voice modulator. A little advice please.

Thread Starter

Fenris

Joined Oct 21, 2007
288
Hello there

Well here's my take on the modulator design with longevity in mind as well as availability of components.

Currently I've only drawn up a wein bridge but am looking to have, possibly, a triangle wave form as well. Purely to add to the variety of the effect. I haven't added component values yet but what do you think?

regards

Fenris
 

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SgtWookie

Joined Jul 17, 2007
22,201
Hi there

I have been looking at boost converters and the like and have come across this circuit. It boosts 12VDC to 24VDC @ 800mA. Is it feasible to then add a resistor divider with complimentary caps or an op-amp based circuit to split the 24V into +12V, Gnd, -12.

http://www.circuitstoday.com/12v-to-24v-dc-dc-converter

I appreciate there may be losses but would there also be an adverse effect on how the 800mA is split?

Of course if anyone can point me at a relatively simple positive to negative circuit with enough oomph to drive a few op-amps AND a bridged TDA2003. The TDA is not a must have but is of interest.

regards

Fenris
Hello Fenris,
I started looking at this yesterday a bit. The inductor he wound on a Sendust CS166060 toroid works out to be about 122uH. After double-checking his numbers, he could not have used 60 turns of AWG22 wire, as it would not have fit. He must've either used AWG-25 (would have been tight) or AWG-26.

Secondly, he used an LM324. While this is not a completely horrible opamp for very low-speed use, it is absurd to use it as an astable multivibrator to drive an SMPS, because it simply does not have the necessary bandwidth.

The choice for Q1, a BD139, isn't all that bad, but R7 being 420 Ohms would not allow Q1 to saturate past around 230mA collector current; maybe on a good day with a tailwind it could get ~ 500mA collector current. With a 50% duty cycle, that means a maximum of 250mA output.

Also, they used an FR502 and 1N4007 diodes; there are simply far better choices they could have made. The 1N400x series diodes should not be anywhere near the switch in an SMPS. The FR502 isn't as bad; it's 5A @ 100PIV, but recovery time is ~150nS. A Schottky diode would have 1/10th or less that in recovery time, which means less power loss. There is no need to have a high Vf for these diodes; anything over 30v would be OK.

I think this circuit is simply a case of wishful thinking on the part of the person who posted it; it's as if they just drew something up, but never actually built it.

I have a circuit using a 555 timer around here somewhere; it's actually reasonably efficient, quite simple, and I doubt that they will ever stop making 555 timers.
 

Thread Starter

Fenris

Joined Oct 21, 2007
288
Hi Sgt

The power trickery is grabbing my interest. I had a look round the forum but my 'search Fu' must be a tad weak :D But googling has brought a few items of interest.

A 555 based negative from a positive supply. Not sure what mA it can handle. I have also found a 24V from 12V circuit based on readily available components. I had a bit of fun using google translate to change the Spanish text to English and it all seems very doable.

The CA3080 IC's should be with me soon so I plan on knocking the -VE 2 +VE circuit up as well. Obviously to run on 9V IN. Would the Zener diode require changing?

The ring mod circuits with those 'hard to get IC's' I am going to draw up on vero boards with a full parts list and basic guide and pointers to suppliers who still stock 'those IC's'

I'll then put them in the voice mod section of the dalek forum as 'alternative' options to dalek voicing. I'll pop them in the projects section here as well when I've done them. They may be of interest to someone.

There is a little 'oddness' with the translation of the 12V 2 24V text but it seems to make sense.

regards

Fenris
 

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