VoltageDAC with B1 output buffer

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#3
Coupling capacitor

I have now made 2 variations of this DAC. I have attached the schematics of one single channel B1 buffer that I use.

The DAC's built are equal down to C9, the coupling capacitor.

Version 1 have 3 cap's in parallell: 100uF electrolytic || 1.1uF Solen PA (metallized polypropylene) || Vishay MKP 1837

Version 2 have 2 cap's in parallell: 1.5uF unknown film cap || Vishay MKP 1837

The sound difference was bigger than expected. I have grown used to version 1. Version 2 were much more forward, the bass was harder and there was less space around the instruments and voices.

All of these film-caps were intentionally bought for passive crossover use. I have never really read any much about capacitor choice in active electronics, so my question here is: Could anyone point me in a direction here?
 

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  • b1_single_channel.jpg
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#5
why you need input caps ?

just kill gnd reference for input gates , then place caps on buffer output

well - I suppose that's matter of preference , and type of caps you prefer 😉

edit - I have impression that cap on buffer output is somewhat less critical than cap in input
 
#7
The outputs of the DAC sit at about 2.5V, so you need to take that into account. Blocking caps make it easy.
But maybe there is some way to bias the buffer so that it deosn't care about the offset.
I know how to do that with an opamp, but not the B1. 😉
 
#8
as I said - just delete gate gnd resistors

in that case - made lowpass filter differentially on input , or blahlah on output .

without gate gnd resistors , each upper jfet will float up and sit where it feel comfortably

and - yeah - if you are lacking some drive from DAC , instead of double B1 - make Jfet BOSOZ , with all XCCSwhatever suffixes and prefixes ..... , and make it SUSY , what else ........

:rofl:

there are plenty of options .....
 
#10
Nelson Pass said:
Why do you need the input coupling cap? Is there DC at the
output of the DAC?

😎

Nevermind - I see on your previous schematic.
Click to expand...

Isn't it so that these DACs run off +5 V (and GND), hence each output is more or less midway between. (2.6 V is almost midway....) But as they have differential outputs (Aout+ and Aout-) all will be hunky dory. Or maybe I should have read the rest of the replies before writing... But I had this cup of damn good coffee in front of me and wanted to type something... :deer:
 
#11
Yes, the outputs are at about 1/2 of the Vcc. With an dual opamp buffer on the outputs of the DAC chip, you just connect the 1/2Vcc (offset) to the + inputs of the opamps. The signal goes to the inverting (-) input. Normally you'd connect the + inputs to ground.

Don't know how that would work with the B1. Wish I knew what Z.M. was talking about, but he lost me, too! (Bozo, Susy, Xccs, kazzam!)
 
#12
I'm lazy to type .......

anyway - here is diff buffer stage ;

point is that you don't need caps on input .....

you don't need them at all if you're gonna feed xformer with that buffer .... in which case you also don't need any type of diff Low Pass

with XCCSwhatever Jfet Bosoz I meant on BOSOZ variant - with cascoded Jfets , SUSY-ed , with CCS in LTP tail .

search ....... dunno where is it

edit - gate to gnd resistors are deleted ;

you can leave them in circuit , but referenced not to gnd but to Rf ( is that name of reference pin for all fluffy OPs after DAC , in datasheets ?)
 

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#16
naah ....... bad habit thinkin and drawing before coffee

I see that I drew one redundant cap multiplier , not redundant because of few parts , but because of possibility that extra part is really extra :rofl:

I just drew similar thing for AR2 - intended between DCX DACs and Lundahls ,and off course that I put this time adequate number of cap multipliers in negative leg .......

:clown:

this time you can't see LP blocks - they're not needed , most probably for his usage
 

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#17
Don't know how I didn't think of this before.... but this would be perfect for a buffer to follow my twisted pear opus dac. I had planned to use a salas shunt reg to power it - now I will use a stunt reg to power the dac and a dcb1 for the output.

Need to go study!



Fran
 
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