How convert Creek OBH-8 to MC cartridges? - diyAudio
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Old 12th September 2009, 05:21 PM   #1
Ludwik is offline Ludwik  Poland
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Default How convert Creek OBH-8 to MC cartridges?

As above: is there any possibility to adapt OBH-8 circuit to MC cartridges? Any comments is welcome.

Ludwik
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Old 17th September 2009, 10:21 AM   #2
h_a is offline h_a  Europe
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I assume this phono amp is MM only?

If so, there's no real way to 'convert' it to MC, as these MC-buggers need much more voltage gain (with the exception of high-output MCs, but in that case a MM-stage is already perfectly suited).

Of course you could use an input transformer.

Have fun, Hannes
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Old 17th September 2009, 06:30 PM   #3
Ludwik is offline Ludwik  Poland
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Here is OBH-8 circuit diagram. Any comments?
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File Type: gif creek_obh8.gif (16.9 KB, 740 views)
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Old 14th November 2009, 09:28 PM   #4
es44 is offline es44  Denmark
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Quote:
Originally Posted by Ludwik View Post
Here is OBH-8 circuit diagram. Any comments?
Yes... Can You upload in a better resolution I'm about to get one myself, and would like to see if there are any chance of improving it.

Best regards
Ebbe
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Old 15th November 2009, 08:05 PM   #5
Ludwik is offline Ludwik  Poland
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Default OK

OK, I try.
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Old 15th November 2009, 08:26 PM   #6
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Quote:
Originally Posted by Ludwik View Post
OK, I try.
Exactly this topology also used by the Cambridge Audio phono modul for the integrated amp "Atac 3" and the "A3i". It sounds very fine. Because this modul uses a SRPP, you must add for moving coil cartridges with low output (200-400uV) a MC head line amp (gain approx. 10 times). I recommend a used JC-1 from Mark Levinson,
http://www.zenn.com.sg/ML_JC1.JPG
for MC cartridges >500uV output voltage (medium- and high output) gain factor of your OBH-1 must be enough. Perhaps a lower value of input termination resistor you must choice (mostly arround 1-2 kohms).
From the low cost MM RIAA preamplifiers this is one of the best sounded, that I know.

Last edited by tiefbassuebertr; 15th November 2009 at 08:32 PM.
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Old 17th November 2009, 11:35 AM   #7
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There is another edition of OBH-8 - special edition with jfet.
http://obh-8se.narod.ru/obh8SE_S.jpg
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Old 19th November 2009, 10:09 AM   #8
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As Alex Nikitin said, it is possible to raise voltage up to 40V and changing R13 to 1Watt. It will double the output voltage and gives ~70dB gain.
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Old 20th November 2009, 06:31 PM   #9
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Quote:
Originally Posted by jah_zoldat View Post
There is another edition of OBH-8 - special edition with jfet.
http://obh-8se.narod.ru/obh8SE_S.jpg
The developer of this RIAA head amp from Creek with interesting descriptions is to find there:
Cambridge Audio A3i repairs and mods
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Old 23rd September 2012, 05:06 PM   #10
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Default Enhancing Capacitors for RIAA Network (1000 times, uF instead nF)

For bigger capacitor values in the RIAA network I have to increase significantly the idle current through the SRPP stage.
How I can realize this?
Genuine schema you will find about post #5+7.

And another question: why is the emitter current through Q2 not defined by a resistance, rather depends on the Hfe of Q3 ??

Last edited by tiefbassuebertr; 23rd September 2012 at 05:11 PM.
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