You are absolutely right about this.First, let's be sure that we're all using the same pin numbering associated with their normal uses for the XLR connection. There are a few instances where your pin numbering doesn't seem to align. That could be a fundamental issue, or it could just be typos.
As an example, when using SE inputs on some amps, you would normally short pins 1 and 3 vs. pins 1 and 2. Pin 3 usually carries the inverted signal, not pin 2.
Depending on your wiring, that could be part of your issue. Usually the "hot" pin of the RCA for an SE input would be tied to pin 2 of the XLR. If you are actually shorting Pin 2 to ground with that wiring....
I had the chance to look further and indeed I named the wrong xlr pin numbers. But checking IRL turns out I used all the right connections.
GND from the XLR's is tied to GND from power supply board. These boards also have Earth connection with the thermistor inbetween.
So, checking functionality, it is indeed pin3 that gets shorted to pin1 (or AGND), pin2 carries the +sig.
I still have the feeling the unbalanced input source is a little less revealing in sound reproduction, it could offcourse be a 'lesser quality' of what I thought to be a high-end DAC (which is a Chord Qutest in the case). OR:
INPUT LEVELLING in comb with Aleph P output volume control (as per schematic: 8-bit)
I can't get this volume control right. Measuring the output impedance, it is really low just until I reach the higher volume settings, then it goes up to over 1K and sound starts to distort (on the Aleph5). According to Mr. Pass the output volume should be as high as possible, with internal gain as low as possible. Because volume step 1 was already too loud for the loudest source, I had to reset things. Or I did something wrong with the volume control.
How do you guys do that input levelling and low-level listening?
I have only 3 sources:
- A CD-player with fixed balanced outputs, non configurable. I love this player a lot, it has long be (and may still be) my best source available. Marantz UD7007 with the upgraded audio circuitry on top of it's very good video features for bluray discs (I don't use video/hdmi).
- Just recently a Pass Xono-based phono preamp that has more/some XP-17 functionality (RSTaudio). Balanced output is configurable (by gain), but is commanded by the cartridge used. I have a low output MC cartridge, so full gain @ 76db is preferred. (this unit is astonishing!)
- the above-mentioned Chord DAC, which is single-ended and fed with Roon music.
The CD-player is by far the loudest. The Xono in highest gain setting does come close, but not there yet. Then the Chord dac is much more quiet due to it's single-endedness. It has configurable output to 3V, still more quiet then balanced sources.
So in practice:
The CD and Xono play too loud for late-evening listening on volumeStep 1. It can go loud enough for these times it needs to.
The DAC plays not loud enough for these times it needs to. And when half-loud playing there is already a rather large output impedance presented to Aleph5.
For now, I have much better results controlling volume (a little better sound-wise) by setting gain as low as possible (the input dip's), and turning down the internal gain with the 2K trimpot untill the CD-player is still way loud on (almost) highest volume setting. The internal gain has always been at the highest setting.
Offcourse, I still have the issue of input level differences. Could it be a solution to add a quality inverting stage to the single-ended source, so it becomes a balanced source?
Or, alternatively, switch the input gain DIP's together with source selection (involves bypassing the DIPs by relay)?
For now, I had laying around a cheap tube preamp with one input and high gain, which I placed inbetween the DAC and Preamp input, to match the level of the xono or cd.
How come this CD-player has such high output level?
Thank you for insights.
I'm still waiting for mine from https://www.kk-pcb.net (guy from Croatia) Way back I've built Aleph 4 and got my PCB from this guy as well. They were excellent. I'm still wandering if Aleph 5 has enough base as my Aleph 4 were (mono blocks)