big muff opamp version

[nelson]

I've checked the schematic that I worked from and it matched my real BMP3. I went through a couple periods of obsessing over it and retraced my real one over and over, and tried to perf it up a bunch of times, and then I finally made a pc layout and that's the one that finally worked for me, though like I said, the output level is quiet compared to the real thing.

Roger

Which Schematic did you work from?

[Gila_Crisis]

a pair of things i wanna try that i saw on the DBM schem are the 24.3k resistor in place of the 62k and a 47ohm in place of the 10k just after the first half of IC1.

[nelson]

a pair of things i wanna try that i saw on the DBM schem are the 24.3k resistor in place of the 62k and a 47ohm in place of the 10k just after the first half of IC1.

The 47ohm resistor is there in other versions.

Let's look at the non-inverting opamp stage.

(ignoring the cap to ground)

In my version the gain = (560K/62K)+1

Gain = 10


In the Japanese schem:

Gain= (220K/24.3K)+1

Gain=10


Makes no difference.

[Gila_Crisis]

oops... i didn't notice the 220k ....
but if you leave the 560 then you have (560/24.3)+1 = a gain of 24!

[nelson]

oops... i didn't notice the 220k ....
but if you leave the 560 then you have (560/24.3)+1 = a gain of 24!

Er, there is no 560K resistor.....

[Gila_Crisis]

ehm my idea was to change in the 560k/62k (like in your schem) the 62k resistor with a 24.3k

[nelson]

ehm my idea was to change in the 560k/62k (like in your schem) the 62k resistor with a 24.3k

ahhh, ok. I don't see much point.

[Gila_Crisis]

do you mean it?
i got 2 schem i found on japanese sites about the Deluxe BM and both have a 15v bipolar supply

I have those schematics too (seen the thread). They don't show bipolar, they show single polarity +15v.
Personally, I think this is a mistake, or EHX subbed some of the transformers in some units. Bernaduur measured 9v on his Deluxe which matches the japanese deluxe except for V+.

I checked those schems again and you're right! one works with 9V and the other with bipolar 5V! on the japanese i don't know why i thought i read somewhere 15..... shame on me

[Gila_Crisis]

so i finlly got back my OPBM and i tried some mods on it. all those mods are based on many schems i found around of BM1977/1978 and Deluxe Big Muff.
the result is more volume reserve and e brighter livefull sound. enjoy!

[nelson]

I have updated my opamp muff page with a new layout - this is the 1977 opamp muff with "sustain" mods.

http://electroconducive.googlepages.com/ehxopampmuff