AX84 BBS Recent Posts as of Fri, Oct 31st, 2014 @ 10:44:37 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com RE: Firezog and headphones(by HallwayMinstrel) I don't have any bass ports on my cabs. The bass port on my stereo speakers seem to be low to the ground. So put the bass port low would be my guess. And to reiterate, the Firezog works fine with headphones, you just need to change the 150K resistor down to 100 ohms. Yes, 1m log volume pot works fine, but a 250k log pot may give more travel, since most of the action is at the end of the pot. (I did not have a spare 250K.) With the Firefly, you can get cranked tones at low volume - that is what it is for - so the Firezog is unnecessary. I was just repurposing a chassis from an SS amp and it already had the Headphones-out jack. Good luck with your build. Let us know how it goes.Fri, 31 Oct 2014 06:43:00 -0400 http://ax84.com/bbs/dm.php?id=487159 RE: Adventures in Digital Control(by Chris Hurley) I found some short slide pots recently and I'm pretty sure I can control them with servos easily enough. Since digital servos can be commanded to a specific position, I won't need dual-gangs for positioning feedback. I haven't seen the pots yet so I'm not sure if I can thread in a ball for the servo arm link or if I'll have to JB-Weld something. One of those options should work. Fri, 31 Oct 2014 05:46:50 -0400 http://ax84.com/bbs/dm.php?id=487158 RE: Firezog and headphones(by DutchMarco) Thanks guys! I suppose I will just make a zog-less FF, if only because my tinitus is nastyenough as it is. A 1x8 cab with my old Celestion Blue Dog speaker. Guess I'll make it closed back - no reason to open upthe behind, as it is a bedroom amp, I do not intend to carry it with me to band practice (and thus needing a place to store spare tubes, the power cord etc.), besides, I'm not in a band anymore, anyway. If the 8" sounds lousy, I'll use a 2x12 cab too, been long since I've used it! BTW where do I look up info on bass ports? (would that even make sense on a FF (1x8)?Fri, 31 Oct 2014 05:08:22 -0400 http://ax84.com/bbs/dm.php?id=487157 myvvrtop1.gif(by DutchMarco) <a href="http://rh-tech.org/public/VVR/VVR_MyVVRTop1.gif " target="newwin1414766680">[link]</a> I have a question about this layout (which I converted to SVG using Inkscape, to facilitate neater printing), see <a href="http://www64.zippyshare.com/v/83863068/file.html " target="newwin1414766680">[link]</a> cile name: "MyVVRTop1.gif(3 hole instead of 5).svg" I converted it to a 3 lug eyelet strip because I still had one in stock). and I was wondering about the wiring of the pot: is this the view from the top (as the name suggests), or the bottom? BTW, this is the site I got the layout from: <a href="http://yeomansinstruments.blogspot.nl/2008/07/vvr-gretest-thing-ever.html " target="newwin1414766680">[link]</a> (but it doesn't seem to load atm).Fri, 31 Oct 2014 04:16:34 -0400 http://ax84.com/bbs/dm.php?id=487156 RE: KT120 Driver(by jazbo8) <div class="quoteblock" >On 10/30/2014 @ 16:35, tooltime wrote : : So, I have a couple questions before wiring in the MOSFETs. : 1)Do I have the BIAS supply and tap wired correctly? (The more negative voltage sitting at the source, with the actual tube bias voltage sitting at the gate) : 2)My bias voltage is around -40V, so my supply voltage will need to be around -80V. This exceeds the maximum Vgs of 20V. </div> You need a Zener (say 12V) to clamp the Vgs... Also, not sure why you would need one SF per tube, 1 for each side of the PP should be more than sufficient. The drains do not need to be at such high voltage, so perhaps you can create a lower voltage tap say 150V on the B+ line for the drains. The negative rail should be lower say -150V (more on that later)... <div class="quoteblock" >Even though it's not putting out anywhere near where I was hoping, it sounds incredible. Those KT120's put out some massive heat.</div> Did you draw a load line yet? I did a quick sketch and the 1.5k Ra-a puts the peak Pda well above the 60W limit, so I think a higher load (~2.5k) might be safer. This is a moster amp, which power transformer are you using? Thu, 30 Oct 2014 21:27:10 -0400 http://ax84.com/bbs/dm.php?id=487155 RE: Design "best of two worlds" amp...(by Stephen Keller) <div class="quoteblock" >On 10/30/2014 @ 20:06, Darren Porter wrote : Well apparently mixing 6V6 with EL84 using a "blend" pot has been done.... </div> When it comes to vacuum tube amplification, pretty much everything has been done before. A hundred years of experimental development has that effect on a technology. stphThu, 30 Oct 2014 20:48:04 -0400 http://ax84.com/bbs/dm.php?id=487154 RE: Inkscape for Panel Layout(by jazbo8) <div class="quoteblock" >On 10/30/2014 @ 09:22, Tim Mc wrote : Very nice jazbo8. I'm not where I can try this right now so I'll ask.... what's a 'point'? : : Tim -- </div> a "point" = 1/72th of an inch, e.g., 12pt font has a height of 12/72" or 1/6".Thu, 30 Oct 2014 20:09:18 -0400 http://ax84.com/bbs/dm.php?id=487153 RE: Design "best of two worlds" amp...(by Darren Porter) Well apparently mixing 6V6 with EL84 using a "blend" pot has been done. The Eggnater Rebel does this. I assume they still use just one PI though. I am thinking of another build now... lol... kind of in the same vein though... a nice Fender-based clean with a Marshall-inspired lead channel and some sort of power scaling, switchable fixed/cathode bias. So my quest still continues! This isn't going to be a cheap build though, so I may have to buy-and-build as I can afford the pieces. Maybe after New Years I can get it done.Thu, 30 Oct 2014 20:06:33 -0400 http://ax84.com/bbs/dm.php?id=487152 RE: KT120 Driver(by RickTown) Glad you got it going. A couple issues I see. Your source load resistors should be bigger. You have them at 10K but as Ardencaple suggested, increasing them to 47K will minimize idle source current. It might also modulate a bigger signal to the power tubes with the same amount of source current. Your MOSFET gates need to be biased directly between the power tubes' grid bias and B+. A large resistor between B+ and the gate and a small trimmer between the gate and bias supply. This will create your gate bias without the need for the additional "bias tap" to the gates. Actually, I assume the "bias tap" is a trimmer off the grid taps already, but you still need to complete the voltage divider by adding a large resistor to B+. John Hynes also had a good point about dropping your grid stoppers on the power tubes. I would add them back only if needed. I looked back at your bias supply circuit from your Oct 9th. As is, your least negative voltage coming off the 50K bias pots looks to be about -39V. If coincidentally, you're aiming for -38V at the grids then you would need to increase your 82K slightly while lowering your 27K's slightly. I don't think it'll take much of a change. Say 10 percent on both? If you've already reworked that part of the circuit and are happy with your grid voltage then disregard this one. I'm not super slick with MOSFET's so hopefully you'll get a few more responses.Thu, 30 Oct 2014 18:16:36 -0400 http://ax84.com/bbs/dm.php?id=487151 RE: KT120 Driver(by tooltime) It's been a while, but I finally got the amp powered up. I do no have any CF/SF before the power tubes, and its only putting out under 100W. Here is my latest schematic of what I want to try, including all my current voltage readings - <a href="https://picasaweb.google.com/100312329643818163848/October302014?authkey=Gv1sRgCP7TlZ7-0qPe7wE#6076160264303815522 " target="newwin1414766680">[link]</a> So, I have a couple questions before wiring in the MOSFETs. 1)Do I have the BIAS supply and tap wired correctly? (The more negative voltage sitting at the source, with the actual tube bias voltage sitting at the gate) 2)My bias voltage is around -40V, so my supply voltage will need to be around -80V. This exceeds the maximum Vgs of 20V. How do I get around this, or am I not thinking of this correctly? Will the source be almost the same votlage as the gate, with the 10k resistor dropping the voltage difference? Even though it's not putting out anywhere near where I was hoping, it sounds incredible. Those KT120's put out some massive heat.Thu, 30 Oct 2014 16:35:26 -0400 http://ax84.com/bbs/dm.php?id=487150 RE: Adventures in Digital Control(by Tim Mc) I have not paid any attention to the part numbers used but in some of the amateur radio tuners the current draw when not actually changing components is low enough that it will run on 12 VDC worth of AA batteries for well over a year. TimThu, 30 Oct 2014 13:23:37 -0400 http://ax84.com/bbs/dm.php?id=487149 RE: Adventures in Digital Control(by Kursad K) <div class="quoteblock" >On 10/30/2014 @ 12:46, AdamM wrote : bulky & power hungry, but simple : : reed relays would reduce the size (and increase the cost) : : SS relays maybe? watch out for max voltage capability. -- </div> There are small pcb mount relays, as large as an 8-pin chip. SS relays are not necessary if the size is a problem. KursadThu, 30 Oct 2014 12:55:13 -0400 http://ax84.com/bbs/dm.php?id=487148 RE: Adventures in Digital Control(by AdamM) bulky & power hungry, but simple reed relays would reduce the size (and increase the cost) SS relays maybe? watch out for max voltage capability.Thu, 30 Oct 2014 12:46:18 -0400 http://ax84.com/bbs/dm.php?id=487147 RE: tonight's random? picks(by Kursad K) <div class="quoteblock" >On 10/30/2014 @ 12:04, tedmich wrote : there's no accounting for taste! -- </div> Aha that was the point:) I get it KursadThu, 30 Oct 2014 12:37:29 -0400 http://ax84.com/bbs/dm.php?id=487146 RE: tonight's random? picks(by tedmich) there's no accounting for taste!Thu, 30 Oct 2014 12:04:39 -0400 http://ax84.com/bbs/dm.php?id=487145 RE: advice on building and designing amps for a living(by MasonAtom) <div class="quoteblock" >On 10/15/2014 @ 18:55, CChurchill wrote : I fell into this rabbit hole of amp, guitar, and effects building about five or six years ago. : To make a long story short, building tube amps quickly became as much of an passion as playing guitar. I've been reading everything I can get my hands on regarding the subject. : I want so badly to build and design amps for a living, and the thought of doing anything else blows(quite frankly). : It can be frustrating learning on my own, but there aren't many job postings for Tube amp apprentices. : I'm looking for any advice I can get. </div> Building a successful boutique amp company is certainly possible, but it is damn hard. I have a business on the side (TMI Amplification) that I have been running for 2 years and so far I still haven't recouped my investments (still a few thousand in the hole). Granted I have done a lot in sales and have turned all of that back into the company in terms of equipment and stock/components, but sometimes it is hard to think that I haven't paid myself a single cent for all the work I've done (which, believe me, is a lot). On the other hand, I have a ton of really cool tools and toys now and have gotten to the point where I can make pretty much anything I would want. I'm pretty sure I could turn a decent profit if I could work on this stuff about 70-80 hours a week, but unfortunately I only get 10-20 hours a week to put towards this since I have a demanding day job that is my first priority. There are a number of challenges beyond the technical challenges of knowing what you're doing with the electronics. These include 1) The profit margin is extremely small. In addition to making guitar amps, I do a number of other things with my business (faceplates, signs, engraved cell phone cases, coasters and taphandles for homebrewers, etc). Of all the things I make, guitar amps have far and away the lowest profit margins. To put in perspective: I did an order of 200 engraved cell phone cases that took me about 12 hours to complete. I built a fully custom 20W guitar amp with dovetailed curly maple enclose that I sold for $2450 that took me 60 hours in total to build (including the finishing of the cabinet). I made $1000 more profit from the cell phone cases in 1/5th amount of time... 2) Administrative stuff. Owning a small business and keeping track of accounting, taxes, inventory, etc is a major time sink that is hard to account for before you start. I spend waaaaaay more time on this stuff than anticipated. 3) Customer communication. This is a huge time sink. I spend so much of my time answering emails. It is really disheartening to exchange 20 emails with a potential customer over the course of a month, only to have him/her send you a text that says, "oh, I just went to guitar center and bought a dual rectifier". 4) Design time. Staring your own CAD library is a great idea because in the long run it will save you time, but you'll find when you are designing a product for production that the design times will be many times more than when you are designing something for yourself, because you will be constantly thinking about how to make the build easier in the long run. I spend more time on my computer doing CAD than I do actually building stuff... 5) Estabilishing a Presence. Designing a website, interacting with customers on social media, showcasing your wares, videos, pictures, branding, etc etc etc takes up a huge amount of time and often with little return on your time investment. I must admit that a lot of the issues above I bring on myself because I have a tendency to 1) charge too little for my time, 2) care too much about the customer and the product I deliver, 3) I am more interested in making something cool and unique than I am interested in making a lot of money so I tend to try to make anything and everything, and 4) I like to do everything I can by myself so I end up being the designer, manufacturer, social media guru, website developer, etc, etc when it would make more sense to farm out some of these tasks. My advice to you if you want to make money doing this is cut out everythign that is NON ESSENTIAL to making the amps. Focus on only 1 or 2 products and perfect them. Design them so they are quick and easy to assemble. Budget time to market yourself (webiste, social media, etc). It's theoretically possible to do this successfully, but if I were turning this into a fulltime job I would probably try for at minimum $250k loan to get things rolling. Fortuantely this is really still just a glorified hobby for me, but I do hope to turn it into my main source of income after I retire... I figure I have about 20 years to recoup those last couple thousand dollars... -MasonThu, 30 Oct 2014 11:35:18 -0400 http://ax84.com/bbs/dm.php?id=487144 RE: Firezog and headphones(by HallwayMinstrel) Ah, here is a better link to the actual post: <a href="http://www.ax84.com/bbs/dm.php?id=485791 " target="newwin1414766680">[link]</a> Thu, 30 Oct 2014 10:41:43 -0400 http://ax84.com/bbs/dm.php?id=487143 RE: Firezog and headphones(by HallwayMinstrel) <div class="quoteblock" >On 10/29/2014 @ 04:09, DutchMarco wrote : I was wondering about the Firezog mod. Would I be to be able to use it with a headphone? Or would it blow up a headphone? (I only have 9mm earbuds, not the shell models like used in studios), and the same question in amps other than the Firefly, does tthe same schematic work OK? : Also: is the 1M LineOut Level pot audio taper, or linear? I'd guess it is Audio taper : : BTW, I was referring to <a href="http://web.archive.org/web/20050627183340/home.cfl.rr.com/dbhammond/Firezog.gif " target="newwin1414766680">[link]</a> -- </div> I am using the Firezog mod with my Firefly. I use a 100ohm resistor instead of the 150Kohms in order to drive my headphones. They are the shell-kind. <a href="http://www.ax84.com/bbs/index.php?area=17 " target="newwin1414766680">[link]</a> I use a 1m log pot coming off of the tip of the speaker out jack. I have to turn the pot almost all the way up to get my headphones loud enough for my taste. I can disconnect the speakers if I want and the main signal is then shunted over a 10ohm 5W resistor to ground. (Yes, I said speaker(s), I put my firefly into a 2x12 combo, ha ha.) Sounds good actually. Naturally the cab sounds better - that goes for all tube amps - but it's quite useable when I don't want to make any noise.Thu, 30 Oct 2014 10:39:32 -0400 http://ax84.com/bbs/dm.php?id=487142 RE: Adventures in Digital Control(by Corn Trooper) This is an interesting topic, I'd love to see a successful result. <div class="quoteblock" >On 10/23/2014 @ 08:39, Chris Hurley wrote : That smooth feeling means they will require a good bit of torque. </div> Have you thought of a worm drive? Using worm gears you'll cut down on torque requirements and subsequently cost of the motor. The pots will be rotated at reduced speed, which might give you better control. <a href="http://en.wikipedia.org/wiki/Worm_drive " target="newwin1414766680">[link]</a> In any case that motors are involved, making the system aware of the positions of the pots, especially when 'waking up', could perhaps be somewhat challenging. Some kind of memory or initialization procedure might be needed.Thu, 30 Oct 2014 10:10:54 -0400 http://ax84.com/bbs/dm.php?id=487141 RE: Adventures in Digital Control(by Tim Mc) Perhaps you've seen this "Relay Pot" already. If not it may give you some ideas. A similar technique is used in ham radio applications for constructing remote antenna tuners where they switch inductors and capacitors in and out of the circuits. <a href="http://stiftsbogtrykkeriet.dk/~mcs/index.html " target="newwin1414766680">[link]</a> TimThu, 30 Oct 2014 09:27:40 -0400 http://ax84.com/bbs/dm.php?id=487140 RE: Inkscape for Panel Layout(by Tim Mc) Very nice jazbo8. I'm not where I can try this right now so I'll ask.... what's a 'point'? TimThu, 30 Oct 2014 09:22:41 -0400 http://ax84.com/bbs/dm.php?id=487139 RE: tonight's random? picks(by Kursad K) <div class="quoteblock" >On 10/30/2014 @ 05:16, tedmich wrote : <a href="https://www.youtube.com/watch?v=9UotQ5T-f1o " target="newwin1414766680">[link]</a> : skip to 7:30 for guitar playing : : <a href="https://www.youtube.com/watch?v=wEOFMHgkHzI " target="newwin1414766680">[link]</a> : Ron Thal: Guitars Suck : : <a href="https://www.youtube.com/watch?v=GiFKTvd7mn4 " target="newwin1414766680">[link]</a> : Ron Thal: Guitars Still Suck -- </div> Well the first one was fine at 7:30, I could not understand why you have posted the last two though:) KursadThu, 30 Oct 2014 09:13:18 -0400 http://ax84.com/bbs/dm.php?id=487138 RE: tonight's random? picks(by spud) I'm not saying it's bad or sucks or anything like that, just not my thing - don't get me wrong, I can appreciate the ability and talent to pull it off but I prefer more dynamics in my music rather than the full on, unrelenting onslaught of notes. I'm more of a blues guy with a tad of hard rock to spice it up - more classic rock as opposed to classical. To me, Black Sabbath and Led Zep were metal enough - after that my interest is limited. Don't get me started with the cookie monster stuff! (Which my daughter listens to - so I've been exposed to quite a bit - I'm still not sold.) JimThu, 30 Oct 2014 07:55:32 -0400 http://ax84.com/bbs/dm.php?id=487137 RE: tonight's random? picks(by tedmich) Probably not a fan of Paganini either? Thal is an acquired taste, undeniably masterful on the 6 string, slumming it with GNR to pay the bills... He has a great voice too, singing a dead on cover of JP's Running Wild on the utubes until lawyers had it removed, did a perfect RRhodes tribute recently too. He's about as good a player as Govan, but with a harder edge that I appreciate.Thu, 30 Oct 2014 07:43:42 -0400 http://ax84.com/bbs/dm.php?id=487136 RE: Wood working shop(by PhilS) Some time ago, I stumbled across this on eBay: <a href="http://www.ebay.com/itm/251321407054?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT " target="newwin1414766680">[link]</a> I keep it in my list of auctions I am watching. I keep thinking that one day I'll contact him and tell him what I want for a guitar cab. I keep thinking, for a reasonable price, he will cut a knock down for flat shipping that I can assemble. 5/8" Maple with dovetail construction is going to be very good for a head cab or a 1-12. It may be a little light for a 2-12, but I'm thinking it would be OK. The 1/8" difference between 3/4" and 5/8" seems fairly insignificant and I believe we use 3/4" wood simply because it is the stock dimension and 1/2" is thought to be too thin. He just needs to modify the design to omit the slots for the bottom of the drawer (one less thing to do) and to cut front (or baffle with speaker hole) and back panels. It wouldn't be too much of a challenge to get some 1" or 3/4" square stock locally and cut it by hand in a miter box for the bracing needed to hold the front (or baffle) and back. Yeah, I'll bet he'll do the roundover on it, too. It's not a big deal once you have the wood cut. It wouldn't take even 10 minutes to put the bit in the router and run it through. If I understand his formula correctly...let's look at a head box that is 9"H x 9"D x 20W. Tilt it like a drawer, so it is 20"W + 9"D. That's 29". Multiply by 9"H price @ $1.10. That's $32. Subtract something for the 1/4" plywood bottom, and add something for 5/8" front and back (maybe $16?). I am guessing $50 for the head box, which is a pretty nice price for a custom item. Someone's got to ask him. I haven't because I'm not ready. I have a router and make my own. My problem is that I don't have a planer and making boxes with wood that's not flat doesn't produce the best result. Wood from the home despot or blowes often has a small bow to it. I keep thinking, if this guy knew there was a market for flat pack guitar cabs, he'd be on it like flies on you know what. In some respects it is easier production because it is only raw unfinished wood. He takes time and materials to assemble and coat his drawers. There are others who sell head boxes and combo cabs on eBay, but the pricing is considerably higher. Just some thoughts that might be relevant...or not.Thu, 30 Oct 2014 06:35:57 -0400 http://ax84.com/bbs/dm.php?id=487135