AX84 BBS Recent Posts as of Thu, Nov 27th, 2014 @ 21:18:58 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com heyboer transformer substitutes?(by stinni) Hello there people of ax84 land. I'm looking into building the ax84 october-stage version but the heyboer transformers seem to be hard to get, or at least I can't find them online. has anyone any experience with making the october-stage version and if so did you use a substitute for the heyboer PT and OT? cheers from iceland!Thu, 27 Nov 2014 16:24:38 -0500 http://ax84.com/bbs/dm.php?id=487586 RE: (Old-ish) 5F1-clone puzzle(by sajyho) <div class="quoteblock" >On 11/27/2014 @ 03:41, Stack wrote : <div class="quoteblock" >On 11/27/2014 @ 00:57, sajyho wrote : : Connecting 6.3V heater wires directly to ground may cause Hum. : </div> : : Correction. Connecting the 6.3V heater wires directly to ground will cause a short circuit. -- </div> Sorry, I didn't make my point clear. I didn't mean conneting both wires directly to Ground; of course that will cause a short! I meant "connectin each of heater wires that carrying 6.3V AC directly to Ground will cause main frequncy noise." Because heater is physically very close to cathode in a tube, and it carries an AC current with mains power frequency, so imagine if it has much lower potential than cathode; Yes it may introduce a noise with mains power frequecy into the signal that is called "HUM". According to Merlin's book, you can connect your heater supply center tap to Ground to avoid that(if it has a center tap!); If it doesn't, you can itroduce a virtual center tap with two resistors(100 ohms is typical), and connect it to the circuit Ground. A method that works the best(at least it did for me!) if you don't have a center tap is to connect the virtual center tap to a cathod that carries ratherly high voltage. In a Champ type amp, the 6V6 Cathode is ideal for this method(the schematic that I've posted in my last post!)Thu, 27 Nov 2014 10:02:14 -0500 http://ax84.com/bbs/dm.php?id=487585 RE: The secret to a hum-free stand-alone preamp is...(by ormen) <div class="quoteblock" >On 11/27/2014 @ 08:12, tedmich wrote : I should think its a ground loop, rather than AC line noise, an isolation transformer could work. You could also look at designs like the PV Rockmaster, a relatively high gain design which lacks debilitating noise. For isolation trannies, Edcor is cheap and Jensen has very useful designs. -- </div> The Rockmaster has a diode noise-gate. So of course it has little noise, if any. Good preamp by the way.Thu, 27 Nov 2014 08:26:00 -0500 http://ax84.com/bbs/dm.php?id=487584 RE: negative feedback(by dsmith) <div class="quoteblock" >On 11/26/2014 @ 06:05, DutchMarco wrote : <div class="quoteblock" >On 11/25/2014 @ 23:15, Kursad K wrote : : <div class="quoteblock" >On 11/25/2014 @ 10:13, Dan Moos wrote : : : I've never done an amp with negative feedback before, but am now craving the touch sensitivity and guitar control of distortion it enables. : : : : </div> : : : : Are you sure any of this is related to negative feedback? : </div> : I second Kursad's question, isn't NFB supposed to reduce distortion? or at least delay it until higher volume levels (where it will suddenly burst into the sound) -- </div> The link on this <a href="http://www.ax84.com/bbs/dm.php?id=485716 " target="newwin1417141142">[link]</a> has a long thread with lots of detailed measurements. Apparently, a very finely balanced NFB contributes greatly to the famous TW touch sensitivity, amongst other things, like the PI and PS sag. Thu, 27 Nov 2014 08:19:33 -0500 http://ax84.com/bbs/dm.php?id=487583 RE: The secret to a hum-free stand-alone preamp is...(by tedmich) I should think its a ground loop, rather than AC line noise, an isolation transformer could work. You could also look at designs like the PV Rockmaster, a relatively high gain design which lacks debilitating noise. For isolation trannies, Edcor is cheap and Jensen has very useful designs.Thu, 27 Nov 2014 08:12:14 -0500 http://ax84.com/bbs/dm.php?id=487582 RE: Best way to wire the heaters?(by Henrik Lidbjrk) <div class="quoteblock" >On 11/26/2014 @ 05:05, GreenCanoe wrote : : "I'm thinking about redoing the filament wires altogether, but I think they're near perfect anyway." : : If you want any opinions on the work you have done before you move on to the next step feel free to post some pictures. We give opinions freely. ;^) </div> Sure, as soon as I'll get the time, I'll take a picture. In the meantime, I'd like to change my statement about "near perfect" to "hopefully good enough" :DThu, 27 Nov 2014 03:48:05 -0500 http://ax84.com/bbs/dm.php?id=487581 RE: (Old-ish) 5F1-clone puzzle(by Stack) <div class="quoteblock" >On 11/27/2014 @ 00:57, sajyho wrote : Connecting 6.3V heater wires directly to ground may cause Hum. </div> Correction. Connecting the 6.3V heater wires directly to ground will cause a short circuit. Thu, 27 Nov 2014 03:41:32 -0500 http://ax84.com/bbs/dm.php?id=487580 RE: debugging a P1(by mikerl) Thanks for the replies everyone. I will try the above suggestions and get back to you. Thu, 27 Nov 2014 03:07:50 -0500 http://ax84.com/bbs/dm.php?id=487579 RE: (Old-ish) 5F1-clone puzzle(by sajyho) Connecting 6.3V heater wires directly to ground may cause Hum. If your 6.3V heater supply has a center tap connect it to Ground for the best noise suppression. If it doesn't have a center tap using this method is my favorite one for a champ: <a href="http://music-electronics-forum.com/attachments/7137d1259788878-5f1_ground.gif" target="newwin1417141142">[link]</a> Thu, 27 Nov 2014 00:57:25 -0500 http://ax84.com/bbs/dm.php?id=487578 Output transformers(by Audiosalvage) I've got two push pull OTs for sale for the price of $30. I know one powered a pair of 6v6s and the other 7868s. I would also consider a trade for a Single end OT. Thanks, MarkWed, 26 Nov 2014 19:24:06 -0500 http://ax84.com/bbs/dm.php?id=487577 RE: (Old-ish) 5F1-clone puzzle(by Mitch Markin) According to the usual 5F1 schematic, one of the heater wires on the transformer goes to ground. The other one goes to the pilot light and one of the heater pins on each tube. The other heater pin on each tube goes to ground. If your heaters are wired this way and your transformer has a center tap on the heater winding it should not be connected to anything. The 0 volt wire on the transformer's primary should go to the neutral side of the AC line, through the fuse according to the usual schematic. The other primary wire goes to the hot side of the AC line through the power switch. Pictures of your amp's wiring would help.Wed, 26 Nov 2014 18:22:07 -0500 http://ax84.com/bbs/dm.php?id=487576 RE: negative feedback(by Kursad K) Searching google for "negative feedback and touch sensitivity" returned a thread with opposite conclusion: <a href="http://www.thegearpage.net/board/showthread.php?t=359264 " target="newwin1417141142">[link]</a> the author states: <div class="quoteblock" > I had a Frenzel Super Champ with a pull knob that defeated the negative feedback loop. The result was a more "raw" sound with a substantial increase in overdrive (what we'd commonly call gain), but less compression. That combo of more overdrive but less compression made for a very touch-sensitive overdrive sound. Nice. But it doesn't give you that singing sustain that you get from a lot of amps (unless you really wind up the preamp to get some compression from that part of the signal chain). I found for rock leads, I liked to hit it with a bit of additional overdrive from a pedal to get some more sustain. </div> My guess is that either way negative feedback is not directly related to the observed result. It's just that whatever the case may be, it's subjective and the amp is better either with or without NFB and one can associate that situation with any description in words. KursadWed, 26 Nov 2014 10:13:58 -0500 http://ax84.com/bbs/dm.php?id=487575 RE: (Old-ish) 5F1-clone puzzle(by sajyho) Cathode resistor, correction ;))Wed, 26 Nov 2014 06:59:35 -0500 http://ax84.com/bbs/dm.php?id=487574 RE: (Old-ish) 5F1-clone puzzle(by sajyho) The heater center tap should be connected to ground(0V) as a , or if it doesn't have a center tap one of heater wires should be connected to ground via a 100R resistor or through a Cathode cap...Wed, 26 Nov 2014 06:58:07 -0500 http://ax84.com/bbs/dm.php?id=487573 RE: negative feedback(by DutchMarco) <div class="quoteblock" >On 11/25/2014 @ 23:15, Kursad K wrote : <div class="quoteblock" >On 11/25/2014 @ 10:13, Dan Moos wrote : : I've never done an amp with negative feedback before, but am now craving the touch sensitivity and guitar control of distortion it enables. : : </div> : : Are you sure any of this is related to negative feedback? </div> I second Kursad's question, isn't NFB supposed to reduce distortion? or at least delay it until higher volume levels (where it will suddenly burst into the sound)Wed, 26 Nov 2014 06:05:45 -0500 http://ax84.com/bbs/dm.php?id=487572 (Old-ish) 5F1-clone puzzle(by DutchMarco) It has been a long time now since I've used my existing amps, never mind about building new ones. So I wanted to get my Vamp (5F1 clone) back up and running, I have used that amp so much in the past, that it amazed me to find several stray wires inside, and it not working anymore, in spite of fresh tubes (after which I found the wires disconnected, if I had known, I would not have powered it up, of course. There's one coming from the speaker, going to nowhere. but I realized that it was from a discarded attempt at creating switchable NFB. So that has that question solved, now my question: There are 2 loose wires inside, on the PT (inside the chasis), one was the 6.3VCT wire, and the other was from the primary, 0V.I'm affraid (as said, it has been a long time since I've used them) that my skills as an (ahem!) master amp maker seem to have been forgotten, but am I horribly (electrocutibly) wrong when I think that the heater center tap wire has to go to ground, together with the 0v primary? They have both been cut too short to reach to the on/off and standby switches, so I'm guessing they had to go there. And can basically only reach eachother, nop other component (like a switch, or a capacitor...)Thu, 27 Nov 2014 10:02:14 -0500 http://ax84.com/bbs/dm.php?id=487571 RE: LEDs for Blues Pre(by DutchMarco) Thank you two! To make sure I won't forget this, I've copy-pasted the site + Melin's tip into an ODT-document, which I've then, using Calibre, converted to an epub to keep on my phone. I'm sure this'll help me get going with my projects.Wed, 26 Nov 2014 05:41:34 -0500 http://ax84.com/bbs/dm.php?id=487570 RE: Best way to wire the heaters?(by GreenCanoe) <div class="quoteblock" >On 11/26/2014 @ 01:44, Henrik Lidbjrk wrote : Thanks for the reply! I tried the drill trick, and golly what a perfectly twisted wire I got! Awesome idea! I did realize, eventually, that it makes sense to partly untwist them in order to solder them to the filament lugs, etc., just like you describe. Actually, I haven't done this in practice yet, since I already soldered handtwisted wires to the sockets before I tried the drill. I'm thinking about redoing the filament wires altogether, but I think they're near perfect anyway. For the mains wire, I'll use the drill-twisted wire, though. -- </div> "I'm thinking about redoing the filament wires altogether, but I think they're near perfect anyway." If you want any opinions on the work you have done before you move on to the next step feel free to post some pictures. We give opinions freely. ;^)Wed, 26 Nov 2014 05:05:44 -0500 http://ax84.com/bbs/dm.php?id=487569 RE: Best way to wire the heaters?(by Henrik Lidbjrk) Thanks for the reply! I tried the drill trick, and golly what a perfectly twisted wire I got! Awesome idea! I did realize, eventually, that it makes sense to partly untwist them in order to solder them to the filament lugs, etc., just like you describe. Actually, I haven't done this in practice yet, since I already soldered handtwisted wires to the sockets before I tried the drill. I'm thinking about redoing the filament wires altogether, but I think they're near perfect anyway. For the mains wire, I'll use the drill-twisted wire, though.Wed, 26 Nov 2014 01:44:54 -0500 http://ax84.com/bbs/dm.php?id=487568 RE: The secret to a hum-free stand-alone preamp is...(by Merlin) <div class="quoteblock" >On 11/25/2014 @ 11:08, Darren Porter wrote : : My last attempt was Merlin's mid-gain example from his preamp book as a preamp only feeding my Simple Preamp/20W Push-Pull and it buzzes like a hive full of baritone bees. </div> Need more info. In no particular order: 1) How does the hum change when you adjust the volume control on the preamp (with AND without the guitar plugged in)? 2) How does the hum change when you adjust the volume control on the guitar? 3) What does it sound like? 60 or 120Hz hum, or harsh buzz? 4) Does the hum disappear immediately after you switch off the power, or does it hang around while the amp cools? 5) Have you switched off any possible sources of interference in the room, e.g. switch-mode power supplies / computers / monitors...? 6) Are you using humbuckers or single coils? 7) What sort of power supply are you using? Transformer / tube recto / SS / how much capacitance... 8) What sort of heater supply do you have? Centre tapped / elevated / humdinger...Wed, 26 Nov 2014 00:00:02 -0500 http://ax84.com/bbs/dm.php?id=487567 RE: negative feedback(by Kursad K) <div class="quoteblock" >On 11/25/2014 @ 10:13, Dan Moos wrote : I've never done an amp with negative feedback before, but am now craving the touch sensitivity and guitar control of distortion it enables. </div> Are you sure any of this is related to negative feedback? KursadTue, 25 Nov 2014 23:15:59 -0500 http://ax84.com/bbs/dm.php?id=487566 RE: The secret to a hum-free stand-alone preamp is...(by RickTown) Would an input coupling cap be worth trying then? As far as an input tranny, I would probably look for something with a ratio as close to 1:1 as possible. That's just my initial thought. I'm not sure if that helps at all.Tue, 25 Nov 2014 15:03:32 -0500 http://ax84.com/bbs/dm.php?id=487565 RE: The secret to a hum-free stand-alone preamp is...(by Darren Porter) Isolation transformer... been reading this may work. What would I use? Anyone have a part number? Is there something I could get quick-n-dirty at RadioShack just to test it out?Tue, 25 Nov 2014 14:14:51 -0500 http://ax84.com/bbs/dm.php?id=487564 RE: Best way to wire the heaters?(by GreenCanoe) <div class="quoteblock" >On 11/21/2014 @ 06:26, Henrik Lidbjrk wrote : <div class="quoteblock" >On 11/19/2014 @ 14:50, Stack wrote : : : Use a drill to twist the wires together, (I do about 2 or 3 ft at once)... Cut way over the length needed to get from socket to socket, unwrap a few of inches, splice them back together along the curvature left from the initial twisting and leave the tails longer than needed for connection to the sockets. Once the wire is in place to your liking then it can be soldered to the sockets. : </div> : : Sorry bout my ignorance, but why do you unwrap the wires after drill-twisting, only to splice them back together? -- </div> When you go to actually wire the socket with the twisted wire you will find it much easier to work with a single strand, strip the wire, prepare one connection, and then reassemble / retwist the strand for before you move on to the second connection to the socket. It is something that once you try it in real life you'll find the best way for you to perform the action. In all likelihood, if you are trying to maintain twisted wire as close as possible to the socket, you will end up with a method very similar to what is described above. Quite simply, once you try it you will understand.Tue, 25 Nov 2014 12:23:56 -0500 http://ax84.com/bbs/dm.php?id=487563 RE: debugging a P1(by AdamM) I reckon you might have the pot wired wrong, with the wiper to ground instead of one of the outer lugs. This would have the effect of, at one extreme, pulling the output of the first stage to ground, and at the other, pulling the grid of the second stage to ground - this would sound like you have described...Tue, 25 Nov 2014 11:47:11 -0500 http://ax84.com/bbs/dm.php?id=487562