Author Topic: To all the audio guys out there.  (Read 2071 times)

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Online popeTopic starter

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To all the audio guys out there.
« on: November 12, 2024, 10:15:32 pm »
I have a QuantAsylum QA403 and although I like it quite a lot, I'm having hard time to measure the maximum level and headroom of pro audio DUTs (compressors, EQs, mic pres, etc...). The QA403 will output "only" around 20dBu which won't cut it for such measurments.

So, the idea is to use some sort of an amplifier between the QA403 and the DUT. It has to be balanced I/O with low THD and noisefloor. Bandwidth isn't too critical I suppose. Anything above 40kHz would do.

Has anyone run into a similar situation and if so, how did you resolved it?

 

Offline KungFuJosh

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Re: To all the audio guys out there.
« Reply #1 on: November 12, 2024, 10:25:26 pm »
I want one of those, but don't have it yet. Have you tried their forum? https://forum.quantasylum.com/
"Right now I’m having amnesia and déjà vu at the same time. I think I’ve forgotten this before." - Steven Wright
 

Online popeTopic starter

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Re: To all the audio guys out there.
« Reply #2 on: November 12, 2024, 10:27:30 pm »
I want one of those, but don't have it yet. Have you tried their forum? https://forum.quantasylum.com/

Not yet. I though I'd try my luck here first  :)
 

Offline bson

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Re: To all the audio guys out there.
« Reply #3 on: November 12, 2024, 10:33:53 pm »
Input and output signal levels?  What is the input impedance of the DUT?  Unless it's too demanding this should be easy to whip up yourself with one or two fully differential opamps.
 

Offline KungFuJosh

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Re: To all the audio guys out there.
« Reply #4 on: November 12, 2024, 10:37:27 pm »
I want one of those, but don't have it yet. Have you tried their forum? https://forum.quantasylum.com/

Not yet. I though I'd try my luck here first  :)

Sure, but here you'll get EE answers to an audio question that I'm sure has been asked there before. If you do get an answer from there, please share here. 😉
"Right now I’m having amnesia and déjà vu at the same time. I think I’ve forgotten this before." - Steven Wright
 
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Online popeTopic starter

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Re: To all the audio guys out there.
« Reply #5 on: November 12, 2024, 10:39:52 pm »
Input and output signal levels?  What is the input impedance of the DUT?  Unless it's too demanding this should be easy to whip up yourself with one or two fully differential opamps.

Not sure I follow. "Input and output signal levels" of which device?

Input impedance of the DUT will vary depending on the DUT. Anything above 600Ω I'd say.
 

Offline Messtechniker

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Re: To all the audio guys out there.
« Reply #6 on: November 12, 2024, 10:41:25 pm »

Has anyone run into a similar situation and if so, how did you resolved it?
By making this:


and this

[ Specified attachment is not available ]
Agilent 34465A, Siglent SDG 2042X, Hameg HMO1022, R&S HMC 8043, Peaktech 2025A, Voltcraft VC 940, M-Audio Audiophile 192, R&S Psophometer UPGR, 3 Transistor Testers, DL4JAL Transistor Curve Tracer, UT622E LCR meter, UT216C AC/DC Clamp Meter
 
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Offline Messtechniker

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Re: To all the audio guys out there.
« Reply #7 on: November 12, 2024, 10:42:24 pm »
and this power supply
« Last Edit: November 12, 2024, 10:48:26 pm by Messtechniker »
Agilent 34465A, Siglent SDG 2042X, Hameg HMO1022, R&S HMC 8043, Peaktech 2025A, Voltcraft VC 940, M-Audio Audiophile 192, R&S Psophometer UPGR, 3 Transistor Testers, DL4JAL Transistor Curve Tracer, UT622E LCR meter, UT216C AC/DC Clamp Meter
 

Offline KungFuJosh

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Re: To all the audio guys out there.
« Reply #8 on: November 12, 2024, 10:44:31 pm »
But then the Analyzer is profiling those things also...
"Right now I’m having amnesia and déjà vu at the same time. I think I’ve forgotten this before." - Steven Wright
 

Offline bson

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Re: To all the audio guys out there.
« Reply #9 on: November 12, 2024, 10:46:19 pm »
Not sure I follow. "Input and output signal levels" of which device?
Of the amplifier you need!

Amplifying 5 to 50V is very different from amplifying 0.5V to 5V even though the gain is the same.

The DUT input impedance is important because it determines the power you need on the amplifier output (apart from the signal level).

Edit: spelling it out
« Last Edit: November 12, 2024, 10:48:02 pm by bson »
 

Offline TimFox

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Re: To all the audio guys out there.
« Reply #10 on: November 12, 2024, 10:46:50 pm »
Profile the additional gadget, then de-convolve its properties from the overall properties with gadget and device-under-test.
 

Online popeTopic starter

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Re: To all the audio guys out there.
« Reply #11 on: November 12, 2024, 10:58:12 pm »
Not sure I follow. "Input and output signal levels" of which device?
Of the amplifier you need!

Amplifying 5 to 50V is very different from amplifying 0.5V to 5V even though the gain is the same.

The DUT input impedance is important because it determines the power you need on the amplifier output (apart from the signal level).

Edit: spelling it out

I would probably need a maximum of 10db of gain so something like 7Vrms to 24Vrms I suppose

Quote
The DUT input impedance is important because it determines the power you need on the amplifier output (apart from the signal level).

Well, the point is to be able to test various DUTs, isn't it?   :) Pro audio gear Input impedance can range from 200Ohm all the way to 1Mohm with 600, 10K and 100K being some of the most common values.

Ideally, I was hoping to find an off the shelf solution.
« Last Edit: November 12, 2024, 10:59:54 pm by pope »
 

Offline KungFuJosh

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Re: To all the audio guys out there.
« Reply #12 on: November 12, 2024, 11:02:53 pm »
Ideally, I was hoping to find an off the shelf solution.

 :popcorn:  ;)
"Right now I’m having amnesia and déjà vu at the same time. I think I’ve forgotten this before." - Steven Wright
 

Offline Messtechniker

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Re: To all the audio guys out there.
« Reply #13 on: November 13, 2024, 03:58:11 pm »
Because I could not find such a thing, I built one.
Agilent 34465A, Siglent SDG 2042X, Hameg HMO1022, R&S HMC 8043, Peaktech 2025A, Voltcraft VC 940, M-Audio Audiophile 192, R&S Psophometer UPGR, 3 Transistor Testers, DL4JAL Transistor Curve Tracer, UT622E LCR meter, UT216C AC/DC Clamp Meter
 
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Online popeTopic starter

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Re: To all the audio guys out there.
« Reply #14 on: November 13, 2024, 04:13:08 pm »
Because I could not find such a thing, I built one.

What are you using it with? QA403?
 

Offline Messtechniker

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Re: To all the audio guys out there.
« Reply #15 on: November 13, 2024, 07:58:14 pm »
M-Audio Delta AP 192 and Audio Tester software.
And Siglent 2042X
Agilent 34465A, Siglent SDG 2042X, Hameg HMO1022, R&S HMC 8043, Peaktech 2025A, Voltcraft VC 940, M-Audio Audiophile 192, R&S Psophometer UPGR, 3 Transistor Testers, DL4JAL Transistor Curve Tracer, UT622E LCR meter, UT216C AC/DC Clamp Meter
 
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Offline David Hess

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Re: To all the audio guys out there.
« Reply #16 on: November 14, 2024, 01:58:09 am »
The QA403 will output "only" around 20dBu which won't cut it for such measurments.

20 dBu is 22 volts peak-to-peak. so the QA403 is probably relying on integrated operational amplifiers with a 30 volt supply.  This matters because it means an external amplifier will have to use a higher voltage design making it non-trivial.

Quote
Has anyone run into a similar situation and if so, how did you resolved it?

I have, and I immediately designed and built a small amplifier.

Unfortunately high voltage operational amplifiers are not usually suitable for low distortion audio, so some kind of hybrid design will probably be required.
 

Online Someone

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Re: To all the audio guys out there.
« Reply #17 on: November 14, 2024, 06:20:13 am »
The QA403 will output "only" around 20dBu which won't cut it for such measurments.
20 dBu is 22 volts peak-to-peak. so the QA403 is probably relying on integrated operational amplifiers with a 30 volt supply.  This matters because it means an external amplifier will have to use a higher voltage design making it non-trivial.
30dBu/25Vrms/70Vp-p is achievable for a differential signal (as pro audio tends to) on 36V rails so those levels aren't out of this world or impossible to find in commercial products. However pro audio does get off into crazy prices for what it is.
 

Offline AVGresponding

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Re: To all the audio guys out there.
« Reply #18 on: November 14, 2024, 10:04:49 am »
nuqDaq yuch Dapol?
Addiction count: Agilent-AVO-BlackStar-Brymen-Chauvin Arnoux-Fluke-GenRad-Hameg-HP-Keithley-IsoTech-Mastech-Megger-Metrix-Micronta-Racal-RFL-Siglent-Solartron-Tektronix-Thurlby-Time Electronics-TTi-UniT
 
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Online Zero999

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Re: To all the audio guys out there.
« Reply #19 on: November 14, 2024, 11:14:13 am »

Has anyone run into a similar situation and if so, how did you resolved it?
By making this:


and this

(Attachment Link)
It appears as though you either forgot to upload the second attachment, or the forum lost it.

Regarding the first attachement. To change it from 125V to 48V, R4 and R10 need to be decreased from 47k to 18k, otherwise T1 and T6 will be off.
 

Offline David Hess

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Re: To all the audio guys out there.
« Reply #20 on: November 14, 2024, 01:47:16 pm »
The QA403 will output "only" around 20dBu which won't cut it for such measurments.

20 dBu is 22 volts peak-to-peak. so the QA403 is probably relying on integrated operational amplifiers with a 30 volt supply.  This matters because it means an external amplifier will have to use a higher voltage design making it non-trivial.
30dBu/25Vrms/70Vp-p is achievable for a differential signal (as pro audio tends to) on 36V rails so those levels aren't out of this world or impossible to find in commercial products. However pro audio does get off into crazy prices for what it is.

The specifications say they are using +/-12.5 volt supplies to generate a 22 volt peak-to-peak output (single ended) with 1.5 volts of headroom.  Modern 40 volt audio operational amplifiers running on +/-18 volt supplies under the same conditions could produce 33 volts peak-to-peak single ended, or 66 volts peak-to-peak differential, although driving even a 10 kilohm differential load would be questionable.  I am not sure that is a worthwhile improvement, and the limited output current may not be enough.  That leads me to a hybrid design with a discrete output to get enough performance with a much greater output level.

I would probably start with the design shown below, doubled and modified to make a differential amplifier, however I do not know anything about its distortion performance.  There are plenty of examples online of boosted operational amplifier designs.
« Last Edit: November 14, 2024, 01:49:42 pm by David Hess »
 

Online squadchannel

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Re: To all the audio guys out there.
« Reply #21 on: November 14, 2024, 02:03:43 pm »


Mark's videos are always interesting. :-+ The comments also makes me laugh. :-DD

Amplifier design, well $25,000 is ....  :wtf:
It's ok, it's for audiophiles. >:D
« Last Edit: November 14, 2024, 02:06:06 pm by squadchannel »
 

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Re: To all the audio guys out there.
« Reply #22 on: November 14, 2024, 09:36:40 pm »
The QA403 will output "only" around 20dBu which won't cut it for such measurments.
20 dBu is 22 volts peak-to-peak. so the QA403 is probably relying on integrated operational amplifiers with a 30 volt supply.  This matters because it means an external amplifier will have to use a higher voltage design making it non-trivial.
30dBu/25Vrms/70Vp-p is achievable for a differential signal (as pro audio tends to) on 36V rails so those levels aren't out of this world or impossible to find in commercial products. However pro audio does get off into crazy prices for what it is.
The specifications say they are using +/-12.5 volt supplies to generate a 22 volt peak-to-peak output (single ended) with 1.5 volts of headroom.  Modern 40 volt audio operational amplifiers running on +/-18 volt supplies under the same conditions could produce 33 volts peak-to-peak single ended, or 66 volts peak-to-peak differential, although driving even a 10 kilohm differential load would be questionable.  I am not sure that is a worthwhile improvement, and the limited output current may not be enough.  That leads me to a hybrid design with a discrete output to get enough performance with a much greater output level.

I would probably start with the design shown below, doubled and modified to make a differential amplifier, however I do not know anything about its distortion performance.  There are plenty of examples online of boosted operational amplifier designs.
You said (and I quoted) that higher than 30V is non-trivial. Yet there are numerous high current drive opamps with 36V supply rails (abs max 40V or higher) that can drive 10k easily, supported by both data sheet typical characteristics and real world uses. The 600Ω request from the OP is a little harder but paralleling operational amplifier outputs is considered pretty trivial in the audio world. Again, a quick perusal of some candidate parts readily finds solutions.

Not hard at all, while sticking with well defined distortion and dynamic performance.
 

Offline timeandfrequency

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Re: To all the audio guys out there.
« Reply #23 on: November 15, 2024, 12:16:17 pm »
Hello pope,

Because I could not find such a thing, I built one.
:-+

Maybe using a high voltage  :bullshit: opamp with power output (200 mA) ?
For the power supply, two 30 VA 2 x 24 VAC toroidal transformers + rectifiers + heavy filtering + fuses : https://www.amazon.fr/dp/B00MWRLX8W will lead at least to ± 75 VDC rails (low output load on a small transformer leads to +15 % output voltage).

Signal peak voltage will probably be able to scrape 65 Vp  (35,5 dBu). With this power opamp, asking for 20-26 dB of gain is not a problem even with tens of kHz of bandwidth.


Put the opamp on a huge heatsink. Keep all wires/tracks as short as possible.


PS : it would be so nice if the title of this thread reflects what we are discussing about
« Last Edit: November 15, 2024, 12:20:34 pm by timeandfrequency »
 

Online trobbins

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Re: To all the audio guys out there.
« Reply #24 on: November 15, 2024, 12:49:09 pm »
The OP appears to just want to measure headroom and simple signal stuff, not harmonics down to -120dB, so perhaps any form of battery powered linear amp with sufficient output signal level would seem fine - including an opamp, assuming it can drive the anticipated lowest loads at the max signal.  May need to use a few 12V batteries, or 9V batteries, and an opamp with say 30V or +/-15V supply, or multiple of batteries.  I have an LM1875 board for that purpose, with a suitable gain to just not clip with available level from my soundcard, but there would be many other simple boards on ebay etc.
 


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