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Old 4th October 2011, 02:30 PM   #211
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It would be nice if diyAudio.com could work out some US distribution of the Cordell DM.
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Old 4th October 2011, 02:32 PM   #212
Botte is offline Botte  United States
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Quote:
Originally Posted by Tea-Bag View Post
Botte, what product are you using? I am in the market. Thanks.
I'm using ARTA in the spectrum analyzer mode on a PC laptop. The built in sound card has a THD of .008 in loop back, so using the DM I can measure down to .00008 or 40 dB lower. That's low enough!

See ARTA

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Old 4th October 2011, 05:20 PM   #213
generg is offline generg  Germany
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The joy of bringing k2 to zero is very good......

Later you remark......

- How stable is the point after closing the case and all heating up?
- the zero point is only for one position of the volume pot. Mine is direct coupled to the input, when I change from lower to a louder signal the mixture of K2 to K3 changes.
- k2 has a maximum with a position at 5 o'clock and goes down again at full volume.
- maybe it is useful to minimize k2 in the region I am normally hearing.
- maybe it is better to have a coupling cap, so the pot not interacts directly with 74/170
- I was not very successful to reduce the distortion of input and output stage combined like Botte did.
- I will treat output stage separately

My pot is a 10k pot, might a higher value less influence the J74/K170 combo? Even the offset changes in a small amount when I change the volume....

O.k. Life is more complicated than thought in the beginning......

We are used to......
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Old 4th October 2011, 05:58 PM   #214
Botte is offline Botte  United States
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Quote:
Originally Posted by generg View Post
The joy of bringing k2 to zero is very good......

Later you remark......

- How stable is the point after closing the case and all heating up?
- the zero point is only for one position of the volume pot. Mine is direct coupled to the input, when I change from lower to a louder signal the mixture of K2 to K3 changes.
- k2 has a maximum with a position at 5 o'clock and goes down again at full volume.
- maybe it is useful to minimize k2 in the region I am normally hearing.
- maybe it is better to have a coupling cap, so the pot not interacts directly with 74/170
- I was not very successful to reduce the distortion of input and output stage combined like Botte did.
- I will treat output stage separately

My pot is a 10k pot, might a higher value less influence the J74/K170 combo? Even the offset changes in a small amount when I change the volume....

O.k. Life is more complicated than thought in the beginning......

We are used to......
I have my source capacitivly coupled to the input of the BA-3, it would seem to me that your potentiometer is raising and lowering the impedance on the input FETs.

I did all my testing at 2.8 volts (8v p-p) output, the input board has lower distortion than the follower and once hooked up I found that the set point for lowest distortion of the second harmonic was different than before I hooked it up. Now this could be the capacitive load from the follower or an interaction with the distortion of the follower, I’m not sure.

By the way, when I adjusted P3 it didn’t change the odd harmonic level, only the even.

The offset and bias are quite stable even in the heat.

I hope this helps.

Last edited by Botte; 4th October 2011 at 06:01 PM.
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Old 4th October 2011, 07:58 PM   #215
generg is offline generg  Germany
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Thank you Botte for your comments, I will go on.....!
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Old 5th October 2011, 08:33 AM   #216
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Q3, Q4 - ?

http://www.diyaudio.com/forums/image...chive/fig4.jpg
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Old 5th October 2011, 12:13 PM   #217
Gyuri is offline Gyuri  Hungary
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Hi, Andrej, Q3, Q4 are:

"The 2SJ313 and 2SK2013 are still available, and you can use them or substitute other Mosfets, such as the Fairchild FQP3N30 and FQP3P20. The Vgs of the Toshibas is about 2 volts. Some of the alternatives will be in the region of 4 volts or so, requiring a higher value for P1 and P2, probably 1K ohm."

From N.P. article
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Old 5th October 2011, 02:19 PM   #218
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Quote:
Originally Posted by Botte View Post
By the way, when I adjusted P3 it didnít change the odd harmonic level, only the even.

The offset and bias are quite stable even in the heat.

I hope this helps.
Can we say that once the 1V across R10 and R11 have been achieved via P1 and P2 then we can adjust and listen to the variations using P3 without going back to adjust P1 and P2 each time?
Chris
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Old 5th October 2011, 02:24 PM   #219
Tea-Bag is offline Tea-Bag  United States
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Quote:
Originally Posted by Gyuri View Post
Hi, Andrej, Q3, Q4 are:

"The 2SJ313 and 2SK2013 are still available, and you can use them or substitute other Mosfets, such as the Fairchild FQP3N30 and FQP3P20. The Vgs of the Toshibas is about 2 volts. Some of the alternatives will be in the region of 4 volts or so, requiring a higher value for P1 and P2, probably 1K ohm."

From N.P. article
I am ordering some of those.
I might offer a few matched up to sell if JackinnJ does not.
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Old 5th October 2011, 03:04 PM   #220
Botte is offline Botte  United States
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Quote:
Originally Posted by Backbones View Post
Can we say that once the 1V across R10 and R11 have been achieved via P1 and P2 then we can adjust and listen to the variations using P3 without going back to adjust P1 and P2 each time?
Chris
I was referring to the follower stage. With the input stage all the controls interact but not that bad, so you can spin P3 and watch the change in second harmonic distortion, then just tweak P1 or P2 to restore the DC balance on R13. Once you are in the 50mA range itís not such a big deal to have them exactly the same itís the DC across the load R13 you are trying to minimize.
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