John Curl's Blowtorch preamplifier part II - Page 3403 - diyAudio
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Old 1st February 2013, 07:25 PM   #34021
PMA is offline PMA  Europe
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I have never designed anything with them. What I know is I did not like the sound. But BV has had enough experience with them, he can tell us.
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Old 1st February 2013, 07:37 PM   #34022
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Thanks for your input, PMA. I was afraid that you might not like their sound. '-)
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Old 1st February 2013, 07:39 PM   #34023
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Again, THD figures for PGA are for gain diferent (lower than) from 0dB worse, than for 0dB. This not valid for MDAC, nor relay atenuator. .
It seems not logical: they use one switch by step, the same for each, it is not like DACs. So i do not see why distortion wouls change with position of the attenuator. With level of the signal, yes, as MOS are less linear at high level.
May i ask-you the same question ? Can you try to describe the differences you found between all those solutions, on a subjective point of view ?
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Old 1st February 2013, 07:48 PM   #34024
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Originally Posted by john curl View Post
Well, what about distortion at other settings? Anybody?
One of the reasons ADevice's converters (AD1955?) won me over - just with the spec sheet - is they had the confidence- the guts - to spec the thd at -60 input !! Not just at 0 level.

Thx-RNMarsh

Last edited by RNMarsh; 1st February 2013 at 07:53 PM.
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Old 1st February 2013, 08:08 PM   #34025
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Richard, DACs commute DC. At 0 dB all the steps are used to compose the signal. The distortion is just a factor of precision of the R-2R network.

BV, what was the source impedance, when you got so bad measurements with PGA ?
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Last edited by Esperado; 1st February 2013 at 08:23 PM.
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Old 1st February 2013, 08:40 PM   #34026
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PGA driven via 33R direct from previous stage (unity gain follower with OA, distortion at this input point was 2 orders lower than at output). Sound diferences against MDAC or relay attenuator -less resolution, something as "sound smog", less details and missing of something that I call "silence between notes". It is difficult to describe with words, subejctive impact can be different. And look at block diagram for PGA in datasheet, here are for sure more switches in action than one by step. Input divider, and feedback network.
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Old 1st February 2013, 09:03 PM   #34027
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Attached is one measurement for preamp with relay attenuator, difference is visible.. I organized more "sessions" and listeners always prefered version with relay attenuator against PGA or DAC regulation. Most audible are difference between PGA or WM8816 against DAC +OA,and again, DAC is superb compared to PGA or WM, difference DAC vs. relay attenuator is more subtle
Did you compare the relay attenuator to switching attenuator?
Possibly avoiding relays, which are magnetic, can be beneficial.
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Old 1st February 2013, 09:06 PM   #34028
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I come from the "chain is only as strong as its weakest ..." line of thinking: chain A is made from 99 links of strength 100, 1 link of strength 50; chain B is made from 100 links of strength 50 - which chain is stronger? In the audio world everyone will put up their hand to say chain A is obviously superior; everything in my experience says it works just that real, hard metal "rope" - that single, lesser link sets the standard for everything else.

Not very palatable, but that's how it works, IME ...

Frank
Hi,

If you would convert the chain length strength to equivalent THD values and sum them you would see your error.
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Old 1st February 2013, 09:10 PM   #34029
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Quote:
Originally Posted by BV View Post
PGA driven via 33R direct from previous stage (unity gain follower with OA, distortion at this input point was 2 orders lower than at output). Sound diferences against MDAC or relay attenuator -less resolution, something as "sound smog", less details and missing of something that I call "silence between notes". It is difficult to describe with words, subejctive impact can be different. And look at block diagram for PGA in datasheet, here are for sure more switches in action than one by step. Input divider, and feedback network.
Well, there is two switches, i believe, one in the feedback loop cancelling the input one's distortion. They use-it to increase the gain of the amp between 0 and +15dB.
Thank-you for your answer and description, BV, clear enough, and you describe all that i do not like. Strange that i do not experience the same thing.
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Old 1st February 2013, 09:10 PM   #34030
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This not valid for MDAC, nor relay atenuator. Try it , I tried personaly in last ten years MDAC ( a bit complicated "driving" for dB steps), WM8816, PGA2310, MAS6116 (all very covenient for use), and finally I stick with relay attenutor. It is simply sonically the best solution with best measured parameters.
How did the Levinson measure so well and win the, ahem, listening contest?
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