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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 4th February 2018, 08:26 PM   #661
Gerben is offline Gerben  Netherlands
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Join Date: May 2004
Location: Deventer
Hi,

I finally came around to build mine, not without problems and i could use some help ...

The problem i still face is the fact that in 30% of the time i turn the power on the sound is distorted. This is with both channels.
The power supply measures OK in both cases: +/-12,8V before rectification, +16,3V&-15,8V after rectfication, +/-12.0V after the Hypexregs and all ic's see 23,8V between the pins 4 and 8. There is no DC at the outputs (<1mV) in both cases.

Some initial problems was with the volcb in place the positive rail was almost zero volts, despite the rsgs turning on. Replacing the volcb with some 4k7 resistors and measuring for shorts in the caps i didnt find a problem in the bpbp nor the volcb. In volcb there isnt voltage present on the pins P1 to P10and the resistance is should. I did check for loose metal parts on both pcbs without any clue.

Any suggestions? Damaged positive regs? Something in the outputrelay circuit?

Any help is appreciated!
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Old 6th February 2018, 12:52 PM   #662
NATDBERG is offline NATDBERG  United Kingdom
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Join Date: Nov 2006
Is it working with a 10K linear pot installed as per the original design?
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Old 6th February 2018, 05:29 PM   #663
Gerben is offline Gerben  Netherlands
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Join Date: May 2004
Location: Deventer
Hi,

I placed 2x4k7 to simulate the pot and reinstalled the volcb, the preamp is working. The issue that there is occasionally a distorted sound when switching on the powersupply is an issue since i wish to switch the primary with the relays of the maya controller.

However, i have been listening to it for some hours yesterday and today and the problem is gone.... strange. Also the sound changed in this short time from bright, on verge of the aggresive, to a much more detailed and coherent sound. I have no idea what caused the problem but i leave it for now, thanks!

[IMG]Click the image to open in full size.[/IMG]
[IMG]Click the image to open in full size.[/IMG]
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Old 6th February 2018, 05:30 PM   #664
Hans Polak is offline Hans Polak  Netherlands
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Join Date: Mar 2005
Location: Blaricum
Quote:
Originally Posted by Gerben View Post
Hi,

I finally came around to build mine, not without problems and i could use some help ...

The problem i still face is the fact that in 30% of the time i turn the power on the sound is distorted. This is with both channels.
The power supply measures OK in both cases: +/-12,8V before rectification, +16,3V&-15,8V after rectfication, +/-12.0V after the Hypexregs and all ic's see 23,8V between the pins 4 and 8. There is no DC at the outputs (<1mV) in both cases.

Some initial problems was with the volcb in place the positive rail was almost zero volts, despite the rsgs turning on. Replacing the volcb with some 4k7 resistors and measuring for shorts in the caps i didnt find a problem in the bpbp nor the volcb. In volcb there isnt voltage present on the pins P1 to P10and the resistance is should. I did check for loose metal parts on both pcbs without any clue.

Any suggestions? Damaged positive regs? Something in the outputrelay circuit?

Any help is appreciated!
Hi Gerben,

Sorry to hear that you have some issues.
I have a few questions:
1) 30% of the time you have distortion after turn on. Does this mean that in 70% of all cases everything is working fine, including all steps the VolCB offers for both channels ?
That would imply that you have assembled the VolCB correctly. Since there are only resistors an relays in the circuit path, there is nothing that can cause distortion that I can imagine.

2)You mention an initial problem with the VolCB, making the positive rail almost zero. Do you mean with this that the +12V power supply was almost zero?
What was the cause and how did you solve this problem.

3) You mention having <1mV out in both cases. Is this with vol in the max setting ? If so, that seems O.K. It should become less when stepping down the volume.

4)You mention no voltage on P1 and Pin 10. You probably mean Pin 1 and Pin 8, do you? May I assume that you have connected both pins to the proper GND point on the BPBP board ?

So far I can only imagine 2 possible reasons and assuming you are using the Maya remote controller:
1) the output relay K3 is not switching properly
2) the Channel select relay Re7 on the VolCB is not properly connected or relays K1 and K2 on the BPBP are not switching properly.


Hans
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Old 6th February 2018, 05:53 PM   #665
Gerben is offline Gerben  Netherlands
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Join Date: May 2004
Location: Deventer
Quote:
Originally Posted by Hans Polak View Post
I have a few questions:
1) 30% of the time you have distortion after turn on. Does this mean that in 70% of all cases everything is working fine, including all steps the VolCB offers for both channels ?
That would imply that you have assembled the VolCB correctly.

2)You mention an initial problem with the VolCB, making the positive rail almost zero. Do you mean with this that the +12V power supply was almost zero?
What was the cause and how did you solve this problem.

3) You mention having <1mV out in both cases. Is this with vol in the max setting ? If so, that seems O.K. It should become less when stepping down the volume.

4)You mention no voltage on P1 and Pin 10. You probably mean Pin 1 and Pin 8, do you? May I assume that you have connected both pins to the proper GND point on the BPBP board ?

So far I can only imagine 2 possible reasons and assuming you are using the Maya remote controller:
1) the output relay K3 is not switching properly
2) the Channel select relay Re7 on the VolCB is not properly connected or relays K1 and K2 on the BPBP are not switching properly.


Hans
Thanks for your reply!

1)Correct. I also measured every resistor in situ after i soldered it in place, before placing the relays since this was the first time soldering SMD

2)Cause unknown, removed the volcb, placed some resistors and replaced the board and everything is working.

3)Correct and with input shorted. Didnt check with less than 0db

4) My bad, i meant the pins on the volcb. I did place the pins going to ground (4 and8) at the groundplane on the otherside of the board, very close to the net-ties.

I use the extra input board, so no relay7, the relay on this board is switching input relays on the bpbp correctly and i measured every relay for continuity in their energized state.

My wild guess was that the positive regulator got a slightly damaged with the initial issue and sometimes comes "on" slower than the negative supply. I read that the LM4562 IC are prone to a latch when using a single supply and that this might be the cause (?)

Anyway the maya with the volcb and extra input board is working OK!
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Old 6th February 2018, 06:04 PM   #666
Hans Polak is offline Hans Polak  Netherlands
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Join Date: Mar 2005
Location: Blaricum
Quote:
Originally Posted by Gerben View Post
My wild guess was that the positive regulator got a slightly damaged with the initial issue and sometimes comes "on" slower than the negative supply. I read that the LM4562 IC are prone to a latch when using a single supply and that this might be the cause (?)


You are probably right.


Hans
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Old 1st March 2018, 03:35 AM   #667
hanswolek is offline hanswolek  Spain
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Join Date: Feb 2003
Location: Spain
Default Mute - does it not 'burn' LM4562 ?

An externally hosted image should be here but it is no longer accessible. Please upload images instead of linking to them to prevent this.


hi all, i was thinking about adding 'Mute' via PIC/Relay - but wouldn't in that case while e.g. music is playing LM4562 see output impedance of 2x22 Ohm ... which would when playing 5-6V RMS (max volume) suddenly cause over 100mA (0.1A) output current ?

Last edited by hanswolek; 1st March 2018 at 03:36 AM. Reason: tipfehler
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Old 1st March 2018, 11:48 AM   #668
Hans Polak is offline Hans Polak  Netherlands
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Join Date: Mar 2005
Location: Blaricum
Quote:
Originally Posted by hanswolek View Post
An externally hosted image should be here but it is no longer accessible. Please upload images instead of linking to them to prevent this.


hi all, i was thinking about adding 'Mute' via PIC/Relay - but wouldn't in that case while e.g. music is playing LM4562 see output impedance of 2x22 Ohm ... which would when playing 5-6V RMS (max volume) suddenly cause over 100mA (0.1A) output current ?
Using relay K3 works very well for implementing a mute function.
5-6V RMS sounds rather bizar but nevertheless, the LM4562 is short circuit proof and output current will never be more that 50 mA.
For a 22 Ohm resistor that would mean only 55 mWatt !

Hans


P.S. I cannot open the image that you had placed.
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Old 1st March 2018, 04:59 PM   #669
hanswolek is offline hanswolek  Spain
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Join Date: Feb 2003
Location: Spain
Quote:
Originally Posted by Hans Polak View Post
Using relay K3 works very well for implementing a mute function.
5-6V RMS sounds rather bizar but nevertheless, the LM4562 is short circuit proof and output current will never be more that 50 mA.
For a 22 Ohm resistor that would mean only 55 mWatt !

Hans


P.S. I cannot open the image that you had placed.
Thank you Hans - i didn't know how to 'upload' a pic - if you right click in browser - 'Open Image in another Tab/Window' it does seem to load - but it's only portion of BPBP output stage with mute relay and 2x22Ohm resistors thank you - all clear - you described earlier in the thread what needs to be done (connecting base of T3 to -VOP would 'close' the relay and shortcircuit those resistors). THanks !!!


One last question - and - my BPBP (and VolCB/Maya) are not in metal case - obviously all XLR connections are connected to the same 'ground' plane on BPBP ... but my case ground connection is 'isolated' from BPBP. Should i find a way to connect ground from BPBP to 'Ground' of IEC power input ?

Thank you !
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Old 1st March 2018, 05:02 PM   #670
tvicol is offline tvicol  Europe
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Location: Bucharest
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)
Here it is.

Regards,
Tibi
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