Thanks for that Simon - neutrality is certainly what I'm chasing. One board will be used for home studio monitor levels for example.
And I'm running ncores too - currently with a pass labs X2 - so it sounds like a great match. Just got to stop fretting about perfect casing and implementation and just finish the BPPBP, worry about the rest later!
EDIT: Did you mean to say something else in the post above?
For what it is worth, I had a Mark Levinson 320S, but was not completely happy with the sound, so I was thinking of making something myself.
But then came the BPBP. It gave me all I was looking for, a fantastic amount of space without a hint of being sharp in the high end.
You can keep following each individual instrument, no matter how much the music grows in complexity.
In many recordings I can hear people talking in the background, cars driving by etc, just to show how revealing the sound is without getting fatigue of listening.
It is simply the most musical preamp I have ever heard, and I heard a lot.
Hans
I was wondering what potentiometer quality would bring on this preamp. Would you just go for for more expensive or the design make it not as important?
I usually buy TKD, Goldpoint, AMB relay ladder type and LDR3x.
Thanks
Do
I usually buy TKD, Goldpoint, AMB relay ladder type and LDR3x.
Thanks
Do
OK! I have read about your attenuator but I must say I'm a bit lost on the total solution level. How to connected, which parts are needed etc...
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If you read Bruno Putzey's white paper that introduces his design for this pre-amp, he specifically designed the volume stage so that all fancy pots and attenuators can be forgotten about (because they all have problems - hence their differences in sound).
No audio signal passes through the pot at all - it only serves to provide a potential divider (?) in the feedback circuit and so adjusts the final output indirectly.
It's not an attenuator in the BPPBP - there is no audio signal attenuation other than via adjusting the feedback of one of the stages. That is why Bruno made a point of choosing a very very cheap pot and for it still to measure perfectly and sound superb (except he made a mistake with his type of pot and didn't notice until after he'd made the measurements... - he talks about this in the white paper too).
But the tracking of cheap pots are usually pretty bad and thus it could mean different potential from left and right channel, no? Or slightly different?
Thanks
Do
Thanks
Do
(click on the attachment) But also go to Hans' new thread to ask questions about his board and remote control etc : http://www.diyaudio.com/forums/analog-line-level/291226-remote-control-bpbp.html
Stereo tracking? Not 100% sure to be honest but no-one has complained yet! I wouldn't have thought that the track laying process of a 2 channel pot is really going to vary between those on the same production line. It's a mechanical process afterall. The track itself won't be precisely linear but that is not of concern here because any non-linearity is cancelled by design.
Bruno only stated "cheap 9mm “car stereo” pot" (which is probably why he accidently used a log pot instead of the linear one it requires - because it was an audio pot which are log).
A very, very good stereo pot will track within 1dB between channels in the mid position, and even worse at the extremes.
A more down to earth pot will track 1.5 to 2 dB in the mid position and also worse than that at the extremes.
Because most music will be played somewhere between -20dB and -30db, you will already be pretty close to the extreme, giving a noticeable difference in loudness between stereo channels.
Easy to check with a signal generator and a voltmeter.
Hans
Output within a few mV on mine right across the pot range when sweeping white noise. Essentially flat. I'm using the more expensive conductive film pot though.
I´m a bit puzzled how you can measure white noise within a few mV.
To measure the tracking between channels you need a rock stable signal of between 400Hz and 1Khz.
And to calculate the tracking you need to now the magnitude of the input signal and of both channels output.
Like in 2 Volt, left out 1.06Volt, right out 0.95 Volt.
Tracking is now: 20*log(1.06/0.95)=0.95dB tracking @-6dB volume setting, and so on and on for -12,-18 -24 and -30dB.
Hans
Hello Tfboy, in case your are going to order a smaller quote, I'm in for a 2nd one. Would someone be so kind, to tell me which input voltage (ac powersupply) is usefull without overheating the regs?
I didn't check the tracking per se, just measured the output voltages when provided with a mono signal via a splitter. Think the signal generator was an HP, not my bit of kit, my mate Greg did it. He's a lab rat for Siemens medical device's. Im sure it was done correctly.