Relays in input and volyme switch...

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i have just get a hold of a couple of kickass relays in a dirt cheap surplus shop, the same kind ericsson used in there AXE stations have im been tool so they will work quite a while...

But im a litle dubuious in hove to operate them....

there were elna 24 rotary switches..., use some kind of MUX and buffer it the relays is realy easy driven 5v 100mW

if i where to use som kind of microcontroller i could make the relays make different combinations of parralleld resistors and achive more than 24 steps....

does anybod know of any solution i can copy ;-) or have any ideas or advices??

relay use....


I'm 'afraid' =) you can find a very direct approach to copy from the Aleph P service manual... there you will find an use for relays while selecting diff. inputs and a volume control.

The truth is that you don't need a micro controller to play with them, just plain good old logic components...

Sometime ago I did an input selector using relays and plain logic circuits and it did work well, but maybe because climatic conditions or bad quality, one relay becomes noisy. What i did at that time was to use both contacts for one channel and I have never again experienced problems...

By the way, I like to use relays, but there are people that dislike them because the contact switching noise.

hmm the circuit for P1.0 looks easy enough...and if i have understand it correctly it leaves more than one relay open at a time to better match the level of the referens pot? ... it would be a little bad with only 8 different settings....

hmm does anybody have a layout for that design? (just the volyme controll part)

my relays are 4-pole types would you suggest parrallelling them to one pole? it wouldnt be a problem......

how did you controll the logic? or rather how did you controll the relays only one relay open at a time or? parralell for mor settings?


The way this relay volume work is by opening and closing more than one contact if that is required. Probably you are familiar with binary numbers... well, for the Aleph P 1.0 you will see 6 relays... that implies that you can have 2^6 = 64 different switch combinations. this imply that you will have a digital volume control in 64 steps, some of these steps will require just one switch, some a little more...

Regarding the ADC802, well, this is an old voltage to binary word converter.

The trick was to use just one volume pot. to control 4 (two per channel) highly matched volume controls.

In your case, you can assign just one pole per channel if you wish, also, you are not forced to have an ADC chip to control them, in the simplest approach, you can control them manually or just with two buttons ('up' and 'down') and little logic 'such up and down counters'.... etc.

The volume setup that I did before was, basically, the same that you saw on the Aleph manual but using 7 (128 steps) relays. In fact originally I used 8 (256 steps) but it was an overkill and its LSB relay 'oscillates' a little.

hello, well thats what i thougth when looking att the schematic the two least significant bits of the dac isnt connectet i will draw my laytout with room for those two extra relays but if the clicking is to anoying i will remove them...

overkill is what makes diy diy =))))

I'm on a similar path, but using some 60/80 dpdt mercury wetted relays to create a ladder attenuator rather than series attenuator - so the control logic is simpler (to my mind, anyway). If it is of any help, however, my current intention is to use adapt the following circuit (thanks Alex)to control the relays as well as display leds -

Interfaced with a rotary encoder using this little chip -

I don't know how you could go about adapting this to control a series attenuator, I'm sure if its possible there will someone else with more knowledge (and that ain't hard) of digital electronics who can help.

Directly connected, no logic ...

If you start with a Grey code (after name of person, not colour) optical encoder (looks like a pot) with direct binary out, you essentially have 7 bits (128 steps) which could control the relays -- made particularly easy if you choose shunt mode. To set up for logarithmic, play with resistor values.


It seems like a very good idea to use a gray code optical encoder, to make a shunt type of volume control. But do you know where to get one? I did a little searching on the net, but I couldn't find any company in Sweden that sell those rotary encoders. Perhaps there even are motorized rotary encoders so I can make the volume remote controlled :)

Hifi -- yes, binary out. Grey code means that only one "bit" of encoder changes at any given time. This bit pattern is converted to binary, and the circuitry can be found inside certain units so you do get direct binary out.

Freddie -- No time to find it right now, but I think I saw Bourns had 128 step units (7 bits) at good prices. I can look into it later.



Using a Bourns ACE128 in my preamp to determine the volume.
Using an Alps with motor for the volume itself. The problem with the Bourns is that the output is kind of random. There is a value for every position, but they it is not counting up in the normal way.

You need a microcontroller (or logic+EPROM) to convert the output into the actual position. I used a PIC for that. The table itself is loaded into a I2C EEPROM.

Have a look at my website, allthough the code and table itself are not there. The table content depends on how you connect the decoder to the micro (like not connecting bit 0 to a port bit 0 since it was easier then with the connections on the PCB).

Have fun,

Aleph-p volume control

Dear fellow DIYers to help things a bit i allready have designed the aleph p volume control attached to the aleph-L , The pcbs are in pass labs forum :
The only reservation I have is that the load the preamp sees varies from about 60ohms to a max 4800ohms so it might be a bit difficult to be driven from other preamplifiers than the Aleph series.

Please comment on that as I would love to use it on some other preamplifiers as i love tube pres also


Use relays with normally closed contacts, then pull open all but the one(s) you want to use. No magnetic field in the relay in the signal path. I don't think the magnetic field from the others could distort space/time, but anything is possible! Wasteful of current of course, but that's what we like to do here.

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