Parasound DAC-1000 - DC blocking capacitor

xionc

Member
2009-11-30 8:50 pm
Hi,

Long time lurker, first time poster - greetings to this great community!

Don't know why my post was deleted, mods please let me know...

From personal experience I can say that DC blocking capacitor has profound impact on the character of the DAC sound. Unfortunately I'm unable to read complicated schematics - and DAC-1000 has really complicated analog stage. Is there anyone here who could help me finding DC blocking capacitor?

service manual
 
I hate schematics drawn so as to fit in to the fewest number of sheets possible. Anyhow, it appears to me that the analog output circuit is D.C. coupled (has no output coupling capacitors). There are alot of op-amps in there, but many of them appear to comprise a pair of Generalized Impedance Converters, implemented as Frequency Dependent Negative Resistor image rejection filters. It's possible that have overlooked D.C. servos hiding somewhere in there, though.
 
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Hi,

there are no DC-blocking Caps between the Output transistors and the RCA-connector. There are 330R-Emitter resistors (R328/R322 for left, R428/R422 for right channel), two 22R series resistors (R301for left, R401 for right channel) and the normally open relais contacts from signal to gnd.
Offset calibration is done with Trimpots. Just for left channel:
1K - TRV303, trimming the IV-converter-ICs AD841 input offset.
500R - TRV301 and TRV302 are used to set the bias current trough the output transistors and to trim the output offset voltage to 0V.
Own the DAC-1000 for probabely 12years now and still have it hooked into my system and love it, though I haven´t used it for 5-6years due to our music servers simply beeing much more convenient and sounding better to my ears.
But for OPamp based DACs it´s always been a good device. Just springs to my mind that in all my HiFi-years it is still the most expensive component I bought...but it was worth it, every penny. Sourcing all the parts built into the DAC alone would have been more expensive at that time than buying the thing!

jauu
Calvin
 

xionc

Member
2009-11-30 8:50 pm
Thanks guys!

This DAC has powerful output and offers great resolution, however there is slight roughness to the sound that I would like to eliminate. Maybe it's noise introduced in the analog stage? From my pcm2702e experiments: low noise op amps (such as AD797) buffers made the sound smooth without covering details, while AD8620 and similiar were better in controlling the low end (punchy) at the cost of similar to dac-1000 roughness. BG N as DC blocking capacitor eliminated all hissing and smoothed the texture of sound UNBELIEVABLY for a passive part, compared with same value MKP, MKSE. That's the reason of my original question.

Do you have any proposition for modern i/v-analog output stage for this DAC? I'm amplifying with passively attenuated GC, so simple R based i/v is out of the question.
 
Thanks guys!
Do you have any proposition for modern i/v-analog output stage for this DAC? I'm amplifying with passively attenuated GC, so simple R based i/v is out of the question.

If you are sure you want to go the route of custom modification (including, cutting the PCB), then you might consider using a low value resistor to perform I/V, connected to a passive band-limiting filter, followed by some signal amplifier (op-amps, if you prefer). Some of us have found this basic post D/A topology to enable outstanding sound.