Wanted : design PCB for relay controlled volume

[Helix]

Originally posted by Jens
Bernhard - I use in my Balanced Zen Line Stage (see above) voltage divider of 40db(MSB), 20db, 10db, 5db, 2.5db, 1.25db, 0.62db and 0.31db(LSB), which means we get nearly -80db control out of the 8-bit converter. BTW: 6-bit still delivers -76db with single steps of 1.25dB - Jens

Jens, how do u do this ? If you use the Aleph 1.7 pre-amp relay setup and drive it with BCD you get a linear steps unless you put a resistor across the ouput ala Rod Elliot for a 'fake' log, which is still -48db attenuation (for 8 bits as shown in the service manual)

[Jens]

We are talking about two different thinks here. Even I get “only” –48db attenuation in my AP1.7, simply I use Nelson’s relay set-up. Having said that, I use a completely different relay set-up in my Balanced Zen Line Stage, which allows for nearly –80db via voltage dividers!

Let’s assume the output impedance should be 5K (as happen in my BZLS), than the following resistor combinations for the voltage dividers are needed:
R1 R2
-40db = 4.990R and 51R (MSB)
-20db = 4.530R and 560R
-10db = 3.400R and 2.320R
-5db = 2.200R and 6.490R
-2.5db = 1.240R and 15.000R
-1.25db = 665R and 32.400R
-0.62db = 348R and 68.000R
-0.31db = 174R and 137.000R (LSB)

Example: Input---R1---Output---R2---GND

I hope this clarifies the situation, if not let me know… Jens

[Helix]

Aha, I see, we were talking about difrent things !

With your dividers, I am assuming you have the -0.31b one first in the signal path and the -40db one last....
But what i don't understand is, if you had say -47.5db selected, then therefore the -40db, -5db and -2.5db attenuators are selected, won't the -40db and -5db attenuator affect the 'seen' impedence of the -2.5db attenuator? and cause accuracy problems

[Jens]

You are right, but it works just great!

[Helix]

No.. hang on, isn't it the -40db attenuator first in the path and the -0.31db one last...

[Jens]

Oh I forgot, it doesn't matter if MSB/LSB relays are on the input or output side - Jens

[jackinnj]

I thought I would put up a rendition of the LCD+ -- note the 8 10 bit ADC inputs, 4X4 keypad and ULN2803 relay driver. It is unbelievably simple to program with a Stamp, PIC or BX24:

[ElectroNick]

Hi there,

I've tried to make a PCB-board for the volume control. It's based on the Aleph P1.7 design.
If any of you has any comments or tips please let me know....

ps : Its made with Eagle 4.01

Grtz,
Nick

[Mark A. Gulbrandsen]

I'm getting sort of disgusted with Eagle. I tried to open the file but get a load error 295 pop up. Anyone have any idea....This is the freebie version of the Eagle software that I'm using...perhaps thats the problem??? Nick, Could you post a picture of the pcb? If you can't look at a 4.01 version board with the 4.09 version software this thing is worthless.


On another note I finished the 8 bit comtrol by Jens and it works nicely. I had the relays hooked up in the wrong order at first but straightened that out quickly! I want to see more resolution out of this sort of digital control and I don't think it would be that hard to do....say like the 23 positions on the Aleph L preamp. Can one keep ganging together more 8 bit counters to do this? Sure, it would be alot of relays, but they are not that expensive, neither are the counters for that matter.

I think it would be far better quality than a switch type attenuator would be...even better that the DACT atenuators. Another thought...can one gang together several ADC chips, or bargraph chips to achieve this as well?
Mark

[ElectroNick]

Please help me out Mark...

How do i get a picture of the PCB. If i make a screendump you'll get a lot of useless extra.

I can send you a zipped file with all the contents for the design.

Gr,
Nick