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redjr 13th March 2015 09:59 PM


Originally Posted by Rudi_Ratlos (

I have taken a holiday in the past days and returned home today.

Rick, Adrian: since all the functions (Power On/Off, attenuation, source selection, ...) can be controlled via a remote control unit, I do not need a switch, neither do I need a knob on the front panel.
This is the reason why I have installed the motorized dual potentiometer into the case.

But this potentiometer looks like (is) a real anachronism, and I would like very much to replace it by a "digital potentiometer" (MCP4151, which has 128 wiper steps) followed by a VCCS (see attached image 1).

I have already done a layout for this schematic and have etched and populated two of the resulting PCBs (see attached image 2).
I am using simple LEDs instead of LDRs on this "evaluation-PCB".

My problem: I am no good at programming a PIC - ÁProcessor in "C".
I have been programming IBM-mainframes in Assembler for more than 35 years of my life, but now, when I program a PIC in "C", I get lost and desperate, if I forgot to insert a ";" or a "}" into the code.
I am of course able to change the existing VCPre's code (whose inital programming has been done by METAL), if required, but implementing a new function, ...?

If there is anybody among you (I am sorry that Paul does not have the time), who has the time to assist me, who knows the internals of the PIC16F887 and has a PIC-evaluation board and who knows,
how to program it in "C" (for example the SPI-interface): I will happily send him one of the two evaluation PCBs and will program together with him the digital potentiometer interface.
And of course I will send him a couple of the resulting Pre - PCBs (see my P.P.S.).

Best regards - Rudi_Ratlos

P.S.: I am currently not having any "Black-Beauty SYMASYM" - PCBs anymore. Maybe I will order a small couple of them in a month or so.
Ryan, Rick; please have some patience. Your PCBs will definitely arrive soon.
P.P.S.: I will also post this reply in my "PRE - thread":

Thanks for the clarification Rudi. I know you had mentioned in an earlier post about a digital pot, so I will follow with interest those developments. I just wasn't sure if the motorized pot was fully installed inside, or just laying there temporarily. However, even with a remote controlled pot, I still like manual access on the front of an integrated amp too.

I'm not worried about the PCBs and other parts. I'm sure they'll show up soon.


metal 13th March 2015 10:08 PM


Originally Posted by redjr (
However, even with a remote controlled pot, I still like manual access on the front of an integrated amp too.

I can replace that motor with a rotary encoder so you still have a direct physical interface. I and Rudi will talk about it to see what can be done.

atupi 13th March 2015 10:11 PM

Would be great end result to be a pot replacer as i have two ldr preamps from Rudi.

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RKH 14th March 2015 06:42 AM

My boards arrived today!
Thank you.

redjr 14th March 2015 10:28 PM

Hi Rudi,

My package of PCBs and parts showed up today. Thanks! The boards are gorgeous. I certainly don't want to muck them up accidentally. I'll be extra careful with my parts placement and soldering for sure. I'll PM you later about the other small bag to be sure I know what to do with them.

Thanks again,

ipolyakov 17th March 2015 11:53 PM

Hi Rudi,

I received my boards yesterday and I agree that they are gorgeous!


Rudi_Ratlos 21st March 2015 03:48 PM

2 Attachment(s)
Dear SYMASYM-friends,

I have had some time yesterday and have adjusted the quiescent current of my current SYMASYM - build (the left channel - without using the light-bulk delimiter anymore).

I have measured the DC-offset on the output during the adjustment phase.
There is no DC-offset at all. Andrew_T will appreciate.

I will go on with the right channel today and do some thinking about the case's front panel.

Best regards - Rudi_Ratlos

P.S.: Before you ask me: I am using a Wall-Market speaker-cable (1 meter costs 3€) and RG59 - RCA - cable for internal wiring.
Maybe the lettering is too big.

redjr 22nd March 2015 12:20 PM

1.3mm Soldering Pins?
1 Attachment(s)
Could you post a picture of what a 1.3mm soldering-pin looks like that is used in your VCPre? I assume they are individual vertical pins, rather than some type of connector. What do they look like?


Similar to this?

Rudi_Ratlos 22nd March 2015 03:35 PM

Rick: your image shows is exactly what I call "soldering-pin".

Best regards - Rudi

redjr 22nd March 2015 04:16 PM


Originally Posted by Rudi_Ratlos (
Rick: your image shows is exactly what I call "soldering-pin".

Best regards - Rudi

Great. Thanks. Those I don'the have in my hardware supply so need to order some. :)

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