I'd look at the Modulus-86 as well. It provides vastly better performance than the 'naked' LM3886. On the surface, it looks much more expensive, but in the grand scheme of things (i.e. by the time you include chassis, heat sinks, power supply, etc.) going with the Modulus-86 rather than the LM3886DR adds less than 10% to the project cost.
An ideal buffer is an ideal amplifier with a gain of 1 V/V (0 dB). I.e. the output voltage is a true copy of the input voltage and that's it. An ideal (voltage) amplifier has infinite input impedance and zero output impedance. It doesn't match the impedances. In fact, it almost does the opposite. However, a buffer makes it possible for a non-ideal source (i.e. a source with a high output impedance) to drive a low-impedance load (some volume pots fit this category). A well-designed buffer can also drive a long cable without degrading the signal.
Yep. That's what I have in mind.
If you want to support both differential and single-ended sources, I'd recommend:
Universal Buffer - Input Selector - Volume Control - Universal Buffer.
Tom
Hi Tom, all the best for the new year!
I'd be grateful if you'd specify whether the balanced output of the Universal Buffer is a floating output, where either side of the output can be tied to any reference voltage (within some limit of voltage difference to the Universal Buffer's own reference) or whether it is a two-phase output, each phase referred to the Universal Buffer's own voltage reference.
I'd be grateful if you'd specify whether the balanced output of the Universal Buffer is a floating output, where either side of the output can be tied to any reference voltage (within some limit of voltage difference to the Universal Buffer's own reference) or whether it is a two-phase output, each phase referred to the Universal Buffer's own voltage reference.
Hi Tom,
When sandwiching Universal Buffer - Input Selector - Volume Control - Universal Buffer, what would be the ideal potentiometer impedance (10K, 20K, 25K, etc)? I'm guessing the lower possible the better, right?
I have a preamplifier which consist of the following parts :
AMB α10 backplane + LCDuino-1 display I/O processor
AMB δ1 relay-based R-2R stereo attenuator
AMB δ2 relay-based stereo input/output selector
Fab's USSPA gain modules set to a gain of 3
If I wanted one of the output to be balanced, I would use one of your universal buffer. How would I need to set it up? I certainly do not want to add any gain to what I already have. Would you recommend feeding it the same +/-15Vdc supply used by the gain modules or its separate supply?
And for one of the inputs to be balanced to unbalanced, add another buffer with unity gain?
Thanks & Happy New Year!
Do
When sandwiching Universal Buffer - Input Selector - Volume Control - Universal Buffer, what would be the ideal potentiometer impedance (10K, 20K, 25K, etc)? I'm guessing the lower possible the better, right?
I have a preamplifier which consist of the following parts :
AMB α10 backplane + LCDuino-1 display I/O processor
AMB δ1 relay-based R-2R stereo attenuator
AMB δ2 relay-based stereo input/output selector
Fab's USSPA gain modules set to a gain of 3
If I wanted one of the output to be balanced, I would use one of your universal buffer. How would I need to set it up? I certainly do not want to add any gain to what I already have. Would you recommend feeding it the same +/-15Vdc supply used by the gain modules or its separate supply?
And for one of the inputs to be balanced to unbalanced, add another buffer with unity gain?
Thanks & Happy New Year!
Do
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Hi Tom,
Looks fantastic! Chapeau!
One question: why is the fundamental in the first graph shown at -60dBA? At 2V level I would expect it at +6?
Jan
“Measuring the -140 dB THD of the Universal Buffer is a significant challenge, in particular as the analyzer section of the Audio Precision APx525 analyzer is only good to -125 dB and its source to -112 dB. Thus, I use a precision oscillator with a THD below -140 dB and a notch filter to attenuate the fundamental frequency. The resulting measurement of the distortion residual is shown below. As shown, the third harmonic is just below -140 dB at 2 V RMS output voltage.”
Best,
Anand.
Thanks. You too!
It is not a floating output. The common-mode voltage of the output is set to the ground reference of the circuit.
Lower is better. I'd use a 5 kΩ if you can find one. Otherwise a 10 kΩ one.
I'd attach the Universal Buffer input to the output of the volume control or to any single-ended output of the preamp. That will give you a differential output (and an extra single-ended output should you need one).
Yep. The PSRR of the Universal Buffer is on the order of 120-140 dB. It does need to be a regulated supply, but the Buffer can share with others.
Correct.
I would not recommend the Universal Buffer as a headphone amp. That's not to say it can't drive headphones. It should drive a 300 Ω headphone just fine, but I doubt the performance would be up to my standards with the lower impedance phones.
If you'd like a headphone amp, I suggest looking at my HP-2.
I had the same reaction when I reread my HP-2 page, so I added annotation to the plot. Looks like I need to do that for the Universal Buffer plot as well. I suspect many just scan the pictures. I know I do...
Tom
I have Tom's Mod86 power amps that replaced XY3886 eBay PCB's so I got to back to back listening, and I can tell you that the difference is light years. The Mod86 is far superior in every way, more detail tighter bass, etc etc.
I also have the NP B1 and it does not have the Volume pot between buffers. The pot is before the buffer.
Hi Tom,
An input selector would be very welcome. From the above, am I correct in understanding that, if you were to design one, you would design it to select one balanced input from however many the selector will take, and route it to the input of just one Universal Buffer?
An input selector would be very welcome. From the above, am I correct in understanding that, if you were to design one, you would design it to select one balanced input from however many the selector will take, and route it to the input of just one Universal Buffer?
Tom
Congratulations on this, it looks like a superb product. I think there will be a lot of people who would like to use it as a preamp, so now we need you to bring out an input selector and volume control with equally good specs ! I predict that a modular preamp such as you would then be able to offer would be a big hit
Congratulations on this, it looks like a superb product. I think there will be a lot of people who would like to use it as a preamp, so now we need you to bring out an input selector and volume control with equally good specs ! I predict that a modular preamp such as you would then be able to offer would be a big hit
Hi Tom,
If you decide to make the volume PCB and source selector, could you also add footprint to accommodate TKD, such as the 2CP-601 series? I always find the tracking to be better with them.
TKD Potentiometer 10K 2CP-601 Series 6R25 Log Taper
Thanks
Do
If you decide to make the volume PCB and source selector, could you also add footprint to accommodate TKD, such as the 2CP-601 series? I always find the tracking to be better with them.
TKD Potentiometer 10K 2CP-601 Series 6R25 Log Taper
Thanks
Do
Tom
I’d be interested to know if you have any thoughts on this volume control:
LDR V25 Preamp Controller | Tortuga Audio
A digital microprocessor is apparently used to perform error correction on each LDR to compensate for their non-linearity and mismatching.
I’d be interested to know if you have any thoughts on this volume control:
LDR V25 Preamp Controller | Tortuga Audio
A digital microprocessor is apparently used to perform error correction on each LDR to compensate for their non-linearity and mismatching.
For PSU I was thinking to use one of Jan's SilentSwitchers. Seems a perfect match to me
Yep. Those would be good candidates for a power supply.
I can certainly consider that.
The micro controller compensates for tracking errors and (possibly) any deviations from the logarithmic response. It does not (and cannot) compensate for any nonlinearities caused by the resistor material itself. You can see my measurements of a Tortuga LDR3 LDR-based volume control here: Review: Tortuga Audio LDR3 - LDR "passive preamp" – Neurochrome
I don't think I need to reiterate my opinion on it here. The measurements should speak for themselves.
Tom
Hi Tom,
Can the SE and Differential outputs be used at the same time?
Thank you
Yes they can.
Also: Now the volume discount (i.e. the price breaks at QTY = 3, 5, 10) now show correctly on the Cart page of my website. The prices have always been correct on check-out.
Tom