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The BA-3 as preamp build guide
The BA-3 as preamp build guide
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Old 9th March 2018, 08:52 PM   #901
6L6 is offline 6L6  United States
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The BA-3 as preamp build guide
Huh! Look at that - the current one on the website (v2.1) does use opamps, but the schematic linked in the manual above doesn't. I was really confused for a few min looking at the old schematic...

Quote:
Originally Posted by Hikari1 View Post
The TP Placid uses opamps which is why it's probably voltage limited.
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Old 12th March 2018, 04:56 PM   #902
woofertester is offline woofertester  United States
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I am going to build this project for a very good friend. He is a golden ear audiophile and has designed speakers for some big names. He is now 81 and cannot solder so he asked me to build him a new preamp. His highly modded Dynaco PAS died.

The boards and many of the puzzle pieces are on order. I will build it on a piece of plywood to test everything before building it into a case.

The initial plan is to be completely dual mono. Separate transformers and power supplies for left and right channels.

His system is all BNC so I will carry over his I/O jack plate or disassemble and install individual jacks.
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Old 15th March 2018, 06:24 PM   #903
Manolo47 is offline Manolo47  Puerto Rico
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Default How to dial P1 and p2 to 0 ohms

Sorry for this question, but I'm not sure how this goes.

Measure from outer leads?

Doesn't look that too much variance is happening..

Thanks.
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Old 15th March 2018, 06:59 PM   #904
Russellc is offline Russellc  United States
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The BA-3 as preamp build guide
Quote:
Originally Posted by Manolo47 View Post
Sorry for this question, but I'm not sure how this goes.

Measure from outer leads?

Doesn't look that too much variance is happening..

Thanks.
If I remember correctly, I am pretty sure I set mine in the middle of the range....usually they come that way. if unsure, twist one way until it clicks. Then twist the other way until it clicks again, counting each revolution....then turn back 1/2 of that number.

Russellc
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Old 15th March 2018, 07:07 PM   #905
silasmellor is offline silasmellor  Denmark
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The BA-3 as preamp build guide
If you look at the boards, only 2 of the 3 pins are actually used, so just measure the resistance between those two and set to the desired value.
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Old 15th March 2018, 07:11 PM   #906
KevinHeem is offline KevinHeem  United States
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The BA-3 as preamp build guide
Quote:
Originally Posted by Manolo47 View Post
Sorry for this question, but I'm not sure how this goes.

Measure from outer leads?

Doesn't look that too much variance is happening..

Thanks.
You need to be on the middle leg and one outer legs to read a varying resistance. You can zero it out in either direction so it depends on which way you orient the pot. Easiest thing to do is solder the pot in and then measure across C1 using P1 to zero it out. do the same at C2 using P2.

Last edited by KevinHeem; 15th March 2018 at 07:28 PM.
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Old 16th March 2018, 06:18 PM   #907
Manolo47 is offline Manolo47  Puerto Rico
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Default Isolation washers

Do I need to to install isolation washers in the bolt/nuts between the output mosfets heat sinks and the bigger heatsinks, which would be really extensions of the latter?

Thanks.
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Old 16th March 2018, 06:20 PM   #908
6L6 is offline 6L6  United States
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The BA-3 as preamp build guide
Bigger heatsinks? I don't follow...
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Old 16th March 2018, 06:42 PM   #909
Manolo47 is offline Manolo47  Puerto Rico
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Its between the interface between the output mosfet and the heatsink...
The mosfet also has a heatsink...
Thanks
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Old 16th March 2018, 06:49 PM   #910
6L6 is offline 6L6  United States
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The BA-3 as preamp build guide
That't not a heatsink - it's the case and electrically connected to drain.

So yes, you need to insulate the Mosfet front the heatsink using mica and grease, keratherm, or some similar insulator.

These work beautifully - Keratherm Transistor Insulators – diyAudio Store
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