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Post by Deleted on Mar 17, 2009 20:30:16 GMT
That is correct. 68ohm .5W metal film resistors (e.g. Jaycar) may be used. They come in a packet of 8 for 46c Cat. no. RR0544. They have closer resistance tolerance, and will help ensure a good balance between levels in the left and right headphones. Start off with this value, as it seems to suit the majority of headphones . 56 ohms will give a slight amount of added volume and a little more at the top end. Conversely, 75 or 82 ohms will give a little less volume and a slight reduction in treble. Alex Can you tell me why the resistors have been changed from carbon film to metal film and what difference this is likely to make to SQ? Thanks. Paul Paul The original 47 ohm resistors were only there to dampen the choke and did not have any real influence on the sound. I prefer using metal film instead of carbon film, because of their lower noise, stability,and the fact that they are readily obtainable in 1% tolerance as against typically 5% tolerance for the CF resistors. This helps ensures that balance between channels is as close as possible.I also find MF resistors to be more tonally neutral in SS amplifiers in general. Alex
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Post by jphoward on Mar 18, 2009 5:05:36 GMT
...one set left at 47 and the other 68 if you wish both headphone sockets to have slightly different characteristics for use with alternate headphones, or even 2 pairs at once. That's a really nice idea - I think I'll do that. BTW, I put the new tweaked HA together last night (except for the Toshiba trannies, the extra capacitor in the PSU, and the JLH ripple eater, all of which I'm waiting on for parts) and listened for a couple of hours. It's a huge improvement over the stock unit, which nearly no background noise, and greatly decreased sibilance. Better still, this morning my new Logitech Transporter arrived, which is a superb source unit, and it's really made the SCHA sound wonderful. The bass is perhaps still a little unclear, which I expect the remaining parts upgrades will fix up.
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Post by Deleted on Mar 18, 2009 5:14:21 GMT
jphoward The bass should markedly improve in both depth and quality, after the JLH is fitted.Replacing the onboard 470uF filter capacitors with 100uF 25V, will also give a small improvement in clarity of the lower midrange after the full mods are done. This was verified by both Leo and Dave Mitchell as well. Alex
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Post by cyteen on Mar 26, 2009 22:52:35 GMT
@robert
did you ever build up the SCHA with 2SD669A/2SB649A, how did it compare?
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Post by jphoward on Mar 27, 2009 1:58:09 GMT
Since Jaycar doesn't have the Toshiba trannies, I figured I'd just use the BD139/140 in the JLH PSRR. Has anyone listened to this setup vs using the Toshibas, and have a view as to whether it's worth me upgrading them?
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Post by Deleted on Mar 27, 2009 2:25:27 GMT
Since Jaycar doesn't have the Toshiba trannies, I figured I'd just use the BD139/140 in the JLH PSRR. Has anyone listened to this setup vs using the Toshibas, and have a view as to whether it's worth me upgrading them? jeremy The performance of the JLH is audibly not as good with the BD139/BD140. This finding has also been verified by several U.K. members. Many of the available BD139/BD140 also have quite low gain, and a 50MHZ frequency response compared to 200MHZ with the Toshiba devices. Alex
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Post by jphoward on Mar 27, 2009 3:13:07 GMT
Thanks for the info Alex - I'll give WES a call now then.
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Post by jphoward on Mar 27, 2009 3:22:49 GMT
OK, that order is done... While I was there I also tried to order the BC550C and BC560C, but they only had them without the 'C' suffix (i.e. just 'BC550' and 'BC560'). Would they be the same thing? I ordered them anyway since they're only a few cents...
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Post by Deleted on Mar 27, 2009 3:49:19 GMT
OK, that order is done... While I was there I also tried to order the BC550C and BC560C, but they only had them without the 'C' suffix (i.e. just 'BC550' and 'BC560'). Would they be the same thing? I ordered them anyway since they're only a few cents... Jeremy They are unlikely to make the JLH perform at it's optimum, unless the ones you receive have higher than average.The "C" versions have a higher gain, which is why JLH specified "C" versions in his original design. RS Components sells ON Semiconductor BC550C and BC560C at quite good prices if you are prepared to purchase a pack of 50 for the BC560C and 25 of the BC550C Alex
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robertkd
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Post by robertkd on Mar 27, 2009 10:21:33 GMT
@robert did you ever build up the SCHA with 2SD669A/2SB649A, how did it compare? um not as yet, I have them mounted on an SC HA module which I must finish as per my mods and do some comparisons, soon hopefully I know it doesn't count for much but on paper they look damn good ;D Robert
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Post by nickyboyo on Mar 27, 2009 12:33:04 GMT
I want to see lumps of iron and ignition keys like PinkFloyd's
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Post by cyteen on Mar 27, 2009 12:36:42 GMT
I have some here so i'd be interested in the outcome. They do look better on paper and were used in the VAS and driver roles in the better nad amplifiers before 2SC5200/2SA1943. The combination was quite impressive if I remember correctly.
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robertkd
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Post by robertkd on Mar 27, 2009 12:50:31 GMT
I have some here so i'd be interested in the outcome. They do look better on paper and were used in the VAS and driver roles in the better nad amplifiers before 2SC5200/2SA1943. The combination was quite impressive if I remember correctly. Oh and in the VAS and driver(s) on my Onkyo receiver which I might add is devastatingly brilliant for a class AB something Robert
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Post by leo on Mar 27, 2009 19:10:27 GMT
@robert did you ever build up the SCHA with 2SD669A/2SB649A, how did it compare? I've got them in mine at the moment , they seem to sound fine so far , I'll have to fit the Toshiba's back in to know exactly how they compare but they seem ok
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Post by Deleted on Mar 27, 2009 20:10:18 GMT
@robert did you ever build up the SCHA with 2SD669A/2SB649A, how did it compare? I've got them in mine at the moment , they seem to sound fine so far , I'll have to fit the Toshiba's back in to know exactly how they compare but they seem ok Leo They appear fine on paper, but the Toshiba devices are more linear with respect to HFE vs. Collector current. Alex
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Post by leo on Mar 27, 2009 23:39:19 GMT
Only reason I fitted them is because it was mentioned earlier on how these would sound, I think it was Robert who originally mentioned them. I had some sat in my box so thought I'd give a try
Tell you what though Alex, the 2SA1837/2SC4793 sound good in the SCHA too, distortion is quite low
Quite a few options which are better than those BD139/40
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robertkd
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Post by robertkd on Mar 28, 2009 11:07:40 GMT
@robert did you ever build up the SCHA with 2SD669A/2SB649A, how did it compare? Alright to qualify this the situation is yes I have now connected the SC HA with 2SD669A/2SB649A. to answer the question, they are every bit as good as the 2SC5171/2SA1930 combination Robert
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Post by cyteen on Apr 2, 2009 0:16:31 GMT
I've always used fast recovery schottky diodes for rectification over ultrafast, I was wondering if the recommended ultrafast diodes were a special case when compared to other UF diodes.
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Post by Deleted on Apr 2, 2009 0:40:25 GMT
I've always used fast recovery schottky diodes for rectification over ultrafast, I was wondering if the recommended ultrafast diodes were a special case when compared to other UF diodes. Cyteen Schottkies were tried here, in conjunction with the 470pF across the outers of the secondary winding, but seemed to have a slight "haze". Leo tried them too. In this case, the lower voltage UF4001-UF4004 were found to sound a little better. (the higher voltage versions are slower) My preferred option is the SF12, which also has a slightly lower forward voltage drop than average, plus a maximum recovery time of 35nS compared with 50nS of the UF4001-UF4004 Alex
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Post by cyteen on Apr 2, 2009 11:45:04 GMT
Thanks for the info I'll give them a try.
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robertkd
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Post by robertkd on Apr 4, 2009 8:32:29 GMT
Ok got to do some work on my sons SC HA thought I would stat with the earthing and supply decoupling this one is running LM4562HA @ +/-15V 2SD669/2SB649 (same pin out as BD140/BD139) 330uF and 6.2V zeners for LED supply Sprague 2.7uF/100V PP input +/-18V Collector Supply 1000uF on V+/V- Supply Decoupling mmmm nice
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Post by Deleted on Apr 4, 2009 8:44:21 GMT
Robert So how does the 78L15/79L15 version compare against the Zenered version ? Doing similar to my old Marantz CD65 gave very good results. Alex
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robertkd
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Post by robertkd on Apr 4, 2009 8:54:12 GMT
Robert So how does the 78L15/79L15 version compare against the Zenered version ? Doing similar to my old Marantz CD65 gave very good results. Alex Alex, well I'd like to say startlingly better but TBH this seems to the same however it's early days only maybe an hour on the clock so electrolytic capacitors are still young Robert
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robertkd
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Post by robertkd on Apr 9, 2009 12:06:35 GMT
OK following on with some of the mods I have executed here is SC HA Mod 2B now from the first SC HA mod, I'm really finding the bias arrangement to give an extremely clean audio presentation over the stock SC HA. Robert Supplemental Current limit implemented and given the values limits at about 230mA sorry bt don't want to know about having that much current going into my headphones The value was chosen to be far enough outside way past normal listening levels on headphones with 30R impedance or greater and way below the transistors safe area of operation. So far no impairment to sonic's that I can detect however will test on Lindos when I can get hold of it and verify the integrity of the amplifier wilco and out,..
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Post by Deleted on Apr 9, 2009 12:34:19 GMT
Robert Have the 78L/79L made any improvements over the zeners, or is it still fairly similar sounding ? Alexs
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