AX84 BBS Recent Posts as of Sun, Aug 31st, 2014 @ 20:28:50 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com A stab at a Daisycutter(by Borgar Dahle) Hey. for some time i wanted to build a tube amp. I've been messing with it for a while, but i wanted to have some results before posting. I'm an electronics technician, but i have little experience with tubes or audio for that matter. After having my attempt at a Daisycutter shelved for a solid two months, i got it out again. I was having some crazy oscillations last time and i didn't know here to start. Not having a scope at my residence didn't help. I figured I'd just remove the tonestack and see, i had a hunch i messed that up somehow. Sure enough, it worked. a lot of hum though. No shielding what-so-ever and the heatersupply runs right by the input, still a prototype i suppose. I'm not really knowledgeable when it comes to guitar, tone or amps. but i like what I'm hearing so far. I'll get some of my guitar friends to check it out later. the parts is whatever i had from my failed marantz7c build, components from work and of course,Ebay. Nothing was chosen for tonal quality. tubes: 2x Chinese nobrand 7ax12's. just reads: 7ax12 china. 2x russian NOS 6p14p with CCCP branding. Powertransformer: Toroidal 55W supply. Hugely overdimensioned for a marantz preamp. still over overdimensioned for an 18W daisycutter. output transformer: OUTPUT TRANSFORMER 22W 6600 CT. the ebay listing mentioned fender but it looks brandless. the rest is vishey polyester film caps and resistors of different origins, sockets and screwterminals ect. from ebay. I'm powering it through a fusebox I built with 2x 5A automatic fuses, for projects involving mains. when I'm done it will have the regular glassfuse, obviously. Pictures: <a href="http://s6.photobucket.com/user/noppe/slideshow/tubeamp " target="newwin1409531334">[link]</a> Now i will have to read up on building a chassis. I'm not sure i even want a tonestack at this point. Maybe a single pot one, with a pullout switch to bypass. that would be cool. any comments and suggestions are welcome.Sun, 31 Aug 2014 14:11:57 -0400 http://ax84.com/bbs/dm.php?id=486084 RE: schematic for 8 to 12 watt class A EL84 amp(by Darren Porter) <div class="quoteblock" >On 08/31/2014 @ 11:26, David Ray wrote : No, from what I understand AC10 and AC15s and similar amps are cathode-byas with no negative feedback and they carry EL84 tubes which is the reason I was trying it because I've never had what is considered a Class A amp. Whether it's any different from my GT50 stealth head which carries a quartet of 6V6s as far as sound is concerned I am not sure. That being said what I'm looking to build is a 8 to 12 watt amp to practice with and play at home. -- </div> OK, so let's go back to square one... are you thinking this Laney transformer set is a good set because the original amp is Class-A? (which it isn't as far as I can see.) I looked at the schematic for that Laney and it is fixed-bias, not cathode. But that's not what makes an amp class-A anyways. It's the load lines created by the chosen circuit and biasing method is independent of that. You are going to have a hard time finding a true class-A schematic anywhere because all of those "so-called" class-A voxes and such are not really class A, they are really AB like everything else. If you want true class A you will likely have to go single-ended which means getting a new output transformer. Something like the AX84 P1eX. You could probably get away with the power transformer and chassis/combo cabinet you have. If you want the Vox "not really class A" sound with a pair of EL84's then check out the Trinity TC15. I built one of those and it is amazing, but it's not an easy first build and it is LOUD. Also, you will not really hear that much of a difference between 10 watts and 18 watts. You would need to go down to something like 5 watts to start to notice a difference and that will still be pretty loud. If you want a low-watt practice amp for home, I would still suggest an 18-watt but add a VVR. Here is a schematic... <a href="http://rh-tech.org/public/18-Watt/18_Watt_LiteIIb_VVR_PA_PI_141.gif " target="newwin1409531334">[link]</a> In case you don't know, VVR stands for "Variable Voltage Regulation" and it allows adjustable B+ voltages to vary the output of your amp. It is easy to implement with a single MOSFET, a couple resistors, a few diodes and a pot. That will get you a very flexible amp that can be quiet when you want it to be quiet and loud when you want it to be loud. Of course, the VVR can be added to any other amp as well, so if the 18-watter just isn't your cup of tea, you can just as easily add it to an AC15 or Fender Deluxe or whatever circuit you choose. Alternatively, if low-power and cheap is the goal, check out the Firefly you can find in the schematics here.Sun, 31 Aug 2014 11:56:32 -0400 http://ax84.com/bbs/dm.php?id=486083 RE: schematic for 8 to 12 watt class A EL84 amp(by David Ray) As far as the Marshall 18 watt, I definitely wouldn't mind checking out the schematic on it if anyone has it. It never even occurred too me too attempt it, but is tempting. Sun, 31 Aug 2014 11:33:18 -0400 http://ax84.com/bbs/dm.php?id=486082 RE: schematic for 8 to 12 watt class A EL84 amp(by David Ray) No, from what I understand AC10 and AC15s and similar amps are cathode-byas with no negative feedback and they carry EL84 tubes which is the reason I was trying it because I've never had what is considered a Class A amp. Whether it's any different from my GT50 stealth head which carries a quartet of 6V6s as far as sound is concerned I am not sure. That being said what I'm looking to build is a 8 to 12 watt amp to practice with and play at home.Sun, 31 Aug 2014 11:26:11 -0400 http://ax84.com/bbs/dm.php?id=486081 RE: A little recording sample.(by Darren Porter) Sounds nice. I like it!Sun, 31 Aug 2014 11:13:59 -0400 http://ax84.com/bbs/dm.php?id=486080 RE: schematic for 8 to 12 watt class A EL84 amp(by Darren Porter) <div class="quoteblock" >On 08/31/2014 @ 10:16, jazbo8 wrote : Why don't you try converting it a Marshall 18W with SS rectifiers? I don't quite understand the need for Class A operation for a guitar amp, is it for a specific application? -- </div> This is what I'd do and it's probably closer to what that Laney originally was to begin with. From what I've read, that Laney was a nice sounding amp. I am currently building an 18-watt Lite IIb. Sun, 31 Aug 2014 11:07:55 -0400 http://ax84.com/bbs/dm.php?id=486079 RE: KT120 Driver(by tooltime) <div class="quoteblock" >On 08/30/2014 @ 03:40, steve25 wrote : Are you going to use a power supply and Transformer set to use the most that those KT120s have to offer? : A build like the 70s Fender 400PS makes a great Bass amp if you can afford the driver transformer. -- </div> Yes, I have a custom Mercury set headed my way. Wound 250-0-250, which should let me get approximately 350V for the Preamp, and 700V for the KT120 plates.Sun, 31 Aug 2014 10:38:27 -0400 http://ax84.com/bbs/dm.php?id=486078 RE: schematic for 8 to 12 watt class A EL84 amp(by mac dilard) +1 on the Marshall 18 watt, Zaphod Phill's 18 watt Superlite TMB is a heck of an Amp. IMOSun, 31 Aug 2014 10:26:17 -0400 http://ax84.com/bbs/dm.php?id=486077 RE: schematic for 8 to 12 watt class A EL84 amp(by jazbo8) Why don't you try converting it a Marshall 18W with SS rectifiers? I don't quite understand the need for Class A operation for a guitar amp, is it for a specific application?Sun, 31 Aug 2014 10:16:43 -0400 http://ax84.com/bbs/dm.php?id=486076 A little recording sample.(by JeffW) I have been slowly learning how to use Studio One and trying to get back to recording after a long gap. Seems like good software so far. The drums are from Studio One, bass is direct using built in tones, the guitar is a tele I built and the amp is a Kustom Defender that is modded then into a 2x10 open back loaded with Jensen C10R's. Mic is an EV Cardinal. Here is the clip. <a href="http://www.mediafire.com/listen/15i20mx5cszidzs/Ham_Hand_Jazz.mp3" target="newwin1409531334">[link]</a> Sun, 31 Aug 2014 11:13:59 -0400 http://ax84.com/bbs/dm.php?id=486075 RE: schematic for 8 to 12 watt class A EL84 amp(by Darren Porter) I looked at the schematic. It's definitely push-pull. The transformers won't dictate the class of operation. So, while you could make it truly class-A you are not limited to that and you can go class-AB if you wish. Here is a good read about that subject... <a href="http://www.aikenamps.com/index.php/is-the-vox-ac-30-really-class-a " target="newwin1409531334">[link]</a> and <a href="http://www.aikenamps.com/index.php/the-last-word-on-class-a " target="newwin1409531334">[link]</a> Sun, 31 Aug 2014 09:05:15 -0400 http://ax84.com/bbs/dm.php?id=486074 RE: schematic for 8 to 12 watt class A EL84 amp(by David Ray) I've got the specs somewhere, but I do know that particular amp was touted as a "class A" amp, however the schematic for that amp is similar to a JCM 800 which is a push pull design. I'll post the specs as soon as I locate them. I just want to be sure to use the transformers properly.Sun, 31 Aug 2014 04:58:56 -0400 http://ax84.com/bbs/dm.php?id=486073 RE: Return To Solid State(by Douche Baggins) Seems like modeling amps are getting better over the past few years than the garbage that had been out prior. Manufacturer's should never taught their modeling amps sound "like a tube amp" because that is still not the case. For the price, functions, and especially at low level playing they really are attractive. The head phone out/speaker emulator is a nice touch, no more headphone speaker distortion.Sun, 31 Aug 2014 03:17:55 -0400 http://ax84.com/bbs/dm.php?id=486072 RE: Return To Solid State(by Kursad K) <div class="quoteblock" >On 08/30/2014 @ 19:11, Douche Baggins wrote : Downsized from a 3/2 SFH to a 2/2 condo four months ago and had to downsize my guitar volume as well. I'd been looking at a few modeling amps for the past 6 months and was near purchase on a Fender Mustang 3 however, I didn't want to spend that much. I went to Sam Ash today to pickup this: <a href="http://www.samash.com/hercules-gsp38wb-wood-wall-mount-guitar-hanger-hgsp38wbx " target="newwin1409531334">[link]</a> and ended up trying out and bought this amp: <a href="http://www.samash.com/id%3Acore-stereo-10-2x5w-super-wide-stereo-combo-guitar-amp-bcore10xx-p " target="newwin1409531334">[link]</a> : : This amp exceeded my expectations in many ways. The most impressive is the sound doesn't crap out, fade or pulsate when multiple effects are used together. Even, with distortion plus multiple effects together it holds true. It doesn't do low gain very well, but medium gain is good and high gain is great. Big sound for 2 x 3" (stereo) speakers. Here's a couple vids: <a href="https://www.youtube.com/watch?v=_MUAeCKGHEg " target="newwin1409531334">[link]</a> and <a href="https://www.youtube.com/watch?v=DDbulFQUh38 " target="newwin1409531334">[link]</a> : : It's easy to figure out and unlike the other modeling amps (including the Mustang 3) it doesn't have any useless stock settings. For $100 it's a lot of fun and should make a good recording amp. -- </div> I guess the amp manufacturers have discovered the same things that we did in the last 10 years or so: that proper tone shaping and a simple healthy clipping circuit free of blocking distortion artifacts goes a long way and you do not necessarily need to model anything. That wasn`t the way it used to be. I remember expensive effect processing units that included one or two 12ax7`s with cool looking digital EQ adjustments and they used to sound pretty crappy. Nowadays even an ameteur amp builder can do much better. KursadSun, 31 Aug 2014 01:00:59 -0400 http://ax84.com/bbs/dm.php?id=486071 Return To Solid State(by Douche Baggins) Downsized from a 3/2 SFH to a 2/2 condo four months ago and had to downsize my guitar volume as well. I'd been looking at a few modeling amps for the past 6 months and was near purchase on a Fender Mustang 3 however, I didn't want to spend that much. I went to Sam Ash today to pickup this: <a href="http://www.samash.com/hercules-gsp38wb-wood-wall-mount-guitar-hanger-hgsp38wbx " target="newwin1409531334">[link]</a> and ended up trying out and bought this amp: <a href="http://www.samash.com/id%3Acore-stereo-10-2x5w-super-wide-stereo-combo-guitar-amp-bcore10xx-p " target="newwin1409531334">[link]</a> This amp exceeded my expectations in many ways. The most impressive is the sound doesn't crap out, fade or pulsate when multiple effects are used together. Even, with distortion plus multiple effects together it holds true. It doesn't do low gain very well, but medium gain is good and high gain is great. Big sound for 2 x 3" (stereo) speakers. Here's a couple vids: <a href="https://www.youtube.com/watch?v=_MUAeCKGHEg " target="newwin1409531334">[link]</a> and <a href="https://www.youtube.com/watch?v=DDbulFQUh38 " target="newwin1409531334">[link]</a> It's easy to figure out and unlike the other modeling amps (including the Mustang 3) it doesn't have any useless stock settings. For $100 it's a lot of fun and should make a good recording amp.Sun, 31 Aug 2014 03:17:55 -0400 http://ax84.com/bbs/dm.php?id=486070 RE: schematic for 8 to 12 watt class A EL84 amp(by Darren Porter) You could probably do something like an AC15 or an 18watt with that too. Do you have the specs for the transformers? Sat, 30 Aug 2014 19:04:30 -0400 http://ax84.com/bbs/dm.php?id=486069 RE: schematic for 8 to 12 watt class A EL84 amp(by David Ray) Thanks for the input! Now that you mention it I have the schematic far an amp designed by Dave Hunter in "The Guitar Handbook" called the Two-Stroke amp design. It utilizes two 6V6s but you can also use a EL-34 and several other 8 Pin output tubes. What is you opinion on this? I already have everything except for the 8 Pin sockets themselves. Also I wonder if I should change the rectification from vacuum tube to solid state in order to have a faster response for a more modern sound? Being a novest and this being my first amp build I want to start with something simple, yet have some options available as far as output tubes and bias is concerned. My main concern is whether or not the PT and OT already mounted in the chassis would work with with this type of schematic? Sat, 30 Aug 2014 16:45:17 -0400 http://ax84.com/bbs/dm.php?id=486068 RE: schematic for 8 to 12 watt class A EL84 amp(by Stevo) Well, you've got transformers ideal for 3 12AX7s, and 2 EL84s. There's a lot you can do with that. I'd suggest doing a bit of tone research and narrowing in on what kind of amp you want here. Looking at the original schematic, it looks like the LC-15 has some striking similarities to a JCM800 preamp, only with EL88s rather than EL34s. With that, you could build a similar high gain preamp, or a plexi style preamp. If you think you'd like a different power tube, 6V6s are a near drop in substitute performance-wise for EL84s - you'd need 8 pin sockets, though. Whatever you decide, I would suggest finding a place where you can buy a pre-made turret or eyelet board for the amp you want to build. Like here: <a href="http://hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=Boards&ORDER_ID=699983580 " target="newwin1409531334">[link]</a> Sat, 30 Aug 2014 09:13:16 -0400 http://ax84.com/bbs/dm.php?id=486067 schematic for 8 to 12 watt class A EL84 amp(by David Ray) I have a Laney LC-15R chassis complete with the power and output transformers still mounted. The main circuit board is trashed because of one of the plastic EL-84 sockets arching and Charing the board. I also have the reverb/effects board still mounted in the chassis, but the wires have been cut from the main board. I was hoping to reuse the ebd trannys, chassis, etc... To build a 10 or 12 watt class A amp and mount the new board in the chassis. I can read schematics fairly well and have rudimentary soldering skills and the desire to try to build my own amp to play through. Any ideas especially schematics for something between 8 to 12 watts would be a big help, so anyone who has done something similar help me out here. Thanks in advance.Sun, 31 Aug 2014 11:56:32 -0400 http://ax84.com/bbs/dm.php?id=486066 RE: KT120 Driver(by jazbo8) <div class="quoteblock" >On 08/30/2014 @ 06:41, Ardencaple wrote : : By the way, there is a bit of a trick one can play to improve bass response, by using some cathode feedback. This can be done by using the secondary windings to provide the feedback; the cathodes of the output devices are connected to the output windings in the same balanced manner as the primary windings. So one cathode would be connected to the output common, the ground path to the 4 ohm tap, and the other cathode to the 16 ohm tap [if you work out the winding ratios, this means both of the feedback winding ratios are the same]. The voltage feedback ratio is greater when the primary impedance value is lower, as it is with big bass amps.. Anyone had a play with this? I think Alethian Alex did, but I don't think anyone has heard from him for a long time. </div> Yes, quite a few of the old guys that used to hang out here are gone... Alethian was definitely one of the wiz, he came up with a lot of interesting ideas. CFB would be a good idea for the bass amp assuming the correct windings could be found in off-th-shelf OPTs. Claude over at diyaudio built some really big bass amps with the Hammond 1650T and 1650W, both should work well with the KT120s. If I were to build one, I would opt for 4xKT120 but run them conservatively for long tube life and plenty of headroom. So back to the OP's question, I think it is very important to have a good CF/SF driver for these big output tubes.Sat, 30 Aug 2014 06:57:54 -0400 http://ax84.com/bbs/dm.php?id=486065 RE: KT120 Driver(by Ardencaple) Thanks for the info, Jazbo. I also found this: <a href="http://www.audioasylum.com/cgi/m.pl?forum=tubediy&n=224093 " target="newwin1409531334">[link]</a> As to power, well, there are two schools of thought .. 1) keep it conservative .. so if it gets treated as a kT88, then it should survive just about anything one chucks at it! Also, this should allow the output stage to stay fairly clean, and possibly allow UltraLinear operation. Bass probably benefits from a clean output stage with any distortion added in the preamp. 2) extract as much power as possible! Tung-Sol claim 160W is possible; I presume this would be with 800V plate, 600V screen. I think for bass, one needs about 200W up to 300W? The problem is those speakers are not as efficient as guitar versions, since they need a lot more excursion. So.. either two KT120s, thrashed to give maximum power at around 160W or four to give 200W+ comfortably? Iron could be a problem. You want big iron to give the bass response. In Europe I found this supplier: <a href="http://www.roehrenendstufen.de/ " target="newwin1409531334">[link]</a> You can specify a transformer on-line. There are options for bass versions, and plugging in 400W power gives a cost of 160 EURO. Which sounds reasonable, though shipping might be a killer. By the way, there is a bit of a trick one can play to improve bass response, by using some cathode feedback. This can be done by using the secondary windings to provide the feedback; the cathodes of the output devices are connected to the output windings in the same balanced manner as the primary windings. So one cathode would be connected to the output common, the ground path to the 4 ohm tap, and the other cathode to the 16 ohm tap [if you work out the winding ratios, this means both of the feedback winding ratios are the same]. The voltage feedback ratio is greater when the primary impedance value is lower, as it is with big bass amps.. Anyone had a play with this? I think Alethian Alex did, but I don't think anyone has heard from him for a long time. Sat, 30 Aug 2014 06:41:40 -0400 http://ax84.com/bbs/dm.php?id=486064 RE: KT120 Driver(by jazbo8) <div class="quoteblock" >On 08/30/2014 @ 01:13, Ardencaple wrote : : Does anyone have a spice model of the KT120? I can't find anything other than the slightly skimpy datasheet. The point being that presumably the way to drive them to high power would be to use high B+ and a screen voltage of about half that, like in the big HiWatts. </div> There is a SPICE model over at diyaudio, but I'm not sure it is all that accurate. But you can also use the KT88 model and scale it up a bit, the two are basically the same - the KT120 of course has a higher Pda rating, so you can get a bit more power out of them. How much output are you planning for the bass amp?Sat, 30 Aug 2014 04:20:01 -0400 http://ax84.com/bbs/dm.php?id=486063 RE: KT120 Driver(by steve25) Will you use in the build a power supply and Transformer set to use the most that those KT120s have to offer? A build like the 70s Fender 400PS makes a great Bass amp if you can afford the driver transformer.Sat, 30 Aug 2014 03:41:54 -0400 http://ax84.com/bbs/dm.php?id=486062 RE: KT120 Driver(by steve25) Are you going to use a power supply and Transformer set to use the most that those KT120s have to offer? A build like the 70s Fender 400PS makes a great Bass amp if you can afford the driver transformer.Sat, 30 Aug 2014 03:40:59 -0400 http://ax84.com/bbs/dm.php?id=486061 RE: KT120 Driver(by Ardencaple) Cool. I'm interested in this too, since my son plays bass, and I did think that maybe KT120s would be the way to go .. Mind you, I have other things on at the moment, so it would not be soon.. Does anyone have a spice model of the KT120? I can't find anything other than the slightly skimpy datasheet. The point being that presumably the way to drive them to high power would be to use high B+ and a screen voltage of about half that, like in the big HiWatts. [see: <a href="http://hiwatt.org/Schematics/DR_400wOutput.pdf] " target="newwin1409531334">[link]</a> So tooltime, to answer your other questions, the 200 Watt amps used ECC81 / 12AT7 for the PI, but the 400 Watt used ECC81 / 12AT7 cathode followers as well. As Jazbo suggested, they just use the negative bias rail. The Hiwatts usually had a separate bias winding, so this would have been a solid supply. Sat, 30 Aug 2014 01:13:05 -0400 http://ax84.com/bbs/dm.php?id=486060