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| guitarsenal Joined: N/A |  Message [#260] posted on: 12-09-2005 06:48 PM CST (US).   |  |  I made all my AC wiring extra-twisty, but that had no effect on the remaining hum. The buffer is dead quiet. There is no hum before the tube warms up. It's either a ground loop or dirty B+. I'm heading out of town for the weekend, so I'll have to figure it out next week. Thanks for all of your suggestions! |
| borc Joined: N/A | Message [#261] posted on: 12-11-2005 02:58 PM CST (US). | | Just finished my SOHA. Very nice sounding with HD580. No hum. I use transformer with 2 x 15 V and 2 x 7.5 V. With 2 x 10 Ohm in series on 2 x 7.5 V reached 12.6V. Pictures attached. [Edited by borc on 12-11-2005 at 02:59 PM.] Attachment: C1241.jpg,C1242.jpg,C1243.jpg,C1244.jpg |
runeight  Headphone Council Joined: Mar. 8, 2002 | Message [#262] posted on: 12-11-2005 04:23 PM CST (US). | |
Very nice. I like the tube guard. We knew that that blue LED would be used for this. Which version of the amp did you build? It will be nice to know how it sounds after a few days of listening. |
And smart use of the transformer windings!!Batman HeadWizer Joined: May 12, 2003 | Message [#263] posted on: 12-11-2005 05:06 PM CST (US). | | Very nice, Borc  I've seen those tube guards on EBay and thought they'd be just perfect for the SOHA. Maybe now, I'll buy one too. We're glad you like the sound. |
| borc HeadWizer Joined: N/A | Message [#264] posted on: 12-11-2005 05:26 PM CST (US). | | I build mixed version of boths. With bipolar CCS (I like bipolars) and 78L12/79L12 (simpler). OPamps are two single OPA134 with 150 (180) KOhm from positive OPamp input to ground (I think there is one missing in schematics on first page), Shottky diodes on rectifiers. That was what I found at home as remains frome old projects. ECC82 is an old Philips (not NOS but OS). The plate voltage should be 40V. If it's higher you get a large amount of distortion - tested with osciloscope. (or harsh hights and missing bass) |
| Batman HeadWizer Joined: May 12, 2003 | Message [#265] posted on: 12-11-2005 05:31 PM CST (US). | | Yes, you are correct that this amp has a "sweet spot" where the plate voltge is 40 volts. As you say, above 40V, the amp distorts and below that, it doesn't sound as sweet. |
| borc HeadWizer Joined: N/A | Message [#266] posted on: 12-11-2005 05:33 PM CST (US). | | Batman, mine are not from EBay but made at home. A friend of mine machined them as rings for fix EL34 sockets in case. |
| Batman HeadWizer Joined: May 12, 2003 | Message [#267] posted on: 12-11-2005 05:37 PM CST (US). | | Very nice, indeed. |
mains_hum HeadWize Fanatic Joined: Aug. 19, 2003 | Message [#268] posted on: 12-12-2005 11:53 AM CST (US). | | borc, Yes, that is a very nice amp. As you used BJTs (the same as I did), I agree 40V is as high as you can go while keeping the amp sounding its best. This is because we need more volts across the CCS than for the FET version so if the anode volts are too high the CCS stops being constant and you get the distortion you describe. I run the anode at 39V as this seems to be the "sweet spot", as Batman calls it, for the NOS GE 12AU7 I'm using. How did you implement your ground wiring ? |
| borc HeadWize Fanatic Joined: N/A | Message [#269] posted on: 12-12-2005 02:29 PM CST (US). | | I Almost forgot to thanks Mains_hum and Batman for great schematics. Thanks ! Mains_hum, I didn't take any special attention on ground wiring. Both center taps (2 x 7.5V, 2 x 15V) on transformer connected together and to starr ground. I prefer to wire all modules (buffer , DC stabilizer, etc) to own ground and then connect all grounds to starr ground. [Edited by borc on 12-12-2005 at 04:58 PM.] |
| Guitarsenal HeadWize Fanatic Joined: N/A | Message [#270] posted on: 12-13-2005 12:01 PM CST (US). | | I went all over my wiring, and replaced the bridge rectifier that I suspected might have been damaged when I wired the negative 12 v regulator incorrectly. My B+ is now exactly 60 volts, so replacing that bridge made a difference. I also went all over the grounding. No effect on the hum. I'm thinking that trying a different tube might make a difference, so I've ordered the tube that was in the parts list published back on page 14 of this thread. I've also thought about trying DC for the filiment, but I'll wait until after the tube arrives to see if that is necessary. |
| Guitarsenal HeadWize Fanatic Joined: N/A | Message [#271] posted on: 12-13-2005 12:04 PM CST (US). | | Borc, Very cool! I love that tube guard. I need to add something like that to my design the avoid having to remove the tube when I transport the amp. |
| runeight Headphone Council Joined: Mar. 8, 2002 | Message [#272] posted on: 12-13-2005 12:10 PM CST (US). | | It could be the tube if there is hk leakage and the heater ac is getting to the cathode. But, if there is no problem here, then the tube is not likely the culprit. Is it a new tube or an NOS? |
| Batman HeadWizer Joined: May 12, 2003 | Message [#273] posted on: 12-13-2005 12:16 PM CST (US). | | Try moving the wires around your chassis. In my prototype, I find that if the filament supply wires are oriented just so in relation to the trafo, I get hum. YOu might try moving the filament and input wires around to see if you can reduce the hum. I had seen someone selling those tube guards on EBay and now I can't find them again. I'd like to order one too. |
Blooze HeadWizer Joined: Jun. 28, 2005 | Message [#274] posted on: 12-13-2005 12:31 PM CST (US). | | Tube guards: http://cgi.ebay...1QQcmdZViewItem I think DIYAudio? has them also. What is a good size protoboard to assemble the SOHA on. I'm getting ready to order the parts in the next week or so for a Xmas present to myself. [Edited by Blooze on 12-13-2005 at 12:36 PM.] |
| Batman HeadWizer Joined: May 12, 2003 | Message [#275] posted on: 12-13-2005 12:47 PM CST (US). | | Thanks, I just bought two of them. Most builders should be able to build it on a 4X6 inch perfboard. I highly recommend that you mount the filament resistors between two terminal strips for ventilation, rather than on the perf board. |
| Blooze HeadWizer Joined: Jun. 28, 2005 | Message [#276] posted on: 12-13-2005 01:00 PM CST (US). | | I need to order some resistors from Handmade for a crossfeed unit I'm building, so I'll pick up some terminal strips, resistors for the SOHA, and maybe some caps while I'm there. Let us know how those guards look when you get them. I've been curious as to the quality. I had a Nelson Audio amp for about 3 minutes before it shorted (thanks UPS) that had them on there. They look really sharp. |
| runeight Headphone Council Joined: Mar. 8, 2002 | Message [#277] posted on: 12-13-2005 01:02 PM CST (US). | | There is a new version of the Stoopid with a regulated heater supply that Mains, Batman, and I have been working on. Blooze, before you order parts, let me post the schematic. I won't get to it, however, until early evening CST. Guitarsenal, you may want to retrofit the new heater supply to your current Stoopid. |
| Batman HeadWizer Joined: May 12, 2003 | Message [#278] posted on: 12-13-2005 01:13 PM CST (US). | | I recommend the new version even before we've tried it. The new regulator will run much cooler than the filament dropping resistors we orignially used. I'll be retrofitting my units as well. Blooze, don't spend big bucks on parts. One of the nice things about this project is that it uses generic parts and still sounds very good. None of the capacitors in my units cost more than a quarter and some were a dime |
| Blooze HeadWizer Joined: Jun. 28, 2005 | Message [#279] posted on: 12-13-2005 01:22 PM CST (US). | | I won't be spending too much. I'm mainly ordering the Stackpole carbon films for Meier Corda crossfeed and they are only $.10 a piece and I like the carbons better than the metal-films at least in my Millett (got Kiwame's in that, but I'm not spending that kind of money for a crossfeed!). Just thought I might pick up some KZ's while I was paying the shipping. |
| Batman HeadWizer Joined: May 12, 2003 | Message [#280] posted on: 12-13-2005 01:31 PM CST (US). | | We'll all be waiting for the comparison between your Millett and the SOHA. |
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