Metropoulos Forum

MarkCameron wrote:

jerrydyer wrote:sorry for the strange terminology. I use above or below meaning the cathode 100k is below and the blank wire where you might add the 100 k plate resistor and then draw from that instead of the cathode. Ill get it straight someday. Cant wait to try the Rocco on my 2204 though and that diode mod from Larry and Mark. I've been so damn busy. I work for a criminal defense attorney in So Cal. DUI's anyone? ?

Just by looking at the schematic.... the main thing that i see wrong with that circuit is that there is to much bass in the begining of it, Try this.. take the .001 off change the 1uf/1.5k to 2.7k/1uf....33k to 1.8k/1uf..... 4.5k to 1.5k ....put a 470k/500pf to ground at the input of v3b I think that should get you closer. I think you said you are in Ca. (la?) if you need help call me 818-445-2059

i almost posted something similiar 'replace all cathode resistors with 1.5k and see where u are then'- i agree the cathode resistors are way to big. u rock Mark!

thanx guys ... Hey JNGREENe79 there ya go. Its his schem.

just saw a new post pop up .....I'm just getting back here after work and see a lot of replies. I don't know which schematic everyone's referring to, but I'll pretend it was the one I posted. By the way, i need to clear some space on my metroamp account so i can post it here... I did the schematic last night after Mark asked. BTW, those are 22nf (or .022uf). Mark C. - Remove the .001 cap and lower the cathode resistors? I've tried lots of combos, but almost always one or two large resistors with no bypass cap to tame the gain a bit - in theory... It may be making it sound like shit, though. I thought lower cathode resistors would add too much gain to the lower freq. I'll try the cathodes this afternoon/evening. Thanks guys, James

jngreene79 wrote:just saw a new post pop up .....I'm just getting back here after work and see a lot of replies. I don't know which schematic everyone's referring to, but I'll pretend it was the one I posted. By the way, i need to clear some space on my metroamp account so i can post it here... I did the schematic last night after Mark asked. BTW, those are 22nf (or .022uf). Mark C. - Remove the .001 cap and lower the cathode resistors? I've tried lots of combos, but almost always on or two large resistors with no bypass cap to tame the gain a bit - in theory... It may be making it sound like shit, though. I thought lower cathode resistors would add too much gain to the lower freq. I'll try the cathodes this afternoon/evening. Thanks guys, James

lowering the cathode values will give more gain - raising them makes things fatter and less gain.

I'm on it. I might ditch the CF for a test run. One more thing. At home, my speaker/cab setup is a DIY open back 2x12 (greenback and Weber silver bell Alnico). I love the way it sounds... I go to band practice and try it through a 4x12 and it sounds like shit next to a 1987. Might as well be a dual recto - buzzy and inorganic. My theory when building Marshall stye amps is: If it can't sound good in a 1960 cab, it needs to be re-done.,

Cool thread. I'm currently building this:

http://www.thinlizzy.de/idee.gif (schem)

here's a pic:
http://www.thinlizzy.de/NewAmp/DSC00077.jpg
http://www.thinlizzy.de/NewAmp/DSC00078.jpg

Chassis is Herbert, Trannies/Choke are VH4. The "Plexi" channel has no master, the crunch/lead has two plus switchable - and two loops.

DANG ! very nice very clean so far . beautiful cant wait to hear it

so i did larrys diode mode and i like it doesnt sound very solid state at all it just sustains and compresses a little. very cool. i dont know if i am smart enought to post a sound clip though.

jerrydyer wrote:so i did larrys diode mode and i like it doesnt sound very solid state at all it just sustains and compresses a little.

Up to gain 5...7 it's nearly not audible at all, that there are diodes in the circuitry - only higher dynamic peaks will be compressed. First when you crank further, the signal swing becomes that much, that it becomes clipped by the diodes more and more. And because the diodes only are clipping one side of the swing, a certain amount of K2 (the first octave) will be produced, what makes the sound fat and juicy w/o flubbyness.

Larry

interesting build Olaf You've always got interesting amps and ideas. Something I always struggle with is switching... It's nice to have flexibilty, but you sacrifice something always. What type of switching/relay power schematic do you use? I hate messing with them and I can't find something that's quiet and compact. nothing's worse than running grid wires across the chassis in a high gain amp...
Larry, for the hell of it, I put a 5v zener in my nmv plexi (volume pot) It didn't do anything because the voltage never got high enough to clip. what about putting this before the cf? would you need a lower voltage zener? -james

interesting build Olaf You've always got interesting amps and ideas. Something I always struggle with is switching... It's nice to have flexibilty, but you sacrifice something always. What type of switching/relay power schematic do you use? I hate messing with them and I can't find something that's quiet and compact. nothing's worse than running grid wires across the chassis in a high gain amp...
Larry, for the hell of it, I put a 5v zener in my nmv plexi (volume pot) It didn't do anything because the voltage never got high enough to clip. what about putting this before the cf? would you need a lower voltage zener? -james

interesting build Olaf You've always got interesting amps and ideas. Something I always struggle with is switching... It's nice to have flexibilty, but you sacrifice something always. What type of switching/relay power schematic do you use? I hate messing with them and I can't find something that's quiet and compact. nothing's worse than running grid wires across the chassis in a high gain amp...
Larry, for the hell of it, I put a 5v zener in my nmv plexi (volume pot) It didn't do anything because the voltage never got high enough to clip. what about putting this before the cf? would you need a lower voltage zener? -james

rockstah wrote:just do the rocco spec. the suggestions i would give would be very similiar to it. i even added a 4th tube to get back my cathode follower that the rocoo spec omits and didnt like it as much. ( i must adimit i didnt mess with this particular spec much) and went back to teh original spec of 3 tubes.
its one spec ill be going back to since i still havent found anything better for that kind of sound. its a keeper for me.

Rockstah,

Do you have an assload of gain with the rocca spec? I did, it was way to much.

By the way the actual rocca spec uses 1meg linear pots for the bass and master volume. You'll notice a lack of low end if you don't use the linear pot on the bass. If you don't want to change out the pot you can replace the .022uf bass tone cap with a .1uf. On a scope its basically the same as using a linear bass pot.......not exactly but the eq curve is very close.

jngreene79 wrote: Larry, for the hell of it, I put a 5v zener in my nmv plexi (volume pot) It didn't do anything because the voltage never got high enough to clip. what about putting this before the cf? would you need a lower voltage zener? -james

I've never tried it in a NMV design, but in a MV design you'd get very good results.

Larry

jngreene79 wrote:interesting build Olaf You've always got interesting amps and ideas. Something I always struggle with is switching... It's nice to have flexibilty, but you sacrifice something always. What type of switching/relay power schematic do you use? I hate messing with them and I can't find something that's quiet and compact. nothing's worse than running grid wires across the chassis in a high gain amp...

As you can see, James, I'm using a mix of relays and AQYs (PhotoMos-Relays). The AQYs are putting unused channels to ground. Their advantage vs. VTLs is, that they are less sensitive and have much better specs than the VTL - only drawback is their (nano) size.
The powersupply in my amps never comes off the filaments, but either additional trannies or a separate winding on the transformer (like in this, which is 15V downregulated to 6V with a 7806). Intensive filtering and trying around where to ground the switching circuitry is IMO the key - and some additional 1M to 2M2 resistors. Relays are made by "Finder", which do their job flawlessly and pretty quiet.
I'm pretty sure that the "Plexi" adding will make some noise with realy only, so it could be possible that I'll do the switching between crunch/Plexi also with AQYs, triggered by a relay. Thats why I have three DPDT relays in there.