dmp
Well-known member
The gain note on the schematic - right side
Langevin 116B-Possible to DIY?
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dmp
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The similarities between the 116B and the BA2 are pretty interesting. R-5 could be a gain pot I think.
What's the deal with values of R-3, R-4, R-11, R-5? Are they in megaohms?
What's the deal with values of R-3, R-4, R-11, R-5? Are they in megaohms?
Yep, megaohms. Somewhat common method back then. Yes, the 116-A I looked at was indeed 10M on R-11. 390K in the B. Several other EQ correction caps added in the B's I've seen that aren't on that document.
Turn R-5 into gain pot, you undo NFB. Output might or might not be made for a change towards matching Z on the primary. Original probably was, current production probably not.
The better way I think is what I did on 356A's. Put a gain pot across the tertiary to include or exclude it from the cathode circuit. Same Z matching question with the output pri.
And that's a clue to the other very old versus higher NFB later types. The very old with no NFB had to have output transformers that passed full rated frequency with a matching condition from the driver tube. More inductance. Introduce NFB to knock output Z down, you can get away with less inductance so long as you never reduce the NFB. So.....NFB allowed use of cheaper transformers, cost savings for all. That all goes into the witches brew around what the treble sounds like through the respective transformer winding types.
Turn R-5 into gain pot, you undo NFB. Output might or might not be made for a change towards matching Z on the primary. Original probably was, current production probably not.
The better way I think is what I did on 356A's. Put a gain pot across the tertiary to include or exclude it from the cathode circuit. Same Z matching question with the output pri.
And that's a clue to the other very old versus higher NFB later types. The very old with no NFB had to have output transformers that passed full rated frequency with a matching condition from the driver tube. More inductance. Introduce NFB to knock output Z down, you can get away with less inductance so long as you never reduce the NFB. So.....NFB allowed use of cheaper transformers, cost savings for all. That all goes into the witches brew around what the treble sounds like through the respective transformer winding types.
Ok so if there is a sound quality difference it is likely due to cheapening of components?
Ah, but BA-2's were utility standalone amps typically found in the base of transcription turntables. Note the input Pri grounding for unbalanced use. Mics were the rarity with those. They'd have probably had rack mounted 80 series amps with circuits like the 76 consoles, since that's what the broadcast side was using. Exact same transformers on a BA-1 and a BA-2 and pretty much on an 85-B/76 console pre.
dmp
Well-known member
The room: I've spent a lot of time recording in a 60'by60' warehouse room with a high round ceiling past few years. Until you record in a amazing sounding room, you don't appreciate how important it is. The 30th street room was huge.
Distant mic technique: in a big room you can get away with things you'd never try in a small room, or would sound terrible if you did. Point the amps and you can record a 4 piece rock band and the bleed is great between mics.
Preamps: you need good preamps to stack channels and not have the sound degrade. AND I've found good preamps interact with good mics to make them a combo tool. But if you have all of the above, any good preamp will be sufficient (neve, jensen, telefunken, etc...).
I wouldn't get too hung up on the feedback or pentode/triode stuff. Put most of your money into really good transformers and build a tube gain circuit that gets the job done. I personally like a full featured preamp with a gain control etc... others don't mind a fixed gain preamp. Decide what you want then build something.
I know this is a tech talk but here's a Glenn Gould video filmed at Columbia 30th St studio. 1959. A lot of shots in the control room, lots of Ampex machines, mic setup and chat between producer and artist. A genius artist.
It's this console that was used on all the great recordings. If only we could figure out the damn pres!
dmp
Well-known member
I see a few M49s and three (?) KU-3A mics in that video. Nice mics.
yeah it seems like they loved the m49. In an interview video with one of the original engineers they mentioned the AKG C12, but you never see it in photos. The only photographic evidence I have is the cover of "Essential Ray Conniff" which has what must be a C12 in the background (very long, thin tube, swivel mount), and given that Conniff's 50s recordings were made at CBS 30th, it is likely this documents an instance of their use at CBS. Although now that I look at it more closely it is possible this image is a composite. If not, he's clearly singing into a mic out-of-frame, and the C12 is for the choir behind him.
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