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Old 24th November 2005, 09:26 PM   #21
Zen Mod is offline Zen Mod  Serbia
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grounds?

these things are prone to baaad oscilations when ground is in a mess

you triple checked transistor's positiononing, resistors etc ?
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Old 24th November 2005, 09:29 PM   #22
Ila is offline Ila  Germany
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Default Problem solving

Hi steenoe !
The pot is definitively not the problem. It seems that your power supply has difficulties in delivering the required supply current. Therefore you have some undesired coupling between the two channels and between the bias circuitry and the output stage.
Please use a 10000uF/40V cap near to the PCB.
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Old 26th November 2005, 05:26 PM   #23
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Hi Steenoe, i looked at image of your finished board and i think the left IRF shuld be turn around. Check it. I`ve just ended my board :-)
Regards
Alexander
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Old 27th November 2005, 07:15 AM   #24
steenoe is offline steenoe  Denmark
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You are right Alexander, thanks. I saw that earlier and it has been corrected. I will try and place a big cap close to the board as ILA suggested, and check my grounding scheme too. I am looking forward to hear what this circuit sounds like Let us know what you think about it, Alexander

Steen
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Old 27th November 2005, 06:10 PM   #25
Ila is offline Ila  Germany
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Default IRF 610 reversed

If you have reversed the IRF610, you have probably damaged T101/201=ZTX753. Please check the Vbe of this transistor, it should be around 0.65V. I know that well, because one day the same happened to me. The board still worked - sounding a bit strange. It turned out, that the above transistor had a Vbe of 1.3V. Unbelievable but true.

Ivo
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Old 29th November 2005, 05:23 AM   #26
steenoe is offline steenoe  Denmark
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Thanks, ILA It works. It must have been the ZTX753 in the opposite side, I would never have guessed it could be that one I put in a new, and voila! Well, it actually sounds good too I didnt have time to listen a lot to it, but it sounds very promising. The supply I made isn't good enough, as suspected.
Its too noisy.
ILA, do you have any suggestions for a suitable supply?
Thanks for posting this fine, little circuit

Steen
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Old 29th November 2005, 12:28 PM   #27
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Hi Steen!

Is this a BOZ dedicated RIAA board or can be used on other preamps? NS10? Yummm

Cheers

JC
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Old 29th November 2005, 12:35 PM   #28
steenoe is offline steenoe  Denmark
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Quote:
Is this a BOZ dedicated RIAA board or can be used on other preamps?
You can use it with other preamps also.
Keep in mind it runs from a singlerail supply, so if the preamp has dualrail supply, you propably have to build a dedicated supply for the RIAA.

Steen
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Old 29th November 2005, 03:26 PM   #29
Ila is offline Ila  Germany
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Default Power supply

Hi steenoe !

The power supply dependes on your application. If you use the board with the original BOZ board, I would suggest to tab the zener-diodes chain (the one that mister Pass likes best), take another TIP29 and dont forget the 100uF between base and ground.

My own solution is a good old LM317 as 25V preregulator, decoupling the output with a resistor - say 10 ohms or so - and then a bank of 10000uF capacitors.

Ivo
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Old 2nd December 2005, 11:47 PM   #30
steenoe is offline steenoe  Denmark
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ILA, thanks for the supply suggestions. I made a kind of BoZ supply with 24V and it works allright! Well the RIAA stage sounds just great!! You can safely build that one if you consider to I have a small thing with hiss though! I didnt excactly excpect total silence, but the hiss is quite detectable! Between tracks at fairly high level, its not too good Any suggestions?

`Steen
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