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Mezmerize B1 Buffer Preamp
Mezmerize B1 Buffer Preamp
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Old 17th September 2019, 12:22 PM   #391
Salas is online now Salas  Greece
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Mezmerize B1 Buffer Preamp
Quote:
Originally Posted by Junebugvinyl View Post
Hello All!

I have built and enjoyed two B1 units (one balanced) and now want to give the Mez B1 a go. Four questions:
1) I see the boards are still for sale but the SK170 sources seem sparse since the 10 years later board and BOM was issued. Suggestions for sources of well-matched sets for the signal path?
2) I want to build balanced (all the more need for good matching) so is it just a matter of doubling up all parts and the board except using a single tranny that has twice the specified current capacity?
3) I want to integrate a remote controlled relay based ladder type attenuator. See The δ1 relay-based R-2R stereo attenuator Other than space and power supply what other cautionary notes would you have for me?
4) What is the purpose of the 100 ohm resistor on second set of outputs? I intend to have multiple balanced outputs on my unit.

Thank you!
1) punkydawgs on eBay sells 8X matched which are verified and well near together but not cheap.
You could alternatively transplant JFETs from your older B1 builds if you still got them.

2) Doubling up all parts yes. Including two transformers or one with two completely separate sets of secondary wires. Because the PSU sections are independent on bridges and won't share a single AC source correctly.

3) The input to ground resistor of DCB1 (220k but flexible) should be at least 10x higher than the output impedance of the attenuator.

4) Breaking interaction between parallel connected equipment. You may measure significant extra THD on an output if with an idling component hooked directly in parallel. Depends on its input circuitry characteristics and the interconnects also.
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Old 20th September 2019, 01:45 AM   #392
Salas is online now Salas  Greece
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Mezmerize B1 Buffer Preamp
I just saw in the store, Jason updated the IDSS matched Linear Systems JFETs offers

Linear Systems Matched JFETs – diyAudio Store
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Old 24th September 2019, 05:52 AM   #393
Junebugvinyl is offline Junebugvinyl  United States
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Thank you! On another matter, why do you recommend to put a 100ohm resistor in series with the hot for the second set of outputs on a preamp to avoid parasitic influences from one amp to the next when most amps already have a resistor at the input?
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Old 24th September 2019, 05:27 PM   #394
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Mezmerize B1 Buffer Preamp
Because you never know how various parallel connected gear will interact. I have met the odd issue. Its good general practice to have the extra resistors unless willing and equipped to specifically test. Measure THD from the main DCB1 output with and without your other gear hooked up on its secondary parallel output. Without any resistors. If performance remains the same, don't put split out buffering resistors.
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