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Post by dean0 on May 30, 2009 16:24:59 GMT
will do, i have used 2k r3/r6, could this cause problems?
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robertkd
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Electronics Engineer from sunny Queensland
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Post by robertkd on May 30, 2009 16:30:49 GMT
Dean0
yes but R3, R6 is another issue,
for now from what I see in the photos is you haven't fitted LED 1 and LED 3. have a look where the input capacitors are and you'll see that the LED's are missing.
this makes sense with the issue you have, as the capacitors in the bias circuit charge up the bias will shift to the point that you get sod all output.
Robert
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Post by dean0 on May 30, 2009 19:00:43 GMT
robert, YOU ARE THE MAN!! testing now, sounds awesome, will make a lil review with pics soon. feeding from soundcard; Auzentech Prelude, with black NX's , realy need a DAC.........
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Deleted
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Post by Deleted on May 30, 2009 21:48:19 GMT
robert, YOU ARE THE MAN!! testing now, sounds awesome, will make a lil review with pics soon. feeding from soundcard; Auzentech Prelude, with black NX's , realy need a DAC......... deanO Don't forget to allow time for the electrolytic capacitors to fully form. SQ may be a little variable for a couple of days. Leaving switched on overnight will help speed up the process. Surprisingly, this also applies to the metal can version of the LM4562,which BTW, is a very worthwhile upgrade, although a little expensive.If you do eventually fit one, don't forget to attach some kind of small heatsink to it, as shown in photos by various constructors. Alex P.S. Most people get better results if the 47 ohm resistors where the choke (L1 and L2) were originally, are replaced by 68 ohm metal film types. With 47 ohms the upper treble may be a smidgin too bright, and ultimately fatigueing.
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Post by dean0 on May 30, 2009 23:11:27 GMT
thanks ill try some 68ohm tommorow, did notice its a little brighter than my darkvoice 336i and minimax, not a bad thing for electronic music , it doesnt quite have the punch of the darkvoice 336i (fitz mod,5998/6sn7gtw tubes), i know Iam still burning in, but is the LM4562 suited to this kind of music? thanks
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Deleted
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Post by Deleted on May 30, 2009 23:43:09 GMT
thanks ill try some 68ohm tommorow, did notice its a little brighter than my darkvoice 336i and minimax, not a bad thing for electronic music , it doesnt quite have the punch of the darkvoice 336i (fitz mod,5998/6sn7gtw tubes), i know Iam still burning in, but is the LM4562 suited to this kind of music? thanks deanO It depends on whether you want accuracy or added warmth/larger than life. The electrolytics in the JLH especially, take >48 hours of use to stabilise, and it will go through different stages of SQ until fully stabilised. Initially it may sound quite good, then the next morning, as an example, may sound thin and plain lousy. Give it a couple of days switched on after you fit the 68 ohm resistors. Alex P.S. It may also be worthwhile checking the voltage readings of your JLH against the approximate readings shown in the fault finding guide in the "Tweaks" thread. A properly working JLH normally gives the low end a lot more impact.
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Post by dean0 on May 31, 2009 21:54:48 GMT
thanks, have not got any 68ohm resistors to hand, made an order with digikey including LM4562HA ;D could not resist! and few other goodies
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Deleted
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Post by Deleted on May 31, 2009 22:49:17 GMT
thanks, have not got any 68ohm resistors to hand, made an order with digikey including LM4562HA ;D could not resist! and few other goodies deanO The LM4562HA will sound slightly better immediately, but will sound markedly better after 48 hours of use. Alex
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Post by dean0 on Jun 9, 2009 15:06:04 GMT
Parts arrived........ more pics LM4562HE currentley burning in.... pana fm caps on psu and amp. sounds awesome New Soldering Iron!! Auzentech Prelude; Recapped pana fm's and blackgates OPA637 x2 burning in......... Sounds very good nothing like stock My small collection collection of headphone amps DT770, recabled and gel pads
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Will
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Post by Will on Jun 9, 2009 17:58:46 GMT
Hey deano, nice tidy build! It's a cracking amp, the SCHA. What mods have you done and whats your thoughts on how it sounds? Also, I'd like to congratulate you on the size of your knob. Quite a whopper
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Post by dean0 on Jun 9, 2009 18:45:46 GMT
thanks bud I used this thread rockgrotto.proboards.com/index.cgi?board=chitchat&action=display&thread=3622 as a guide, so i guess its 'AK' status! Changed some parts - Panasonic Fm caps - Mundorf 4,7uf polys - No 150pf cap accross +/- , does this make a big difference? - LM4562HE - Toshiba Transistor etc..... - PSRR board Soundwise the best ive heard so far, compared to a headily modded darkvoice 336i and millets minimax. Soundstage is huge, which is great for the dt770's, something they lack. Treble is very foward/bright but smooth at the same time and just right, great for electronic music. I wasnt to impressed with bass performance at first but now ive changed to LM4562HA and heavily modded my source (auzentech prelude) it is just awesome. Compared to minimax, which is bloated and slow imo, this amp blows it away.
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insomniac
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Team Zopiclone
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Post by insomniac on Jun 9, 2009 21:05:41 GMT
Nice build dean0 I like the shielding round the transformer... nice touch. The new Soldering Iron is a warning sign that you may be on the slippery slope
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Deleted
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Post by Deleted on Jun 9, 2009 21:49:46 GMT
dean0 There is no 150pf capacitor. There is a 470pF 100V capacitor added across the outer terminals of the PSU PCB where the transformer's secondary winding is wired to. This seems to remove a small veiling of the music. Nice build. The shield would be necessary with your build due to your layout placing the big input capacitors in close proximity to the transformer. Alex
P.S. If all the sources you use are checked with a DMM, and found to have less than 5mV of DC at their output, you may be able to obtain a further small improvement by shorting out the input capacitors under the PCB.
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Post by dean0 on Mar 25, 2010 19:27:15 GMT
Re-cased my SCHA in somthing a little prettier, but I have a 'slight' problem... Powered up and the amp makes a loud buzzing noise (with headphones), and one of the caps started to smoke/bulge, switched off imediatley and dived for cover! I realy dont understand what the problem could be I am sure I wired up exactley as before, I cannot spot anything obvious, but Iam thinking I have wired the neutral/live wrong way on the traffo input? Is the cap screwed now? Thanks for the assistance
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Post by dean0 on Mar 25, 2010 19:43:47 GMT
Fix one problem, the wiring from the JLH to the Amp was wrong way round, now the amp powers up with no noise (and smoke!), but the 2 LEDS near the M-Caps (Input caps) are not lighting up and no music! Have I fried something? Thanks
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Will
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Post by Will on Mar 25, 2010 20:14:07 GMT
Hi Dean, Have a look at the PCB layout and cct. diagram hereand you'll see that the led's you mention are part of the bias arrangement for Q1 and Q5, which in turn 'feed' Q2 and Q6. I'd start by checking that those transistors are OK, and the associated diodes. Nice case, BTW. One thing I would suggest is to remove your LM4562HA, and put something a little cheaper in it's place (the original opamp with the kit), during any further live testing. Hopefully it'll be OK, but until you get it working, I'd not chance it.
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Post by dean0 on Mar 25, 2010 20:26:38 GMT
Thanks, how would I test the transitors and diodes? ps good thinking changing the op-amp!
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Will
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Post by Will on Mar 25, 2010 20:46:45 GMT
Hopefully you have a multimeter with both resistance and diode settings. The next is to look at this page www.elexp.com/t_test.htm and follow the instructions under diode testing and transistor testing. Don't forget to check your led's also, as they are diodes as well (as you know )
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Deleted
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Post by Deleted on Mar 25, 2010 20:47:29 GMT
Fix one problem, the wiring from the JLH to the Amp was wrong way round, now the amp powers up with no noise (and smoke!), but the 2 LEDS near the M-Caps (Input caps) are not lighting up and no music! Have I fried something? Thanks Dean Before you go any further , rip out those black wires for the JLH, and replace them with colours that are more likely to indicate the actual polarity. Red,orange, or brown are suitable choices for +VE. Blue, white, or black are suitable choices for -VE . Green, or the yellow and green from a piece of surplus mains cable is a good choice for earth or 0 volts. You are likely to have caused major damage to both the I.C.s and the output devices if you inadvertently reversed polarities from the JLH. Are both the red LEDs on one of the channels still working, or just the rear LEDs in the photo ? If you only reversed 0 volts and either -VE or +Ve leads, the damage may not be so severe as reversing +VE and -VE leads. Will's advice is sound. Alex
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Post by dean0 on Mar 25, 2010 21:18:42 GMT
thanks for the help, I made a mistake I actualy reversed the wiring from the psu to JLH if that makes a difference, and yes the other 2 led's are working.
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Deleted
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Post by Deleted on Mar 25, 2010 21:41:00 GMT
thanks for the help, I made a mistake I actualy reversed the wiring from the psu to JLH if that makes a difference, and yes the other 2 led's are working. Dean Yes it does. You MAY have also damaged the JLH. Disconnect the wires at the output of the JLH and check voltages as shown in the "Silicon Chip Tweaks" thread. Alex P.S. For starters, check that the voltage to earth (0 volts) from the BC639 and BC640 base (measure at 120K resistor end) is approximately 1.7 to 1.8V
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Post by dean0 on Mar 25, 2010 21:54:24 GMT
will do, at least I have the Bijou as 'backup' I'll post once ive done testing tomorrow, I hope not too much is damaged, such a stupid mistake...
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Deleted
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Post by Deleted on Mar 25, 2010 22:08:32 GMT
Dean Before you go any further, replace those black wires to the input of the JLH with more appropiate colours to avoid the risk of a repeat mistake. Disconnect the wires from the JLH to the HA PCB, and measure the output voltages at the JLH. You should have approximately +-15V. It is possible that one half of the JLH is damaged, and that the HA PCB MAY have survived. If the JLH is faulty, connect the PSU directly to the HA PCB using appropiate coloured wires, and see if all LEDs now light, and hopefully that correct operation is restored. Alex
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Deleted
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Post by Deleted on Mar 25, 2010 22:52:46 GMT
Dean
Do you mind me asking where you got your case? Its the same as mine but I tried to get another (from China) and the guy said he couldn't get them.
I understand your disappointment with your SCHA but keep at it. Alex got me through my build in the end and its well worth the effort.
I even have a failed first attempt lying in a cupboard.
Syd
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Post by dean0 on Mar 26, 2010 15:57:44 GMT
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