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Bruno Putzeys Balanced Preamp - Group Buy

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jan.didden

jan.didden

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DNi said:
I organized a GB in a different forum, and we had 42 PCB's made. I myself am just about to build my third sample, this time with a relay-switched volume attenuator.
Can with pleasure fully confirm the very high objective and subjective performance of the design.
The original volume control with the pot in the NFB path does indeed produce a problem at the maximum CW rotation point. The gain at this pot position is extremely high and can cause a terrible shock to the loudspeakers (I got burned with my first sample).
The recommendation in the GB project was to mechanically limit the farthest position of the pot near the end of CW rotation.

Regards,
Braca
Click to expand...

Mech limiting rotation will work, but don't use series resistors for that - you'll get tracking problems.

Another option is a small switching control like the one Hans Polak designed for this preamp. I think it is in your other thread.

Jan
 
D

DNi

Member
Joined 2013
Here is my sample No. 2 in a custom-made box together with the Sjöström QRV09 headphone amplifier. In daily use since April of this year.

Regards,
Braca

P.S. None of this would have been possible without the kindness of Jan and Bruno. Thanks again, both.
 

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emyeuoi

emyeuoi

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nik_d said:
That photo is more than a year old, this pre is completed and works happily :). All parts as per original BOM
except Hypex reg's: way to much on transport costs. Sorry guys, whoever arranges shipping...
Click to expand...

Nik_d, nice work!

I am curious about to which "original BOM" you are referring to? Please correct me if I am wrong but looking on your picture I can't see the expensive resistors (4.95 USD each from Mouser and we need 16 :eek:) that as per BOM posted in the first post of this GB should be 0,1% tolerance.

In my previous post I explained that the part numbers in the BOM for the resistors (Vishay/Beyschlagare UMB0207 serie) cannot fit in the pads. The UMB0207 resistors are 6.6 mm long while the pads in the PCB are for the MMB0102 serie that is 2.2 mm. The other available resistors at 0,1% is the serie UMB0204 that is 3.6 mm and that is the one that I use in board.

IMHO reading the Bruno article the 0,1% resistors are a must
 
emyeuoi

emyeuoi

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jan.didden said:
Mech limiting rotation will work, but don't use series resistors for that - you'll get tracking problems.

Another option is a small switching control like the one Hans Polak designed for this preamp. I think it is in your other thread.

Jan
Click to expand...

Hi Jan,
You tried the Hans Polak circuit?
I contacted Hans for a pcb but was not more available. When I designed the input board I was near to design and order this pcb too but the cost of 3 pcbs was too high and I decided to try the preampli with the pot first
Now that I make the preampli I think that a better solution for the pot will be the next step.
The Hans circuit can be one? Or maybe a nice r2r stepped attenuator with display?

Regards,
Enrico
 
jan.didden

jan.didden

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emyeuoi said:
Hi Jan,
You tried the Hans Polak circuit?
Enrico
Click to expand...

No I haven't. Mine was build before that became available. But I am totally happy with the pot solution. It is true that you should not turn it all the way up or all the way down, but who does that anyway??

Bruno took a deliberate decision to go for best quality and almost perfect tracking between channels. I thought that was what we wanted? So why are people (not you) bitching and moaning that we can't turn it all the way up or down? What is the priority here??

And in practise the control range is fine.

Jan
 
D

DNi

Member
Joined 2013
I built the Hans Polak attenuator, but did not retain it for the encased version of the preamp, the reason being that I was not satisfied with the 16 steps it has, i.e. I needed more steps.
With a 2dB step, the attenuator provided for a volume control range of 32dB, and I found this insufficient to accommodate all kinds of music that I listen.

An example: a few days ago I listened to the 1st Movement of the Liszt Piano Concerto (Hyperion, 2011, HD 24/96) and measured an SPL range of 35dB (DIN C) in my lounge. I need an attenuator with a range larger than this.

Regards,
Braca
 
billshurv

billshurv

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Joined 2014
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DNi said:
I built the Hans Polak attenuator, but did not retain it for the encased version of the preamp, the reason being that I was not satisfied with the 16 steps it has, i.e. I needed more steps.
With a 2dB step, the attenuator provided for a volume control range of 32dB, and I found this insufficient to accommodate all kinds of music that I listen.

An example: a few days ago I listened to the 1st Movement of the Liszt Piano Concerto (Hyperion, 2011, HD 24/96) and measured an SPL range of 35dB (DIN C) in my lounge. I need an attenuator with a range larger than this.

Regards,
Braca
Click to expand...

I have to ask why you need more than 32dB attenuation though.
 
A

AndrewT

R.I.P.
Joined 2004
It seems from your question and from your reply that you don't require much attenuation.

That does not mean that no one else requires more attenuation for normal listening than you require.

I would expect that many would be comfortable with a maximum attenuation of greater than, or equal to, -40dB.

As an example DNi has already stated that he worked with an attenuator that limited his attenuation to a maximum of -32dB and he further states that something greater than -35dB is required.
It seems he is at least one Member that needs more attenuation than you seem to think is enough.
 
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D

DNi

Member
Joined 2013
billshurv said:
I have to ask why you need more than 32dB attenuation though.
Click to expand...

The volume control range a reproduction system should provide is basically determined by the worst-case musical material submitted to it, and the SPL range required and/or allowed at the listening location.
We are fortunate to have a rather quiet neighbourhood with an SPL of less than 40dB in the lounge for most of the time. Setting now an SPL of 85dB as the maximum peak level when listening to the music gives an SPL range of 45dB.
As regards the dynamic range of the recordings in my collection, the worst ones have an average RMS value of -4.6dB (LRA of about 3.3dB), i.e. the entire music is compressed into the last 4.6dB of the available signal space. Since I must be able to position this signal range anywhere within the above defined SPL range, it follows that my volume control range must be at least around 40dB. Adding to this a 6dB reserve for the difference between the balanced and unbalanced signal sources gives a rounded value of 50dB for the volume control range I need.
Recordings with a very large dynamic range (LRA of 25dB and more) do not (and can not) use the entire volume control range of 50dB, since they already fill the best part of the available SPL range, and often require even more.

Hope this answers your question.

Regards,
Braca
 
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