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Old 16th November 2013, 10:59 PM   #101
juma is offline juma  Germany
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On a friend's request I did a bit different version of this preamp:
- PSU voltage is lower (+/-18V)
- Gain is lower (11db, 3.5V/V)
- Zout is lower (680R) so the buffer on the output is not mandatory
- Zin is about 21k
- max. output swing is about 13V_peak
- it's an all bjt made, no need for hard to find JFETs
- current draw is about 30mA per rail, per channel
- P1 sets the DC offset which is pretty stable if the BJT pairs are thermally coupled
The most important thing: the sound is still great...
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Old 16th November 2013, 11:17 PM   #102
6L6 is offline 6L6  United States
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Where would you put the volume control? And what's the best value?

Have you made a PCB layout yet?
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Old 16th November 2013, 11:26 PM   #103
PKI is offline PKI  United States
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Quote:
Originally Posted by buzzforb View Post
Full Monty according to Juma. Can post gerbers if anyone is interested in them.
Buzz, will ask here as you posted your pcb layout publicly :-)
Do you think that transformers can cause some noise as it is close enough to the preamp part?
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Old 16th November 2013, 11:53 PM   #104
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It is no high on my worry list, but i am open for comments.
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Old 17th November 2013, 08:31 AM   #105
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one meter will be better
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Old 17th November 2013, 09:26 AM   #106
juma is offline juma  Germany
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Quote:
Originally Posted by 6L6 View Post
1. Where would you put the volume control?
2.And what's the best value?
3.Have you made a PCB layout yet?
1. At input
2. 10k
3. No. It's a 3D point-to-point construction in the recycled sat-receiver's case. That way it was easy to thermally couple the BJTs and since it's a one-time job, done in a day, I didn't want to lose the time on developing and making the PCB. I suppose I'll do it next time (if the need arises).

Anyway the result sounds so good that I decided to put it here...
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Old 17th November 2013, 11:33 AM   #107
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Quote:
Originally Posted by nicoch58 View Post
one meter will be better
Seperately supplies are indeed better. I will probably remove the transformer and use the first board that has dual graetz bridge. My final version, whether SE or balanced, will use Peranders SuperReg. The decision of pre will be this or bālanced and version of BA3.
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Old 17th November 2013, 01:30 PM   #108
audiok is offline audiok  Hong Kong
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Hi Juma,

Fet and Bjt version, which one you like the best ?
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Old 17th November 2013, 02:30 PM   #109
juma is offline juma  Germany
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They both sound really great - during the testing in the same system we couldn't find obvious differences, they are in domain of subtle nuances. OTOH my pre (JFET) is configured for higher gain with buffer at the output (post #66) and the BJT version for my friend (post#101) is low gain, CCS supplied current, without output buffer.
I think it would be interesting to test JFETs and BJTs in the same configuration (same gain, same PSU, same Zout). That would give more conclusive results. If you have the parts, there's a nice test you could do...
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Old 18th November 2013, 04:25 AM   #110
audiok is offline audiok  Hong Kong
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Hi Juma,

Thanks your reply.
On the other hand, if I want to get 20db gain on BJT version. Would you please show me how to modify ?
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