digitally controlled stepped attenuators..??

[mcs]

I finally assembled and tested the control board. Here's a (crappy) picture:

The picture shows the "Moby special edition" with an encoder and no buttons. The position is stored in the E²PROM whenever the posistion is changed.

Other options could be to use a "store" button to save the setting.

Best regards,

Mikkel C. Simonsen

 

[rafafredd]

MCS, that´s just amazing. Let us know when you have installed in an unit.

 

[mcs]

[quote author="pilo"]So I would like to know what are the best value for log and/or anti-log curve?
I don't really know which value to "keep" : 0db, -1db...
Or can I use other value?[/quote]
Sorry about not answering sooner - I didn't notice your post.

I don't know either. I have asked before what the "perfect" taper should look like. What I did was to measure the values at the 32 "clicks" on an old Alps "Black Beauty" pot. I have those values written down somewhere - should I dig those up?

Best regards,

Mikkel C. Simonsen

 

[mcs]

[quote author="rafafredd"]MCS, that´s just amazing. Let us know when you have installed in an unit.[/quote]
That probably wont be me - I never get my own stuff finished...

Best regards,

Mikkel C. Simonsen

 

[Moby]

that probably wont be me - I never get my own stuff finished...

HA! :wink: But i must say THANKS Mikkel, you are genius :!:
I never saw so fast and precise work. Simply i cant wait to drop ATMELS into pcb and hear that nice relay clickin. And, one thing... i will make all attenuators in master console with this little "clickers". Hope that wont last forewer

 

[mcs]

I just drew a PCB for the 6-relay volume control version discussed above. Here it is:

I know it could be made smaller, but I wanted to keep the capacitances low. Here's the final schematic: http://stiftsbogtrykkeriet.dk/~mcs/RelPot/6BITATT2_SCH.gif

Best regards,

Mikkel C. Simonsen

 

[Moby]

Looks cool :!: And i like size of, easyer to solder :wink: BTW, as i can see, thats the stereo or balanced version? Right? :roll:

 

[mcs]

[quote author="Moby"]BTW, as i can see, thats the stereo or balanced version? Right? :roll:[/quote]
Yes. Do you want a mono version? The relays for that will probably be more expensive :grin:

Best regards,

Mikkel C. Simonsen

 

[daArry]

w0w

more great stuff :thumb:

So how does the magic work in this one then? U get control on a stereo source and with only 6 relays?? Does it work in the same way as the 8 relay pot brd but just less steps? Can set various tapers and so forth ye?

Nice1

D

 

[mcs]

Not much magic :green:

It's not quite the same as the 8 relay board - this is (only) an attenuator. You can attenuate an input signal in 63 same-size steps. With the values shown on the schematic it's 0-63dB. You can change the step size to 1.5 or 2dBs (or whatever) if that suits the purpose.

It works the same as the 8-relay board at the programming level, but now with 64 steps instead of 256.

It's basiccaly the same idea as the TI/Crystal attenuator chips, but without the need for opamp buffering...

Best regards,

Mikkel C. Simonsen

 

[PRR]

Mikkel, how does this "sound"?

I don't mean the resistors and relays. I mean: if you change the setting while music is playing, are the steps audible or subtle? 1dB steps are nearly inaudible on a Pro-type rotary attenuator, but the relays have switch-over time. But maybe small?

Would you change gain in the middle of live classical recording, if the alternative was overload distortion from unexpectedly high crecendos?

 

[mcs]

[quote author="PRR"]I mean: if you change the setting while music is playing, are the steps audible or subtle? 1dB steps are nearly inaudible on a Pro-type rotary attenuator, but the relays have switch-over time. But maybe small?[/quote]
I haven't been able to hear the steps on the prototypes I have made, but I guess I should try to record the signal and listen without the relay-noise.

Would you change gain in the middle of live classical recording, if the alternative was overload distortion from unexpectedly high crecendos?

I'll answer that after I record something :grin:

Best regards,

Mikkel C. Simonsen

 

[PRR]

> I'll answer that after I record something

I'd be fairly interested to hear your observations (and samples if possible).

It would be useful to have better gain-control in live recording. Pots go scratchy and never track stereo perfectly, VCAs are fussy and of dubious transparency in minimalist systems, analog switches mostly have limited voltage and current handling ability. Relays and resistors are close enough to perfection for me when static, but I don't know if small relays switch fast enough to avoid dropout or bumps. (Your resistor topology is the best I've seen for potentially switching without bumps.)

Obviously relay-clacks would be a problem when I am in the same room with the string-trio, but that can be solved with metal and foam.

 

[Moby]

Would you change gain in the middle of live classical recording, if the alternative was overload distortion from unexpectedly high crecendos?

I was thinking about same thing, but for mastering purpose... I cant wait to hear results :roll: Of course, i dont mind because of clicking in box, but if i try to use it for remote preamp i will go with foam and hard boxing :idea:
Also what you guys think about difference between reed and usual type of relays? Is there any sound difference?

 

[mcs]

[quote author="PRR"]I'd be fairly interested to hear your observations (and samples if possible). [/quote]
I can see the glitches from the switching, but I can't really hear them. Here's a "closeup" on the waveform: http://stiftsbogtrykkeriet.dk/~mcs/Relay_glitch.gif

Here is a sample in wav format (about 5MB) or MP3 format (about 500kB):

http://62.242.11.12/Shalimar/Air.wav
http://62.242.11.12/Shalimar/Air.mp3

Best regards,

Mikkel C. Simonsen

 

[Moby]

I can see the glitches from the switching, but I can't really hear them

I hear some digital errors in fade in and out :?: Is that weakness of A/D converters, or something else? I hope that is not relay glitches

 

[mcs]

[quote author="Moby"]

I can see the glitches from the switching, but I can't really hear them

I hear some digital errors in fade in and out :?:[/quote]
Do you mean the his/noise? That's something in the ADC or recorder - I don't think relays can make that kind of noise :grin:

Best regards,

Mikkel C. Simonsen

 

[PRR]

> Do you mean the his/noise? That's something in the ADC or recorder - I don't think relays can make that kind of noise

There is hiss and/or fuzz, not any relay-noise that I can hear.

Zooming in on the wave, I don't see the faults I had always assumed a relay-attenuator would cause. Interesting. There are some odd waves, but I can't tell if they are switch-points or just the source.

A VERY tough test would be a pure sine or triangle wave from a decent signal generator. But a switched attenuator can "fail" that test and still be perfectly acceptable on music.

 

[mcs]

[quote author="PRR"]A VERY tough test would be a pure sine or triangle wave from a decent signal generator. But a switched attenuator can "fail" that test and still be perfectly acceptable on music.[/quote]
I'll try that later tonight. Only sinewaves though - my 200CD doesn't do triangles ...

Best regards,

Mikkel C. Simonsen

 

[PRR]

> You have to program the "logic" into the chip.

I know what this means in general, but what do I do?

I've worked with the Parallax Basic Stamp SBC. You write code on the PC, upload it into a port on the SBC, and it runs.

And I'd think the Basic Stamp would be "good enough" for basic control of your relay board.

The Stamp isn't really fast enough for what I would like to add: automatic gain control with limiter-like speed. In short: watch the "Overload" light on the recorder (or a level sensor on the signal) and if it goes "over", count-down the attenuation until it isn't-over. That needs sub-milliSecond response, plus lower-prority tasks like checking user-inputs, updating the display, and sneaking gain back up if the OVER light has been off a while. Since the Stamp is basically a BASIC interpreter, it isn't that fast.

I know the PICs run machine language and a 2MHz machine ought to be fast enough. But I won't write machine code (been there). Can you write in a higher level language and get clean code?