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Old 12th August 2011, 02:02 PM   #2501
kamis is offline kamis  Serbia
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Quote:
Originally Posted by Joachim Gerhard View Post
Here we go .....
How does it compare to Rosi and Nonbrainer circuits presented here?
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Old 12th August 2011, 02:03 PM   #2502
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Yes, Self has studied the effect too and a bigger cap solves the problem. Semelab is doing a lot of second source so that is good. I have no problem getting the Hitachis but sometime you get the E grade that is a bit shallow on Hfe. Anyway, the offset problem can be solved easy. In the beginning of my thread there was a fears discussion on how much offset is allowed. We came to the conclusion the less the better. I then presented listening tests of how much was audible and then later showed how DC can be trimmed away. By that time nobody was interested in the solution any more so reply was nil. Thats the way i experienced it.
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Old 12th August 2011, 02:06 PM   #2503
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I have some THAT340P's (Matched P and N pairs in a DIP14) in the transistor drawer! Will try it this afternoon.
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Old 12th August 2011, 02:20 PM   #2504
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Kamis, it has a lot of the PRAT factor these transimpedance circuits have but it is also well balanced slightly on the sweet side so it is a very good compromise. It does not reach the nth detail that my best stages have and the bass is very tight and rhythmic but not as seismic as my DC coupled stages. On turntables that have a slight rumble problem this is a good choice. In my system i would make the 470uF caps bigger. Noise is good but not exceptional. At very high volume i can hear a soft and faint hiss that is not there with my best stages but then we speak about stages that have up to 8 trannies paralleled, in one case even more ( 13 ). Hum is nil and what really surprised me was the "quality" of the noise. When i fully crank it the hiss has a really soft character without the impulsive popcorn noise that some bipolars have. 1/F noise is also low. There is not much noise in the bass so this old and tired BD437/438 are not so bad at all. JLH must have made a lot of experiments. I would say that i get 85% of the sound of my best stages but they are much more complicated and expensive to make. The relationship between effort and result is superb and the small flaws it may have are forgotten after 5 minutes of the needle in the grove. I decided also to build my version. Itīs really simple. Let us see how that performs.
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Old 12th August 2011, 02:22 PM   #2505
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Jack, that should work well, good luck and tell me if you like the sound.
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Old 12th August 2011, 11:27 PM   #2506
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This version should work too but i have not tried it. It should have lower noise because the feedback resistors appear parallel to the transdiodes. If that works it should be dead quiet.
Attached Files
File Type: pdf JLH Homage Pre-Pre JG low noise.pdf (14.8 KB, 100 views)
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Old 13th August 2011, 02:22 AM   #2507
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I build the circuit from post 2506. It is rather compact. One channel is only 3 x 3cm.
Unfortunately it does not work, so i made a topology mistake or soldered wrong.
I will look at it tomorrow.
Attached Images
File Type: jpg JLH JG up.jpg (89.7 KB, 259 views)
File Type: jpg JLH JG down.jpg (84.9 KB, 253 views)
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Old 13th August 2011, 02:45 AM   #2508
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Well, it is not a big deal. I rebuild to post 2498 and that works although with some offset
( ca. 200mV ) and gain is only x12 so the 10kHz square has an overshot. That can be cured i think.
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Old 13th August 2011, 03:23 AM   #2509
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I made further measurements and the idle in the output transistors is only 3mA. I must have made a mistake. Jumpering the 3.3 Ohm works too. Gain is now 30dB, quite ideal but wait until i am finished.
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Old 13th August 2011, 11:01 AM   #2510
kamis is offline kamis  Serbia
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Quote:
Originally Posted by Joachim Gerhard View Post
Kamis, it has a lot of the PRAT factor these transimpedance circuits have but it is also well balanced slightly on the sweet side so it is a very good compromise. It does not reach the nth detail that my best stages have and the bass is very tight and rhythmic but not as seismic as my DC coupled stages. On turntables that have a slight rumble problem this is a good choice. In my system i would make the 470uF caps bigger. Noise is good but not exceptional. At very high volume i can hear a soft and faint hiss that is not there with my best stages but then we speak about stages that have up to 8 trannies paralleled, in one case even more ( 13 ). Hum is nil and what really surprised me was the "quality" of the noise. When i fully crank it the hiss has a really soft character without the impulsive popcorn noise that some bipolars have. 1/F noise is also low. There is not much noise in the bass so this old and tired BD437/438 are not so bad at all. JLH must have made a lot of experiments. I would say that i get 85% of the sound of my best stages but they are much more complicated and expensive to make. The relationship between effort and result is superb and the small flaws it may have are forgotten after 5 minutes of the needle in the grove. I decided also to build my version. Itīs really simple. Let us see how that performs.
Of circuit published here , which complete MC /MM phono stage is the best in quality of reproduction ? I think that you should make some summary of a large number of designs you have made if you wish to help the members of this forum to start building something realy ultimate in quality. You may quote No. of post with circuits, rejecting less elaborate ones.I think four top designs with different topologies would be enaugh. Forum members should no waste time with others threads textbook level circuits.
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