aleph1.2 to AX100
GL, Oh I found the problem, it seems I missed soldered some resistors feeding the MSP18 transistor setting the bias for the output current sources. In fact I did that when I first built the amp. I wondered why this amp ran hotter than the other mono amp but it sounded good so I left it. I had some outputs running at 700ma bias. They are now all back down to between 550 to 600ma and the amp runs much cooler.
Yes I have been listening all winter-sounds very good indeed. DC offset at the outputs is a respectable 80ma. However my absolute DC offset takes a long time to settle down. It slowly goes down from about +/- 15 volts to 3 volts after warm up and slowly goes down from there. I never really checked to see how low it goes as I don't worry about this anymore. I noticed in mine anyway that the more DC offset at the outputs that I have the faster the absolute DC offset goes down.
I think the MPS18 transistors get warm and things change a bit. I also don't have any heat sinks on the Jfets nor do I have them cemented together. So perhaps the heat is an issue.
I did drill some extra cooling holes in the top of the amp ffor better convection.
I haven't had the chance to run them full range yet as they are being used above 2500k in a bi amped system but I will hook up full range into my old Watkins WE-1's to check them out in the near future. Good reliable and excellent design. Thanks for all your help. Now if I could only get rid of the input caps???????????
saludos, dave
GL, Oh I found the problem, it seems I missed soldered some resistors feeding the MSP18 transistor setting the bias for the output current sources. In fact I did that when I first built the amp. I wondered why this amp ran hotter than the other mono amp but it sounded good so I left it. I had some outputs running at 700ma bias. They are now all back down to between 550 to 600ma and the amp runs much cooler.
Yes I have been listening all winter-sounds very good indeed. DC offset at the outputs is a respectable 80ma. However my absolute DC offset takes a long time to settle down. It slowly goes down from about +/- 15 volts to 3 volts after warm up and slowly goes down from there. I never really checked to see how low it goes as I don't worry about this anymore. I noticed in mine anyway that the more DC offset at the outputs that I have the faster the absolute DC offset goes down.
I think the MPS18 transistors get warm and things change a bit. I also don't have any heat sinks on the Jfets nor do I have them cemented together. So perhaps the heat is an issue.
I did drill some extra cooling holes in the top of the amp ffor better convection.
I haven't had the chance to run them full range yet as they are being used above 2500k in a bi amped system but I will hook up full range into my old Watkins WE-1's to check them out in the near future. Good reliable and excellent design. Thanks for all your help. Now if I could only get rid of the input caps???????????
saludos, dave
I know it was certainly covered before in details, but just want to be sure to buy the correct (and expensive) transformer. For the Aleph-X, for about 100W (in 8 ohms), using a CLC filter, what would be the correct 750VA transformer voltage to order?
I had a 30Vac secondary before, but it was way too high and I had to use multiple CRCRC filtering and a lot of wasted heat to get a decent transistor power dissipation.
I guest that a 24V to 22V secondary would be a better match.
Any recommendations are welcome.
I had a 30Vac secondary before, but it was way too high and I had to use multiple CRCRC filtering and a lot of wasted heat to get a decent transistor power dissipation.
I guest that a 24V to 22V secondary would be a better match.
Any recommendations are welcome.
ax
I just use the formula ac voltage x 1.41 to get the dc voltage after recitication for a full wave bridge. Going backwards +/-30vdc/1.4= +/-21.4volts ac before loading down.
You will lose a few volts across the diode bridge and depending on the resistance of the Inductor a few volts there as well. My iron core inductor was about .3ohms. This times class a current of 6 amps = .3 x 6 (IxR=V)=1.8volts. This would mean that you would need 30 volts dc + 1.8 volts + .7(volts diode drop x 2) or approx 33 volts dc before loading down /1.4 =24volts ac secondaries which can provide 30 amps (24 volts ac x 30 = 750). You can also use the formula's in Nelsons articles for designing power suppliers based on Class A operation to arrive at the transformer size. I have assumed you know already that you need 750va. dave
I just use the formula ac voltage x 1.41 to get the dc voltage after recitication for a full wave bridge. Going backwards +/-30vdc/1.4= +/-21.4volts ac before loading down.
You will lose a few volts across the diode bridge and depending on the resistance of the Inductor a few volts there as well. My iron core inductor was about .3ohms. This times class a current of 6 amps = .3 x 6 (IxR=V)=1.8volts. This would mean that you would need 30 volts dc + 1.8 volts + .7(volts diode drop x 2) or approx 33 volts dc before loading down /1.4 =24volts ac secondaries which can provide 30 amps (24 volts ac x 30 = 750). You can also use the formula's in Nelsons articles for designing power suppliers based on Class A operation to arrive at the transformer size. I have assumed you know already that you need 750va. dave
just done the change overs to my ax-100 and got ax100j up and running.
-With my ax100 and using irfp9610 relative offset was 5 mv, now using 2sj74 relative offset in balanced mode is 80 mV and non balanced is 300 mV
but with nothing connected to input this is 4 V and drops very fast as amp heats up. but only in non balanced mode.
I have no decouple caps at input.
Abolute offset starts about 10 v and drops quickly into mV range.
Am using same schematic as gl.
-With my ax100 and using irfp9610 relative offset was 5 mv, now using 2sj74 relative offset in balanced mode is 80 mV and non balanced is 300 mV
but with nothing connected to input this is 4 V and drops very fast as amp heats up. but only in non balanced mode. I have no decouple caps at input.
Abolute offset starts about 10 v and drops quickly into mV range.
Am using same schematic as gl.
Very happy!
got relative DC down to 14 mV on both balanced and non balanced outputs, with no cap on input.
All I done was just keep swapping Jfets around in jig until required results.
resistor 31 reads 4.575
resistor 32 reads 4.584
Could have got these closer but DC gets worse.
Running at 8A
got relative DC down to 14 mV on both balanced and non balanced outputs, with no cap on input.
All I done was just keep swapping Jfets around in jig until required results.
resistor 31 reads 4.575
resistor 32 reads 4.584
Could have got these closer but DC gets worse.
Running at 8A
In the fullness of time the AC inlet filtering has turned out not to be a big deal in my opinion. No one else has asked about this part of the project until now. Of course I should note that the Aleph service manuals were still available on the Pass Labs web site when the AX100 was first posted. I'm just not all that certain that the inlet filter makes a significant difference in the sound.
The Zen 5 AC input filtering is not the same. It's much simpler.
If I can find the time over the next few days I will create a schematic of the AX100J power supply. I really should have done it when the project was first posted.
Graeme
The Zen 5 AC input filtering is not the same. It's much simpler.
If I can find the time over the next few days I will create a schematic of the AX100J power supply. I really should have done it when the project was first posted.
Graeme
Hi gl,
Thank you for the reply back. I really wasn't expecting you
to be the on to reply back. It would be great to see the power supply
you used but if it is a hassle please don't look to hard.
I've been reading your thread and decided to (attempt) to build
you amps. I've read most of it but still go back to certain post.
Have you really heard a big difference between the IRF9610
vs the 2SJ109BL in sound quality. You said in a post that
there is more detail, is that easily noticed?
Eric
Thank you for the reply back. I really wasn't expecting you
to be the on to reply back. It would be great to see the power supply
you used but if it is a hassle please don't look to hard.
I've been reading your thread and decided to (attempt) to build
you amps. I've read most of it but still go back to certain post.
Have you really heard a big difference between the IRF9610
vs the 2SJ109BL in sound quality. You said in a post that
there is more detail, is that easily noticed?
Eric
Graeme,
The Aleph-x being the flagship statement amp at Pass Labs, $18,000 each, makes me wonder just how good your set of J's sound in comparison to other products you have heard in your years. Does it have a good strong bass?
You created a great deal of interest when this thread was up and going on a daily basis. Now with some several months of listening you should be able to better answer the above question.
Tad
The Aleph-x being the flagship statement amp at Pass Labs, $18,000 each, makes me wonder just how good your set of J's sound in comparison to other products you have heard in your years. Does it have a good strong bass?
You created a great deal of interest when this thread was up and going on a daily basis. Now with some several months of listening you should be able to better answer the above question.
Tad
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