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Help - Balanced Pearl Phono
Help - Balanced Pearl Phono
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Old 20th May 2007, 08:17 PM   #1
Irakli is offline Irakli  United States
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Default Help - Balanced Pearl Phono

Hi All!

I want to build a phono amp for my system and so far the Pearl seems the best choice for me. The only problem is that it is a single ended circuit. So, I converted the circuit to the balanced one, based on several schematics posted on this forum.

By no means, this is an attempt to improve the amplifier performance. I just wanted a balanced phono amp because all the components in my system are balanced.
The schematic is for one cascade only. I want to make a PCB for the circuit which is shown on the picture. I will use two modules connected in series with RIAA network between them.

I really do appreciate if you guys look at the topology and point out if there are any mistakes there. I don't want to order PCBs and then discover that I made some stupid mistake. I am not worried much about component values at this point, because I will tweak them later.

Thanks a lot
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Old 21st May 2007, 12:17 PM   #2
h_a is offline h_a  Europe
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Sorry, but why don't you just use an unity gain inverter? You would avoid all those additional double-fets; the same was used in the Ono.

Cheers, Hannes
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Old 22nd May 2007, 08:43 PM   #3
Irakli is offline Irakli  United States
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Thanks, Hannes

I am little bit confused, double fets are the main gain devices there. How can I substitute them with unity gain buffer?

I will look at Ono schematics. Thanks.

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Old 22nd May 2007, 09:36 PM   #4
GRollins is offline GRollins  United States
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Today has been a rather trying day, so perhaps I'm missing something...or perhaps several somethings. Can you explain how you see the circuit working?
JP2 turns the circuit off? Allows for regulated/unregulated rail comparisons? Changes the rail voltage?
JP1 probably relates to JP2 I'm guessing, but again it depends on what you intend JP2 to accomplish.
It appears that Q9 (should Q9 be a ZTX550?) is intended to be a regulator for a negative rail...but there's nothing that needs a negative rail. Assuming that Q5 is intended to be a current source, there's a problem in that it dumps directly to ground via the connection beneath R6. For that matter, it wouldn't hurt to have a cap to ground at the emitter of Q9.
Etc.
Or maybe I just need to get some sleep. Or something.

Grey
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Old 23rd May 2007, 01:52 AM   #5
Irakli is offline Irakli  United States
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Thanks Grey.

I guess I was tired too when I was drawing the schematics. The ground simbol below R6 should not be there and C9 and R15 should be grounded of course.
Nothing special about jumpers. I just wanted to have an option to disconnect Q6 and/or Q9 capacitance multipliers and use circuit without them.
I'll post corrected picture soon.
Again, thanks a lot
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Old 23rd May 2007, 02:36 PM   #6
h_a is offline h_a  Europe
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@Irakli: I mean you can add a unity gain inverter to the original pearl; thus you still only need 1x 2SK389 per channel.

Cheers, Hannes
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Old 23rd May 2007, 02:55 PM   #7
GRollins is offline GRollins  United States
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Generating a balanced signal at the output is not the same thing as having a balanced circuit.

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Old 24th May 2007, 09:57 AM   #8
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Of course! This is just a simple solution and its only benefit being noise cancelation in the following interconnects. However I don't see a clear advantage in canceling the pure 2nd harmonic distortion character of the pearl by balancing it.

That should give in my opinion quite strong 3rd harmonics which are far more unpleasant.

Cheers, Hannes
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Old 24th May 2007, 10:18 AM   #9
Holger Barske is offline Holger Barske  Germany
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Canceling 2nd order harmonics doesn't raise 3rd order harmonics. Okay, the "balance" between them changes, but the total amount of distortion decreases, and that's an advantage.
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Old 24th May 2007, 02:33 PM   #10
h_a is offline h_a  Europe
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Yes indeed. So maybe this could give really nice distortion reduction.

Cheers, Hannes
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