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Help with hot 4250s in CGS wave multipliers

Help with hot 4250s in CGS wave multipliers

2015-04-28 by spunraddish

Hey guys, my first post here. I wired up my wave multipliers, and almost burned myself on the 4250s - there was no smoke, and I was able to turn it off before anything got destroyed, or so I think, since when I would power it on again, the same thing would happen. I think I've used these 4250s before with other cgs boards, but didn't have to flip them around.


The top and middle section of the wave mults output nothing audible, though there may be a dc offset on the outputs, and the bottom section sounds beautiful.


I don't know much about the 3080s, they aren't a pressing matter with such heat coming off the transistors.


Any ideas?


Thanks,

Eric

Re: Help with hot 4250s in CGS wave multipliers

2015-04-28 by Ken Stone

Is it a 74HC4250? If so, you have the wrong part. I suggest you read the parts FAQ, as it covers the issue. Basically, there are 5V chips that use the same numbers as the CMOS chips, and they get stinking hot.

Ken
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On Tue, Apr 28, 2015 at 2:49 PM, spunraddish@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:

Hey guys, my first post here. I wired up my wave multipliers, and almost burned myself on the 4250s - there was no smoke, and I was able to turn it off before anything got destroyed, or so I think, since when I would power it on again, the same thing would happen. I think I've used these 4250s before with other cgs boards, but didn't have to flip them around.


The top and middle section of the wave mults output nothing audible, though there may be a dc offset on the outputs, and the bottom section sounds beautiful.


I don't know much about the 3080s, they aren't a pressing matter with such heat coming off the transistors.


Any ideas?


Thanks,

Eric




--
Ken Stone otherunicorn@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>

Re: Help with hot 4250s in CGS wave multipliers

2015-04-28 by Scott Young

I think they could need reversed. Ive had similar issues with these when I was building the Smooth / Stepped Generator, in that I think the part number I had was PN4250A which had a different pinout to the PN4250 layout on the board. Also, from the documentation of the Serge noise source module:

"Note that the orientation for the transistors on the overlay is for vintage 2N4250 and 2N3565. The pinout of modern PNXXXX devices is usually the reverse of what was used with the 2NXXXX devices. In this case, BC557B and BC547 variant can be used as direct replacements for the vintage transistors, or PNXXXX devices can be used, but installed in reverse with respect to the transistor outlines shown on the PCB. Whatever your choice, the tiny transistor schematic symbol within the "D" is correct and can be followed. “

So it might be that you’ve used this before and it worked out OK because you were building it for a board marked with the PN4250 pinout rather than the 2N4250?

Cheers,
Scott.
1a Help with hot 4250s in CGS wave multipliers
Mon Apr 27, 2015 9:49 pm (PDT) . Posted by: spunraddish
Hey guys, my first post here. I wired up my wave multipliers, and almost burned myself on the 4250s - there was no smoke, and I was able to turn it off before anything got destroyed, or so I think, since when I would power it on again, the same thing would happen. I think I've used these 4250s before with other cgs boards, but didn't have to flip them around.


The top and middle section of the wave mults output nothing audible, though there may be a dc offset on the outputs, and the bottom section sounds beautiful.


I don't know much about the 3080s, they aren't a pressing matter with such heat coming off the transistors.


Any ideas?


Thanks,
Eric
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Re: Help with hot 4250s in CGS wave multipliers

2015-04-28 by Ken Stone

Doh! Transistors not chips. Scott has the right idea.
Show quoted textHide quoted text
On Tue, Apr 28, 2015 at 3:00 PM, Ken Stone <otherunicorn@...> wrote:
Is it a 74HC4250? If so, you have the wrong part. I suggest you read the parts FAQ, as it covers the issue. Basically, there are 5V chips that use the same numbers as the CMOS chips, and they get stinking hot.

Ken

On Tue, Apr 28, 2015 at 2:49 PM, spunraddish@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:

Hey guys, my first post here. I wired up my wave multipliers, and almost burned myself on the 4250s - there was no smoke, and I was able to turn it off before anything got destroyed, or so I think, since when I would power it on again, the same thing would happen. I think I've used these 4250s before with other cgs boards, but didn't have to flip them around.


The top and middle section of the wave mults output nothing audible, though there may be a dc offset on the outputs, and the bottom section sounds beautiful.


I don't know much about the 3080s, they aren't a pressing matter with such heat coming off the transistors.


Any ideas?


Thanks,

Eric




--
Ken Stone otherunicorn@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>



--
Ken Stone otherunicorn@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>

Re: Help with hot 4250s in CGS wave multipliers

2015-04-29 by spunraddish

Alright, I switched out the transistors for BC557s, and the first two stages had barely any give at the front end. Scott was right, I used PN4250s when I should have placed them backwards. I ended up burning out the two 3080s - expensive mistake. I had two more, though I know I should have gone the 13700 route. Still, it works beautifully, what a monster.

Thanks for you help, Ken and Scott!


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