1081 Style Preamp Schematic Review

[justinheronmusic]

Hello!

So I have been over in the Preamplifiers section of the Project Specific related discussion forums working on this design for a mic pre. It's essentially a Neve 1081 preamp, the BA338 & BA340 wired with a gain switch and an output potentiometer all on the same PCB. I am a complete novice at PCB design and schematic design. I am hoping this will get me to where I am going, but before I order the PCB, can anyone tell me if there is any obvious errors in the schematic?

This schematic is essentially the input of the BA312, the gain switch from the JLM 1081 scheme, a 10k output potentiometer, and the output of the BA312 all sandwiched between some carnhill transformers.

 

[justinheronmusic]

Here is the schematic

 

[abbey road d enfer]

Here is the schematic

You don't need R19, nor R21. There are enough things that discharge capacitor leakage current to ground. And headroom is so rare you don't want to sacrifice.
R213/214 at 1.5k seem very wrong.
Note that values for R15 & C1 are valid only if you use the very same xfmr as the original.

 

[justinheronmusic]

You don't need R19, nor R21. There are enough things that discharge capacitor leakage current to ground. And headroom is so rare you don't want to sacrifice.
R213/214 at 1.5k seem very wrong.
Note that values for R15 & C1 are valid only if you use the very same xfmr as the original.

Tommytones has R213/R214 at 100K, does that sound about right? The schematic looks like 1.5 or 1-S, no "k" stated. I thought it was 1k5 at first glance.

 

[abbey road d enfer]

Tommytones has R213/R214 at 100K, does that sound about right? The schematic looks like 1.5 or 1-S, no "k" stated. I thought it was 1k5 at first glance.

Very likely 1R5 or 1.5 ohm. 100k is nonsense.

 

[justinheronmusic]

Thank you so much for your insight. I would have been scratching my head for ages!

 

[Rocinante]

Justin, great job! And thanks for taking this on.
And thanks Abbey for clearing that up for me too.  With this last little bit of info I can finish mine now too.
Oh and thanks Alex.

 

[tommypiper]

This schematic is essentially the input of the BA312, the gain switch from the JLM 1081 scheme, a 10k output potentiometer, and the output of the BA312 all sandwiched between some carnhill transformers.

It's the B338 amp connected to B340 amp.

Is that how the original 1081 controlled gain?