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Old 16th July 2004, 08:02 AM   #21
xcel is offline xcel  Netherlands
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Lightbulb Noizzzzzzzz

Well,

That depends on your definition of noise ......

a) Since it uses relays there are allways the mechanical clicks when the relays switch over. So when you adjust the volume (up/down), you hear a "rattling" noise of the various switching relays. Actually, when you spin the volumeknob really fast up and down you get this sewing-machine kind of sound. It starts to purr, as I lovingly call it....

The relays don't mind, I use very high quality types with short switch-over times (5ms). For kicks, I connected a relay to my functiongenerator once and drove the swithingfrequency up to 60 Hz. Then it doesn't purr, it starts to buzz !!! The relay performed flawlesly, off course.....

b) At certain volume settings you will hear a slight click in the music when you change them. I don't mind, and I guess this can be improved by reducing the "contact bounce" of the relays.

Hopes this answers your questions,

Xcel
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Old 16th July 2004, 08:43 AM   #22
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Hi Xcel,

On what schematic is your volume control based ?
I mean the relay section, not the "secret encoder part"

I found several schematics on the internet, but i still don't know which one to make.......
Also on the controller side, i'm working on it. My dream is a volume control based on a rotary encoder with display function.
But... time is holding me back

Gr
Nick
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Old 16th July 2004, 09:43 AM   #23
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Quote:

On what schematic is your volume control based ?
I mean the relay section, not the "secret encoder part"

I found several schematics on the internet, but i still don't know which one to make.......
Also on the controller side, i'm working on it. My dream is a volume control based on a rotary encoder with display function.
But... time is holding me back

The relay circuit will depend on the kind of preamp you use.

I have a version with 16F877A, controlling relays, PGA2310, and a 2*20characters display as working prototype.
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Old 16th July 2004, 10:48 AM   #24
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Sorry, maybe the question wasn't clear enough.
I meant if Xcel used a schematic that we already know, or did he (re)design a new relay based attenuator ?

I also have the schematics from the Pass-Labs site. But the fact that Xcel's is version has a constant impedance got my attention. That's why for my question.

Gr
Nick
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Old 16th July 2004, 02:13 PM   #25
LBHajdu is offline LBHajdu  United States
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What is constant impedance? I think the sum of the resistance from output to ground and output in input is the same with every step. Is that right? If thatís right then I have an idea that will work. It does use a lot of relays however. As you can see For 16 steps you need 7.5 relays. For 32 steps you would need 15.5 relays. It works almost like a mechanical stepped latter attenuator.

Even of I had commercial intentions on this design, I would still show it. I know thatís what Mr. Pass would want me to do and without him I would have never in a hundred years though of making an attenuator out of relays and resistors.

I have a bone to pick with the administrators of this site. I tried up loading this is a PDF file, but the file size was too big. So I tried up loading it as a gif. This time the file size was OK, but the size of the pic was too big. Luckily they haven found a way to test the size of a jpg. And how come I can no longer view picks without having to click on a link.
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Old 16th July 2004, 02:25 PM   #26
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XCEL wrote :
Quote:
I designed the relayboards and a separate board for the control circuitry. It uses 6 relays which activate banks of resistors (1 % MF). The impedance is a constant 10k, regardless of the volumesetting.
That's nice for a preamp.
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Old 16th July 2004, 04:43 PM   #27
LBHajdu is offline LBHajdu  United States
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I was just looking at some pictures of the top of the line Mark Levinson pre-amp. It has two volume attenuator boards. It looks like it has some type of resistor latter and 16 Quad Complementary CMOS Analog Switch ICís. The chip is the DG213. Each chip has 4 switches just like a stander relay. I bet they make no noise when they switch.
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Old 16th July 2004, 06:48 PM   #28
xcel is offline xcel  Netherlands
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Lightbulb Questions, Questions, Questions .....

Quote:
I was just looking at some pictures of the top of the line Mark Levinson pre-amp. It has two volume attenuator boards. It looks like it has some type of resistor latter and 16 Quad Complementary CMOS Analog Switch ICís. The chip is the DG213. Each chip has 4 switches just like a stander relay. I bet they make no noise when they switch.
I know for sure.....I've listened to one extensively. That's the big advantage of these kind of IC's, no switchover sounds. But I guess that mandatory for a megabucks preamp. I've talked to an engineer from Burmester (the famous German High End manufacturer), and they preferred the relay solution. It's not a question what's better, both methods result in very high performance attenuators.

To answer the questions;


Quote:
I meant if Xcel used a schematic that we already know, or did he (re)design a new relay based attenuator ?
Well Elektro Nick, I do not know what you know....Too much Zen ? Ok, let me put it this way: I don't know the schematics that you allready know. Please send me some so I can compare 'm.

I'm glad you like the constant impedance concept. What is basically means is that regardless of volumesetting, the resistance remains the same. The stages before and after the attenuator are faced with the same amount of resistance. This is achieved through a number of sections with a fixed amount of attenuation. Such a section consists of a number of precision resistors configured as a voltage divider. The relay is there to either allow the signal to pass trough the section, or bypass it.

The desired amount of attenuation is achieved by putting several of these sections in series. The data from an optical encoder is translated into bits that controll these various sections (see the picture).

And LBHajdu, even Mr. Pass doesn't show us everything .....
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Old 18th July 2004, 11:41 PM   #29
LBHajdu is offline LBHajdu  United States
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Here is an other idea. What do you think ?
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Old 21st July 2004, 12:11 PM   #30
zinsula is offline zinsula  Switzerland
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Quote:
Originally posted by Nelson Pass
#2 is a real artifact, not a function of the pot, but a function
of the A/D converter, which can sit there switching back and
forth between 1 bit values.

You can stick a little hysteresis in such a circuit so that it doesn't
do that, or you can inhibit the A/D until there is a significant
change, or you can just go to a microcontroller.

We went to the microcontroller, as it was cheaper and easier.
That's also what Till did, however, I for myself have a problem with that:
1. Till's solution has not enough source inputs for me (or should I say for my family? )
2. I believe that this would only need some program changes on the microcontroller, but i never programmed such a thing

So I am thinking of integrating a solution with the motor pot (= Aleph P1.0) and the IR Control from Albs / Schuro http://www.schuro.de/Downloads/PDF-P...3513_I_BR.PDF.

My question now: Any hints how to stick this little hysteresis into the circuit? Or would a 12 Bit A/D using only the highest bits, be a cure for this?

Thanks for any hints!
Tino
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