BPPBP - Bruno Putzey's Purist Balanced Preamp (well a balanced volume control really)

Hi Hans, not sure if I understand that. In my current set-up J6 is connected to +/-16 volt, so 16 volt is fed into the Hypex regulators (ignoring the voltage drop across the rectifiers).

The way I had understood the circuit, the "shutdown protection" part, incl. zener D5 is fed by +VOP/-VOP, which is the output of the Hypex regulators. +VOP/-VOP would be +12/-12 volt, and the zener and transistor are driven by that.

Am I missing something? Sorry if this set-up was not clear enough from the start. Reason by the way to use +/-16v instead of plain AC is that I am re-using a transformer that gives too high a voltage, so I am regulating it down before feeding into J6.
 
Hi Hans, not sure if I understand that. In my current set-up J6 is connected to +/-16 volt, so 16 volt is fed into the Hypex regulators (ignoring the voltage drop across the rectifiers).

The way I had understood the circuit, the "shutdown protection" part, incl. zener D5 is fed by +VOP/-VOP, which is the output of the Hypex regulators. +VOP/-VOP would be +12/-12 volt, and the zener and transistor are driven by that.

Am I missing something? Sorry if this set-up was not clear enough from the start. Reason by the way to use +/-16v instead of plain AC is that I am re-using a transformer that gives too high a voltage, so I am regulating it down before feeding into J6.
O.K., I thought your scope image was showing +VOP.
Then the next thing to try would be to change R54 into a much lower value, like 680 Ohm or 820 Ohm, thereby driving T3 less into saturation.
Because switch off should happen within 4 msec and that's not what I see.


Hans
 
Measured the voltages:
+VOP = +12,20 (output of regulator)
-VOP = -11,90 (output of regulator)
Vbase = -11,15
Vcollector = -11,85
the voltage between the zener and R24 is -5,60

That would mean that the base current is around 2 mA as it should be... Details on the parts: T3 is a Taiwan Semiconductor BC846B and D5 is an NXP BZX384-C18.
 
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Thanks Hans, I am learning a lot here. The relay I used is TE MT2-C93402, which draws 12 mA, so I wanted to use 560 Ohms. That didn't solve it. I went as low as 390. Still "pop", but the discharge curve did change (see attached, measuring supply to the onboard regulator this time). Then I mounted a small pot in place of the resistor and found the minimal resistance for saturation: ~260 Ohms. Still "pop"... Then I tried disconnecting the DC supply from the BPBP board (instead of switching off mains like I did before). No more "pop"! The root cause must be somewhere among the mains switch, the transformer and the pre-regulator, but those will be replaced anyway. In the meanwhile I put the 390 Ohms resistor back on, for fast off-switching.
 

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Thanks Hans, I am learning a lot here. The relay I used is TE MT2-C93402, which draws 12 mA, so I wanted to use 560 Ohms. That didn't solve it. I went as low as 390. Still "pop", but the discharge curve did change (see attached, measuring supply to the onboard regulator this time). Then I mounted a small pot in place of the resistor and found the minimal resistance for saturation: ~260 Ohms. Still "pop"... Then I tried disconnecting the DC supply from the BPBP board (instead of switching off mains like I did before). No more "pop"! The root cause must be somewhere among the mains switch, the transformer and the pre-regulator, but those will be replaced anyway. In the meanwhile I put the 390 Ohms resistor back on, for fast off-switching.
Great, that’s what they call a learning curve 😁

Succes, Hans
 
Got the preamp in a decent enough state now to plug it in to my main set. See attached pic and the ones on this post.

I was curious to know the output impedance so I measured it and got to 22 Ohms. Anyone else ever measured it and got to the same number?
 

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Got the preamp in a decent enough state now to plug it in to my main set. See attached pic and the ones on this post.

I was curious to know the output impedance so I measured it and got to 22 Ohms. Anyone else ever measured it and got to the same number?
That's Ro connected to the output amp, so the 22 Ohm is exactly as expected when the other side of the measurement is Gnd.
But in the connection to the main amp when using a balanced input also, output impedance is 44 Ohm.


Hans
 
I'm planning to assemble a multi-channel version of the BPBP or rather a chassis containing 4 BPBP units for a total of 8 channels. I've got a Burl Audio M16 with 2 x BDA4 which will feed this unit.

I bought a Maya Controller from Tibi ... sorry to see he closed his online store front. I've also receive the requisite number of BPBP control boards designed by Hans I believe.

First of all wondering if anyone has one more BPBP from third tfboy group buy. I'm short one...

with my 3 boards I also purchased the Hypex Regs...I was going to run each board with a Sjöström SSR-03 reg power supply.

Any advice from other builders how a multi BPBP system like this has worked out is greatly appreciated.
 
I'm planning to assemble a multi-channel version of the BPBP or rather a chassis containing 4 BPBP units for a total of 8 channels. I've got a Burl Audio M16 with 2 x BDA4 which will feed this unit.

I bought a Maya Controller from Tibi ... sorry to see he closed his online store front. I've also receive the requisite number of BPBP control boards designed by Hans I believe.

First of all wondering if anyone has one more BPBP from third tfboy group buy. I'm short one...

with my 3 boards I also purchased the Hypex Regs...I was going to run each board with a Sjöström SSR-03 reg power supply.

Any advice from other builders how a multi BPBP system like this has worked out is greatly appreciated.

I still have 4 bare BPBP boards, they are 3 euro each plus postage (using standard letter post only). The boards are white, not green, in colour. PM me if interested.
 
Does anyone have the top cream file for the BPBP boards ... looking to make a stencil for solder paste application ... beats soldering individual surface mount parts.

Looking to give me new PCB toaster oven from Ali Baba Express some run.

was wondering the same... I think with a good CAM editor you can extract that from the top copper layer... but in the end, I will go for a long and trusted hand soldering session so I stopped worrying about.

Anyway.

I have another question :

the 10u BIPOLAR caps are rated for 50v... but i think they will never experience such a high voltage...
Found the nichicon Muse (UES) has the same footprint but for a 10uf 35V version instead of the 50v.

Do you think i will be ok with them ?
 
Scroll down for "Gerbers and PCB layout for Bruno Putzeys' article in Vol 5" at Downloads | Linear Audio

Quite unuseful...
miss the point.
The Gerber package misses the paste layer.
I think with a good cam editor you edit the top solder mask and then shrink the pads.

but I have no available solution on hand at the moment.

Persist my question on the cap ratings tho.
 
What do you mean by 'paste layer'?

Jan

Paste Layer is ... usually ... the layer that carries the opening for the stencil mfg.
The stencil is used to place solder paste directly on the board passing into the openings...

It is usually included when SMD parts are used in the design and it is very useful for the automatic setup process... I usually solder by reflow oven and a stencil is still useful.

Anyway... I have armed myself with proper patience and a cam editor.

Attached is the Paste Layer.
But... I have checked very little... the pads are shrunk by 0.1mm on H and W.

for everyone who is thinking of using it, please triple check.

My question about caps still remains...
 

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I see. In my case, I have sometimes ordered a stencil but the board manu created that from the solder mask layer. Its an automatic process. You could ask.

Jan

it's important that the automatic process that creates the stencil properly shrink the solder mask...

USUALLY, you have :

the copper aperture that is a certain size.
then the solder mask is expanded (in respect to the copper)
and the solder paste is shrunk (in respect to the copper)

Is also very important that the process properly ignores the apertures that belong to through-hole components or pads that are designed as test points (or net-ties in this case)

I had mixed experience with automatic creation of stencils on various PCB fab house.

This time i have made mine... check it and use it.