DIY optical cartridge preamp

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#81
The most common problem with using DSP is the quality of the data converters. Good standard measurements do not assure good performance if sigma-delta modulators are in use (and for other reasons).
 
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#82
mikey_audiogeek said:
I have checked over my circuit "map" and am pretty confident it is correct. The circuit is not symmetrical since one channel input is inverted in phase, and this has to be corrected before the output.
I will measure voltages later this week.

This evening I opened the enclosed metal box under the pcb to find...inductors!
View attachment 1325524

These are 39uH inductors (about 25 ohms DCR). Looks like part of the filter network, that incorporates reverse-RIAA and EQ for the optical cartridge??? Or maybe just RF suppression? I need to run the numbers...
If it is part of the filter network, I'll be able to leave it out in my implementation as I will be using DSP.

Cheers,
Mike
Click to expand...
Correction: 39mH inductors. They're in parallel with the 12K resistors; almost certainly part of the EQ.
 
#83
Markw4 said:
The most common problem with using DSP is the quality of the data converters. Good standard measurements do not assure good performance if sigma-delta modulators are in use (and for other reasons).
Click to expand...
A moot point, in my case.
I'll still work to decipher the circuit so that analog techniques can be used.
It would be good to develop a circuit with flat "line-level" output, as opposed to the KA-9021 that still has to go through an RIAA phono stage (which seems a waste).
Cheers, Mike
 
#84
2A3SET, how does your tube equalizer sound?
This should be a perfect opportunity for tubes -- the relatively high signal level coming out of the DS optical cartridges make noise less of a problem, and tubes' superior transient overload recovery should be audible. Anyone know of other tube equalizers for these cartridges?
 
#87
It's very messy as I shared with LCR phono first stage.
LED supply is using Salas ultraBIB circuit.
The -20v is provided with CCS+TL431 and couple of RC filters after,
TL431 sounds better than ultraBIB used as bias.

1721829377614.png
 
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