B1 Buffer Preamp

I had a chance to measure the cross talk on my B1 buffer.

Using a 2.4 VRMS tone in one channel (1 kHz tone), I was getting some leakage into the other channel. It was about 64dB down. Is this the same ball park as what others have found?

I am not complaining since that is a small number. I was just wondering.
 
Are you measuring between the stereo halves or between the selectable inputs?

64dB between channels is a bit low, that's a figure one would tend to see for the treble end of the frequency range where capacitances become dominant.

64dB is OK between the stereo halves. Here, because of the closeness of all the components, capacitive and magnetic coupling is more prominent.
 
I was not clear.

It was between the stereo halves (61 dB down) and also between the pairs of boards (I have a 6 channel version using 3 stereo boards). Between the separate boards the cross talk was 64 dB down. I should also mention that between the 3 stereo boards, the three stereo boards share a common wall wart and a a common 6 channel stepped attenuator (rotary switch)

I now realize that I also forgot to short the input on the "unused half" or the "unused board" when I measured. I will repeat later on. Thanks.
 
Hello,

I have finished my build of my B1 .

I was wondering if anyone know what causing my b1 to hum.

May it be the 24Vdc wallwart thats causing the problem? I do hope so...
It does sound like a ground loop ( low frequency hum that gets higher with volume turned up ) - on both channels.

Should I try batteries?
 
I was not clear.

It was between the stereo halves (61 dB down) and also between the pairs of boards (I have a 6 channel version using 3 stereo boards). Between the separate boards the cross talk was 64 dB down. I should also mention that between the 3 stereo boards, the three stereo boards share a common wall wart and a a common 6 channel stepped attenuator (rotary switch)

I now realize that I also forgot to short the input on the "unused half" or the "unused board" when I measured. I will repeat later on. Thanks.

I made a 6-channel buffer (three boards on a common power supply - wall wart).

Just as a follow up, I was able to measure the crosstalk between the channels within a single board and also between boards (when the unused inputs were properly shorted). The crosstalk between channels within the same board was about 64 dB down (which not as good as what Nelson Pass measured on his production model). The crosstalk between channels on different boards was more than 89 dB down (the instrumentation can not reliably measure smaller amounts).

I am okay with the crosstalk performance. What really made me happy was when I measured the voltages with just the inputs shorted (no signal). The DC voltage was unmeasurable (meaning less than 0.1 mV). When I measured the AC RMS voltage it was about 0.1 mV. So there is little or no hum or hiss.

Overall, I am quite pleased with this project and very grateful for Nelson Pass sharing this with the DIY community.
 
What really made me happy was when I measured the voltages with just the inputs shorted (no signal). The DC voltage was unmeasurable (meaning less than 0.1 mV).
The B1 is AC coupled at Input and Output.
It cannot have an output offset unless the output capacitor is broken.

Hum+Noise measuring <0.1mVac is more likely to be a measurement error/artefact.
From a Preamp/Buffer passing a line level signal of 200mVac to 500mVac, I'd expect <0.01mVac and maybe as much as 20dB below that.
 
The B1 is AC coupled at Input and Output.
It cannot have an output offset unless the output capacitor is broken.

Hum+Noise measuring <0.1mVac is more likely to be a measurement error/artefact.
From a Preamp/Buffer passing a line level signal of 200mVac to 500mVac, I'd expect <0.01mVac and maybe as much as 20dB below that.

I agree. The meter I am using will not allow AC measures below 0.1 mV. Additionally, there are a number of devices near the bench which might be introducing some electrical noise probably through the cabling.

I always worry about the noise, hiss and hum since I use high efficiency horns. The smallest problems can be easily audible.
 
Impedance matching

Dear all

this question might be asked more than once but the thread is very long and I couldn't locate it.

I want to do the following:

phono stage --> B1 buffer --> amplifier

I can set the gain of the phono stage in order to have an output in the range 1-2Vrms, currently the phono stage doesn't have an output buffer and can drive loads >=10KOhms. What pot rating should I use?

Thanks for your help
Pierre
 
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