I see your point...This does sound a bit tricky and I don't want to have to redesign the board to fit in a relay based attenuator. I wonder how noticeable the extra resistor noise will be noticeable with input attenuation.
As it has been pointed out, there are multiple ways to approach the problem.
The approach I took (outlined in the post your linked) works fine.
As they say, "your mileage may vary".
As it has been pointed out, there are multiple ways to approach the problem.
The approach I took (outlined in the post your linked) works fine.
As they say, "your mileage may vary".
What resistance did you choose to go with on your attenuator?
I may be using the wire with HD650's as well with a 3Vrms source, so I would be curious to hear more about what you think of the volume range you have with a gain of 2.
hey, sure, but the distortion added by this way with designs i've seen is significant and it varies in value with temp doesnt it?. if all smd everything was used for the relay based design stacking above the loop would still be quite short, but yeah. i only know the times i have used amps with this method vs a pot at the input works well.
personally compared to dac based volume its all a compromise. great transparency that sounds exactly the same at low or high volume, perfect channel matching and interpolation between 0.5db steps for the price of a cheap adc and a 2 dollar pot....cant complain about that.
anyway i wont keep going, hows it all going opc?
I went with a 50k shunt attenuator. So, the actual resistance on the load will vary a good bit. Depending upon your source, I think a lower value would probably be better (say 10k or 25k) to keep the noise in check.
I have used the amp with my HD650's with the gain of two and it is more than loud enough for me from my sources (i am using a gamma2 or a NAD T585). I still have plenty of clicks left on the attenuator. It really depends upon how loud you like to listen. I would think that with a 3Vrms source, even unity gain should be plenty. Either way, it is easy enough to change.
As a second thought, yes. You are right, but one time I want to try it just for fun.
Hi Guys,
I should have chimed in on this earlier, and now it looks like it has ballooned into a concern for some people.
I'd like to clarify that you should NEVER use the feedback loop to control volume. It's a terrible idea even on a low speed amplifier and it's a really terrible idea on something with this much BW. DON'T DO IT!
Volume control should be done the same way it's done with any amplifier, and that is, you should add a passive or active volume control at the input. You can choose the input impedance by choosing the correct attenuator impedance. The amp doesn't really care, but what you're driving it with might. Pick the lowest value that your source can comfortably drive.
Providing an on-board volume control limits people to using a crappy pot, and I'm not about to do that. Making room for a proper attenuator would mean that I would have to make the board 6 times the size, and provides no benefit whatsoever. When was the last time you saw a high end power amplifier with a $2 pot on the front panel? It's the same story here.
Take a look at post #440 by jdkJake if you want to see a really great attenuator setup (with the exception of his source). If you want something smaller, use a small stereo pot instead. By leaving it open to the end user, the world is your oyster and you can do whatever you want.
As a general update, I'll be posting the updated BAL-SE version and the updated PSU tomorrow afternoon. I apologize for the delay, but as usual, things have been busy here.
Cheers,
Owen
I should have chimed in on this earlier, and now it looks like it has ballooned into a concern for some people.
I'd like to clarify that you should NEVER use the feedback loop to control volume. It's a terrible idea even on a low speed amplifier and it's a really terrible idea on something with this much BW. DON'T DO IT!
Volume control should be done the same way it's done with any amplifier, and that is, you should add a passive or active volume control at the input. You can choose the input impedance by choosing the correct attenuator impedance. The amp doesn't really care, but what you're driving it with might. Pick the lowest value that your source can comfortably drive.
Providing an on-board volume control limits people to using a crappy pot, and I'm not about to do that. Making room for a proper attenuator would mean that I would have to make the board 6 times the size, and provides no benefit whatsoever. When was the last time you saw a high end power amplifier with a $2 pot on the front panel? It's the same story here.
Take a look at post #440 by jdkJake if you want to see a really great attenuator setup (with the exception of his source). If you want something smaller, use a small stereo pot instead. By leaving it open to the end user, the world is your oyster and you can do whatever you want.
As a general update, I'll be posting the updated BAL-SE version and the updated PSU tomorrow afternoon. I apologize for the delay, but as usual, things have been busy here.
Cheers,
Owen
hmm, ok i'll take your word for it, i guess the info at the place i got the design last time i needed one (wont name and shame here then) was incorrect. it was a design that put some small smd relays and thin film resistors in the feedback loop of ths4131. i dont have a scope (certainly didnt back then, i havent used anything but digital for ages) so guess whatever issues caused werent audible. i've seen it used on here several times too, guess you cant believe everything you read. so sorry if i've cause anyone expense. ive seen designs do far worse for gain setting and as mentioned i wouldnt ever recommend it if it meant going to a panel and back.
but ok, i'll take that one on the chin
and for the record, just because i prefer digital its really meaningless to this design, opc has designed the amp impeccably and as he said above, he has left it up to you to choose. i do believe that using the dac for control is the best method as it adds nothing to the signal path, but so what? i believed that something that apparently does it wrong was superior to other methods
but ok, i'll take that one on the chin
and for the record, just because i prefer digital its really meaningless to this design, opc has designed the amp impeccably and as he said above, he has left it up to you to choose. i do believe that using the dac for control is the best method as it adds nothing to the signal path, but so what? i believed that something that apparently does it wrong was superior to other methods
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