Topic: Edirol UA5 distortion *before* 0dB???

[poorlyconditioned]

Richard, I think that the problem you are having is that neither of those op amps have rail-to-rail outputs.  The OP2134's output will swing closer to the negative supply than it will to the positive supply, so when you run too hot, you'll see more even harmonic distortion than odd harmonic distortion in the lower order harmonics.  I see evidence of that in your plots.  You may want to find an op amp that has rail-to-rail output capability and low noise.  I think that the op amps used in the stock UA-5 design also have this issue.

FYI, the 2134 will get within 2.2 V of the negative supply and to within 2.5 V of the positive supply when driving a 600 ohm load.  It will get to within .5 V of the negative supply and to within 1.2 V of the positive supply when driving a 10k ohm load.  I don't know what impedance is seen looking into the A/D circuit, but I suspect that it's probably closer to the 10k ohm scenario.

Yeah, that might be true, but I saw the problem *with the original UA5* too.  I measured the voltage at the ADC pin at about 1V peak-to-peak, which is attainable by any opamp from at +/-5V supply.

I encourage others to take up this challenge if you know some electronics, but I honesty think something is broken in this circuit.  The solution *for now* is just to run -3 or even -6dB down and boost a bit in post.  I find it crazy in a way that we (tapirs) pay so much for gear and never check it out, but the companies don't either!  Just look at all the problems with the microtrack...

  Richard

[SparkE!]

Yeah, that might be true, but I saw the problem *with the original UA5* too.  I measured the voltage at the ADC pin at about 1V peak-to-peak, which is attainable by any opamp from at +/-5V supply.

Yes, and the NEC uPC4570 that the original UA-5 uses also does not swing rail-to-rail.  In fact it's 3 V off the rails with a +/-15V design.  It's going to be really soft with a +/-5V supply like is used in the UA-5.

Also, I checked on the input impedance of the AK4524 and it is typically 10k ohms, so you will get asymmetric soft clipping with the OPA2134.

I've long suspected that the main improvement in sound on a modified UA-5 comes from use of rail-to-rail op amps and the lower harmonic distortion that results. I think this will be much more noticeable than than the noise level improvement you get from going with a lower noise op amp.  For choosing op amps for this application I would search for op amps that have rail to rail outputs, high slew rate, high gain bandwith product and low noise, in that order of importance.

[Chuck]

AD8620 - A good choice for the A/D buffer.
AD712 - I've seen Doug Oade comment how much he like this for it's "warm" sound.

[aberg]

AD8620 - A good choice for the A/D buffer.
AD712 - I've seen Doug Oade comment how much he like this for it's "warm" sound.

That's cool, except for those of us with AKG's or Neumann's.....

[poorlyconditioned]

AD8620 - A good choice for the A/D buffer.
AD712 - I've seen Doug Oade comment how much he like this for it's "warm" sound.

Cool +++++++++++++++T

Now we're talking.  OK, I've got all those chips...

So, I'll put the buffer as AD820.

Before that there are three chips: one chip (a pair of amps) for the left, one chip for the right and one differential output (both L and R use the same chip).

So, would you put an AD712 right on the input, or as the differential, or as all of the above?

  Richard

I'm still working out this ADC though.  There must be something wrong, no???

[poorlyconditioned]

AD8620 - A good choice for the A/D buffer.
AD712 - I've seen Doug Oade comment how much he like this for it's "warm" sound.

That's cool, except for those of us with AKG's or Neumann's.....

Actually, from what I hear the Neumans want transparent and the AKG want warm.  So, I'll try the warm chips with my AKGs

  Richard

[Chuck]

I think the AKG C-480's sound good with a W-mod UA-5.
I don't have the background to be able to pick the right chips. I know the headphone amp builders really like the AD8620 in unbuffered amps and I've heard that it works well as an A/D buffer.

[SparkE!]

AD8620 - A good choice for the A/D buffer.
AD712 - I've seen Doug Oade comment how much he like this for it's "warm" sound.

Cool +++++++++++++++T

Now we're talking.  OK, I've got all those chips...

So, I'll put the buffer as AD820.

Before that there are three chips: one chip (a pair of amps) for the left, one chip for the right and one differential output (both L and R use the same chip).

So, would you put an AD712 right on the input, or as the differential, or as all of the above?

  Richard

I'm still working out this ADC though.  There must be something wrong, no???

You'd use the AD712 as the input amps and the AD8620 everywhere else.  That's if you want the warm front end.  If you want a more transparent front end with lower noise, use the AD8620 everywhere.  The AD8620 was designed for use with +/-5V power supplies and it clips symmetrically at just 1V off the power supply rails.  If you make the mods, I'm betting that your distortion problem will go away.

[poorlyconditioned]

AD8620 - A good choice for the A/D buffer.
AD712 - I've seen Doug Oade comment how much he like this for it's "warm" sound.

Cool +++++++++++++++T

Now we're talking.  OK, I've got all those chips...

So, I'll put the buffer as AD820.

Before that there are three chips: one chip (a pair of amps) for the left, one chip for the right and one differential output (both L and R use the same chip).

So, would you put an AD712 right on the input, or as the differential, or as all of the above?

  Richard

I'm still working out this ADC though.  There must be something wrong, no???

You'd use the AD712 as the input amps and the AD8620 everywhere else.  That's if you want the warm front end.  If you want a more transparent front end with lower noise, use the AD8620 everywhere.  The AD8620 was designed for use with +/-5V power supplies and it clips symmetrically at just 1V off the power supply rails.  If you make the mods, I'm betting that your distortion problem will go away.

OK, the distortion problem did *not* go away.  I put 8620 as the buffer and as the differential amp summer.  I put AD712's on each mic input.  Distortion is still there.  I challenge anyone who has Oade mods to check it out, play my 1600Hz file from line out into your line in (or mic in with gain all the way down).  I think everyone is going to experience this distortion.

Now, I noticed if I go down to -4.5dB, the biggest secondary (3200Hz) goes from about -40 down to -80dB, so it is pretty far down.  At that level, it could be due to distortion from the NJB3 for all I know.  But do not go over -3dB on the input is my suggestion.

OK, I'm curious.  Does anyone know how the clip light works?  It comes on at 3dB. Maybe somehow the chip *is* really clipping there?  Also, I saw the AKM docs for their development board, and they show a spectrum, with great performance, at -0.2dB.  So it should work right at the top.  So my guess is there is a problem in Edirol's implementation, either in setup of the AKM chip (gain settings maybe?) or maybe the sample rate converter after it.  Who knows at this point.

  Richard

[Chuck]

AD8620 - A good choice for the A/D buffer.
AD712 - I've seen Doug Oade comment how much he like this for it's "warm" sound.

Cool +++++++++++++++T

Now we're talking.  OK, I've got all those chips...

So, I'll put the buffer as AD820.

Before that there are three chips: one chip (a pair of amps) for the left, one chip for the right and one differential output (both L and R use the same chip).

So, would you put an AD712 right on the input, or as the differential, or as all of the above?

  Richard

I'm still working out this ADC though.  There must be something wrong, no???

You'd use the AD712 as the input amps and the AD8620 everywhere else.  That's if you want the warm front end.  If you want a more transparent front end with lower noise, use the AD8620 everywhere.  The AD8620 was designed for use with +/-5V power supplies and it clips symmetrically at just 1V off the power supply rails.  If you make the mods, I'm betting that your distortion problem will go away.

OK, the distortion problem did *not* go away.  I put 8620 as the buffer and as the differential amp summer.  I put AD712's on each mic input.  Distortion is still there.  I challenge anyone who has Oade mods to check it out, play my 1600Hz file from line out into your line in (or mic in with gain all the way down).  I think everyone is going to experience this distortion.

Now, I noticed if I go down to -4.5dB, the biggest secondary (3200Hz) goes from about -40 down to -80dB, so it is pretty far down.  At that level, it could be due to distortion from the NJB3 for all I know.  But do not go over -3dB on the input is my suggestion.

OK, I'm curious.  Does anyone know how the clip light works?  It comes on at 3dB. Maybe somehow the chip *is* really clipping there?  Also, I saw the AKM docs for their development board, and they show a spectrum, with great performance, at -0.2dB.  So it should work right at the top.  So my guess is there is a problem in Edirol's implementation, either in setup of the AKM chip (gain settings maybe?) or maybe the sample rate converter after it.  Who knows at this point.

  Richard

Hmmm... Interesting...

[it-goes-to-eleven]

I did some tests last night..  I'll try and post some fft images, etc.

I ran jb3 out >

 v3 AES > 722
 722
 UA5 USB > PC

Suspecting the jb3, I then re-did the test using a Squeezebox3 as the source.  I'd like to test the minime in there and the microtrack too. I would especially like to get data on a Mytek A/D (double good with a Mytek DA as the source).  It would be fun to test a few high end D/A's with the same A/D destination.

Most tests were done at 24/44. UA5 @ 16 bits.  For a couple cases I also did 16/44 on the 722.

In one case I ran the limiter on the 722 and kept increasing the levels until they were absurdly high. The integrity of the sine wave was good, even at extreme levels.  But when 'in' the limiter (above -6 dB), the harmonics increased.

Some portion of the harmonic is probably from the D/A source.

The harmonics in the V3 A/D source were lower than the 722.  But most who own both agree that V3 line > 722 sounds better than v3 AES > 722.  Go figure!  When recording shows, I record V3 line > 722 and also straight into the 722. I run my 722 levels hot. Would those soaring high female folk vocals that touch 0 dB sound better if they were peaked at -5 and raised in post?

Of course.. I now have too much data to make the summary a quick and painless task 

[poorlyconditioned]

I did some tests last night..  I'll try and post some fft images, etc.

I ran jb3 out >

 v3 AES > 722
 722
 UA5 USB > PC

Suspecting the jb3, I then re-did the test using a Squeezebox3 as the source.  I'd like to test the minime in there and the microtrack too. I would especially like to get data on a Mytek A/D (double good with a Mytek DA as the source).  It would be fun to test a few high end D/A's with the same A/D destination.

Most tests were done at 24/44. UA5 @ 16 bits.  For a couple cases I also did 16/44 on the 722.

In one case I ran the limiter on the 722 and kept increasing the levels until they were absurdly high. The integrity of the sine wave was good, even at extreme levels.  But when 'in' the limiter (above -6 dB), the harmonics increased.

Some portion of the harmonic is probably from the D/A source.

The harmonics in the V3 A/D source were lower than the 722.  But most who own both agree that V3 line > 722 sounds better than v3 AES > 722.  Go figure!  When recording shows, I record V3 line > 722 and also straight into the 722. I run my 722 levels hot. Would those soaring high female folk vocals that touch 0 dB sound better if they were peaked at -5 and raised in post?

Of course.. I now have too much data to make the summary a quick and painless task 

Excellent!  Looking forward to the results...

  Richard

[it-goes-to-eleven]

Richard's -6dB result on the left again..

First image is the 722 fed by the sb3 in line mode, 24/44.
Second image is the same with the 722 in low gain mic mode (a higher gain range that will add up to 55dB).
Third image is the V3 in 24/44 as fed by sb3 with output via AES to the 722.

[poorlyconditioned]

My UA5, as fed the signal by the jb3.  My efforts to get the levels exact were clumsy at best. So I tried to increment it up gradually and then pick out the section of interest from the sample.

I seem to have missed most of one channel. Not sure why.  Maybe bad cable seating.

Richard's result is on the left.  He was aiming for -6 dB. Baudline thinks it is higher than that.

Next image is basically the same but the source is the squeezebox3.

Hey, freelunch.  Those are great.  What I'm wondering is can you crank the input up really high, eg., -1 or -2dB?  I want to see how they all compare, namely the UA5, 722, and V3.  At -6dB it looks like V3 is better than 722 is better than UA5, but neither is terrible.  I mean, even -80dB down for the 3200Hz harmonic is not terrible on the UA5.  I want to see when the levels get way up there...

Thanks again,
  Richard