Just having a looksy now ...
Referring to your designations for the ba338 amp module and jlm mic pre scheme
- C5 470uF 25V is wrong way around. The electro + should go to pin 2
- the top junction of C4 100p and R108 2K2 should not connect to the back of D2 NTE519
- pot P1 10K pin 3 should go to rail B- (ground)
- feedback cap-to-ground C7 is wrong way around -ve leg should go to rail B- (ground)
And
- One can use a non-polar electrolytic in your C7 position. If you can get one use it, otherwise a polarised will do
- One can use a non-polarised electrolytic in your C5 position, although a polarised will do
and also
JLM micv pre schematic uses the ba438 module, the later iteration of the ba338 and shows no 'Boost' pin 4 that the ba338 and your version is showing.
I would need to check how that is handled in this hybrid implementation - I think it's left floating but can be connected up for various modified outcomes.
Other than that, looks good
...
These make very nice sum amps and can be used as 'virtual earth' (also known as 'current' summing) or 'passive' (also known as 'voltage' summing) mixing.
It's pretty amazing the performance one can get with so few active devices, and even with the less-than-perfect build values inherent in my efforts
> 100dB of signal-hum margin, THD can had in the 0.002 % range with a boat load of headroom to boot.
Add it to your 'to do' list to make a
passive sum bus, not too many channels, to keep it simple - and hook it up to this mic pre.
Awe inspiring sound. The 'minimal' approach really shines through.
My 'opinion' is that too many opamps in-a-row , like in most mixers, really does detract from the subjective sound quality.
In my music setup, I use a small virtual earth mixer, built around these modules, as the master 'mixer of mixers'.
My diy stuff sounds far and away mixed thru a neve styled sum bus than thru the digital console alone. Much better.
That's why I like building sum bus units
Can be done fairly cheap with heavy weight sound.
I feed the 'master sum bus' my DAW 'ITB mix' stems, the Yamaha digital desk stems (for keyboards, edrums and fx) and feed in yet another mixer (y.a.m
with the sum of all my analog diy channels (for monitoring).
I feel I get the best of all worlds