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Universal Buffer achieving -140 dBc (0.00001 %) THD
Universal Buffer achieving -140 dBc (0.00001 %) THD
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Old 20th February 2020, 02:00 PM   #291
00940 is offline 00940  Belgium
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Oh, I certainly agree with your point. I actually suggested such a measurement in post 163

I meant 10K Ohms. But point taken on the follower case, the measurements in that link are only done at a gain of 3, at which point there is virtually no degradation with a 10k impedance mismatch. The follower case is indeed much worse.
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Old 21st February 2020, 05:48 PM   #292
mocenigo is offline mocenigo  Germany
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Originally Posted by tomchr View Post
If all your inputs are XLR or all your inputs are RCA, you can certainly do that. However, once you have a mix of XLR and RCA inputs, you have to be careful with the connection to XLR Pin 1 from the RCA shell. You could make it work with a three-pole switch, though.
Or with properly programmed relays. I am all for you to sell as many boards as you can, more people need to hear how they “do not” sound. But a full pre with XLR and SE ins and outs can be done “deluxe” with two boards and an attenuator in the middle.

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Old 23rd February 2020, 01:19 AM   #293
tomchr is offline tomchr  Canada
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Originally Posted by sawyers View Post
Yes - I'm very aware of Self's measurements. But common mode distortion has been known about for way longer than Self re-publicising it.
True. It's also been around since before the LM4562/LME49720 was released. However, the discovery of common-mode distortion does not change the fact that the LM4562/LME49720 does not exhibit much common-mode distortion. You can see that from Fig. 4.24 in the EE Times article that 00940 linked to. I've attached the figure to save you the trouble of clicking the link and scrolling.

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Originally Posted by sawyers View Post
and not just under 10kHz or 10k-ohms (not sure what your 10k refers to).
10 kΩ.

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Originally Posted by sawyers View Post
For an LM4562 at 10kHz, 10Vrms and 10k-ohms source resistance the distortion of an LM4562 follower is nearly 0.005%.
Douglas Self measured 0.0004% at 10 V RMS output with 10 kΩ in series with the non-inverting input. The THD+N trace for 10 kΩ is line-on-line with the trace for 0 Ω in his figure.

I'll be measuring my upcoming buffer for the Purifi 1ET400A and Hypex NC500 within the next two weeks. I plan to measure more on the Universal Buffer at that time. Unfortunately, measuring these things at the precision levels I'm dealing with is not exactly plug-n-play. If it was, I would have provided the measurements long ago. Also, please note that I have many tasks and priorities completing for my time.

Tom
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Old 23rd February 2020, 02:49 AM   #294
drpro is offline drpro  United States
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Universal Buffer achieving -140 dBc (0.00001 %) THD
Tom, a question. What type of power supply do you recommend? Would Jan's Silent Switcher be a good choice?
I built a a pair of Pass F4 amps and have been running them bridge mostly and to convert from a SE preamp, I am using a pair of Jensen transformers. No doubt they change the color of the sound.
I would like to try your UB.
Thanks
David
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Old 23rd February 2020, 04:36 AM   #295
tomchr is offline tomchr  Canada
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The SilentSwitcher would be excellent. The UB doesn't need much of a supply. The RECOM AC/DC switching brick mentioned earlier (RAC20 or RAC10 I think) would work too.

±15 V is best. Plan for 100 mA per UB board.

Tom
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Old 23rd February 2020, 02:34 PM   #296
00940 is offline 00940  Belgium
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@Tom: the 0.005% quoted by Craig comes from further measurements by Self on the lm4562 in voltage follower mode. They can be found in his crossover book, some sections of which are free on google books: The Design of Active Crossovers - Douglas Self - Google Livres
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Old 23rd February 2020, 06:00 PM   #297
tomchr is offline tomchr  Canada
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Ah. OK.

If I recall correctly, the list of requested measurements is up to:
  • THD+N vs gain
  • THD+N vs load impedance
  • THD+N vs source impedance
  • Channel separation vs load impedance
  • IMD vs output level

That's 12-16 hours worth of work. I hope it will be worth it...

Tom
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