power mod C7 C8
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Re: power mod C7 C8

by evostars on Sun May 27, 2012 5:31 am

By the way
Power is 9V ac. Gets rectified, so becomes 11.5V. Passes through 100 ohm, and then feeds the opamp...
That opamp will never produce 12V...
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Re: power mod C7 C8

by antto on Sun May 27, 2012 10:19 am

well, yeah.. my 12V is around 11.87 iirc
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Re: power mod C7 C8

by evostars on Sun May 27, 2012 10:53 am

antto wrote:well, yeah.. my 12V is around 11.87 iirc

Measured the ps too?
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Re: power mod C7 C8

by antto on Sun May 27, 2012 11:14 am

haven't but that's the reading for example at the VCO section where it is connected to 12V so..
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Re: power mod C7 C8

by evostars on Sun May 27, 2012 11:18 am

antto wrote:haven't but that's the reading for example at the VCO section where it is connected to 12V so..

Yeah. I guess the ps is never the same.
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Re: power mod C7 C8

by antto on Sun May 27, 2012 11:20 am

component tollerance does make a difference, together with component tollerance of the adaptor (and it's type)

i'm not good with electronics, that's just my impression
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Re: power mod C7 C8

by evostars on Sun May 27, 2012 4:06 pm

antto wrote:component tollerance does make a difference, together with component tollerance of the adaptor (and it's type)

i'm not good with electronics, that's just my impression

Yeah that's what i meant, tolerance of the apaptor, plus the fluctuations of the voltage from the wall. Here its 230V but most of the time it's 235V. Etc...

Time to build...
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Re: power mod C7 C8

by evostars on Mon May 28, 2012 3:28 pm

Building the ps i ran into a problem, i put it in a separate post. Rectifier mod...r
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Re: power mod C7 C8

by aminoacid on Tue May 29, 2012 11:17 am

has anybody measured VCC of the op amp (12V) of the 303? or how much it variates on different 303´s / adapters?
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Re: power mod C7 C8

by aminoacid on Tue May 29, 2012 11:43 am

i was thinking that VCC (depending on the VAC of adaptor) would change the 12V line but thats not how it works if im right...

the 12V line is determined by r178, r179, 5.333V and voltage offset of the op amp.

if i calculated this correct 12V can swing depending on r178 and r179 between 12.53V and 11.23V (regardsless of input voltage offset).

so r178 and r179 would determine the voltage of the 12V line.

ac adapter will determine the current of the 12V line.


i might have to socket r178 and r179 now :)
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Re: power mod C7 C8

by evostars on Tue May 29, 2012 12:13 pm

aminoacid wrote:i was thinking that VCC (depending on the VAC of adaptor) would change the 12V line but thats not how it works if im right...

the 12V line is determined by r178, r179, 5.333V and voltage offset of the op amp.

if i calculated this correct 12V can swing depending on r178 and r179 between 12.53V and 11.23V (regardsless of input voltage offset).

so r178 and r179 would determine the voltage of the 12V line.

ac adapter will determine the current of the 12V line.


i might have to socket r178 and r179 now :)

Just one, 178 or 179. Replace it by a trimpot to adjust the 12v.
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Re: power mod C7 C8

by aminoacid on Tue May 29, 2012 4:20 pm

well how is your psu mod going?
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Re: power mod C7 C8

by evostars on Tue May 29, 2012 6:15 pm

aminoacid wrote:well how is your psu mod going?

I build the PS, and got the right voltages.
But to properly test it, I need to build the VCO and the VCF...
next days I'm busy, so... it will take a while
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Re: power mod C7 C8

by evostars on Wed May 30, 2012 3:53 pm

evostars wrote:Just one, 178 or 179. Replace it by a trimpot to adjust the 12v.


actually its best to replace r178 with a (precision) 4,7k trimpot. I'm gonna do that, so I'll be able to get 12V, although i dont think i really think it will matter...
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Re: power mod C7 C8

by aminoacid on Wed May 30, 2012 4:06 pm

just did it with a multiturn 5k pot.

i dont know whats happening more than cutofff is increasing...

but i liked having the voltage a bit higher how ever.


also i tried two different ac adaptors and seemd to prefer one of them...

i feel a bit like a bull shiter :)
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