AX84 BBS Recent Posts as of Thu, Jul 02nd, 2015 @ 06:30:04 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com RE: Standalone based on Core 50W PP build(by Darren Porter) <div class="quoteblock" >On 07/02/2015 @ 03:06, steve25 wrote : First things first, 2 6V6 outputs in class AB1, even with 500 + volts on them will do a best of 29 watts, not 50 watts not less 50 watts of RMS power if that is what you where looking for! -- </div> Thanks for taking the time to read my post Steve. I'm aware I won't be getting 50 watts out of 6V6's. What I said was... <div class="quoteblock" >1) KT77 output tubes with an eye towards swapping 6V6's in for when I don't need 50 watts - which will honestly be most of the time.</div> That is: KT77's for when I need 50-ish watts 6V6's for "when I don't need" 50 watts (ie: I need more like 20-ish watts) Thu, 02 Jul 2015 06:00:29 -0400 http://ax84.com/bbs/dm.php?id=491221 RE: Standalone based on Core 50W PP build(by steve25) First things first, 2 6V6 outputs in class AB1, even with 500 + volts on them will do a best of 29 watts, not 50 watts not less 50 watts of RMS power if that is what you where looking for!Thu, 02 Jul 2015 03:06:09 -0400 http://ax84.com/bbs/dm.php?id=491220 RE: Book recommendation (by Lord of the Livingroom) You work way faster than me... My last one, the AMZ Super Buffer, was my fastest at two days... and I still made a wiring error! And I didn't include my customary artwork or clearcoat finish to the enclosure.Wed, 01 Jul 2015 17:18:22 -0400 http://ax84.com/bbs/dm.php?id=491219 Parallel Single Ended Amplifier (by T Kaye) Hi J. just read your Parallel single ended amplifier post,,,love the pictures,,,wow super nice job,,i've been thinking about building one but I don't have a schematic to go by,,I was wondering if you would share yours with me,,,thank you,,Terence,,,Wed, 01 Jul 2015 16:20:22 -0400 http://ax84.com/bbs/dm.php?id=491218 Standalone based on Core 50W PP build(by Darren Porter) I've been waiting for the AES 10% off sale and now that it's here and it's summer (lots of free time) I am finally going to build this. I'd like for this amp to serve both as my test-bed for stand-alone preamp builds and as my amp for my live rig. I will probably make it either into it's own head or rack-mountable so I can also rack-mount a preamp into the rig as well and just carry one box. So, I want to do a 50 watt stand-alone power amp based on the October Stage/Core 50W PP Standalone projects with the following features: 1) KT77 output tubes with an eye towards swapping 6V6's in for when I don't need 50 watts - which will honestly be most of the time. 2) Reverb and effects loop built into this power amp so I don't have to build them into every preamp I build in the future. 3) Possibly a cathode/fixed-bias switch. I have a couple of questions about the topology and power supply... Should I go input jack => 12AU7 parallel input stage => effects => PI/AMP -or- Should I go input jack => effects => 12AU7 parallel input stage => PI/AMP I'm thinking the latter but not 100% sure why. For the power supply, this is a weakness of mine. I really don't have much of a clue doing power supply circuit design. The effects loop and reverb design I am looking at uses a total of three 12A_7 tubes. Looking at the standalone 50W power supply, would I just hang a few more nodes off the end for a B+5, B+6 and B+7 node for the three extra tubes? What value of filter caps should I use? 47u or 22u? Do I need to lower the value of R3 so more voltage gets down to those tubes? After I figure out that power supply issue I think I can put a parts order together and get this rolling! Thu, 02 Jul 2015 06:00:29 -0400 http://ax84.com/bbs/dm.php?id=491217 RE: Book recommendation (by Darren Porter) Somebody caught the fever :-) Now go buy a multi-channel oscilloscope so you can visualize what your stuff is doing at each stage! fun fun fun!Wed, 01 Jul 2015 13:29:40 -0400 http://ax84.com/bbs/dm.php?id=491216 RE: Book recommendation (by Kursad K) If you are picky about noise: <a href="http://www.amazon.com/Small-Signal-Audio-Design-Douglas/dp/0415709733 " target="newwin1435833008">[link]</a> KursadWed, 01 Jul 2015 13:24:13 -0400 http://ax84.com/bbs/dm.php?id=491215 RE: Book recommendation (by nonzero) Wow. 4 months ago I posted this thread. Okee dokee then. You guys want to know whats more fun than building amps? You guessed what I was going to say, didn't you. Well it's true. Making these pedals is soooo gratifying. You go to bed thinking about how cool it'd be to have a soft-clipping dirty boost, then wake up with an idea sitting on your mind (and a cat on your chest if you live here). After breakfast you spend a few minutes developing the idea into a block diagram (or directly to schematic if it's a common topology). Since it's Saturday morning you spend another few minutes (or hour. Sometimes you spend an hour) laying out your strip-board. By noon you've got your cuts and jumps completed and cleaned up, your 1590A drilled, mounted, and the off-board wiring finished and neatened, so you break for lunch. I'm thinking cold cereal and an apple. Something light and fast. Then back to the bench. Resistors first: Tape down. Solder. Then the non-vintage diodes. Then short caps, etc. progressing through taller and taller components until it's ready to clip to your test rig (you've got a test rig, you know). Problem. It makes sound if you crank the amp. You can hear it clip as you adjust the gain knob. You can hear it brighten as you adjust the tone knob. But barely. All the solder points are good (3 mins), the polarities on the caps are good (15 secs), and your JFETs are oriented correctly, too. But wait! This little guy has an hfe of, like, 15 or something. No wonder you can't hear it! Good thing you used a socket (right?), so you swap it out lickity-split (5 mins). Next thing you know your wife's calling you down for dinner after noodling for two hours. Oh, and you picked up the parts for THREE PEDALS and got change back from a hundred dollar bill. Wonder what I'll make Sunday. This website is the coolest. Serious props to this community.Wed, 01 Jul 2015 13:09:31 -0400 http://ax84.com/bbs/dm.php?id=491214 AES July 2015 - everything 10% off(by Darren Porter) FYI.... 10% off all items at AES Wed, 01 Jul 2015 09:28:36 -0400 http://ax84.com/bbs/dm.php?id=491213 RE: Solid State FX loop.(by Kursad K) <div class="quoteblock" >On 04/15/2015 @ 17:45, Alva Goldbook wrote : I've never gotten around to doing a shootout between various amps for the quality of their FX loop, but I do know that every stock Marshall loop I've used I've found to perform pretty horribly. The loop on my Fender Hot Rod Deville performs wonderfully in comparison. That amp uses an 741 op-amp for the FX loop. I would think that op-amps would be fairly ideal for FX loops since their output impendence is so low. I just don't know enough about solid state electronics to set one up. -- </div> Interesting, I used to think that nobody would use a 741 while there are much better parts nowadays, but maybe it has a few interesting properties: <a href="https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/datasheets/Opamps/741.html " target="newwin1435833008">[link]</a> KursadWed, 01 Jul 2015 00:36:29 -0400 http://ax84.com/bbs/dm.php?id=491212 RE: 6922 phono preamp idea(by Merlin) <div class="quoteblock" >On 06/30/2015 @ 12:36, Stevo wrote : Okay. Thanks for the replies and the advice. How about this for a topology: 6922 cascode stage => full riaa eq => common cathode gain stage => cathode follower out. </div> Yes, that is not an unusual topology.Tue, 30 Jun 2015 23:38:35 -0400 http://ax84.com/bbs/dm.php?id=491211 RE: Parts selection for a new build(by GeorgeG) May have to take a look at WGS after I get the amp put together.Tue, 30 Jun 2015 19:07:06 -0400 http://ax84.com/bbs/dm.php?id=491210 RE: Parts selection for a new build(by Darren Porter) Yeah i use an ET65 alone open backed with my fenderish build. Sounds amazing. That speaker really put the icing on the cake.Tue, 30 Jun 2015 18:39:33 -0400 http://ax84.com/bbs/dm.php?id=491209 RE: Parts selection for a new build(by Lord of the Livingroom) Just thought I'd chuck in my 2c regarding speakers. I have recently finished building a 2x12" speaker cab, semi-open back (about 1/3 open) loaded with WGS speakers - a Retro 30 and a ET65 in series for 16 ohms. Paired with my JTM45 clone, it's magic! Not quite the same character as the classic combo of JTM45 and Greenbacks, with their early breakup. But it's exactly what I was after in a speaker cab; solid bottom end, clear highs, not too middy, good clean headroom.Tue, 30 Jun 2015 17:07:23 -0400 http://ax84.com/bbs/dm.php?id=491208 RE: Parts selection for a new build(by GeorgeG) 16 it is.Tue, 30 Jun 2015 14:55:27 -0400 http://ax84.com/bbs/dm.php?id=491207 RE: Custom chassis(by Darren Porter) <div class="quoteblock" >On 06/29/2015 @ 08:05, Paul Fawcett wrote : Wyatt's current plan is to focus initially on 16 gauge AX84-style 8"x16"x2" project chassis. Custom sizes are still intended, but not until some future time. : : I have a few of these available now that were from some initial test bends. : : These are solid and perfectly serviceable but typically have minor imperfections such as small deviations (I don't think I measured anything off by more than 1/8") from nominal dimension, or minor cosmetic issues such as machine marks from the brake or scratching of the aluminum. If anyone is interested, these can be had at a significantly discounted rate of for $10 + actual USPS shipping charges (US and Canada addresses only). Email paul@wombatamps.com if interested. -- </div> I sent you an email Paul.Tue, 30 Jun 2015 14:54:10 -0400 http://ax84.com/bbs/dm.php?id=491206 RE: Parts selection for a new build(by Darren Porter) It does if they are mis-matched. Some people like trying that to get a different character but read up on which way you can go with the mis-match and how far before you start running into problems. I just go with a multi-secondary output transformer and use an impedance selector switch (or multiple output jacks.) That will give you the most flexibility. If you think you might want to install those speakers into a 4x12 cabinet someday or run two 2x12 cabinets then go with the 16 Ohm version. Otherwise 8 or 16... doesn't matter as long as your amp has the matching output jack. Tue, 30 Jun 2015 14:47:37 -0400 http://ax84.com/bbs/dm.php?id=491205 RE: Parts selection for a new build(by GeorgeG) Do you think that speaker impedance has any effect on tone either because of the speaker itself or the difference in the OT windings? I am now considering a 2x12 bottom so I can go with either 2x16=8 or 2x8=4 ohms. Closed back (removable) it is. I am leaning towards 16 ohm versions.Tue, 30 Jun 2015 14:37:37 -0400 http://ax84.com/bbs/dm.php?id=491204 RE: 6922 phono preamp idea(by Stevo) Okay. Thanks for the replies and the advice. How about this for a topology: 6922 cascode stage => full riaa eq => common cathode gain stage => cathode follower out.Tue, 30 Jun 2015 12:36:01 -0400 http://ax84.com/bbs/dm.php?id=491203 RE: 6922 phono preamp idea(by Merlin) <div class="quoteblock" >On 06/30/2015 @ 10:17, Stevo wrote : The 1M grid leak on stage three is intended to be a volume control. </div> Hmm... unusual to have a volume control in a phono stage? I guess it would be OK though. You might want to leave the 3rd stage unbypassed though, or the Miller capacitance will begin to choke off the bandwidth. <div class="quoteblock" >I did want it to be suitable to MC as well as MM cartridges. </div> I think you will find it too noisy for MC use. I don't know of any tube or topology that can acheive the low noise needed for MC use. You pretty much have to resort to silicon for that. But don't let me put you off trying it out! <div class="quoteblock" > What about retaining the three gain stages, but leaving the cathodes unbypassed? </div> Don't do that on the input stage or it will increase the noise even more.Tue, 30 Jun 2015 11:56:31 -0400 http://ax84.com/bbs/dm.php?id=491202 RE: 6922 phono preamp idea(by Stevo) The 1M grid leak on stage three is intended to be a volume control. I suppose I should have taken the time to draw that in there. I recognize that three stages is a lot of gain, but I did want it to be suitable to MC as well as MM cartridges. What about retaining the three gain stages, but leaving the cathodes unbypassed?Tue, 30 Jun 2015 10:17:22 -0400 http://ax84.com/bbs/dm.php?id=491201 RE: Parts selection for a new build(by Darren Porter) Scumbacks are nice. But look into the WGS Green Beret speaker. <a href="https://wgs4.com/gb " target="newwin1435833008">[link]</a> You will save yourself a lot of coin and not sacrifice on quality or tone with them. Open or closed or ported... well the speaker cabinet design here on AX84 is a pretty nice ported design. I built one and I really like it but it's rather large. Otherwise, I like open-back for clean/Fender and closed or ported for distorted/Marshall. The cabinets I build have removable panels so I can go either way. For ohm-rating, I just go with 8 because I don't have a need for 4x12. But if I do need 2x12 I can easily combine two and go down to 4 ohms total. All my amps have switchabe 4-8-16 Ohm outputs. Also, most all other amps have at least an 8-ohm extension speaker jack on them. Tue, 30 Jun 2015 08:47:58 -0400 http://ax84.com/bbs/dm.php?id=491200 RE: 6922 phono preamp idea(by Merlin) Three 26dB stages give you a total gain of 78-20=58dB, or x794. With a typical 5mV cartridge you should get around 4Vrms output from this preamp, which is far too much. You really only need two gain stages, i.e. eliminate the third gain stage and feed the 50us filter directly into the cathode follower; this creates a classic topology. I would probably go with larger anode resistors too, for a little extra gain and because you'll want to operate in the 2 to 3mA range for lowest noise. It improves PSRR too. You will want much bigger cathode bypass caps. Try 220uF or more. I haven't checked your RIAA values so I will assume they're OK. There are thousands of DIY phono pre's out there, so I'm surprised you can't find one. Have you seen the tetra at Tubecad.com? <a href="http://www.tubecad.com/2009/10/blog0175.htm " target="newwin1435833008">[link]</a> Or even Hargerman's phono which runs off a low voltage supply with a simple boost converter: <a href="http://www.hagtech.com/pdf/cornet3.pdf " target="newwin1435833008">[link]</a> Here's an octal phono: <a href="http://livinginthepast-audioweb.co.uk/index.php?p=newphonopreamp" target="newwin1435833008">[link]</a> Mon, 29 Jun 2015 23:12:43 -0400 http://ax84.com/bbs/dm.php?id=491199 RE: Parts selection for a new build(by GeorgeG) Also I thought I was going to be picking a variety of Celestion G12M but I actually now think that the Scumback 75M/H PVC sounds closer to a 1967 G12M Greenback than today's Greenbacks Do you think that I should consider an open back 1x12 cab, a closed, or a ported? Also 16 or 8 ohms? ThanksMon, 29 Jun 2015 22:15:08 -0400 http://ax84.com/bbs/dm.php?id=491198 RE: Parts selection for a new build(by GeorgeG) <div class="quoteblock" >On 06/29/2015 @ 21:22, Darren Porter wrote : Also my opinion, you can do a lot better than EH for 12AX7 tubes. Try Tung Sol or even the tried-and-true JJ tubes. I also really like JAN Phillips NOS tubes and currently use 12AT7 JAN-P's in my custom-made on-stage rig. I really like their transition from clean to overdrive. Very warm and smooth. : : What are you building? KT66's... a JTM45? : -- </div> I will look at my pre amp tube selection. A single ended single tube KT66 Went with F&T, Mallory 150, silver mica caps.Mon, 29 Jun 2015 22:07:22 -0400 http://ax84.com/bbs/dm.php?id=491197