Doug Self Preamp from Linear Audio #5

[rmaudio]

"input" not "oinout" of course :-)

[Xpersephone2]

Hi there, are there any boards remaining? I would be interested in two sets .

[Carl_Huff]

Originally Posted by Xpersephone2

Hi there, are there any boards remaining? I would be interested in two sets .

Please check your personal messages. I just sent you one.

[hadihf]

Hi,

Does anybody have any experience of frequency control pots control rotation reversed? Can this happen wit none polarized caps?

Best Regards
Farooq

[Carl_Huff]

Originally Posted by hadihf

Hi,

Does anybody have any experience of frequency control pots control rotation reversed? Can this happen wit none polarized caps?

Best Regards
Farooq

Forooq,

From your description I think about the only way that you can accomplish what you describe is to reverse the wiring on pins 1 & 3 on the pots.

I am guessing that you are not using PCB solder mounted pots but rather chose to use panel pots with wire between them and the PCB.

If that is the case simply swap the wires now on pins 1 & 3. I invite others to comment.

[hadihf]

I notice that C14 on Carl's Schematic is also revered for same C14 in LA article page 150.

[batteryman]

I was pleased to find that Carl still had some pcbs available when I enquired a few days ago.
I decided to built the preamp for use with my dual TDA1541A balanced Dac with Sowter 9545 I/V transformers and IanCanada's I2S to Simultaneous interface. (almost finished)

I did once have a Quad 34 preamp driving a 405-2 and Martin Logan Aeon hybrid electrostatic speaker and found Quad's unusual "Ambler" tilt tone controls more useful than the usual Baxandall type. (which date from 1952)

I once had the commonly held view that tone controls were a no no and I still hold this view of the basic Baxandall type. However, now my Aeons are in a small space where they tend to bass heaviness, and with my age related high frequency hearing loss, I have realised that Doug Self's tone control design is just what I need to drive the Quad & Aeons.

I plan to dispense with the input capacitors + R2/R4 and change R5/6 to 3k3 as they will become the transformers' secondary load resistors. The load is reflected to the primary at the step up ratio (5:1) squared resulting in it seeing about 100R (in parallel with the existing 100r I/V resistors.)

I will probably also reduce the preamp gain since the 405-2 is more sensitive than modern power amps.
Ian

[hadihf]

Originally Posted by Carl_Huff

Forooq,

From your description I think about the only way that you can accomplish what you describe is to reverse the wiring on pins 1 & 3 on the pots.

I am guessing that you are not using PCB solder mounted pots but rather chose to use panel pots with wire between them and the PCB.

If that is the case simply swap the wires now on pins 1 & 3. I invite others to comment.

Thanks Carl,

Yes reversing will defiantly solve the problem. I am just curious why this is happening.

Since nobody seems to have time to answer my query, been experimenting on my own. So far changing the caps to polarized has no effect on frequency control pots rotation.

In my case still has to turn both pots clockwise to 'decrease' frequency instead of increasing, I have checked pots are wired correctly as per schematic.


Best Regards
Fatooq

[Freecrowder]

OK so not wasting time searching forever. Are there boards available. As a complete kit? Power supply included??
Thanks for help

[Carl_Huff]

Originally Posted by Freecrowder

OK so not wasting time searching forever. Are there boards available. As a complete kit? Power supply included??
Thanks for help

Yea, I still have a few kits left. The kit amounts to ...

#1) the main PCB
#2) the 5 x 1 IO PCB,
#3) Power supply PCB (120v but can be easily modded to 230v)
#4) and 2 (hard to find) OEM quad RCA phono connector blocks

All of the parts to build can be purchased from Mouser & Digikey

Please check your in box for a note containing the details.