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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

BPPBP - Bruno Putzey's Purist Balanced Preamp (well a balanced volume control really)
BPPBP - Bruno Putzey's Purist Balanced Preamp (well a balanced volume control really)
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Old 1st January 2019, 10:11 PM   #751
NATDBERG is offline NATDBERG  United Kingdom
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Join Date: Nov 2006
Quote:
Originally Posted by sq225917 View Post
Nat, enlarge those holes or redo the back panel, that tension in the back panel pcb is trouble down the line.
You're probably right !

I intend on making another (I've corrected the CAD) to make two pre-amps so the other will be ok.

I think I'd have to cut the panel in two to remove the extra 2 mm from between those connectors else widening holes will have to be done to all holes to one side of the mistake. I'll make a jig for a multi-tool to keep it straight and bond something to the rear after..
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Old 3rd January 2019, 05:33 PM   #752
sq225917 is offline sq225917  United Kingdom
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Send a message via MSN to sq225917 BPPBP - Bruno Putzey's Purist Balanced Preamp (well a balanced volume control really)
I bypassed the 3 pin power input and diodes today and wired my dc supply directly to the caps. Worked perfectly.

Now I'm totally baffled, dc wouldn't work into the 3 pin plug, but a.c. did. WTH?
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Old 4th January 2019, 02:40 PM   #753
Martant is offline Martant  Finland
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Originally Posted by stephengrenfell View Post
- - - -
I don't need the other 9 PCBs and they might be useful to someone. Therefore I am offering them at 3euro each plus postage (using standard letter post only).
- - - -
Hi all BPPBP preamp builders,

I wonder if stephengrenfell or somebody else has still any leftover PCBs for sale. If so, please contact me by personal message.

Regards
Martti
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Old 10th January 2019, 05:38 PM   #754
sq225917 is offline sq225917  United Kingdom
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Turns out my distortion was from choking the dc voltage to 14.3 volts. 15.2v and it's gone.
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Old 22nd January 2019, 08:02 PM   #755
maartn is offline maartn  Netherlands
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One more question on parts: the BOM I used lists U3 as TI LM4562MA/NOPB (same as U1, 2, 6, 7) with the remark: "TL072 (as originally proposed) has a DC offset that is way too large and is adding offset of its own."

Is that correct? Is LM4562MA/NOPB the right part to use for U3?
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Old 22nd January 2019, 08:26 PM   #756
misterdog is offline misterdog  United Kingdom
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yes,
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Old 10th February 2019, 07:43 PM   #757
maartn is offline maartn  Netherlands
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I desoldered the oversized caps and put right ones in... This pre-amp does sound really good!

One thing I noticed is quite a loud "pop" at shutdown. I measured at the output and there is a 600 mV negative spike on pin 2 (see attached screenshot). I had not expected that, because I thought relay K3 is there to prevent this kind of thing (see attached detail of the circuit).

Do other people also see/hear this behaviour, or is there something wrong with my build?
Attached Images
File Type: jpg IMG_2931.jpg (693.7 KB, 234 views)
File Type: jpg IMG_2932.jpg (884.6 KB, 236 views)
File Type: png BPBP circuit.png (16.2 KB, 230 views)
File Type: png BPBP shutdown measurements.png (194.1 KB, 223 views)
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Old 10th February 2019, 09:09 PM   #758
Hans Polak is offline Hans Polak  Netherlands
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Join Date: Mar 2005
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Quote:
Originally Posted by maartn View Post
I desoldered the oversized caps and put right ones in... This pre-amp does sound really good!

One thing I noticed is quite a loud "pop" at shutdown. I measured at the output and there is a 600 mV negative spike on pin 2 (see attached screenshot). I had not expected that, because I thought relay K3 is there to prevent this kind of thing (see attached detail of the circuit).

Do other people also see/hear this behaviour, or is there something wrong with my build?
Plop on both channels or just one channel ?
And why is the red channel, the power supply, only 8 volt, assuming a 10:1 probe.
I doubt whether your reley is working properly given the timescale that you are showing.

Hans

Last edited by Hans Polak; 10th February 2019 at 09:14 PM.
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Old 11th February 2019, 06:06 PM   #759
maartn is offline maartn  Netherlands
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Hi Hans, it is on both channels. The voltage axis of the red channel is displayed on the right of the chart: 16 volt.

I do hear the relay click and checked with a multimeter just now: the resistance between pins 2 and 3 is ~2 ohms at power off, and ~46 ohms at power on. Not sure if these values are as they should be, but it does look like the relay is at least operating. I will try coming weekend to measure the timing of the relay switching, relative to the power down. Any other suggestions are welcome.
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Old 11th February 2019, 06:41 PM   #760
Hans Polak is offline Hans Polak  Netherlands
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Originally Posted by maartn View Post
Hi Hans, it is on both channels. The voltage axis of the red channel is displayed on the right of the chart: 16 volt.

I do hear the relay click and checked with a multimeter just now: the resistance between pins 2 and 3 is ~2 ohms at power off, and ~46 ohms at power on. Not sure if these values are as they should be, but it does look like the relay is at least operating. I will try coming weekend to measure the timing of the relay switching, relative to the power down. Any other suggestions are welcome.
I see your problem.
Instead of +/- 12Volt you are using+/-16 volt. Nothing wrong with that but the zener should then be 26 volt instead of 18 volt. The transistor is now driven into hard saturation with a base current of ca 6mA instead of 2mA.
Instead of the zener, you could change the 2k2 into 6k8, and you could also lower the lower resistor into 1K.

Hans
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