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Interest in PCBs for Bruno Putzey's Preamp and Hans Polak's relay volume control


Paid Member
2009-06-09 8:55 pm
In Jan Didden's Linear Audio Vol 5, Bruno Putzeys published an excellent article, called “The G Word, or How to Get Your Audio off the Ground”. The article includes a demo project - a minimalist balanced preamp - and Vol 5 came with a free PCB to make the project a practical build. Then Hans Polak designed an alternative volume controller and a three-way input selector for the preamp. The discussion has been going on here in this thread.

I would like to gauge interest in a group buy for any combination or subset of the following items:
  1. Bare PCB for Bruno Putzey's preamp (BPPBP, a.k.a. MicroPre);
  2. Solder paste stencil for (1), courtesy of Brent from OSH Stencils.
  3. Bare PCB for Hans Polak's 3-way balanced input selector with a pass-through ("Tape") output and a separate output from the preamp.
  4. Bare PCB for Hans Polak's 64-step relay volume controller (I2C control, requires an external MCU, which is not included)
  5. Bare PCB for Hans Polak's 16-step relay volume controller (a simpler alternative to (4), no MCU - it uses a 16-position coded rotary switch to control relays)
Attached are some rendering of the boards.

The pricing would depend on the level of interest, but a blind estimate is $10 for each board (green with HASL finish) and $20 for a polyimide stencil with free shipping to the continental U.S. and $15 shipping elsewhere. If we go for a fancy color (one color for all participants) and ENIG (gold) finish, it may cost a little more.

To put things in perspective, OSHPark - a great service BTW - will charge you $5 per sq inch, or something like $50 for three copies of the BPPBP boards (purple with gold finish), with free shipping worldwide.

Let me know if you are interested.

Update: To give you an idea of the cost of parts for BPPBP, I posted a sample BOM for BPPBP at Mouser.com. It follows the original Linear Audio article and includes Panasonic ERA 0.1% resistors, Nichicon FW and ES electrolytic capacitors, Fujitsu RY relays, 7812 and 7912 regulators instead of HPR12/NHR12 (if you want HxR12, order them at diyclassd.com), PTD902 potentiometer as specified in the original article - although I would replace the pot with one of the relay boards from above or at least with a Vishay Sfernice P9.

Also if needed, I may be able to buy and solder, for a fee, all SMT parts on a few BPPBP boards. A sample SMT-only BOM is here.


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Is there any possibility that you could arrange to supply boards with all sm components soldered (as per BoM); there was this option with the original boards i believe. [Being in my late 70s I have difficulty with this task!!! However I have an electronics assembly line not too far away and they have offered to carry out this work for me; I am sure that many would rather pay extra so that this work can be avoided.


Paid Member
2009-06-09 8:55 pm
I can buy and solder SMT components for you, it is not a problem, however the BOM and the cost need to be agreed upfront. The BOM variations I have seen are in the type of resistors (some say it must be MELF; I made one BPPBP with MELF, and as the saying goes, Most Ended up Lying on the Floor; I switched to Susumu RR for subsequent builds) and opamp upgrades (TI has some very nice SoundPlus opamps in its portfolio, and some people don't like TL072 in the LPF).

Thank you for that; it may encourage some of us less capable people to 'have a go'!

[Re the Hypex reg - I had the impression that it is no longer available...yet on searching the Hypex site I see that it costs about UK£30 for a pair So that problem solved!]

I do hope that enough interest is generated in this great preamp as those who know it hold the design in the highest regard. What I found with an unorthodox version is that it not only has all of the plus elements we look for, but that it also helps to pinpoint problems in other parts of the system with greater accuracy.


Paid Member
2009-06-09 8:55 pm
I put together a table:
		BPPBP	Sel.	64step	16step	Services
brianco		1	1	1	1	SMT soldering
astromo 	?	?	?	?	
Bennyboyph  	1	1	1	1	
cowanaudio	1	0	0	0	
Quantensprung	?	?	?	?	
Mituisho	1	0	0	1	
shattered_dream 1	0	?	?	
Morde		1	0	0	1	
maartn		1	0	0	2	SMT soldering
GfromG		1	0	0	0	SMT soldering
pixelpusher 	0	0	?	?	
av-trouvaille  	0	0	?	?	
vasillis 	0	0	0	2

For those who has question mark(s) across from their names: may I ask you to clarify what specifically you are interested in?