but that would require me to get up to speed on opamp circuits but since it sounds great as is, I just can't justify the time. If you follow the link to jdcorp's V5 thread you'll find a discussion and some links on modding the V5. What's interesting is they decided to just bypass the opamp section entirely. That solved the shrillness but leaves you with just about no clean-headroom. Not the best solution, but a solution nonetheless. One could probably put in a switch so you could easily flip between them - that might be a pretty funky mod to try. On the V8, and just about any other amp with an effects loop, your signal will hit a "gain makeup" stage between the FX return and the power tube. On this amp that's seen as the second 1/2 of the 12AX7. My point is that bypassing the preamp with the FX return doesn't let you drive the power tube directly. A [large] part of the OD you're hearing is coming from the 12AX7, not the EL84. How much, I couldn't tell you scientifically, but I'd venture it's probably most of it. Link to comment Share on other sites More sharing options...
Members Knutsaq Posted April 13, 2011 Members Share Posted April 13, 2011 Verne, you're def right about the preamp tube, I am getting a fair amount of noticeable gain from the 12AX7. I'm driving it pretty hard through this method, and also getting some nice compression from the EL84, which is really what I am going for with this amp. I've had a lot of 15/18/20 watt EL84 powered amps and it has always been hard to get that VOXey sort of compressive, singing distortion that EL84s do so well without blowing the windows out of the house. This way, it's still loud, but not unreasonably so and I can back off the guitar volume and the power amp cleans up nicely while still giving me some grind from the 12AX7. I'n not looking for headroom in a -84 powered amp, the natural gain of the power tube is kind of the point of these amps, I think. I have other amps with ample clean headroom if that's the tone I am going for. It really is a nice sounding little amp used this way, although I hate the speaker and really should change it. And I kind of always suspected that the op-amp circuitry was the culprit in the preamp, so I might just do that mod and see how it works. Link to comment Share on other sites More sharing options...
Members Verne Andru Posted April 13, 2011 Author Members Share Posted April 13, 2011 And I kind of always suspected that the op-amp circuitry was the culprit in the preamp, so I might just do that mod and see how it works. Great - keep us posted. Link to comment Share on other sites More sharing options...
Members Knutsaq Posted April 14, 2011 Members Share Posted April 14, 2011 Thanks for your input and advice - this is an amazing thread, and I'm blown away by all the work you have done to the little amp. Wish I could hear yours. Link to comment Share on other sites More sharing options...
Members Verne Andru Posted April 14, 2011 Author Members Share Posted April 14, 2011 A EUREKA moment! Remove C2! It's the opamp shrillness culprit! This should work on the new V5 as well. All this talk got me looking over the V8 schematic this AM and C2 just jumped out at me as being wrong. When a circuit is done properly, extremes on the controls should do just that - give you too much bass/treble/whatever. While my V8 sounded great, I've needed to have the bass control cranked all the way up to get a nice ballsy tone leading me to believe there was something that still eluded me. Pop C2 out of the circuit and everything works as it should. Too much bass when the bass control is dimed and too much treble when it is dimed. Both of them around 5 [on a scale of 10] and she purrs like a kitten. I would include removing C2 as part of the "Simple Tone Mod's." It's really easy to get at it and you don't have to pull the board. Not exactly sure how it will work in in isolation, as my amp has all the other mods, but if somebody is giving this a go, it would be nice to hear back on how it works. Link to comment Share on other sites More sharing options...
Members Wayne2 Posted April 15, 2011 Members Share Posted April 15, 2011 I can't wait to try this. Will do this weekend. All I've done to my V8 is tube changes, remove C9 and C12, and speaker change. I'm still not happy with all the shrillness and lack of bass going on. Link to comment Share on other sites More sharing options...
Members Verne Andru Posted April 15, 2011 Author Members Share Posted April 15, 2011 Wayne2 - that's the perfect config to test it out. Waiting with baited breath... Link to comment Share on other sites More sharing options...
Members Knutsaq Posted April 15, 2011 Members Share Posted April 15, 2011 I'm going to try it this weekend as well. Thanks! Link to comment Share on other sites More sharing options...
Members jrcorp Posted April 15, 2011 Members Share Posted April 15, 2011 As soon as I find the time and get ready for it, I'll look at some schematics and try to do some modding on my V5. Verne, I would love to consult you or maybe seek help in deciding what to do, as working on the circuit os a bit above my head. But I can do it. I'm going to order a different power tube, then go to circuit stuff. I'll try this C2 as well as try to translate other nods if I can. I wish I had waited before I bought the 5, as I've seen some combos and heads cheap lately - including a few Palominos. Link to comment Share on other sites More sharing options...
Members Verne Andru Posted April 15, 2011 Author Members Share Posted April 15, 2011 Buyers remorse already? Considering what you paid for it jrcorp, consider it a fun experiment. There will always be something bigger, better, etc. just around the corner. If I was to do it again I'd probably look at the VHT Ultra 6 pretty seriously. But I got what I got and it serves me fine. Just post any questions, etc. you have in here and I'll [and others] will do what we can to get you happening. Link to comment Share on other sites More sharing options...
Members Wayne2 Posted April 17, 2011 Members Share Posted April 17, 2011 YES! Removing C2 works. Very nicely. I have the tone control at 12 noon and it sounds good at moderate or quiet volume, with little gain, lots of gain, guitar volume up or down. It has a nice warm growl to it that was exactly what I had in my head when I went to buy a tube amp in the first place, or with low gain can be clean and chimey and plenty loud for my purposes. There is lots of compression and sustain when the gain is cranked. One thing I noticed before I made the change was when playing a low E, you could hear more harmonics than the fundamental tone. Now that's gone. It almost sounds like a piano string now, very touch-sensitive and expressive. All up and down the scale it's very well-balanced and natural-sounding. It's still not blowing me away with excessive bass, but it sounds good. This is my amateur opinion, but what I think was happening before was the fundamentals of the low notes weren't making it through, and all kinds of harmonic/overtone mayhem was there that made the midrange/highs seem harsh. I found myself always turning it down because my ears were ringing, yet it didn't even seem that loud. Now at the same settings you can still easily talk over it but it just seems calmer. All this from one capacitor. It was also screwing with the tubes because by choking out low frequencies the tubes weren't getting hit with the energy they needed to sound good (as low frequencies carry more energy than highs of similar amplitude). I almost think the capacitor might have been going bad. Is that even possible in such a short time? The amp sounded so much better to me when I bought it. I haven't had the opportunity to crank it yet, but I really hardly ever do anyway. I'll update if anything changes. Thanks Verne for all your efforts. Kind of funny how after years of this we got so hung up on the goony tone stack that C2 slipped through the cracks. If I had to do this again I would try C2 first, then the tubes, then C9 and C12, then the speaker. I noticed some capacitors around the second op amp too. Any thoughts on those? Link to comment Share on other sites More sharing options...
Members Verne Andru Posted April 17, 2011 Author Members Share Posted April 17, 2011 Most excellent! Well, the goony tone stack is still goony and C9/C12 were not doing the amp's tone any favours. I have no regrets on that part. Now that C2 is confirmed, I'll update the schematic with this as part of the Simple mods. As far as the other 1/2 of the opamp goes, my mods do include changing C5. This helps add a bit more bass into the equation. Getting rid of C6, C8 and R11 also help increase bass response. But these require pulling the board so you can get to the backside to do a proper job. I suppose you could get at some of them from the component side if you're careful. As a side note, I jumpered R3 when I was mucking with C2 just to see what it would do. The amp took on a more vintage tonal flavour, but I also lost gain/volume. This might be okay if you're running a 12AX7, but I found it was too much of a loss with a 12AT7. You could easily try it by carefully soldering a piece of wire to either side of the resistor which will effectively bypass it. One of the things to keep in mind is that you won't get pounding bass out of this, or any guitar amp. The cabinet size does inhibit the speaker a bit, but generally you want a guitar to sit in the mid-range of the mix otherwise it'll get lost. Mine does have a great ka-chunk to it and the zingyness is now history. Link to comment Share on other sites More sharing options...
Members Knutsaq Posted April 18, 2011 Members Share Posted April 18, 2011 Wel, I got a chance to check the mod with the amp completely dimed over the weekend. The shrillness is pretty much gone and it finally has some girth. Tonally, it was able to cut through suprisingly well at volume, even with my buddy comping on a silver face Twin. It's not gonna replace my Rivera, but it has definitely been transformed into a very solid, serviceable little practice amp. Thanks again for the input Verne. Link to comment Share on other sites More sharing options...
Members Verne Andru Posted April 18, 2011 Author Members Share Posted April 18, 2011 My pleasure, and thanks. As I noted above, getting rid of C6, C8 and R11 really helps to open the amp up. You're basically removing stuff in the audio signal so more of the pure tone can flow through. These need to be jumpered, meaning once removed you need to put a wire in place of the component so the signal can flow through. If you're careful you can do this on the component side of the board. I can't remember if the caps are cans or not - if so it might be a bit tricky getting at the leads to snip them but not impossible. Pretty tough putting it up against a Rivera, but once it's singing it can hold it's own. Link to comment Share on other sites More sharing options...
Members Knutsaq Posted April 18, 2011 Members Share Posted April 18, 2011 I was able to jumper them on the component side, without removing the board. Was a little tight, but with a little patience got it done. Link to comment Share on other sites More sharing options...
Members Verne Andru Posted April 18, 2011 Author Members Share Posted April 18, 2011 Notice a difference? Link to comment Share on other sites More sharing options...
Members Knutsaq Posted April 19, 2011 Members Share Posted April 19, 2011 Verne,I think you may be referring to the jumpers - I actually did those at the time that I "modded" the amp. If I am wrong, and you mean a difference with the amp in general, then the answer is a resounding yes. I think I like the tone of the amp enough now to drop a better speaker into it. I looked through the recommendations but just have not decided which one to try out yet. The stock speaker is miserable. Link to comment Share on other sites More sharing options...
Members Verne Andru Posted April 19, 2011 Author Members Share Posted April 19, 2011 Fair enough - wasn't sure where you were at with it.Re speakers: Check Craigslist for old Jensen's. People around my area routinely pull apart old organs that came with really sweet Jensen Alnico's they sell off, sometimes for a pretty good deal. The Weber I used is really nice, but also really expensive plus requires modding the cabinet to fit. The Weber Ceramic Silver Bell might be a better fit if you don't mind ceramic. The Eminence Lil Buddy is an awesome sounding speaker, but there's no way you're getting it and the amp in that tiny little cabinet.Try hooking the amp up to a different speaker cabinet to get a real sense of how it sounds. I bet it sounds awesome through the 12 in your buddies Fender.Rock on... Link to comment Share on other sites More sharing options...
Members Verne Andru Posted April 20, 2011 Author Members Share Posted April 20, 2011 Schematic C2 update:http://www.verneandru.com/WebApp/Dow...-schematic.pdf Link to comment Share on other sites More sharing options...
Members Wayne2 Posted April 26, 2011 Members Share Posted April 26, 2011 I got a new toy, the MXR 10 band equalizer. It's been great. It works nicely in front or in the loop, and really really well if I'm just jacking into the line in and want to clean up the guitar signal a little first.It's kind of sad though because I'm realizing just how zany the eq is coming out of the preamp. It's all over the mids too, like from 250 Hz all the way up to 4K. The amp is already moderate in bass (judging by just power amp), but there's something in the preamp that knocks it down even further. It's like a massive, angry frown face with a spike around 500 Hz - 1K. Getting it close to normal requires bass boost, mid cut, and treble neutral or slight cut. It's been really educational though to have this thing and find out what frequencies are where.The other issue is I'm comparing it to my Fender Champion 110 w/Lil' Buddy speaker and that amp sounds great with no eq, and maybe a little better with some subtle tweaks on the MXR. Also the eq knobs on the amp actually work, and the 25 watts just sounds bigger to me. Maybe I'm expecting too much from the Palomino.Anyway the MXR is big fun and I highly recommend if you're looking for something else to mess around with. It kind of goes against the philosophy of removing crap from the signal path, but whatever. Link to comment Share on other sites More sharing options...
Members Verne Andru Posted April 26, 2011 Author Members Share Posted April 26, 2011 What mods have you done? If you've only done a few I can see where you need some outside help. That MXR EQ is a good choice. But once fully modded you'll have no EQ issues at all.FYI - I finally got around to ordering a reverb tank yesterday and am finalizing my plan to add a spring reverb to the V8. Stay tuned. Link to comment Share on other sites More sharing options...
Members Wayne2 Posted April 26, 2011 Members Share Posted April 26, 2011 C2, C9, C12, tubes, speaker. That's exciting about the reverb. Before I crack this thing open again I want to see how you do with that. Link to comment Share on other sites More sharing options...
Members Wayne2 Posted May 10, 2011 Members Share Posted May 10, 2011 I've been staring at the schematic and checking around on the internet and have been bitten by the amp design bug, so to speak. I'm going to order a book pretty soon.Anyway, what it looks to me like is someone set up a computer program with two op amp stages and two 12AX7 stages and picked Fender values for everything.i.e. both 12AX7 stages have a cathode resistor of 1.5K and cathode bypass capacitor of 22 Link to comment Share on other sites More sharing options...
Members Verne Andru Posted May 10, 2011 Author Members Share Posted May 10, 2011 Hey Wayne2 - I have no doubt there are more mods that will further improve the tone of the V8 and look forward to you testing out some of your theories and letting us know how they've worked out. Link to comment Share on other sites More sharing options...
Members Wayne2 Posted May 10, 2011 Members Share Posted May 10, 2011 I tried soldering a wire around R12 today. Sounds bad. I pulled it right off afterwards. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.