The BA-3 as preamp build guide

[6L6]

Totally fine.

 

[McQuaide]

Totally fine.

Thanks, here's the build so far. Just need the regulator and case.

 

[McQuaide]

What's the input impedance of this preamp? I looked at Nelson's post on the BA-3 but didn't see it.

 

[Zen Mod]

R2, 47K

 

[McQuaide]

R2, 47K

Thanks. If I'm feeding this pre with a Pearl 2, the calculator tells me I should have a 2uf coupling cap in the Pearl as opposed to the 22uf that's stock. Is this right? I'm new to the world of coupling caps.

 

[Zen Mod]

F3=1/(2 x Pi x R x C)

so 2uF looking at 47K is resulting in F3=1.7Hz

you're good even with 1uF

catch is ........ there is usually volume pot in between RIAA pre and line stage

 

[McQuaide]

Ok so a 25k stepped attenuator that goes down to 0k is what the phonostage sees.

 

[Zen Mod]

nope

worst case will be 25K (atten.) in parallel with 47K (line Rin) , when wiper is on top position ( max volume)

 

[Russellc]

Thanks. If I'm feeding this pre with a Pearl 2, the calculator tells me I should have a 2uf coupling cap in the Pearl as opposed to the 22uf that's stock. Is this right? I'm new to the world of coupling caps.

For what its worth, I feed my BA3 pre with standard Pearl 2, works wonderfully.

Russellc

 

[McQuaide]

nope

worst case will be 25K (atten.) in parallel with 47K (line Rin) , when wiper is on top position ( max volume)

25K in parallel with 47K is 16K. So input impedance would be between 47K at max volume and 16K at minimum?

 

[McQuaide]

I don't see a way to edit my post but I think I have this backwards. If the stepped attenuator is at 8K, then the load in parallel would be at 6.8K.

 

[Zen Mod]

no Bubba

 

[Russellc]

no Bubba

I used 25K, with Pearl 2, anything I need to change for best operation, or is it all good? Seems to work fine, but you could fill battleship with what I dont know....

Russellc

 

[Russellc]

Above in regard to Mcquaides coupling cap query....

Russellc

 

[McQuaide]

I did some reading on input impedance and it seems you need a signal generator and a mathematical formula to measure it.

 

[McQuaide]

I'd like to add a stereo/mono switch to this preamp. Where in the chain should this be added and is there anything to look out for?

 

[vdi_nenna]

Summing circuit after the BA3-Pre.

stereo to mono converter circuit - Google Search

 

[McQuaide]

Summing circuit after the BA3-Pre.

stereo to mono converter circuit - Google Search

I found this: A rotary switch for phono playback that presents three positions: mono, mute, and stereo.


Although it says to put it between the phono pre and preamp.

 

[Dennis Hui]

Yes! A mono switch. I wish my preamp has one.

 

[vdi_nenna]

If it's leaving a phono stage, it should still be line level, a volt or more.

Something like this might buffer, that correct?
Stereo to Mono Converter Using FET Circuit Project

Basic buffers?
Basic Buffers