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Post by bigtony on Nov 24, 2009 10:09:39 GMT
Just a quick note : I've just ordered this kit today, so I should have something to do over the holidays rather than just eat pie! One thing I can't understand, what do the inductors do? Cheers BT
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Post by Deleted on Nov 24, 2009 10:31:36 GMT
bigtony I have sent you 2 emails with more info. Alex
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jonclancy
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Post by jonclancy on Nov 27, 2009 23:09:46 GMT
A quick Jaycar PSU question: How hot does your +ve rail run? Mine's hot, -ve rail is pretty cool. Cheers Jon Jon Do you still have those 5W resistors there ? Alex Did have, Alex. But not any more!! ;D Runs much cooler now, thanks!
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jonclancy
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Post by jonclancy on Nov 27, 2009 23:10:41 GMT
PS, please may I have the info emails again, Alex??
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Post by bigtony on Dec 2, 2009 17:45:39 GMT
Well the postie brought the kit today, guess i should think about an enclosure and get soldering. Seems alot more parts in the flesh than i the pictures! and smaller too.
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Post by johnmclean on Dec 13, 2009 11:13:09 GMT
Hi Alex, Hope you are well in this silly season, I have a problem with a Jaycar amp I built for a friend of mine. The amps around 6 months old, just recently the right channel has been dropping out intermittently. I got the amp on friday and it tested fine, but tonight the right channel dropped out. I replaced IC1 thinking it may be the chip, but the problem persists, DC offset is all good as well at under 2mV or on both channels. The 4.7ohm resistors all read around 262mV quite high. The psu and amp both are modded as per your spec, it’s really hard to troubleshot this as it happens only so often - do you have any thoughts on what may be acting up? Any help would be appreciated.
Cheers John
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Post by Deleted on Dec 13, 2009 11:55:33 GMT
Hi John The DC readings are much higher than expected, in fact almost double. I presume you checked them originally ? Your DMM could be a little high reading too.The output devices are quite up to it though. Usually, you would expect a fault like that to result in the DC offset changing markedly. I would be taking the PCB out in the sunlight and make 100% sure there isn't a dry joint somewhere. Another possibility could be a strand from the input cable's outer braiding shorting the input, also with the lead from the potentiometer to the PCB. Check that you can read the resistance of the pot from the input sockets . An easy way would be to plug in an input cable and read from the RCA plugs at the other end. If you are using gold RCA sockets from Jaycar, it isn't unknown for them to go high resistance,as well as often a loose fit on the inner . Over the years I have replaced more gold RCA sockets for intermittent operation than I care to remember. Also check that you can read that 2mV DC leaving the headphone socket on both channels, or check that you can read the resistance of the headphones when plugged in, between an earth point and the output resistors Alex
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Post by johnmclean on Dec 14, 2009 11:48:21 GMT
Thanks for the quick reply Alex, upon inspection of the board I indeed found a cold joint on the right channel input wire from the pot. The wire was basically hanging loose in the joint, I can’t believe I missed this first time round. All the best wishes to you and your family for Christmas and the New Year.
Thanks John
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Post by Deleted on Dec 14, 2009 12:18:11 GMT
John Isn't it funny how we all seem to usually look for the worst possible cause initially ? All the best for your family too. At least you shouldn't have quite as hot a time as the Richmond and Penrith boys, as well as Sydney. IIRC, you are in the lower Blue Mountains ? Regards Alex P.S. The new Class A HA is even better than the preamp you heard. It's amazing what increasing the voltage rails from +-15V to +-20V can do ! I presume the 800s are nicely broken in by now ?
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Post by johnmclean on Dec 26, 2009 12:18:29 GMT
Hi Alex, Now that’s very interesting regarding the voltages, what other features are new with the HA from the older version? I was impressed with the older version although I wasn’t familiar with the phones. Yes you remember correctly, I’m lower mountains in Blaxland, the HD800’s are broken in well and truly, I’m also using a Sabre32 DAC as a source which replaced the Cambridge Audio 840C. Cheers John
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Post by Deleted on Dec 26, 2009 20:55:05 GMT
So Alex, should I send you my Jaycar HA for these latest mods? Miguel We are talking about the Class A HA here, not the Jaycar kit version. Yours is up to date, although there may be still things to try like the latest Linear devices which have even lower distortion. They are SMD though, and I doubt that there would be any significant improvement over the LM4562HA.Unless they were also available in metal can versions, they are likely to be not quite as good. Alex P.S. What I haven't tried yet is beefing up the JLH with 2 x 4,700uF low ESR caps per rail,(instead of 2, 2,200uF) as in the X-DAC V3 PSU where it gave a further improvement.
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Post by Deleted on Dec 26, 2009 21:06:58 GMT
Hi Alex, Now that’s very interesting regarding the voltages, what other features are new with the HA from the older version? I was impressed with the older version although I wasn’t familiar with the phones. Yes you remember correctly, I’m lower mountains in Blaxland, the HD800’s are broken in well and truly, I’m also using a Sabre32 DAC as a source which replaced the Cambridge Audio 840C. Cheers John Hi John I have now also upgraded the original preamp that you heard to +-20V rails. As Will has now confirmed, there is a further improvement at the low end, and it's more 3D sounding on good material, even with headphones. The new Class A HA is very similar but uses dual metal can transistors in the front end, which are very closely matched. What you haven't been able to hear is the HUGE improvement via the PC route into the same DAC, when the .wav files are ripped to a 32GB Corsair Voyager GT USB 2.0 pen and played from there. The PC's HDDs etc have been noise and vibration dampened using 3M 2552 aluminium tape. Forget what you heard at Richmond, it doesn't even come close. The JLH in the PSU for the X-DAC V3 has also been beefed up, for a further across the board improvement. Regards Alex P.S. Leo can verify just how good these ripped files can sound after being downloaded, when played via his Sabre DAC . Leo is also using expensive Paul Hynes regulators.
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Will
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Post by Will on Dec 29, 2009 16:33:06 GMT
John, If you get a chance to listen to Alex's Class A, it'd be worth it for sure. The 20V mod has made a big difference. Perhaps you could tempt him by offering to take your B32 down? Also, on the B32, splash some cash and invest in some PH regs if you can. I've seen your build on Head Fi, and can imagine it sounds good, but the difference I heard moving from the LM317 regs to the PH regs is massively worthwhile. Have a look in the ESS sabre thread
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jonclancy
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Post by jonclancy on Dec 29, 2009 19:38:02 GMT
P.S. What I haven't tried yet is beefing up the JLH with 2 x 4,700uF low ESR caps per rail,(instead of 2, 2,200uF) as in the X-DAC V3 PSU where it gave a further improvement. Just done this cap swap on the pre-proto boards. Fit perfectly, and the charge-up time wasn't appreciably longer. Soundwise, dunno yet. Works a treat, but haven't has the chance to have a decent listen. Really need to make a second set for comparison... but you know how it is! ;D
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Post by Will on Jan 2, 2010 22:06:55 GMT
What's your thoughts on this...
Robert suggested in the SC Class A thread that a 20V supply line would give a worthwhile improvement. Alex tried it and loved it. I tried it, and I too love the improvement.
Now then, Robert did his own way of modifying the Jaycar Amp, which included. amongst many things, going for a larger supply voltage, which was reduced for the op-amp. I, like many, went the 'SandyK' Way.
How about a mix of the approaches, the relative ease of the SandyK, with the increased supply rail of Roberts version?
To me, it would be fairly straightforward to do this. I'm thinking that we could place some 78L15/79L15 on the supply pins of the op-amp in the SCHA (LM4562 in a lot of cases), along with the appropriate track cutting. This would be followed up with replacing the traffo with a 18-0-18V unit, and then change the resistor values on the PSU board to supply 20V.
Robert has effectively done this already, but also did a lot with de-coupling and additional transistors.
What do you guys think?
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Post by ollie3151 on Feb 4, 2010 10:11:18 GMT
Just built the amp. Added low noise caps during the build. Just changed 2134 to LM4562. Can anybody tell me why it gives such an improvement? What the next mod I should try?
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Post by robertkd on Feb 4, 2010 10:25:53 GMT
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Post by ollie3151 on Feb 4, 2010 10:49:33 GMT
Excellent!
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Post by punkjr on May 13, 2010 8:51:31 GMT
well i have all the mods done (except the JLH) and this thing sounds fantastic. I was hoping for an improvement, but I didn't think that my crappy ears would hear any improvement. I was very happy with the standard unit. It's been buring in for about ten hours now, and wow! With only a quick listen this evening, I can tell that myy soundstage is wider, there is more detail, and imaging is more precise. Thanks again to all those who have helped. BTW, I have a few spares, so if anyone needs anything, I'm happy to send it off in the post. I don't have any LM4562HA's though . I do have a mix of the Toshiba tranny's, some 100v caps for the power supply input rails, a heap of .25w 4.7ohm resistors and more. Just pay for postage.
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Post by Deleted on May 13, 2010 9:15:55 GMT
Tom It may be wise to retain the Toshiba devices until you get the JLH working. Surprisingly, the JLHs have got more people into trouble than the main larger PCB ! Alex
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Post by punkjr on May 13, 2010 12:18:47 GMT
the problem I have Alex is that I have three of one type, and one of the other, so I'm going to order another five of each. I'll keep a few pairs, but I'm happy to let the odd one go if someone wants.
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XTRProf
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Post by XTRProf on Jul 7, 2010 10:12:03 GMT
Without going thru the tremendous amount of info here, how's the SCHA rated against the rest of the commercial breeds like the MF V8? Curiousity got the better of me. Thanks.
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Post by Deleted on Jul 7, 2010 10:47:01 GMT
Without going thru the tremendous amount of info here, how's the SCHA rated against the rest of the commercial breeds like the MF V8? Curiousity got the better of me. Thanks. Chong AFAIK, it hasn't been compared with the MF V8, which is a relatively new comer. Alex P..S. Tom, in the post above in the Jaycar thread now has it working with a JLH, and his comments to me were almost identical to what he posted originally. i.e. He didn't expect to hear a further improvement, but he did.
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XTRProf
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Post by XTRProf on Jul 7, 2010 11:38:33 GMT
Without going thru the tremendous amount of info here, how's the SCHA rated against the rest of the commercial breeds like the MF V8? Curiousity got the better of me. Thanks. Chong AFAIK, it hasn't been compared with the MF V8, which is a relatively new comer. Alex P..S. Tom, in the post above in the Jaycar thread now has it working with a JLH, and his comments to me were almost identical to what he posted originally. i.e. He didn't expect to hear a further improvement, but he did. Alright, then a V1, V2 or V3 will be ok. Any other commerial ones will do as well. Just a reference point as this SCHA can drive 8 ohms and above which is very good for such a cheapo. Most HA can't do that in a stable way except for the newer HA. Btw, how many watts can this SCHA pump out?
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Post by Deleted on Jul 7, 2010 11:49:31 GMT
Chong AFAIK, it hasn't been compared with the MF V8, which is a relatively new comer. Alex P..S. Tom, in the post above in the Jaycar thread now has it working with a JLH, and his comments to me were almost identical to what he posted originally. i.e. He didn't expect to hear a further improvement, but he did. Alright, then a V1, V2 or V3 will be ok. Any other commerial ones will do as well. Just a reference point as this SCHA can drive 8 ohms and above which is very good for such a cheapo. Most HA can't do that in a stable way except for the newer HA. Btw, how many watts can this SCHA pump out? Chong The basic SC HA is only an average, good value for money, performer. All the mods lift it way above that, and some say it is then better than the GS SRG2.However, it then can't readily drive 8 ohm headphones unless the Zobel network is retained. I will email you more info. Alex
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