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DIY Workshop » The SOHA - Thread 3 [continued] jefnando  HeadWizer Joined: Jan. 14, 2009 |  Message [#300] posted on: 03-01-2009 10:36 AM CST (US).   |  |  Biarritz, i just got my SOHA running today, I have 3 tubes from different manufacturers, but i am not using the 12AU7, tubes from 2 manufacturers sounded nice on this amp, but the tube from another manufacturer gave me the exact problem you have. since no pros are helping you yet, why not try swapping tubes to see what happens? BTW, my plate voltage wouldn't go lower than 46.7V, but then it sounds good nevertheless. Previously i had a defective opamp running in this amp, only highs are distorted. Well, just so you know sometimes opamp defect can be the prob too. |
| Biarritz Member Joined: Jun. 13, 2004 | Message [#301] posted on: 03-01-2009 01:05 PM CST (US). | | Jefnando, I have replaced each and every part including the opamp and even setup my second PCB. Today I throw the whole project against the wall Kind regards, Patrick |
. My nice Black Gates, Rusian PIO's and Alps pot were destroyed (not the NOS tubes though) 
. This was my most frustrating project ever. So no SOHA for me ever again.| jefnando HeadWizer Joined: Jan. 14, 2009 | Message [#302] posted on: 03-01-2009 02:27 PM CST (US). | | whoops, really sorry to hear that.I completely understand how you feel, my other project, the 6N1P OTL amp burned 4 of my soundcards and electricuted me 2 times and up till now i still havent able to get it running yet, but i haven't given up because i know when i finally manage to complete it, it'll be a real victory for me. I would've smashed everything to pieces like you but i took my frustration off my building completing this SOHA, who knows if you try completing some other projects, you might learn what you did wrong in this amp. I wish you luck. |
| Biarritz Member Joined: Jun. 13, 2004 | Message [#303] posted on: 03-02-2009 02:06 AM CST (US). | | Jefnando, I have cooled down now. I now regret that I did not desolder the components I wanted to salvage before demolishing it. The SOHA uses a PCB, which was fried and completely messed up after soldering and desoldering the components more then once. I have also build the 6N1P OTL. Never had any problems with it. The 6N1P is hard wired, so if you modify someting it can alway be mended nicely. I used it with an USB DAC from dddac.com. never had any problems. I now bought a simular headphone amp from 8audio.com. This one comes with all parts on the PCB
Patrick |
. I hope it fits the enclosure I already purchased for the SOHA.Stixx HeadWizer Joined: Feb. 6, 2004 | Message [#304] posted on: 03-02-2009 05:36 AM CST (US). | | Biarritz, did you ever check your board for faults, like bad traces or connections in the wrong places? Also too late to let you know that my fully completed SOHA including output buffer et all is on german Ebay now... regards, |
| ilanco Member Joined: Mar. 5, 2009 | Message [#305] posted on: 03-06-2009 10:19 AM CST (US). | | Hello all! I'm new here at headwize and I have finished 2 small DIY audio projects. First is CMOY, second is the Tube/Mosfet Hybrid (diyaudioproject...-Headphone-Amp/). Both ended up sounding great I constructed the power supply on the breadboard, including the heater supply and led, but without the 78L-79L 12V supply. The docs state I should get a B+ of around 80V with no load connected. I measured only 63V on the B+. By the way, the transformer I'm using is custom made and has an double secondary 0-15.8V, 0-15.8V
Ilan |
| dBel84 HeadWize Fanatic Joined: May 5, 2006 | Message [#306] posted on: 03-06-2009 04:14 PM CST (US). | | Hi and welcome. The simple answer is yes - you would normally set the voltage to 40V on the plates which equates to about 1mA on the cathode. As long as the supply voltage doesn't drop too low, you should still have 10V to swing the signal..dB |
| ilanco Member Joined: Mar. 5, 2009 | Message [#307] posted on: 03-06-2009 04:52 PM CST (US). | | Hi dBel84 Any idea why the voltage is lower than it should be ? |
| dBel84 HeadWize Fanatic Joined: May 5, 2006 | Message [#308] posted on: 03-06-2009 07:31 PM CST (US). | | as you have a custom wound transformer it could be that it is rated for it's voltage unloaded while many others are rated under a specific load. I have seen this with some commercial transformers too..dB |
| ilanco Member Joined: Mar. 5, 2009 | Message [#309] posted on: 03-07-2009 07:43 AM CST (US). | | i see, so i'm continueing this project ... thanks for your help so far ! |
| ilanco Member Joined: Mar. 5, 2009 | Message [#310] posted on: 03-08-2009 03:16 AM CST (US). | | Hi all! Got my one channel prototype ready on a breadboard (managed to fit it in with the power supply). I am getting a constant hum, with and without source connected. Any ideas how I can get rid of this? Ilan |
| jefnando HeadWizer Joined: Jan. 14, 2009 | Message [#311] posted on: 03-08-2009 03:39 AM CST (US). | | how is the output? do you get any music from the output? does the hum increase together with the output volume? |
| ilanco Member Joined: Mar. 5, 2009 | Message [#312] posted on: 03-08-2009 04:55 AM CST (US). | | Hi jefnando, The amp sounds good. I have tested the amp with cheap ipod headphones so far and I was very pleased with the qualityof the sound. |
| jefnando HeadWizer Joined: Jan. 14, 2009 | Message [#313] posted on: 03-08-2009 08:14 AM CST (US). | | I had that problem with another amp as well, but adding an output resistor seemed to have solved my problem, that might not be the best solution but worked for me. How did you wire your power supply? |
| ilanco Member Joined: Mar. 5, 2009 | Message [#314] posted on: 03-08-2009 09:26 AM CST (US). | | My power supply is a 2x15.8V custom wound transformer. I set up the circuit exactly as explained on the website, but I did change the 1mA CCS by a 20k resistor because i'm still waiting for the LND150 to arrive. |
| ilanco Member Joined: Mar. 5, 2009 | Message [#315] posted on: 03-08-2009 05:13 PM CST (US). | | Frustrated with the hum, I began checking out all connections and moving them around. Seems the wire connecting the top and bottom rows on the breadboard (you know + and -) was causing the hum. Too close to a cap or so ... Now I have a very, very faint hum that is barely audible and is probably due to the connected wires on the breadboard. Hope it will go away when soldering everything together. Just to let you know, the transformer I am using is NOT a toroidal one and it is hum-free. Even when placing the tube and transformer really close there is no hum. I plan to put everything in an empty internal cd-rom casing with the transformer mounted on top and the tube sticking out of the center. I you have ever disassembled a cd drive you know that is has a convenient hole in the top plate Thanks for all your help ! Ilan |
| ilanco Member Joined: Mar. 5, 2009 | Message [#316] posted on: 03-18-2009 07:21 AM CST (US). | | Hi everyone, I have begun soldering all the parts together, blew up some 78L and 79L's and for now the power supply circuit is working fine. My local electronics shop does not stock the LND150 or J113 I tried to wire both in the circuit as the LND150 and as J113 with no success. Can anyone point me in the right direction or am i better off with a simple resistor? BTW with a 20k resistor the amp performs pretty well, but i wanted to see if there was a difference with a mosfet ccs Thanks, Ilan |
| jefnando HeadWizer Joined: Jan. 14, 2009 | Message [#317] posted on: 03-18-2009 07:29 AM CST (US). | | how about PN2907, that is more widely available i think. |
| ilanco Member Joined: Mar. 5, 2009 | Message [#318] posted on: 03-19-2009 03:13 AM CST (US). | | Reading the datamanual for the LND150 i noticed that it's a depletion mode mosfet. (should have seen it earlier but didn't know what it meant) Is it possible to use a power enhancer mosfet as a ccs for this amp or should i get a depletion mode mosfet? Ilan |
| dBel84 HeadWize Fanatic Joined: May 5, 2006 | Message [#319] posted on: 03-19-2009 01:51 PM CST (US). | | in this application, it should be a depletion mode mosfet. an alternative is to use the CRD 1N5297 that is mentioned in the article..dB |
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