Mn3207, 3102 testing

[Locrian99]

Hello,

So I picked up a few mn3207, mn3102 sets from some Chinese seller on eBay.   With the idea that I'd test them before actually putting them onto vero or a pcb.   I searched around and found this circuit.




Put it together on a breadboard.   And the first mn3207 starting smoking and got really hot.  Not looking good... second set though works.   The effect from this circuit seems pretty subtle almost like a hall type reverb I guess.   But it's there (comment in original thread makes me think that is correct effect).   The weird thing is though when I audio probe the circuit at pin 8 of the mn3207 I have a high pitched whine or hiss, this goes away around q2, probably filtered out by the cap right there I'm assuming.   Is this normal?   I wouldn't be concerned normally since it's gone by the output.   But since a big part of the purpose was testing these I'd thought I'd ask.   

I isolated the grounds so the only place the grounds from the mn3207/3102 side hit the signal side is actually at the test box ground (I just realized the 3207 has signal so there's one spot they mix oops I can fix that easily enough.).  Here's the breadboards...





Anyways yes mainly concerned with that hiss/whine oh and also if I want to try to make the delay time a little longer or just to play with it where do I add a pot, sounds like the resistor between 6/7 on the clock is for wave form.  Couldn't find anything on delay time in my looking. 

Thanks again

[ElectricDruid]

And the first mn3207 starting smoking and got really hot.

Ouch!

Not looking good... second set though works.   The effect from this circuit seems pretty subtle almost like a hall type reverb I guess.   But it's there (comment in original thread makes me think that is correct effect).

From the schematic, it looks like a single echo, so I'd expect something more like a "slapback" effect. There's no recirculation/feedback of the delayed signal to give multiple repeats.

The weird thing is though when I audio probe the circuit at pin 8 of the mn3207 I have a high pitched whine or hiss, this goes away around q2, probably filtered out by the cap right there I'm assuming.

Yes, some clock feedthrough at the output of the chip would definitely be expected. You'll see some circuits include a trimmer there to reduce it by balancing the signals from pins 7 and 8 better, and while that might help *a bit*, it never entirely rids you of it. That's why the following stage around Q2 is a filter to remove clock noise.

Is this normal?   I wouldn't be concerned normally since it's gone by the output.   But since a big part of the purpose was testing these I'd thought I'd ask.

Yes, entirely normal, I'd say.

I want to try to make the delay time a little longer or just to play with it where do I add a pot, sounds like the resistor between 6/7 on the clock is for wave form.  Couldn't find anything on delay time in my looking. 

Yes, you could replace the 33K resistor between pins 6 and 7 with a pot to get variable delay time. Maybe add a 1k / 2k2 / 4k7 resistor (I'm guessing!) in series with the pot so that the resistance can't go to zero, in case that might fry the clock chip. Be aware that the filter is probably set up for the clock frequency that is currently used. A filter cutoff at 1/3rd of the clock frequency is usually recommended, but some people push that to 1/2 to try and get a bit more bandwidth at the cost of more noise. If you change the clock frequency, you might need to increase the caps in the Q2 filter. Usually with filters, you're ok if you shift things by the same factor: e.g. to go down an octave, double both caps, so 2n2 become 4n7, 10n becomes 22n. You get the idea.

If you halve the 33K value, you'll double the clock frequency, so you could halve the filter caps too. If you double the 33K value, you'll halve the clock frequency (and double the delay) so you'd also need to double the filter caps.

Hope this helps.

[Locrian99]

Hey thanks.   Yes slapback is probably more accurate than my reverb description.    Recalling what something sounded like is not my forte I was more just happy there was an effect after the first one fried.   Still on the breadboard I'll try some of those suggestions out and see what I can get.   Just wanted to experiment a bit with it since I have two sets and only one set is going into a planned circuit ag this point.