Phatline

dout > lo-fi audio switch (transistors?)

10 posts in this topic

i need some audio-switching in my crumars 198 organ,

the bass pedal is just a analog switching matrix, which decides which note will be played... to bad that all 13 notes via AUDIO are going to the pedal, not the other way around (not:pedal send gates to oscillator...this: frequencedivider sends audio signals to pedal)

i want to controll the bass section via midi... or better said via a doutmodule > 5V > sound, 0V > no sound.

so i need 13 Dout Pins = 2xHC595, done

i dont want to use releais to swich all the 13 audio signals...

i dont have a problem with  distortion... ( i thought of Transistors???)

i want that it is quiet when the 595 is LO.

the Audio signals are coming from a frequenc devider IC that sends out 6V Sinus, the orginal shematic sends that signal thru a 100K resistor, and it ends with an voltage @ 265mV.... and the worst: the "orginal shematic" i buyd is not identical with the reality i have in front of me...large.pedalboard-shematic.JPG.83eb2e822dlarge.pedalboard-picture.JPG.8eb46bfaf37

i thought of using a bc547, in a shematic like in the sid module... by feeding the emitter with the 5V from the dout-pin,... when i now switch the DOUT off (lo) or clamp it to ground, i get a Base-Collector voltage by around 20mV, which is enough to be heard.......a resistor @ audio-out from that circuit end up by lowering the loudness in hi-state...

 

a played around with potentiometers to set up the bc547...not worked @all, i think i have problem, which i cant solve alone > thanks

 

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Hello Phat

Not sure to understand everything.

What I see, is a DPDT switches for each note (pedal).

Transistor act as SPST, plus you don't want your digital DC signal going at audio side.

One thing I have in mind now is an optoisolator switch driving 4 FET (2P and 2N chanel) ???

Also have a look for "analog switch" IC, some ships are "rail-to-rail" for the analog side switching, but it still in most case 0/5v supply so your 6v sin (pk? rms?) will clip...

Zam

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hi!

Digital DC & Tranisostors: is there a change to clean that DC with a Capacitor? Transistor would be the cheapest soluditon

it is not necessery to be DPDT.... it is also possible to hear all notes together (i soldered 2 "Notes" together and there is no problem), i could do that software side anyway (but i dont need it)

6VAC peak...: @ the end of the day i need 0.26V to drive Bass-Post-Amp, so it want peak.

as far as i know from transistors is: that there is a BASE-Collector Voltage, even if there is no Voltage on the Emitter - so have a LEAK, i measured 20mv, which i alreaedy said - is hearable  as silent bass (since the base is the bass-signal).... i was thinking to make a noise-gate circuit after summing all Bass-notes...but then i thougt when i summing all 13 Bass-Notes, with its 13 20mV leaks, it would be pretty loud, and maybe then i have to set the threshold to high...and also i will hear all notes together - of course the played note is louder then the other,there will be "hum" if i cant avoid the B-C-Leak.

 

i searched for analog switch ic, and found this:

MAX4066:

http://www.mouser.at/ProductDetail/Maxim-Integrated/MAX4066CPD+/?qs=sGAEpiMZZMvbyeSUH4qH%2fNdIvyU6Oqzm

http://www.mouser.com/ds/2/256/MAX4066-MAX4066A-72194.pdf

...i am looking for a lofi locost solution.... when i want it better i just connect my waldorf pulse via midi to the pedal.

but 2.66€x5=14€... thats ok

do you think the max4066 could do the job?

 

optoisolators are to expensive (keep in mind there are x13notes)

 

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hey

 

are you sure you don't need dual throw switching???

max4066 (or similar dual or quad DT) deserve a try.

opto like 4N25 is 30c...I don't call this expensive :)

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Pharline,

I think you best bet to use the reed relay approach that is described on the midibox website.  That way you will get the o imped. connection.

johnc

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yes i am sure... the other contacts are for rythm automatic, and autocord stuff... wich i completely replaced with my own things...

 

@reed relais as describet here 1,54€x13= 20€  http://www.reichelt.com/SIL-7271-D-5V/3/index.html?&ACTION=3&LA=446&ARTICLE=27672&artnr=SIL+7271-D+5V&SEARCH=sil7271

max4066 =15€

4N25 0,25€*13=3,25€ http://www.reichelt.com/index.html?&ACTION=446&LA=446

but i am doing hard to find a 2n 2p fet, and i dont have any expirence downside pipolar transistors

 

 

 

 

 

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Yes I see you have a rythm trig at the top raw switch, so single pole is ok, but I still saw a dual throw switching ?

Small signal jfet is easy to source, don't they have some at reichelt ?

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you see right, but, thats also for some play-automatic thing which pcb´s i already trashed. the bass working great with only the middle row switch parts...

ya reichelt: http://www.reichelt.com/index.html?&ACTION=446&LA=446&SEARCH=jfet&OFFSET=16&SORT=artnr&SHOW=1

or english:

http://www.reichelt.com/index.html?&ACTION=446&LA=446&SEARCH=jfet&OFFSET=16&SORT=artnr&SHOW=1

 

but 2n 2p jfet > like i said > i know nothing about fet-types - is there a nother word for that 4channel type you suggested? I am interested in this because up to now it seems to be the cheapest solution.

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jfet transistor !!! not op-amp :) i have in mind J112 or bf245 etc...

I don't know now, maybe as John suggested, reed is certainly the easy solution if you need SPST only. He also made a point about ON resistance

Don't have you some around to check commutation noise at audio side? can't be way worst than original mechanical switches!  because all other solution event fet switching will have commutation noise 99% of the time. In fact each time you switch with the audio wave not null. A zero crossing detector switch is another story... (is max4066 fitted ???)

1.5euros reed with only 4 wire and one resistor to solder is maybe cheaper than IC or opto+fet with more complicated layout, reed give you isolation and no control voltage involved at audio side, that's two important requirement.

Is that saving few euros interesting if you consume days and brain for a solution that maybe is not more efficient ?

Zam

 

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ok then reed relais - thankz folks.

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