Od808 Schematic

[YouAre]

I built an od808 from MarkM's layout. I tried PM'ing him for a schematic, but I just found out that he's not online anymore. Does anyone have the schematic for that pedal?

thanks,
murad

[GonzoFonts]

Is this the schematic you are looking for?

[YouAre]

YES! thank you sir.

[GonzoFonts]

You are welcome.

Have fun.

GF

[YouAre]

sorry if my terminology is terrible but....

upon comparing this to a regular screamer...the clipping diodes on the od808 are connected to the negative input of the opamp, whereas the regular ts808 goes to the positive input. Does this make a difference?

[YouAre]

disregard the last post, i just checked a bunch of screamer schematics, and they are consistent with the od808 schematic.

i was looking at THIS schematic http://img113.imageshack.us/my.php?image=fmonts808kj6.png

So is this new schematic flawed in that one spot? Or does it not matter

[Mark Hammer]

The only difference between this and a Tube Screamer is that the TS uses discrete transistors for the input and output buffers, and this uses a dual op-amp.

[YouAre]

yeah thats what i figured. I still feel that it has a more aggressive sound. Like instead of being a nice smooth mid hump, its a little hairier and more crunchy. I don't think its my selection of clipping diodes because i used the same configuration in both. Does the use of dual opamps instead of transistors cause that more aggressive crunchy sound?

[Mark Hammer]

yeah thats what i figured. I still feel that it has a more aggressive sound. Like instead of being a nice smooth mid hump, its a little hairier and more crunchy. I don't think its my selection of clipping diodes because i used the same configuration in both. Does the use of dual opamps instead of transistors cause that more aggressive crunchy sound?

No, it shouldn't, because they are being used simply as buffers and are not being overdriven.  The schematic shows use of LM1458 dual op-amps, however, so there might be something in that, but I'm doubtful.  The actual values of the various components can make a much bigger difference.  You make one cap on the high side of its tolerance range, and a resistor on the low side, and boom you have more gain applied to more bandwidth and a "more aggressive sound".  It happens.

[JHS]

A MC1458 has more gain, is less middy and more agressiv sounding than a 4558D when overdriven. A National 1458 sound even more agressiv and has way better better dynamic response than a MC1458 or 4558D.

The Maxon OD-808 is patterned after the '79-TS-808  which has an identical circuit (+FET switching) with 2 RC1458 chips.


JHS

[12afael]

A MC1458 has more gain

open loop?

[JHS]

A good 1458 produces in a TS circuit a bit more output voltage with less compression than a JRC4558 or RC4558.

JHS

[YouAre]

i'm using regular JRC's, i'm going to try the 1458

[Mark Hammer]

A MC1458 has more gain, is less middy and more agressiv sounding than a 4558D when overdriven. A National 1458 sound even more agressiv and has way better better dynamic response than a MC1458 or 4558D.

Not to question your judgment, but those sorts of claims require some elaboration on the circumstances under which you noticed that.  Are you talking specifically about swapping a JRC4558 for an MC1458 in a TS-9 circuit, or in general?

Not sure how an op-amp could be described as having more gain unless you configure it for more gain, so you'll excuse me if that part doesn't make much sense.

Just trying to clear stuff up before the less-informed take those claims, misconstrue them, and run with them to Harmony-Central.