Pro Audio Design Forum

I don't think that is a differential. The extra transistors are just ground connected using a variable DC current to they can bias the input device emitter to be 0V so it can be DC coupled. The extra junction's noise is adding to the input device so not the quietest solution. A few thousand uF shun...

Leach, Lee, Hiraga all used common base topologies for "head" amps. Virtually all the rest I can find are common emitter inputs. Common base isn't used often in audio small-signal design probably due to it's low input impedance. Fortunately, for moving coil inputs, the tens of Ohms input i...

Thanks Richard. One thing that's not obvious in that circuit is the collector load. For our readers it's the grounded 1K at the output. I also spotted a non-floating supply version having separate collector loads to split supplies. The common base topology looks ideal. I tried a THAT1512 in common b...

I can't think of a single audio application where I've seen the offset trim on a 5534 used. Or for that matter any 5534 circuit. As JR points out a capacitor across the feedback resistor might be good to have on the board as a "DNP." With a 2K Rfb you won't need it but if you decide to sca...

After using and living with the flat phono preamp and RIAA EQ monitor switcher for awhile I think I know where to put all the jumpers. Pauls' suggestions, particularly the inverse RIAA EQ for dub plate cutting, really helped. I tried to put in a lot of flexibility and make it a "Swiss Army kni...

TI's datasheet explains it's to compensate for the input offset voltage arising from mismatch from input stage. Unfortunately this does not make a whole lot of sense to me yet. It is pins 5 and pin 8. Pin 8 does double-duty including offset. You do not need an offset trim between pins 1 and 8. You ...

I looked up the Shure SE22 and immediately remembered the UREI 1122. I think UREI made that for Shure because they are identical except for the silkscreen. There were a ton of UREI 1122s in broadcast. EDIT: Just found this: https://proaudiodesignforum.com/images/jpg/Richard_Lee_MC_Preamp_WW_Jul_81.j...

OK, looks much better. You might want the option to add a compensation capacitor between pins 5 and 8 of the NE5534. If you wind up not adding input pots, then you might put a 100K from the input capacitor (+ side of C connected to input jack) to ground to bleed off any stored DC. I suggest that you...

I drew C11 as 10 uF. You may be seeing the "u" as an "n."

Your 159 Hz is correct for 10 nF.
The desired 10 uF value is 1.6 Hz.

I finally had a chance to wire the preamp umbilical up properly. I trimmed the shielded twisted pair balanced DIN tonearm leads to 3 feet. The line output leads from the flat preamp are 48 feet feeding the RIAA EQ/Monitor protoboard. I had NJM2068s already installed in the flat preamp so I used them...