Hafler 112 Pre-Preamplifier

jackinnj · 18th October 2011, 06:16 PM

The Hafler 110 which I purchased almost 30 years ago needed an update to the RCA connectors. I decided to take out the "Model 112 Pre Preamplifier" and traced it out. Uses the now unobtanium 2SB337 and 2SD786 for a gain of 20dB:

Original Burnedfingers · 25th October 2011, 11:11 AM

Can't you tweak the circuit and use some low noise transistor? Weren't the original transistors germanium or something like that?

jackinnj · 25th October 2011, 12:26 PM

Those were Erno Borbely's favorite bipolars -- something like 0.55nV/Rt Hz. You could use 2N4400/4403.

The circuit works well, but doesn't sim well! Marsh had done something similar in 1982, and Leach in 1999.

I had it on the bench out of its steel enclosure and THD% was negligible. I am going to assume that they matched the transistors for small signal gain. It would be easier to buy a bag of 100 of the 4400/4403 and match than to buy (probably fake) B337/D786

Original Burnedfingers · 25th October 2011, 11:16 PM

How about 2n5210 and 2N5087?

jackinnj · 26th October 2011, 12:08 AM

See Dr. Leach's article.

Original Burnedfingers · 30th October 2011, 04:05 PM

Can you put a link to the article?

18th October 2011, 06:16 PM	#1
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	Hafler 112 Pre-Preamplifier The Hafler 110 which I purchased almost 30 years ago needed an update to the RCA connectors. I decided to take out the "Model 112 Pre Preamplifier" and traced it out. Uses the now unobtanium 2SB337 and 2SD786 for a gain of 20dB:

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25th October 2011, 11:11 AM	#2
Original Burnedfingers diyAudio Member Join Date: Nov 2002	Can't you tweak the circuit and use some low noise transistor? Weren't the original transistors germanium or something like that?

25th October 2011, 12:26 PM	#3
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	Those were Erno Borbely's favorite bipolars -- something like 0.55nV/Rt Hz. You could use 2N4400/4403. The circuit works well, but doesn't sim well! Marsh had done something similar in 1982, and Leach in 1999. I had it on the bench out of its steel enclosure and THD% was negligible. I am going to assume that they matched the transistors for small signal gain. It would be easier to buy a bag of 100 of the 4400/4403 and match than to buy (probably fake) B337/D786

25th October 2011, 11:16 PM	#4
Original Burnedfingers diyAudio Member Join Date: Nov 2002	How about 2n5210 and 2N5087?

26th October 2011, 12:08 AM	#5
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	See Dr. Leach's article.

30th October 2011, 04:05 PM	#6
Original Burnedfingers diyAudio Member Join Date: Nov 2002	Can you put a link to the article?

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