DIAMOND DIFFERENTIAL INPUT POWER AMPLIFIER EBay kit - Page 15

janusz · 01:05 AM

OK, back from holidays.
I have removed all VAS transistors, checked them and they are all OK!!!. All the other components are OK. Bias transistor is OK (I have even repalced it with a new one), all the resistors in bias citcuit are fine. LTP is fine. Why do I get 1.3V across C15???
- while you get less voltage drop in the same circuit.
Even if the circuit oscillated that DC V drop across C15 should be within limits.

I can increase values of R17 and R20 from 47k to 120k or 240k as these together with the remainder of VAS circuit also affect voltage drop across C15.
Any suggestions???

cheers,
PS I'll be using 2sa1370/2sc3467 in VAS as I have enough of these and these are more linear and have even lower Cob. I also could replace Q9 and Q13 with jfets: 2sk170 and 2sj74. In simulation these give much lower phase shift but that would affect mainly sonics not voltage drop across C15 by 50%.

spurlte · 27th November 2012, 05:56 AM

Quote:

Originally Posted by ARTISAND

I

May I ask, where did you get your voltage regulators I think I see in the middle of you case.

spurlte · 14th December 2012, 06:41 AM

Quote:

Originally Posted by janusz

OK, back from holidays.
I have removed all VAS transistors, checked them and they are all OK!!!. All the other components are OK. Bias transistor is OK (I have even repalced it with a new one), all the resistors in bias citcuit are fine. LTP is fine. Why do I get 1.3V across C15???
- while you get less voltage drop in the same circuit.
Even if the circuit oscillated that DC V drop across C15 should be within limits.

I can increase values of R17 and R20 from 47k to 120k or 240k as these together with the remainder of VAS circuit also affect voltage drop across C15.
Any suggestions???

cheers,
PS I'll be using 2sa1370/2sc3467 in VAS as I have enough of these and these are more linear and have even lower Cob. I also could replace Q9 and Q13 with jfets: 2sk170 and 2sj74. In simulation these give much lower phase shift but that would affect mainly sonics not voltage drop across C15 by 50%.

I am wondering if you have given up on your amplifier? I was going to give it a try.

janusz · 14th December 2012, 07:30 AM

Well, I might give it one more try. Actually, I have two different modification versions of it but haven't tried them yet. Apparently many people had problems with it. In simulation it easily turns into a current sink (that's what happened to my amp) or it oscillates - it's very sensitive to the quality of Iput and VAS PS.

cheers,

spurlte · 14th December 2012, 05:15 PM

Quote:

Originally Posted by janusz

Well, I might give it one more try. Actually, I have two different modification versions of it but haven't tried them yet. Apparently many people had problems with it. In simulation it easily turns into a current sink (that's what happened to my amp) or it oscillates - it's very sensitive to the quality of Iput and VAS PS.

cheers,

I have been working on Jim's Audio KSA-100 MKII. Here is the thread:
KSA 100 from Jim's Audio on EBAY
I am 'spurlte', and had problems with fake components with vintage components especially transistors. Many jumped up to help. It is totally amazing the kindness of others here at diyaudio.com. I read and will look to find where later to post here, that many components that fail lot testing are not just thrown away as they should, are illegally sold to those who pass these on as workable devices. I finally, with the help of others, got good parts to complete my boards. There are some crooks who are also taking old transistors and passing them on as newer updated devices. So, specifications could be all over the place. Someone said that you learn more when things are not working as they suppose to be working. Forcing you to investigate and I am learning alot. Check out page 25/quote #243 on Jim's Audio KSA 100. But in your case, could you have components out of spec?

spurlte · 14th December 2012, 05:42 PM

Also, you will see how Kaplaars completed his Krell KSA-100 MKII Clone and is totally enjoying his effort. Kaplaars found a couple of major uncorrect art work, component markings and a faulty circuit passage. It is all details at different pages thoughout the thread. One example is what was found and explained by Kaplaars on page 15, quote #141. So attention while compairing schematics to PCB clone's circuitry passages is extremely important.

janusz · 17th December 2012, 04:07 AM

I did not have problems with components. I tested each one and transistors at different currents. I did not check everything but most of each board for consistency with schematics ane these seemed to be OK. Both of my boards seemed to display exactly the same fault: voltage drop across C15 was too high so up to 2-3mA bias current everything seemed to work well. Only exceeding that bias current made it rise quickly.

cheers,

8th August 2012, 01:00 AM	#141
janusz diyAudio Member Join Date: Oct 2004	OK, back from holidays. I have removed all VAS transistors, checked them and they are all OK!!!. All the other components are OK. Bias transistor is OK (I have even repalced it with a new one), all the resistors in bias citcuit are fine. LTP is fine. Why do I get 1.3V across C15??? - while you get less voltage drop in the same circuit. Even if the circuit oscillated that DC V drop across C15 should be within limits. I can increase values of R17 and R20 from 47k to 120k or 240k as these together with the remainder of VAS circuit also affect voltage drop across C15. Any suggestions??? cheers, PS I'll be using 2sa1370/2sc3467 in VAS as I have enough of these and these are more linear and have even lower Cob. I also could replace Q9 and Q13 with jfets: 2sk170 and 2sj74. In simulation these give much lower phase shift but that would affect mainly sonics not voltage drop across C15 by 50%. Last edited by janusz; 8th August 2012 at 01:05 AM.

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14th December 2012, 07:30 AM	#144
janusz diyAudio Member Join Date: Oct 2004	Well, I might give it one more try. Actually, I have two different modification versions of it but haven't tried them yet. Apparently many people had problems with it. In simulation it easily turns into a current sink (that's what happened to my amp) or it oscillates - it's very sensitive to the quality of Iput and VAS PS. cheers,

14th December 2012, 05:42 PM	#146
spurlte diyAudio Member Join Date: Aug 2011	Also, you will see how Kaplaars completed his Krell KSA-100 MKII Clone and is totally enjoying his effort. Kaplaars found a couple of major uncorrect art work, component markings and a faulty circuit passage. It is all details at different pages thoughout the thread. One example is what was found and explained by Kaplaars on page 15, quote #141. So attention while compairing schematics to PCB clone's circuitry passages is extremely important.

17th December 2012, 04:07 AM	#147
janusz diyAudio Member Join Date: Oct 2004	I did not have problems with components. I tested each one and transistors at different currents. I did not check everything but most of each board for consistency with schematics ane these seemed to be OK. Both of my boards seemed to display exactly the same fault: voltage drop across C15 was too high so up to 2-3mA bias current everything seemed to work well. Only exceeding that bias current made it rise quickly. cheers,