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Focus on SINAD Gives Vendors Hiding Space

restorer-john

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I have started putting disclosures in my reviews that pots and vary and performance I show may not be typical.

It does draw attention to the widespread use of poor tolerance dual gang pots from dubious manufacturers and that's a good thing. :)

TCA is using much higher spec Alps pots in his products and we know Alps can make pots with extremely close tracking gangs if you pay more. Back in the 1970s, they had guaranteed errors of 0.2dB available, so it's not a stretch to expect at least that now.

This is an Alps 4 gang inside a Pioneer Spec1 preamplifier, circa 1978:
1592869968130.jpeg
 

restorer-john

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Wow, it is great to see the spec and guarantee right on the pot!

Each resistor element on each substrate layer was individually laser trimmed to match. When you pull them apart, there are tiny laser cuts on each step in the material. Must have been an early application of laser trimming?

Unfortunately, people squirt Deoxit into those wonderful pots and well, you know what happens after a bath in Deoxit...
 
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DDF

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In my DIY I moved to using dual low inductance wirewound 10-turn linear pots with a vernier on each. Less handy (need to turn 2 dials) but rarely use more than the first two rotations so they were easy to use, they take tons of power and don't deform, are extremely precise and reliable (we used to use them in bread boarded laser driver circuits in the lab) and give infinite balance adjustment. Not for everyone but I love them.
 

pozz

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restorer-john

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I'd like to see a test of how a DAC handles sample rate changes. A recording of the output will show any noise signals on sample rate changes.

I have a D/A that makes an awful burst of noise if it gets a DD stream when it was previously humming along with 44.1/16. First few times I thought I'd killed my tweeters.
 

amirm

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I'd like to see a test of how a DAC handles sample rate changes. A recording of the output will show any noise signals on sample rate changes.
That is tricky to do as when the AP software is capturing measurements, it won't let me change anything. I would need to do that externally so not very convenient.
 

Theriverlethe

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That is tricky to do as when the AP software is capturing measurements, it won't let me change anything. I would need to do that externally so not very convenient.

Couldn’t you just check for any audible glitches by ear? It should be pretty obvious.
 

restorer-john

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Couldn’t you just check for any audible glitches by ear? It should be pretty obvious.

There's an awful lot of combinations when you think about it. It'd need to be automated maybe using the data recording function using an external device to generate various sampling rates in sequence and capturing the spikes in the audio.
 

KPH

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I have started putting disclosures in my reviews that pots and vary and performance I show may not be typical. If pot variation is an issue for someone, best approach is to get a DAC+Amp combo where the attenuation is digital.
What are the benefits of using an analog volume pot rather than using a digital one?
 

Daverz

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There's an awful lot of combinations when you think about it. It'd need to be automated maybe using the data recording function using an external device to generate various sampling rates in sequence and capturing the spikes in the audio.

Yeah, generate some silent audio files, say each 10 seconds long, at each of the sample rates up to 192000. Put them in a playlist. Hook up your ADC to the analog output and start recording. Start your playlist. You might want a reference tone at the beginning and end of your playlist to make sure it's playing back properly.
 

Theriverlethe

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There's an awful lot of combinations when you think about it. It'd need to be automated maybe using the data recording function using an external device to generate various sampling rates in sequence and capturing the spikes in the audio.

Maybe... Is it necessary to test every possible combination? Just a cursory switch between a couple sample rates and formats (eg., PCM, DSD, MQA) would reveal any obvious problems.
 

Blumlein 88

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It does draw attention to the widespread use of poor tolerance dual gang pots from dubious manufacturers and that's a good thing. :)

TCA is using much higher spec Alps pots in his products and we know Alps can make pots with extremely close tracking gangs if you pay more. Back in the 1970s, they had guaranteed errors of 0.2dB available, so it's not a stretch to expect at least that now.

This is an Alps 4 gang inside a Pioneer Spec1 preamplifier, circa 1978:
View attachment 70259
I've put those pots in some gear for other people, and also used a nearly identical (lower impedance) version in some passive volume controls. One of those items that just oozes quality when you handle it or use it. Performance backed up that feeling too.
 

Blumlein 88

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Yeah, generate some silent audio files, say each 10 seconds long, at each of the sample rates up to 192000. Put them in a playlist. Hook up your ADC to the analog output and start recording. Start your playlist. You might want a reference tone at the beginning and end of your playlist to make sure it's playing back properly.
You actually couldn't use silence. Some DAC's turn off on all zeros. Need at least a bit or two active. Dithered silence would work.
 

JohnYang1997

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Name me a 4-gang/2-gang pot with 2k-5kohm, matched to the bottom(-60db) for every unit and yet small enough to put in the chasis. Then we will use it.
The l30 uses same pot as a90 both for wolf and amir. It's simply a occasional case.
 

solderdude

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  • channel balance vs volume (see nasty result for L30 just posted by Wolf)
  • ground isolation (risk of ground loops)

Channel imbalance is tested, as Amir said but is only valid for THAT device. Could be worse, better, different for every pot. Smaller sized pots are usually worse. You can 'partly solve' the issue by having some gain settings on the amp.
Small sizes of devices (everyone wants small and cheap with top performance) has real world limits.
It is much easier to design a well performing (volpot) device when it is allowed to cost a lot more and the device can be a LOT bigger.

For the E30/L30 users the solution is extremely simple.
Set the volume control to a high position on the amp and adjust volume on the E30 or via the source.
Top level performance in small cheap devices !

ground isolation (very, very rare !) can simply be tested with an Ohm meter.
Injecting a specific current is a totally different ballgame. This needs specialized equipment and even when a device doesn't show much troubles on the test bench with specific 'test signals' one throws at it you can still be bothered by audible ground-loops in home situations.
These loop currents can take all kinds of paths and may actually manifest themselves in another device as the one tested.

Using proper grounded wall sockets, decent interlinks etc. should give less problems.
Trouble shooting groundloops and making cheap solutions for it generally isn't easy.

So yes, one can make a test for it but may not be conclusive because real world situations may differ a lot from home situations.
 

JohnYang1997

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Just for clarification. It's not an excuse for having poor channel imbalance performance.
https://www.audiosciencereview.com/...udio-hpa-1-headphone-amp-review.10416/page-13
Earlier this year, I was proud that we got the channel imbalance down.(at that time we had 3-5 machines all having -50db to -60db of -1db range) I also specifically added -9db setting to improve usability. Of course I care about these things because I was a user of many many products. I listen at very low volume so these are my biggest problems as well as noise floor. Try plug a super sensitive iem to any THX based amp it will be noisy especially sp200(loud as fuck). These are the issue I used to have with many devices that I have to fix. The low distortion thing is just simply be able to compete with the products on the market. Who cares if you have -9db setting or not when you get 0.00x% thd+n only? How much praise was to A50 and fiio K3pro? Minimal. No one buys A50. K3pro? No one asked about it. They both have very good JRC volume control chip inside. But they are simply noisy and give a glare in the highs, shallow and glary.
I don't want to say anything more. Lastly, both Amir and Wolf measure channel imbalance basically from day 1. And no one was hiding about these issues.
 

ShiZo

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I kind of agree, but only on sinad not meaning everything. It takes into account a noise floor that cant be heard. For instance, I'd take a dac with a higher noise floor if it had lower distortion products vs the device with higher sinad but higher spikes.

Multitest is really useful because it shows distortion while playing multiple tones, like music.
 
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