robertkd
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Electronics Engineer from sunny Queensland
Posts: 111
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Post by robertkd on Apr 9, 2009 13:05:20 GMT
Robert Have the 78L/79L made any improvements over the zeners, or is it still fairly similar sounding ? Alexs Alex difficult to say if they bring up front differences, I suspect from a tech prospective better supply isolation and lower noise, but it's not an "in your face" change. of course I'm all for it based on the numbers, however the unit I'm building was close to my unit in terms of sonic's with regard to over all presentation but retained slight roughness or edginess to some portions as also the stock build. after bias mod, an example Dianna Krall Boulevard of Broken Dreams just has such a smooth texture about her vocals shyt like that   |
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robertkd
Been here a while!
Electronics Engineer from sunny Queensland
Posts: 111
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Post by robertkd on Apr 10, 2009 11:14:23 GMT
Ok here is the new low impediment input configuration, stripped out all the garbage still under development.  captian bodger signing out,... |
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robertkd
Been here a while!
Electronics Engineer from sunny Queensland
Posts: 111
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Post by robertkd on May 11, 2009 11:28:02 GMT
Robert Have the 78L/79L made any improvements over the zeners, or is it still fairly similar sounding ? Alexs Alright it's about time I reported on this mod, originally I modded the SC HA to allow for higher supply rails on the output transistors more on that latter. I first implemented a basic resistor and zener diode arrangement to keep the opamp supply at +/-15V and with suitable decoupling as per diagram this proved pretty good. Well finally had the time to make this change and so added the 78L/79L 15 regulators which made some improvements, surprisingly more so in the noise aspect. Having also modified the other build of the SC HA with improved earthing to the opamp portion of the circuitry I also modded the test bed. This also improved noise as well as IMO better sound quality. Would be interested if anyone else is in a position to try this as a second opinion would be good. So far with the change in output transistors and bias configuration, higher collector supply voltage, better supply for the opamp, a clean up of the input circuit around the opamp, MKK input capacitors, earthing and a DACT look-a-like attenuator (switched resistor) this thing is sounding great Robert |
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Post by Deleted on May 11, 2009 11:50:08 GMT
Robert Have the 78L/79L made any improvements over the zeners, or is it still fairly similar sounding ? Alexs Alright it's about time I reported on this mod, originally I modded the SC HA to allow for higher supply rails on the output transistors more on that latter. I first implemented a basic resistor and zener diode arrangement to keep the opamp supply at +/-15V and with suitable decoupling as per diagram this proved pretty good. Well finally had the time to make this change and so added the 78L/79L 15 regulators which made some improvements, surprisingly more so in the noise aspect. Having also modified the other build of the SC HA with improved earthing to the opamp portion of the circuitry I also modded the test bed. This also improved noise as well as IMO better sound quality. Would be interested if anyone else is in a position to try this as a second opinion would be good. So far with the change in output transistors and bias configuration, higher collector supply voltage, better supply for the opamp, a clean up of the input circuit around the opamp, MKK input capacitors, earthing and a DACT look-a-like attenuator (switched resistor) this thing is sounding great Robert Robert Surprisingly, the added VREGs near the opamp do further noticably reduce noise. I think their main contribution is however a lower supply imedance over a wider frequency range. I seem to remember the little buggers having a little higher output impedance than their bigger brothers, but over a wider frequency range. I used this setup to good effect in an old Marantz CD65. Next step is to check the DC out of your source, and if minimal, try short circuiting your input capacitors. You just may be surprised what difference the absence of your typical input capacitor makes. The 2.2uF-4.7uF Wima caps, although better sounding than electros, do noticeably degrade the SQ, as do most polyprops too, which may even give a false soundstage . (Really!Documented elsewhere too) Alex |
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robertkd
Been here a while!
Electronics Engineer from sunny Queensland
Posts: 111
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Post by robertkd on May 11, 2009 12:04:48 GMT
Alright it's about time I reported on this mod, originally I modded the SC HA to allow for higher supply rails on the output transistors more on that latter. I first implemented a basic resistor and zener diode arrangement to keep the opamp supply at +/-15V and with suitable decoupling as per diagram this proved pretty good. Well finally had the time to make this change and so added the 78L/79L 15 regulators which made some improvements, surprisingly more so in the noise aspect. Having also modified the other build of the SC HA with improved earthing to the opamp portion of the circuitry I also modded the test bed. This also improved noise as well as IMO better sound quality. Would be interested if anyone else is in a position to try this as a second opinion would be good. So far with the change in output transistors and bias configuration, higher collector supply voltage, better supply for the opamp, a clean up of the input circuit around the opamp, MKK input capacitors, earthing and a DACT look-a-like attenuator (switched resistor) this thing is sounding great Robert Robert Surprisingly, the added VREGs near the opamp do further noticably reduce noise. I think their main contribution is however a lower supply imedance over a wider frequency range. I seem to remember the little buggers having a little higher output impedance than their bigger brothers, but over a wider frequency range. I used this setup to good effect in an old Marantz CD65. Next step is to check the DC out of your source, and if minimal, try short circuiting your input capacitors. You just may be surprised what difference the absence of your typical input capacitor makes. The 2.2uF-4.7uF Wima caps, although better sounding than electros, do noticeably degrade the SQ, as do most polyprops too, which may even give a false soundstage . (Really!Documented elsewhere too) Alex Alex, yes I do concur having gotten rid of the output capacitors on the 8*1543DAC made quite a significant difference. Although removing the input capacitors comes with it's own Caveat emptor  anything plugged into the input or switched on whilst the amplifier is on, can literally blow you away, you really need to be on the ball and be aware of possible,yes possible equipment damage headphones tweeters etc, But other wise I will set up one day and maybe provide a switch to bypass the input capacitors. Robert |
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Post by Deleted on May 11, 2009 12:31:15 GMT
Robert Not quite so dangerous in my version . Alex |
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Post by ngquan on May 25, 2009 3:59:12 GMT
Hi guys, wonder how good is the SCHA as a pre-amp? and also how do you wire it up as pre-amp?  |
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Post by Deleted on May 25, 2009 5:57:35 GMT
Hi guys, wonder how good is the SCHA as a pre-amp? and also how do you wire it up as pre-amp? ngquan My version makes an excellent preamp, especially if the metal can LM4562HA is used. At either side of the PCB (headphone jack end) there are 2 missing components, a 10 ohm resistor and a 47nF capacitor. Fit 68 ohm MF resistors where the 10 ohm resistors were originally, and a PCB pin in each hole where the 47nF capacitors were originally. Run shielded cables from these PCB pins to a couple of new RCA sockets at the rear. The holes for the PCB pins will need enlarging slightly with a .9mm PCB drill, or you can solder the cables directly to the copper side where the pins would go. See also SC HA tweaks diagram for a picture, but use 68 ohms, not 47 ohms as marked. Alex see reply 11. rockgrotto.proboards.com/index.cgi?board=chitchat&action=display&thread=3622&page=1 |
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Post by ngquan on May 25, 2009 10:52:05 GMT
Thank you for clarifying that up Alex- i will try that-
sorry -MF means metal film?
How does it compare -as a preamp to commercial product or shall i say audiophile product?
Quan.
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Post by Deleted on May 25, 2009 11:07:05 GMT
Thank you for clarifying that up Alex- i will try that- sorry -MF means metal film? How does it compare -as a preamp to commercial product or shall i say audiophile product? Quan. ngquan MF means metal film resistor. My SC HA with JLH is quite close in performance to that of my own Class A preamplifier, but not as 3 dimensional. Given suitable input switching, it should outperform many commercial preamps. As you already have a working SC HA, why not give it a try? It should cost less than $8 for good quality red and black RCA sockets, and a pack of 68 ohm resistors from Jaycar, to find out. Alex |
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Post by ngquan on May 25, 2009 11:34:24 GMT
Thanks Alex, the reason why i am asking how to do this because
my usual pre-amp is a parasound but it won't work with DIY Pass Aleph-X due to impedance mismatching. But when i try using the headphone jack out to rca conversion of SCHA then it works???
I was told that the amp was built without the buffer?
Sorry this does not means much to me, and also the concept of unity gain buffer.
I don't want the sound quality to be affected as much as possible.
Quan
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Post by ngquan on May 28, 2009 11:58:18 GMT
Hi ,Alex- once again thank you for your advice. I took the courage to open it up and ripped out the 10ohm resistor and the 4.7cap and widened the track but nearly nearly destroyed it. But hey it worked  can you tell me what is the output impedance of the SCHA? ;D ;D |
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Post by Deleted on May 28, 2009 12:37:08 GMT
Hi ,Alex- once again thank you for your advice. I took the courage to open it up and ripped out the 10ohm resistor and the 4.7cap and widened the track but nearly nearly destroyed it. But hey it worked can you tell me what is the output impedance of the SCHA? ;D ;D ngquan I hope that yours isn't the original version with the output chokes, because those components are there for stability reasons.The original version would have a very low output impedance. Certainly much less than 1 ohm, as it is capable of driving 8 ohm headphones. My version using the 68 ohm output resistors, but no choke, would have an output impedance close to 70 ohms. Alex |
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robertkd
Been here a while!
Electronics Engineer from sunny Queensland
Posts: 111
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Post by robertkd on May 28, 2009 12:47:49 GMT
Hi ,Alex- once again thank you for your advice. I took the courage to open it up and ripped out the 10ohm resistor and the 4.7cap and widened the track but nearly nearly destroyed it. But hey it worked can you tell me what is the output impedance of the SCHA? ;D ;D ngquan I hope that yours isn't the original version with the output chokes, because those components are there for stability reasons.The original version would have a very low output impedance. Certainly much less than 1 ohm, as it is capable of driving 8 ohm headphones. My version using the 68 ohm output resistors, but no choke, would have an output impedance close to 70 ohms. Alex mmm another for the add series resistance to the output brigade and bask in increased ringing ;D Robert |
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Post by ngquan on May 28, 2009 12:53:52 GMT
Hi Alex, my version is certainly the original version with the output choke in place-Should i get rid of them? I builded my as per kit except the mods -ripple -eater,caps and new op-amp. I did the RCA out as pre-amp because my normal pre-amp does not work with the Pass aleph-X. Any advise  |
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Post by Deleted on May 28, 2009 21:22:59 GMT
Hi Alex, my version is certainly the original version with the output choke in place-Should i get rid of them? I builded my as per kit except the mods -ripple -eater,caps and new op-amp. I did the RCA out as pre-amp because my normal pre-amp does not work with the Pass aleph-X. Any advise ngquan As it is the original magazine version, put back the components you removed, and feed the added RCA output sockets from a parallel connection to one of the headphone jacks under the PCB. Alex |
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Post by ngquan on May 29, 2009 6:52:57 GMT
Alex, what would happen if i am continue to use it as it is?  |
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Post by Deleted on May 29, 2009 7:13:20 GMT
Alex, what would happen if i am continue to use it as it is? ngquan If it is working O.K. like this at the moment, although it isn't optimum, it should be O.K. Alex |
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Post by ngquan on May 29, 2009 9:23:49 GMT
Hi Alex, what else to i need to do to optimise it?
Thanks
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Post by Deleted on May 29, 2009 10:04:43 GMT
Hi Alex, what else to i need to do to optimise it? Thanks ngquan You can't take the original version much further without major mods as per my version with the JLH, or Robert's version. Alex |
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Post by ngquan on May 29, 2009 10:25:28 GMT
Thanks Alex- i will try to source those Toshibas transistors.
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Post by johnmclean on Jun 26, 2009 1:14:26 GMT
Hey Alex,
I’m in the middle of building my second Jaycar amp, I want to take it as far as I can without adding the JLH board. I’ve done all the mods on the psu. On the amp besides the LM4562 chip what else would you recommend modding?
Cheers
John
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Post by Deleted on Jun 26, 2009 1:30:49 GMT
Hey Alex, I’m in the middle of building my second Jaycar amp, I want to take it as far as I can without adding the JLH board. I’ve done all the mods on the psu. On the amp besides the LM4562 chip what else would you recommend modding? Cheers John John I would recommend replacing the BD139/BD140 with 2SC5171/2SA1930,(W.E.S. Components at Ashfield,but make sure they have the stylised "T" for Toshiba on them, NOT in a circle) or similar devices as mentioned by Robert. I would remove the 1n2 capacitors, and leave the holes vacant. I would also remove the Zobel network components as per my modified schematic, and fit 68 ohm MF resistors in place of the 47 ohms that was associated with the Zobel network. If your HA is going to be used SOLELY with a source that used an output capacitor, or had less than 10millivolts DC at the output, I would also bypass the input capacitors. If you were an Electronics Engineer, you could be horrified at most of those suggestions !  Alex P.S. As there will be no JLH, you could also try leaving the fuses in circuit, and change the 470uF electros on the PCB to 1,000uF 25V. |
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Post by johnmclean on Jun 26, 2009 7:00:05 GMT
Thanks sandyk,
Do you think the 68 ohm MF resistors would be a good match for the K702? Should I put links where the fuses are supposed to be? Sorry to be a complete pain are the 1n2 capacitors located at the input, I’m not sure which ones you mean?
Cheers
John
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Post by Deleted on Jun 26, 2009 7:27:52 GMT
Thanks sandyk, Do you think the 68 ohm MF resistors would be a good match for the K702? Should I put links where the fuses are supposed to be? Sorry to be a complete pain are the 1n2 capacitors located at the input, I’m not sure which ones you mean? Cheers John John The 1n2 capacitors are in the middle of the PCB, and directly above the LEDs and 100uF capacitors. As you won't be using a JLH, I would suggest not bypassing the fuses, and fit 1,000uF 25V capacitors instead of the 470uF capacitors. The fuses have a small amount of resistance, and in combination with the larger 1,000uF capacitors, may give a fraction more supply filtering. If you don't find this beneficial, you can always solder links across the fuses under the PCB. The 68 ohm resistors seem to suit most common headphones,but this value can be decreased to 56 ohms if a little more treble is required, or increased to 75 or 82 ohms if a little too much treble. Alex |
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