The only DAC chip which quickly comes to mind as having an output bias current is the PCM1792 family (such as the PCM1794, 1798, etc). The Philips TDA-1541 family may also, but I don’t recall. The AD1865 DAC chip utilized in your AN DAC box does not feature an output bias current, so it does not produce a D.C. offset voltage across an I/V resister.
As Marcel, and ErikdeBest point out, the are a number practical circuit concerns with a resistive control as I/V. The usable (non-fiddly) attenuation range will probably be 40dB at best, and may be as low as 20dB. Parasitic reactances within the control may also prove problematic in the presence of the wideband signals a DAC chip sends to an I/V stage. While it may seem elegant at first, the practical details of implementation probably make a standard type of volume control circuit the better choice for DIY.
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I can't speak for others, but my amp's or headphone amp's (or TV's for that matter) volume control rarely varies in position.
20-26db would be more than adequate a range for me otherwise I just pause playback so 10-20:1 attenuation is enough.
20-26db would be more than adequate a range for me otherwise I just pause playback so 10-20:1 attenuation is enough.
It's not about the peak to peak current. There should be an idling current as well. There are DACs with idling current higher than the p-p. I don't know about the DAC in question, it has to be verified.
EDIT: @Ken Newton answered that. 👍
The OP clearly stated he has an Audio Note Kits Dac 4.1 which I believe uses an AD1865 and tube output.
I once owned a Dac1.1 which looks to be very similar but without some of the more esoteric components and interstage transformers.
The IV resistors were 300r directly coupled to the 12AU7 tube through a 1k grid stopper and series inductor.
The AD1865 has a + - 1ma bipolar output, which I already mentioned, so there is no reason not to use some method of switched parallel resistors.
Check for yourselves - there is no need to waffle on about irrelevant complications as happens all too often on these forums.
https://ankaudiokits.com/product/dac-4-1/
I once owned a Dac1.1 which looks to be very similar but without some of the more esoteric components and interstage transformers.
The IV resistors were 300r directly coupled to the 12AU7 tube through a 1k grid stopper and series inductor.
The AD1865 has a + - 1ma bipolar output, which I already mentioned, so there is no reason not to use some method of switched parallel resistors.
Check for yourselves - there is no need to waffle on about irrelevant complications as happens all too often on these forums.
https://ankaudiokits.com/product/dac-4-1/
Regarding potmeters:
Carbon track potmeter wipers slowly get anodized when there is some DC current flowing out of the wiper, according to an application note I read long ago (Panasonic trimming potmeter application note, I think). As there will always be some DC offset, it's probably a good idea not to use carbon.
If I understand it correctly, the potmeter will be used as a variable resistor. If so, the volume temporarily goes to maximum when the wiper temporarily loses contact.
Carbon track potmeter wipers slowly get anodized when there is some DC current flowing out of the wiper, according to an application note I read long ago (Panasonic trimming potmeter application note, I think). As there will always be some DC offset, it's probably a good idea not to use carbon.
If I understand it correctly, the potmeter will be used as a variable resistor. If so, the volume temporarily goes to maximum when the wiper temporarily loses contact.
@analog_sa
I think you are confusing the DAC with another model. What I am talking about is the Audio Note Kit DAC 4.1, which uses IV transformers with a 3.3K resistor, and the spec for Zout = 13 Ohm.
https://ankaudiokits.com/product/dac4-1x-professional-edition/
I think you are confusing the DAC with another model. What I am talking about is the Audio Note Kit DAC 4.1, which uses IV transformers with a 3.3K resistor, and the spec for Zout = 13 Ohm.
https://ankaudiokits.com/product/dac4-1x-professional-edition/
I suppose that the coupling between dac and output circuit is well designed from AN ( there are trafos between them)
So changing something in that position is not a good idea
Probably a circuit type ladder potentiometer ( with remote control) in output as Tent lab.
With relays and 64 step , 10k , is a good solution
So changing something in that position is not a good idea
Probably a circuit type ladder potentiometer ( with remote control) in output as Tent lab.
With relays and 64 step , 10k , is a good solution
Neither of these numbers are mentioned on the linked page. Nor do they make a whole lot of sense. Where did you get them from? R19/R20 seem to be the I/V resistors in your dac and they look like 330R.
1mA * 0.7 * 0.33 = 0.231v RMS after the resistors
Assuming 12AU7 together with the follower amplify x14, that is 3.2v RMS at the output. Unless i have an entirely wrong idea of the topology that doesn't leave a whole lot of options for the output transformer to reduce the impedance, so it's pretty much the ECC99 cathode follower determining the impedance here. So, assuming no series resistor with the output and zero DC transformer Rout = 100R or thereabouts.
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The link you sent has a 12AU7 on output board
There is a version with 5687
https://ankaudiokits.com/product/dac-4-1/
Which one you have?
Why? 1:1 transformers, not really rocket science.
Curious about the effect of the 330R iv upon distortion. Surely someone has measured this.
This is a manual
https://ankaudiokits.com/ankmanuals/DAC 4.1 C-Core Manual V 6.07.pdf
Page 9 is the basic circuit
https://ankaudiokits.com/ankmanuals/DAC 4.1 C-Core Manual V 6.07.pdf
Page 9 is the basic circuit
There are R and C ( in parallel) in input and output of the I/V
It will a good idea to check the Freq answer after the mods at different setting
A 3k3 resistor cannot work on the dac side. It may work if the little transformer is a step up and the iv resistor is loading the secondary. It should be trivial to open the lid and make sure.
The output impedance could also be possible if instead of CC/CA the tube topology is CC/CC. Then a step down transformer, similar to what AN have in some preamps, with a voltage ratio of 33:1, is used.
Not sure why all the obfuscation in the user manual.
Opening the lid and drawing up a partial circuit seems essential.
The output impedance could also be possible if instead of CC/CA the tube topology is CC/CC. Then a step down transformer, similar to what AN have in some preamps, with a voltage ratio of 33:1, is used.
Not sure why all the obfuscation in the user manual.
Opening the lid and drawing up a partial circuit seems essential.
Actually my mistake, there is a 330 Ohm resistor before the IV resistor right at the output of the DAC chip and a 3.3K resistor on the secondary.
I don't know what the turn ratio is, but I believe it's 1:1, which would give a Riv = 300 Ohm
I don't know what the turn ratio is, but I believe it's 1:1, which would give a Riv = 300 Ohm
Is there any practical situation in which a ladder D/A doesn't improve in monotonicity (of low level distortion) with decrease in the value of this resistor?
Could this volume control be accomplished with the volume pot in the feedback path of a summing amp, as already present in most DACs?
Much thanks,
Chris
Could this volume control be accomplished with the volume pot in the feedback path of a summing amp, as already present in most DACs?
Much thanks,
Chris