Cohen/Transamp output stage

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
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JR.
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Re: Cohen/Transamp output stage

Post by JR. » Sat Jan 02, 2021 10:14 am

Gold wrote:
Fri Jan 01, 2021 1:25 pm
JR. wrote:
Thu Dec 31, 2020 10:26 am
One final caveat, null testing only reveals that two stems are different, not which is which.
In the case of a transformer input microphone preamp vs transformerless pre the one that has artifacts might be preferable in use.
I won't debate personal subjective preferences for inaccuracies, BUT on the subject of null testing, nulling an artifact rich d.u.t. vs a clean reference path allows you to isolate those differences (artifacts?) for closer inspection.

As already cautioned the null product from a less accurate phase and amplitude response will show up in the null residual also. Phase and amplitude related null errors will sound less abrasive than distortion differences when so isolated.

JR
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mediatechnology
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Re: Cohen/Transamp output stage

Post by mediatechnology » Sat Jan 02, 2021 4:44 pm

Phase and amplitude related null errors will sound less abrasive than distortion differences when so isolated.
The phase an amplitude differences will just sound like EQ.

Gold
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Re: Cohen/Transamp output stage

Post by Gold » Sun Jan 03, 2021 12:06 am

JR. wrote:
Sat Jan 02, 2021 10:14 am
I won't debate personal subjective preferences for inaccuracies, BUT on the subject of null testing, nulling an artifact rich d.u.t. vs a clean reference path allows you to isolate those differences (artifacts?)

I wasn’t looking for a debate. I think the most popular spot for a transformer in pro audio is as a step up transformer in a microphone preamp. There is probably a reason for it.

I’m not bashing measurements. I like to try to hear what I measure and measure what I hear. I want to learn to take better measurements and interpret the results.

I’m slowly getting a computer test set together. I struck out with the bit scope. I just got an Analog Discovery 2. I hope I like that better. I have REW with an interface. That’s been slow going. I don’t really trust what I’m seeing.

I got a used Microsoft Surface Pro3 and I’ve been liking Windows 10 touchscreen. I got Samplitude for it so I can record and play music and do null testing with that. So far I’ve been able to run Samplitude from the touchscreen without too much difficulty. Pretty cool.

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mediatechnology
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Re: Cohen/Transamp output stage

Post by mediatechnology » Mon Jan 04, 2021 7:16 am

Paul - Now that you've got a Windows machine get a Focusrite 2i2 (USB) and a licensed copy of AudioTester. Your total outlay will be about $200.

Gold
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Re: Cohen/Transamp output stage

Post by Gold » Mon Jan 04, 2021 10:58 am

mediatechnology wrote:
Mon Jan 04, 2021 7:16 am
Paul - Now that you've got a Windows machine get a Focusrite 2i2 (USB) and a licensed copy of AudioTester. Your total outlay will be about $200.
I have an Native Instruments interface. I could try Audio Tester. Maybe l’lI like it better than REW. I find having to check calibration every time really annoying. Either I adjust the level in the driver and loose it every time I close it. Or adjust the line trim and have to check that or glue it in place. I don’t see that changing with different software. I just got an Analog Disvovery 2. It has a hardware interface so I think I’ll like it better. I’ve already played with the software and I liked it better than REW. It’s a 14 bit scope so I’m hoping I can look at noise floors.

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Re: Cohen/Transamp output stage

Post by ilya » Mon Jan 04, 2021 11:12 am

AD2, while useful, is not that low noise (but ok for general purpose work).
You may check QuantAsylum QA401. This is the most affordable and versatile analyzer that I found (and use regularly).

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Re: Cohen/Transamp output stage

Post by Gold » Mon Jan 04, 2021 11:49 am

ilya wrote:
Mon Jan 04, 2021 11:12 am
AD2, while useful, is not that low noise (but ok for general purpose work).
You may check QuantAsylum QA401. This is the most affordable and versatile analyzer that I found (and use regularly).
The first QuantAsylum was unbalanced so pretty useless for pro audio. The ne one is balanced but uses a pair of BNC’s for the connection. It doesn’t inspire confidence. What a stupid choice. I use 5 pin XLR’s for all my builds. I’d have to stuff four BNC cables into an XLR housing or build a breakout box.

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Re: Cohen/Transamp output stage

Post by ilya » Mon Jan 04, 2021 11:56 am

Gold wrote:
Mon Jan 04, 2021 11:49 am
The first QuantAsylum was unbalanced so pretty useless for pro audio. The ne one is balanced but uses a pair of BNC’s for the connection. It doesn’t inspire confidence. What a stupid choice.
I'd argue that's not that stupid. First, you can easily make an XLR to double BNCs break-out. Second, there're other uses for the test gear where BNCs are actually very convenient. For example, I'm using QA to measure the noise of the SMPS and LDO PSUs. The whole chain is BNC connected: DUT->LN amplifier->QA.
Your applications may not call for BNCs, but I'd not call this solution stupid.

Gold
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Re: Cohen/Transamp output stage

Post by Gold » Mon Jan 04, 2021 12:26 pm

ilya wrote:
Mon Jan 04, 2021 11:56 am
I'd argue that's not that stupid. First, you can easily make an XLR to double BNCs break-out.
I use 5 pin XLR’s for stereo connections. I’d either have to stuff four BNC cables into an XLR housing or build a breakout box with XLR’s and binding posts. I would much rather see binding posts than a totally non standard connection scheme. If you work on unbalanced gear it’s fine.

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mediatechnology
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Re: Cohen/Transamp output stage

Post by mediatechnology » Tue Jan 05, 2021 6:12 am

Paul -

With AudioTester under Win 7 I don't lose level calibration.
I do have to be careful about bumping the input pots on the Focusrite but that's it.
Both AudioTester and the Focusrite support ASIO to avoid Windows sound.

You can download and run the full-function AudioTester: The unlicensed version simply stops measuring after a few minutes.
For $39.95 its not a huge outlay.

I never have liked the QA.
It seems designed for rapid Quality Assurance testing in a production environment.
I do understand that they now support sine and swept sine testing.

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