Author Topic: To all the audio guys out there.  (Read 2069 times)

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Offline timeandfrequency

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Re: To all the audio guys out there.
« Reply #25 on: November 15, 2024, 01:44:16 pm »
The audio analyser pope owns already outputs + 20 dBu (11 Vpeak) which can be generated by using ± 15 VDC rails.

As pope needs signals with higher values, a low distortion PA (<> Class C) needs voltage rails above the 15 VDC mark.

With ± 22 VDC (max value for most opamps), 17 Vpeak (24 dBu) can be obtained, best case. That is just 4 dB more that the analyser.

For more output voltage, amplifiers that accept higher voltage rails are required.
By pushing the LM1875 that trobbins suggested to its' limits (so 60 VDC or ± 30 VDC supply), 24 Vpeak (27 dBu) should be possible : a 7dB improvement.
But pushing a PA to its' limits always raises distortion.
 

Online Messtechniker

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Re: To all the audio guys out there.
« Reply #26 on: November 15, 2024, 07:09:57 pm »
I also built this one using an OPA 551 PA
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 djsb

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Re: To all the audio guys out there.
« Reply #27 on: November 15, 2024, 07:20:37 pm »
They have a transducer driver

https://quantasylum.com/collections/frontpage/products/qa461-transducer-driver

The forum is probably the place to ask about your requirements

https://forum.quantasylum.com/

I have a QA403 but have not had a chance to use it yet. It's a nice piece of kit.
David
Hertfordshire, UK
University Electronics Technician, London, PIC16/18, CCS PCM C, Arduino UNO, NANO,ESP32, KiCad V8+, Altium Designer 21.4.1, Alibre Design Expert 28 & FreeCAD beginner. LPKF S103,S62 PCB router Operator, Electronics instructor. Credited KiCad French to English translator
 
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Offline David Hess

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Re: To all the audio guys out there.
« Reply #28 on: November 15, 2024, 08:09:18 pm »
That OPA551/OPA552 is a good option for the simplest design with good performance.  I wonder if a hybrid design using something like an OPA1611 could do better.  Noise would be 1/3rd, and distortion potentially up to -136dB instead of -106dB, which I think points out the problem of combining the best audio performance in a high voltage and current part.

It is difficult to evaluate the LM1875 because the datasheet only discusses performance with 4 and 8 ohm loads.  I have used parts like that within the feedback loop of a better amplifier for lower distortion and noise, but the frequency compensation can be difficult.  Better is to use a power current feedback amplifier, but I do not know of any with higher voltage ratings, leaving discrete designs like the one I posted.
 

Offline The Soulman

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Re: To all the audio guys out there.
« Reply #29 on: November 15, 2024, 08:19:53 pm »
Easier to implement is a dedicated line-driver ic such as:
https://thatcorp.com/that-1606-1646-balanced-line-driver-ics/
 

Online popeTopic starter

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Re: To all the audio guys out there.
« Reply #30 on: November 15, 2024, 08:44:11 pm »
Thank you all for the replies. A lot of valuable information to digest once I find some time.

I have some 1646s laying around.

I hadn't thought of the qa461 but it seems to be unbalanced, right?

 

Offline trobbins

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Re: To all the audio guys out there.
« Reply #31 on: November 15, 2024, 10:24:00 pm »
Another option is an audio signal step up transformer.  Not sure about your software's capabilities, but with REW you could do a loopback calibration curve to normalise the amplitude response, and if you really wanted to lower harmonic levels of your test setup then you could null the loop harmonics out by modifying the harmonic levels/phases of the signal generator.
 

Offline The Soulman

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Re: To all the audio guys out there.
« Reply #32 on: November 15, 2024, 11:22:58 pm »
Thank you all for the replies. A lot of valuable information to digest once I find some time.

I have some 1646s laying around.

I hadn't thought of the qa461 but it seems to be unbalanced, right?

I couldn't find much if any specifications on the qa461 apart from "up to 1 Watts" that may not even give you enough output voltage and highly likely the speaker negative output terminal is connected to common ground as it is only designed to drive transducers.

Instead you could have a look at the commercial audio manufacturers that make unbalanced to balanced audio converters such as:
https://www.sonifex.co.uk/redbox/rbul1_ld.shtml
24dBu output is fairly common, 28dBu or anything above not so much.

 

Online popeTopic starter

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Re: To all the audio guys out there.
« Reply #33 on: November 16, 2024, 10:37:49 am »
Thank you all for the replies. A lot of valuable information to digest once I find some time.

I have some 1646s laying around.

I hadn't thought of the qa461 but it seems to be unbalanced, right?

I couldn't find much if any specifications on the qa461 apart from "up to 1 Watts" that may not even give you enough output voltage and highly likely the speaker negative output terminal is connected to common ground as it is only designed to drive transducers.

Instead you could have a look at the commercial audio manufacturers that make unbalanced to balanced audio converters such as:
https://www.sonifex.co.uk/redbox/rbul1_ld.shtml
24dBu output is fairly common, 28dBu or anything above not so much.

Thanks for that. I remember coming across this device many years ago.

The RB UL2 is a bit tempting as it's reasonably priced but I think the specs are not up to the task.

The +28dBu output is really just a ballpark figure. At this point, anything >= +25dBu should suffice, I suppose. I will only use it a handful of times per year.
 


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