Thoughts on Quickie for Tube Buffer w/ DAC

[skidave]

OK, so I am going to ask my wife for a Quickie for my Birthday (that could be a real play on words!) and I would like to use it as a tube buffer w/ my DAC.  Question; I would like to leave the original analog output connected and connect the quickie after the I/V resistor and before the OP AMP.  Physically simple, but not sure about performance?  I'm a great DIYer, but a little lacking on the engineering background.  Would this work?  I'm not sure about input impedances and the signal after the I/V resistor.

New to the Bottlehead Forum, but I have a Seduction Phono (which is wonderful) and other hand crafted equipment.

Thanks in advance.

Dave

[Paul Joppa]

Normally a DAC does not use an I/V resistor, the current output is connected directly to the opamp input at the "zero impedance" node and a feedback resistor makes the opamp behave like a current to voltage converter. The actual voltage at that point is very small, and filtered by the opamp's dominant pole. I imagine you'd have to put in a switch to choose between the two topologies.

[skidave]

Paul, thanks for the response.  I've attached a similar schematic of what I would like to do.  I'm not sure of the Quickie topology. 

[jvm]

I have a very similar question. I want to connect the Quickie directly to the dac output of my cd player, but the output voltage is only 1.1V. Do you see this as presenting any problem? BTW, what is the gain factor of the Quickie?

[Paul Joppa]

Stock Quickie gain is about 2.2 times (7dB).

skidave, R35 is the I/V resistor; the rest can be replaced by a Quickie.

The stock CD player probably does not have R35; the Iout pin of the DAC chip probably goes to the - input of the opamp instead. The - input of the opamp would be a "virtual ground" point with almost no voltage - it's a current-summing junction instead of a voltage node.

[jvm]

Then I could do it with the addition of an I/V resistor?

[Paul Joppa]

Hey guys, I really am trying to be helpful here. But I don't know the circuits you are asking about, and I'm not a digital audio whiz. All I can really say is the Quickie has a gain of a bit over 2 in stock form, and up to 4 if you use a current source or choke load. If you can get a volt (or a half volt) out of your CD or DAC, then Quickie will amplify it to 2 volts (i.e. the Red Book standard for CD players).

[Grainger49]

The digital question might get more response on the Digital Drive over on AA.