AX84 BBS New Threads as of Thu, May 28th, 2015 @ 12:20:01 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com Bugera V22 for modding/gutting?(by Darren Porter) There is a used Bugera V22 on craigslist near me. Asking $200. Looking at some pictures it seems like this might be a good chassis, cabinets and halfway decent 18-Watt transformer set for a custom build. What do you guys think? Worth $200 for that? The chassis, cabinet and power transformer would cost me more than that new. I'm thinking use the existing tube holes and just run long terminal strips on either side of them and do a point-to-point layout. Maybe do an October Club in there if I drill some holes for 6V6 sockets? This google search has some good pics... <a href="https://www.google.com/search?q=bugera+v22+schematic&espv=2&biw=1364&bih=950&tbm=isch&tbo=u&source=univ&sa=X&ei=Wk5nVfK2HcfgoAS1rIO4Cg&ved=0CB0QsAQ# " target="newwin1432830001">[link]</a> Thu, 28 May 2015 11:23:55 -0400 http://ax84.com/bbs/dm.php?id=490812 Whacky microphonics(by Denny Gracey) I’m struggling with some whacky microphonics/oscillations in my UHG build. The amp worked great for couple weeks. I literally moved the chassis into a headshell I built, only to confirm fit, didn’t bolt it in. Plugged in the amp and got nasty honky mids-feedback. Removed from cab, still trouble. Since then I’ve been on an adventure in microphonics, but exhausted nearly all options and turning to the experts. One more curious behavior: plug in guitar cable (no guitar), hover the tip over the chassis and when near the pre-amp tubes I get strong theramin-like feedback. So here’s what I think I’ve learned to date, and what I’ve done: • Microphonics nearly always manifest in stage 1 (is this correct?) • Amp is microphonic and lots of noise, even with no input cable connected (i.e. input is grounded) • When I ground output of first stage at coupling cap, noise and microphonics drop to normal (i.e. where it was in original build). • Tried 3 different 12AX7’s • Since I used P2P wiring, I moved most components back to the board and connected via flexible multi-strand wire to minimize transferring vibrations back to the tube • Rebuilt stage 1 & 2, including new socket. Replaced coupling cap stage 1; Replaced gain control pot. • Replaced input lead with shielded (even though only 2” long) I’ve done everything I can think of except adding rubber washers to the tube mounts. But having the amp work originally, and to start misbehaving having done no changes is confounding me. Any help appreciated! Wed, 27 May 2015 09:29:13 -0400 http://ax84.com/bbs/dm.php?id=490804 Ideas for presence controls.(by Alva Goldbook) I've been thinking of taking some new approaches to presence controls. What rather bugs me about it is that it almost always is linked to the amount of negative feedback in the amp. For some designs that use very little negative feedback, this makes for a very ineffective presence control. On older Marshalls, which used a 100k NFB resistor, I've always said the presence control is "the knob that does nothing" because the effect is so subtle. I suppose if I increased the amount of NFB by dropping the 100k resistor, the control would be more effective. But this would reduce the amount of distortion you get in the amp. I was reading Merlin's book, and found a neat trick for adding a presence control without having any NFB at all in the amp. I'm wondering if there would be any problem doing this in an amp with NFB, and still have an amp that has a more effective presence control. Wed, 27 May 2015 07:15:56 -0400 http://ax84.com/bbs/dm.php?id=490803 Practice amp with I-pod plug in(by JaapK) I have a simple practice amp, something like a Fender Champ: 2 preamp stages and a single ended power amp. I would like to be able to plug in an I-pod and play along with songs. To make that more versatile I took an extra preamp tube for the I-pod. My current set up is: I-pod -> preamp stage -> bax hifi tone stack + volume control. And then I mix the I-pod signal and the guitar preamp out signal together through mixer resistors 220K into a sort of recovery gain stage and from that stage to the power amp. (So you could say that the Champ now has 3 preamp stages, to make it more clear (I hope)) It works and sounds better than putting guitar and I-pod through the same preamp. But maybe there are other ways? Like to hear your experience or ideas. Thanx. Wed, 27 May 2015 00:38:55 -0400 http://ax84.com/bbs/dm.php?id=490802 Adding a gain stage(by Sirppi) So yesterday I finished building a combination of the EA MV120 preamp stage and the KT88 SE 20W power amp. I'd like to add the unused V1a in the circuit to get more gain out of it, since I have no phase inverter to drive into clipping that the original EA has. Would this be as simple as calculating the right values for the anode and the cathode and putting it in somewhere, or do I need to do major modifications to the whole amp? Here's the schematic I made: <a href="https://dl.dropboxusercontent.com/u/43516629/ampage/vaf.png" target="newwin1432830001">[link]</a> Thu, 28 May 2015 07:42:45 -0400 http://ax84.com/bbs/dm.php?id=490773 Introduction + what to build ?!(by Ryan Boeur) Hi all, This is my first post on ax84. I'm up in Vancouver BC Canada, play "professionally" with Fish & Bird (fishandbird.ca) and Jenny Ritter (jennyrittermusic.ca). I suppose that's my main occupation. I also build pedals, and just about anything else I can think of.. Good with my Hakko. I'm here because I would like to build myself an amp to solve a logistical situation I find myself in. I am occasionally touring back to back in the UK and North America, and I would like to use the same amp wherever I go, and not lug step down power transformers around with me ( I have not found a rental solution that does the trick for my needs.) I used to play a silverface Champ, now I play a brownface Princeton, so I am used to low watt amps (play in bands with lots of acoustic instruments/mics on stage). I suppose I could change my power transformer in the Princeton to dual primary, but I would like a lighter weight amp for fly in touring. I'd like 2 to 10 watts of power, 115/230v input, very light weight (luggage fees!), push/pull output. It will either be a head, or a combo with 1 10" speaker. Hoping to use a Hammond 1590BB or similar size/weight chassis. I think the ECC99 may be a good power tube for my application, but am open to suggestions on all of this, that's why I am here! Any recommendations on what to build would be super, this will be my first tube amp build, tho not my first time doing mains/HV wiring. Tue, 26 May 2015 18:11:24 -0400 http://ax84.com/bbs/dm.php?id=490756 HO shuts down with a full volume hum(by Chris Linkous) Hi everyone, This is my first build. HO has octal mod and external bias adjustment. The amp plays fine with very little noise until about fifteen minutes and then it switches to a full volume hum. After cool down it will play again and repeat. Preamp tubes make no difference when pulled. All noise stops when power tube pulled. When switched to standby the hum drops considerably in volume but is still loud. I've checked all the ground points against the input chassis ground and they all check out. Have 255V at plates and run 40ma on el84 or 46ma with 6v6. Have triple checked (resoldered) the OT and PT connect points as well as filter cap joints and I don't SEE any bad solder joints. This shut down will happen if I'm playing with either tube installed, wide open or low volume. I've timed it at eleven minutes twice in a row with no input and all knobs zeroed. Always have a speaker connected and have experienced this with different speaker loads on different outputs. Also checked resistor values, all line AC connections, filament connections and standby connections and everything looks right. I am obviously missing something important! Any suggestions would be GREATLY appreciated at this point as I've long since outrun my knowledge level! Thanks in advance, Chris Wed, 27 May 2015 18:58:50 -0400 http://ax84.com/bbs/dm.php?id=490755 Celestion G12C(by James Marchant) Hi folks, I've got a couple of G12C prototypes if anyone wants them. In case you don't know, the C was the immediate predecessor to the G12M greenback. The C was produced for a few months before the final spec of the M was settled on. They are a little softer than the M and slightly lower efficiency. They sound a but more broken in. If you are interested, drop me a line on ax84 (at) jmarchant (dot) co (dot) uk Sending from UK so more interest to uk dudes. Will take £40 for them plus postage. As they are protos, they don't have labels, but they do have the greenback cover.Tue, 26 May 2015 17:22:51 -0400 http://ax84.com/bbs/dm.php?id=490750 Another Tube Reverb Question (by Alva Goldbook) Well, not so much a question, as I'd like the opinion of the board. So I'm working on a reverb circuit. I'd like to get the kind of reverb that's as rich as found on blackface amps. These circuits are typically driven by parallel 12AT7 triodes with a 12ax7 triode on the recovery side. The amp I'm working on already has 4 pre-amp tubes without the verb. (3 pre-amps, plus 1 for a tube driven FX loop) I'd hate to end up with 6 pre-amp tubes and just leave one half of a 12ax7 unused. To avoid this, I'm kicking around two ideas. A) Use a parallel pair of 12AT7s to drive the reverb, and use the recovery triode from the FX loop for the verb return. Or B) Use a 12DW7, and drive the reverb pan with the single 12AU7 side of the 12DW7 and use the other half of the 12DW7 (a 12AX7 triode) as the recovery. Each approach has it's significant down sides. Approach A would mean that a normal reverb control would also effect the FX return levels, while Approach B would provide the reverb pan with less current than a pair of 12AT7s would provide. Thu, 28 May 2015 11:14:54 -0400 http://ax84.com/bbs/dm.php?id=490720 Modded my Simple Preamp with additional gain stage -too much bas(by Darren Porter) So, when I built my Simple20, I did it with an eye towards expansion by adding two additional 9-pin sockets and running the heater wires to them. So far, I have used one of the sockets for a one-tube reverb. This week, I wired-up one triode of the remaining socket as an additional 12AX7 gain stage between the second stage and the MV. I used Ra=100k and Rk=680R and unbypassed. Basically the final stage of an October/JTM. My ultimate plan, after I get it tweaked to taste, is to make it foot-switchable. WOW! This thing sounds freaking amazing. I think I am getting VERY close to my goal of not having to rely on pedals for overdrive. I do only have the one tone stack that needs to cover both clean/crunch and overdrive modes. But, there is just WAY too much bass and I have to turn the bass knob all the way down to tame it - obviously I don't want to run my clean-ish mode with no bass. So, what do you think the best way to attenuate that bass is? Should I just put in a fixed high-pass filter, should I add a bass tone control? If I add the bass knob, would I need to drive it with a CF or would just the one knob not have a huge impact. I'd like to get away without using a knob if I can though. A switch for "more cut" and "less cut" might be good for going between my strat-ish and les paul-ish guitars. Or can I get away with just a different coupler value (currently 22n)? This circuit would of course be inside the switched area so it would only be active when this gain stage is active. Thanks for any insight!Thu, 21 May 2015 12:02:14 -0400 http://ax84.com/bbs/dm.php?id=490713 Tube FX loop on HO(by sajyho) Hi guys, It's been a while since I added Mark L's FX loop to my HO: <a href="http://www.diyitalia.eu/forum/download/file.php?id=4917 " target="newwin1432830001">[link]</a> It sounds amazing with my Rebote delay, but when I use it with my FV-1 based digital multi-effect it sometimes overload the effect at high gains and the overload LED on the effect keeps blinking. My question is; What is the best way to attenuate the signal before the send jack? Can a simple knob do the job without any significant tone loss? I totally a noob in impedance concept so please help me through this one... Thanks SajadFri, 22 May 2015 22:22:07 -0400 http://ax84.com/bbs/dm.php?id=490706 Tube Reverb and Phase. (by Alva Goldbook) I'm working on an amp with a classic Blackface style reverb circuit, and I'm trying to figure out where to place the reverb return back into the preamp circuit without having phasing issues. The reverb driver tube will invert the preamp signal, and the recovery triode will flip the phase again to a non-inverted signal, but the thought occurs to me that I'm not sure of the reverb driver transformer will invert the signal, or the reverb pan itself might invert the signal. I can imagine that reverb pan transducers may in fact do this, but I wasn't sure. Does anyone have any clarification on this?Thu, 21 May 2015 05:43:02 -0400 http://ax84.com/bbs/dm.php?id=490705 BAD MONKEY!!!(by RickTown) Well, spider monkeys and parts bins don't mix. We have self-closing hinges on most of the doors in the house including my shop door but the spring in one of the two self-closers broke a while back which I've been ignoring. Lucy found the shop door unlatched and decided to explore. Luckily, she only had a few seconds before she was caught. <a href="http://www.cuttingedgediamond.com/amps/mess1.jpg " target="newwin1432830001">[link]</a> <a href="http://www.cuttingedgediamond.com/amps/mess2.jpg " target="newwin1432830001">[link]</a> Looks like I've got some sorting to do. Here's a picture of the culprit. <a href="http://www.cuttingedgediamond.com/amps/lucyguitar.jpg " target="newwin1432830001">[link]</a> She dragged that guitar down the stairs to bring it in the living room and play with it. It's the only one I don't keep locked up. She loves to sit at the piano and "tink" as well.Sun, 24 May 2015 07:14:19 -0400 http://ax84.com/bbs/dm.php?id=490697 5F6A Bassman Mods(by robrob) I have just completed a 5F6A Bassman mod web page. Most of the mods have accompanying layout diagrams. The mod page can be found here: <a href="https://robrobinette.com/5F6A_Modifications.htm " target="newwin1432830001">[link]</a> Thu, 21 May 2015 08:22:43 -0400 http://ax84.com/bbs/dm.php?id=490667 Finally built my Crazy El84 6V6 Parallel, Problems.(by lkrasner) Alright, I finally built this thing. SEL like preamp, cleaned up a bit, switch on the first stage to give a clean and lead setting, FX loop, simplified LOW HIGH tone stack, parallel 6V6 and EL84 output with independent volume control. Overall, working well, but there are some issues. The FX loop isn't working. the recovery triode is dropping to 111 volts on the plate, and it causes the whole amp to be distorted with low output. It's a bit better if I put a 12ax7 in to draw less current, but still bad. Works fine if I completely bypass the FX stage. Any Ideas? Here's the latest schematic and layout. note that the layout is not perfect in the jack wiring and some of the other wiring, but the electronics are all correct. Schematic: <a href="https://drive.google.com/file/d/0B3ky9WMiU0TvREJ6dkstcTJ1VDQ/view?usp=sharing " target="newwin1432830001">[link]</a> Layout: <a href="https://drive.google.com/file/d/0B3ky9WMiU0TvaHZYeEkxSWREM1E/view?usp=sharing" target="newwin1432830001">[link]</a> Mon, 18 May 2015 15:22:46 -0400 http://ax84.com/bbs/dm.php?id=490657 stand alone power amp question(by Darren Porter) If I was to build a stand alone power amp is there any reason why I should NOT put an effects loop and reverb in it so I would not have to then add those to every preamp I build to go with it? I can't think of any reason why it wouldn't work. I'm thinking that would be a good way to keep costs down.Sat, 16 May 2015 10:33:34 -0400 http://ax84.com/bbs/dm.php?id=490654 Motorboating Merlin(by Balijukka) <a href="https://www.youtube.com/watch?v=8QSTkw0Wq6k&feature=youtu.be " target="newwin1432830001">[link]</a> Spunds like motorboating, but there may be a diode encrusted humdinger behind the noise.Fri, 15 May 2015 07:50:30 -0400 http://ax84.com/bbs/dm.php?id=490638 The Thrill is Gone(by Brutus) RIP BBFri, 15 May 2015 12:42:09 -0400 http://ax84.com/bbs/dm.php?id=490636 Practically STOLE a really nice new guitar(by Darren Porter) So I've been wanting to buy a strat because I didn't have one and no collection is really complete without at least something that has that sound. So I sold a nice guitar that I had lying around that I haven't touched in like at least five or six years for $650 and I was going to buy that Mexican Deluxe Players Strat. It goes for $649 everywhere and gets good reviews, but no music stores ever stock them for some strange reason. So I played a bunch of Mexican standard strats and some American strats and I decided I was going to buy this cheap Mexican standard that had been hanging on the wall of my favorite guitar store for few years and just Frankenstein it up to be what I wanted from a strat. I figured for $299 I had a lot of extra cash to do that. Well, then I stumbled on a Godin Session which is a HSS guitar. I know that Godin has a great reputation from the people that own them... kind of like an underground cult-following almost. I saw one on Amazon of all places for only $535. Beautiful transparent black finish with blackburst edges, cream pickguard, HSS config, maple fingerboard, volume and single tone knob. I hemmed-and-hawed about my decision and saw at work one morning the Godin's price dropped to $405 for some unknown reason. When I got home I took that as a sign that this was the guitar to get. So, I went to amazon and the price had dropped to $395 so I went ahead and bought it. The moment I bought it, when I went back to the page for that guitar, it went back up to $535. Crazy. I was able to get overnight shipping for only $11 so I went with that too. I was amazed when I received the guitar. The finish is impeccable... not a blemish ANYWHERE on the guitar. The setup was absolutely perfect... action was just right, intonation was spot-on. It has a VERY nice two-point floating tremolo bridge. It also came in a VERY nice gig bag superior to any others I have ever seen. Out of the box this guitar plays better than ANY Mexican strat I played and on-par with the Americans I played, except for maybe some of the non-standard ones which cost around $1700+. I also ordered the Seymour Duncan P-Rail bridge pickup with a Triple Shot pickup ring for it. The P-Rail is a full P90 mated with a single rail single-coil pickup. (Think one half of their hot rails humbuckers that fit a single coil slot.) The two together are exactly the same size as a standard humbucker. With the Triple Shot, I can switch between single coil P90, single coil rail, series humbucker and parallel humbucker all without having to drill for any new switches. Amazing versatility! So, this thing now sounds absolutely amazing. And to think I only paid $500 total for it blows my mind. I have my strat tones AND the P90 AND the humbucker at the bridge all in one guitar that plays and looks fantastic. One of the best guitar purchases I have ever made at any price. My hats off to Godin and Seymour Duncan!Thu, 14 May 2015 18:08:46 -0400 http://ax84.com/bbs/dm.php?id=490629 a quick question regarding an equation, and variables.(by proton45) Hello... Here is the equation.. Plate voltage^2 / tube dissipation. This is used to roughly determine the output tubes impedance load, when figuring out the best OPT primary impedance. Now my question...would this calculation be "more" accurate if you used your "actual" bias watt(?). Or...is the calculation so (generalised) rough, that it matters little? I realize that there are certain realities of the fluctuating loads...that maybe the "max" dissipation is used? Thanks in advance... I realize that some numbers could be close enough...and then there is the "sound' and preference...but I would still like to know. Thnx CSun, 17 May 2015 14:47:53 -0400 http://ax84.com/bbs/dm.php?id=490627 weird tone artifact at very low volume levels(by vicrattlehead) So I think I’ve got my build just about perfected but I have one lingering issue. At low volumes (low on the MV; maybe set at 1-1.5 if it were numbered), and only when being pushed with a pedal (a Digitech RP500 if it matters), I have a kind of ‘choppy’ crappy sounding artifact in my distorted tone. The best I can describe it as, is like that really bad power amp distortion that comes from pushing a solid state amp too far. It is most noticeable when the guitar is switched to the neck pickup (the warmer, bass-ier tone sets it off more). It’s not the dominant sound that comes out though, it’s more like if my tubey goodness was being mixed 70/30 with some SS crap. I’ve tried adjusting pre-gain, tone controls, and every conceivable adjustment on the pedal but the sound is always there to some degree. What strikes me as odd though is that if I turn up the master volume past 2 or so (maybe 20-25% vol) it clears up and sounds awesome. It’s only at very low levels that I get this artifact. The problem is, even at 2-3 on the MV this thing is pretty loud and is really pushing what I’d consider ‘bedroom levels’. Anybody have any thoughts on this? I’m kind of at a loss. I thought maybe it might be some kind of blocking distortion but increasing the volume actually makes it sound better and adjusting the preamp Vol or the pedal has very little effect. Mon, 18 May 2015 04:06:02 -0400 http://ax84.com/bbs/dm.php?id=490622 Down tuning explained(by Kursad K) <a href="https://www.youtube.com/watch?v=AlLOIV5WiZs" target="newwin1432830001">[link]</a> Thu, 14 May 2015 03:19:30 -0400 http://ax84.com/bbs/dm.php?id=490619 DC coupled cathodyne PI with MV(by ralfos) I just wanted to hear some opinions on my V3 to PI design that I came up with. Maybe someone with more experience can tell me if he sees anything totally stupid or pathologic in here as my expertise is limited. I reworked an old german Dynacord amp that is pcb based with 2 x 12AX7, 2xEL34 and a cathodyne PI. the options for redesigning the circuit are limited due to the pcb, but i still managed to modify it quite a bit. The original PI was an AC coupled cathodyne type. I didn’t like the break up at all until I tried to DC couple it and it instantly sounded great so I stuck with that. Since I only have 3 gain stages and I wanted to add a master volume I wanted to place the MV in between V3 and PI. That is of course hardly possible when the PI is DC coupled, but I came up with this solution which works quite well. I am using a 12DW7, so V3 is a 12AX7 and the cathodyne PI is 12AU7. The voltage divider drops the grid voltage on the PI to about 60V. here’s a schematic: <a href="https://dl.dropboxusercontent.com/u/27654100/V3-PI.pdf " target="newwin1432830001">[link]</a> maybe there’s already a commercial design that uses this technique, I have no idea. I have to say the MV does somewhat alter the frequency response a little in this configuration, so you can see it as a combination of MV and tone shaping. But it does the job of making heavy sounds possible at lower volumes. I had to choose a huge value of 47uF because smaller ones left too much bottom end in the signal on lower settings and messed with the frequency response even more. Thu, 14 May 2015 05:49:12 -0400 http://ax84.com/bbs/dm.php?id=490606 125CSE for high octane???(by Ben Sykora) For the PCB high octane, I was planning to use a 125ESE that I have sitting around. I also have a spare 125CSE, which is rated for 8W output and 60mA DC bias. I've used a 125CSE before on a champ style amp with good results. Reviewing the high octane "general notes" on page 3, it says 70mA DC bias rating is required. The test voltage values of 6.62V with a 130R cathode bias works out to 51mA DC bias. Furthermore, the power transformer is only rated for 65mA DC. In my book, the 125CSE is a fine choice for the high octane. And if it weren't for the fact that this build may be repeated by others I wouldn't even hesitate. Does anyone have an argument against the 125CSE?Tue, 12 May 2015 10:14:26 -0400 http://ax84.com/bbs/dm.php?id=490587 Merlin's Ultra High Gain (by Denny Gracey) Components just arrived for converting my L2L (Brian’s) into Merlin’s UHG preamp. After building the L2L, I decided to use the chassis & power amp to build the UHG, basically to expand my education on high gain topologies. Also want to build it point-to-point. First, I pulled apart the L2L pre-amp, moved the preamp tubes just behind the front panel (and 4” apart per Merlin’s book), and rebuilt the L2L preamp using P2P. Wow – what a difference in noise! No hum and only modest hiss with everything dimed. There are only 4 wires in the circuit, including the input lead which is only 2" and not shielded, and only the longest (4” between stage 2-3) is shielded. Totally diggin’ P2P for high gain designs. Looking for anyone who’s built Merlin’s UHG to share ideas, etc. I plan to install pots for voltage dividers and cat resistors to tweak values for fun. Wed, 27 May 2015 18:50:51 -0400 http://ax84.com/bbs/dm.php?id=490581