Beefy dac ? Is it possible to use passive preamp

[elviukai]

hi, I have nice parasound d/ac 1500 laying arround. it uses 102 000uf PS filter, 3 trafo, cs 8412 receiver and 4x Burr brown pcm 63P (K) 2 operating in push-pull to every channel ,fully balanced digital operation.
it has folowing outputs
balanced- 6V nominal 1.2Kohm
unbalanced 3V nominal 600 Ohm
manuf recomends minimum 10Kohm suitable load
some rewiewers notice that output even is too strong.

question - is it good iea to put in discrete volume attenuator and run directly to poweramp. this dac will work without any loss in quality feeding one amp? I even thinking feed 2 amps.
poweramp is Pass labs xa100 clone and Aleph 5 clone.

is it posible to attenuate balanced signal and how to do this.? this is the main question.

pass labs power amp aleph 5 has 10kohm unbalanced and balanced probably 25 kOHm. aleph x ???

so will they work together? I dont mean SPL but quality. I have noticed that sometimes even cheap preamp works better that DACT atenuator.greater image and microdynamic at low levels. and how to make discrete atennuator to reduce balanced signal?

thanks for any help.

[DragonMaster]

Maybe, the DAC probably is already preamped, so buffered at the same time. If the amp is buffered at it's input, there should be no probs IMO.

[AndrewT]

Hi,
at the receive end put a series resistor in each feed to the power amp. Put an adjustable resistor between the + & - after the series resistors. When the pot is max volume is max. when the pot is minimum the volume is zero (or very close).

Since your recommended load is 10k then use 10k series resistors and try a range of log pots between 20k and 100k to check the feel of the adjustment to suit your attenuation needs.

You could use a stepped attenuator instead of the pot.
That would make balance between stereo channels more accurate and maybe sound better as well.

If your balanced output and input is achieving good CMRR then upsetting the very accurate resistor balance needed to achieve this will throw off the CMRR. You should select the resistors as accurately as you can to maintain good CMRR.

[elviukai]

thanks Andrew.

now I am using precision elma dact 24 gang stepped atenuator with smd resistors. it is 10k OHM and will fit in pass preamp in other project. now I put in series 8k ohm resistors to this DACT , because sound apeared very quickly,even at firs step it souned alrready loud.

so in balanced opetration you sugest to put stepped attenuatorutor in power amp, not in DAC? but as I undesrtand i need to put balanced mode resistors in series with - and gnd?

and after theese fixed series resitors(to clear myself - they are more far ) put attenuator( to clear myself- it is nearer amp) with 2 pins where one pin conects to + and other to - ?

[AndrewT]

Hi,
I'm afraid I have to start with an apology, I am having trouble understanding exactly what you are telling me.

The DACT must be at the receive end otherwise it will destroy your upper frequency response and reduce your CMRR.

I think the DACT you have is for connection to line in, line out and ground, specifcally designed for unbalanced use.

However you can use it for balanced use if you DO NOT connect it to ground. The value may be a little low but try it anyway. A low value gives more attenuation, i.e. less volume.

+ve dac output- - - - - - - - 10k00 series resistor - (+ve) input.

-ve dac output- - - - - - - - 10k00 series resistor - (-ve) input.

Connect one pole of the DACT between the +ve & -ve inputs. Leave the ground connection floating. Keep the second pole for the other channel.
All the connections from 10k00s to DACT to inputs must be kept short and very compact.

[elviukai]

hi again, thanks for helping

yes You understand what I am saying more or less. its not my english bad, just my electronic skills



like in atached picture it must be?


what is CMRR?

[elviukai]

Mr. Nelson as I unerstand recomends only variable resistor between + in balanced mode ?

"The best way to attenuate the input to an X amp is to place
resistance in series. The Alephs generally will prefer a
divider on the input."

[elviukai]

Mr. Nelson as I unerstand recomends only variable resistor between + in balanced mode ?

"The best way to attenuate the input to an X amp is to place
resistance in series. The Alephs generally will prefer a
divider on the input."