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Can amplifier speed and resolution be measured?

tomelex

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Apologise about going on here sort of off topic about LDR stuff, but other than ability to have near infinite attenuation range which is a plus for the LDR over the stepped attenuator, this type of stepped attenuator has been around in one form or another for about 50 years, see:



http://www.dact.com/html/attenuators.html

SPECIFICATIONS
Number of steps
24
Bandwidth (10kOhm):
50 MHz
Channel matching:
+/-0.05 dB
Attenuation accuracy:
+/-0.05 dB
THD:
0.0001 %
Mechanical life, min.
25,000 cycles


Also, LDR (from when I looked into these about 10 years ago) will lose linearity over time simply because their source of light will not always be the same, despite constant current sources or other more elaborate feedback circuits to retain linearity. And, it hard to beat the consistency of the stepped attenuator. True, both types will need to be replaced over time, but the stepped attenuator will be IMO more repeatable and reliable over its lifespan.

An LDR could be viewed as a step up over a simple ALPS pot that's for sure.
 
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SIY

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An LDR could be viewed as a step up over a simple ALPS pot that's for sure.
In what way? I grabbed an old, well-used ALPS pot out of my junkbox and ran a distortion spectrum. There's no shielding, it's a high value pot (100k), and it's all done with clip leads, so there's a bit of noise pickup at -120 dB, but that's pretty much it. Harmonics are at the residual level of the APx525 I use. I'm just not seeing a problem here.
 

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tomelex

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In what way? I grabbed an old, well-used ALPS pot out of my junkbox and ran a distortion spectrum. There's no shielding, it's a high value pot (100k), and it's all done with clip leads, so there's a bit of noise pickup at -120 dB, but that's pretty much it. Harmonics are at the residual level of the APx525 I use. I'm just not seeing a problem here.

Hi, thinking of a stereo pot here, channel balance across the range will not be very good on an ALPS pot, even the so called "audiophile" ones, where with the LDR properly set up should beat it as a stereo pot setup for tracking. A well set up LDR should have distortion low enough to not be audible. Again, I feel the dact attenuator I showed above would be a better deal than the ALPS stereo pot on all accounts except the pot will not be stepped and thus you can get the volume jussssst right, ahahah.

SIY, appreciate your test measurements! That's what we are all about here.
 
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SIY

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SIY, appreciate your test measurements! That's what we are all about here.
Well, if I'm going to assert things, I like to have evidence. :D

If tracking is the main concern, yes indeed, a stepped attenuator is better. As a practical matter, I never had a noticeable issue when I still changed volume with a knob. Of course, digital attenuation is still king...
 

stereo coffee

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Well, if I'm going to assert things, I like to have evidence. :D

If tracking is the main concern, yes indeed, a stepped attenuator is better. As a practical matter, I never had a noticeable issue when I still changed volume with a knob. Of course, digital attenuation is still king...
My digital pot gathers dust as it sounds pretty poor ( dreadful in fact ), in comparison to the LDR
 

stereo coffee

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Of course it does. Of course.

And I'm sure you have controlled listening data to back up your assertion since you're selling this stuff, right?
I have a PGA2311 digital pot, as like you I needed to know where they fit in with regard to sound quality, and I am just
relaying my own experience with them. Lets await to see how my product measures- you can then look back at some
of these comments in a few months, to see if I was right or wrong.
 

rebbiputzmaker

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I have a PGA2311 digital pot, as like you I needed to know where they fit in with regard to sound quality, and I am just
relaying my own experience with them. Lets await to see how my product measures- you can then look back at some
of these comments in a few months, to see if I was right or wrong.
It would be good to wait but not everyone can.
 

Sir Sanders Zingmore

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Lets await to see how my product measures- you can then look back at some
of these comments in a few months, to see if I was right or wrong.
That implies confidence that it will measure well.
Presumably this confidence can only come from having measured it yourself. If so, why keep us in suspense? Please share
 

SIY

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I have a PGA2311 digital pot, as like you I needed to know where they fit in with regard to sound quality, and I am just
relaying my own experience with them. Lets await to see how my product measures- you can then look back at some
of these comments in a few months, to see if I was right or wrong.
So, no, you have no actual listening data, either.

It strikes me that hawking your products without measurements or listening data at an audio science forum is not appropriate.
 

stereo coffee

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Amir has kindly agreed to measure the LDR pre, so I do not see any inappropriateness ( gosh that's a big word )
as you will see and read about the result in a month or two - be patient please.

I am presently arranging a 120v plugpack to be sent to me - our voltage is 230v so Amir can power the unit with 12vAC
when it arrives to be tested.

I reviewed some of Tom's comments and see already there is much stability with signal side resistance with signal present,
however today I have further reviewed the timing of the negative load side of the slave rectifiers, and corrected their turning on
characteristics.
 

SIY

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Nonetheless, you're selling a product NOW. You are making sonic and technical claims for it, and claims denigrating competing technologies. You refuse to provide any evidence backing up these claims and have at this point strongly implied that there you have no evidence.

We have a word for this sort of commercial approach.
 

stereo coffee

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OK so you don't want to be patient and wait for actual measurements - and at the same time you will not accept many prior
independent subjective opinions.as they are not the evidence you need or you will accept. Hope you have a great day :)
 

stereo coffee

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This is a science forum. Opinions are not evidence.
So how about asking me how I corrected the turn on characteristics might be a more productive use of your time.
rather than await your reply, and in the spirit of science - it was done with thyristors to time the anode turn on at the gate
of the two mosfets in common source , it worked exceedingly well.
 

Thomas savage

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So a search for measurements to uncover the potentially bogus impressions of speed and timing has morphed into a circular back and forth about ‘LDR’ . No measurements I see, one would think this a relatively fruitful undertaking which should show conclusive results either way.

Why can’t the guy promoting the idea of this LDR not provide some measurements? Surly in all the effort to ‘engineer’ the latest implementation they must of kept a record of how the thing performs?

Further still why not create a thread for all this ? You want to start a diffrent topic create a thread, it really does help everyone out, especially our readers .

( insert Picard and Riker double face palm emoji)
 

tomchr

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Hi, thinking of a stereo pot here, channel balance across the range will not be very good on an ALPS pot, even the so called "audiophile" ones [...]
True. The Alps "Blue Velvet" (RK271-series) offers 3 dB channel tracking to -60 dB and 5 dB tracking below -60 dB attenuation. That said, all of the Alps pots I've measured have offered very tight channel matching except for where the resistance taper changes. So you get tight matching for 99.9% of the pot rotation, but will have 2-3 spots of maybe 1º of pot rotation each where the matching is worse. I've never had an issue with this in practice. You can see Amir's measurements of various headphone amps, including my HP-1, for examples of the channel mismatch that occurs in practice.

A "logarithmic" pot is made from several sections of linear taper. It's at the changes between sections that the matching is the worst.

Tom
 

tomchr

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I have a PGA2311 digital pot [...]
That's a digital attenuator, but that aside. I agree that the PGA2311 is not fantastic. It has higher noise than I like and also higher distortion. You can find the numbers in the data sheet. There are other options, however. CS has a nice one... It's still tough to beat an actual volume pot, though.

Tom
 

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