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Old 25th June 2011, 08:35 PM   #561
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Relays usually need space. This wouldn't be the shortest path. For that i would use an LDR (light dependent resistor) instead.
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Old 25th June 2011, 08:41 PM   #562
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Originally Posted by qusp View Post
noise created by the resistors and contacts is to a degree averaged out with feedback, no extra resistors are added, as they simply replace those that are already there.

one problem is that you must find a way to achieve having the pot mechanism as close to the opamp as possible, extending the feedback loop to the front panel and back is not such a great idea.

best way imo would be a relay based attenuator in the loop, this allows very short paths.

again, all a matter of taste
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.
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Old 26th June 2011, 02:50 AM   #563
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Wouldn't I be able to just put the attenuator between the inputs and connect it to the input pads of the pcb like in post #440?
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".
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Old 26th June 2011, 05:35 AM   #564
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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.
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Old 26th June 2011, 11:47 AM   #565
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Originally Posted by Earfanatic View Post
Relays usually need space. This wouldn't be the shortest path. For that i would use an LDR (light dependent resistor) instead.
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?
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Old 26th June 2011, 02:21 PM   #566
jdkJake is offline jdkJake  United States
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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.
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.
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Old 26th June 2011, 07:26 PM   #567
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Hi, new to the forum.

Put me down for 1 SE-SE + PSU kit.
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Old 27th June 2011, 08:28 AM   #568
qusp is offline qusp  Australia
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yep, with 3vrms (i'm assuming sabre dac) unity voltage gain (but reasonable current gain as here) is easily enough to drive my hd600 very well indeed.
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Old 27th June 2011, 09:15 AM   #569
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Does a higher gain impact performance negatively (apart from a potentially higher noise floor)?
I am asking because I think a gain of 2 would be more versatile as I plan to use it as a preamp as well.
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Old 27th June 2011, 12:01 PM   #570
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preamp for what? with what source? from 1->2 probably nothing but higher noise, the opamps are unity gain stable, but might even enjoy having a bit of gain.
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