[BUILd] PM660 / PM670 SCAmp Booster build and tips help thread

[lolo-m]

Chuck,
Another easy test you can do is to swap the Mode switches from one side to the other if you wired them with connectors on the SCAB. An error in wiring can do tricky things there. Just an idea...

 

[ChuckD]

No I tried that it is the one side as mentoned before.
I took out the board which was really difficult in mine. It is so tight.

I checked all the connections and added the 75ohm resistor since I never did that.
Everything looks good.

Problem is still there.

 

[SIXTYNINER]

hi moby
if the pdf in mediafire is the right one
that in the first page ?

Yes, there's two missing wires on the wiring guide  Grin. It was an evidence to me, but I agree it isn't !!!
The PSU feeds the PM660 board with GND and -17V and SCAB Board with -17V/GND/+17V.

Sorry, my mistake  :-X Here's the revised file  ;D
http://www.mediafire.com/file/mzzwzmmwhy2/PoorMan+SCAB-WiringGuide-R1.pdf

 

[dagoose]

What happens now is that when switched to scamp it works for a few seconds (it compresses) and after like 3 seconds it sounds like a cap discharging and it starts to distort because of the rising level and meters that go positive (From 0 to + 2db) instead of negative (from odb to - ..db)
Does that sound like blown 5534's? guess so..

OK, reposting my old post because it seems that i have the same problem again.
It runs fine in analag mode but when i switch to scanb mode it works for a few seconds and then it sounds like the compression slowly fades away and after about 10 seconds there is no compression.
When i switch back to analg mode again the meters peg and it's distortin because of high gain and after a few seconds it is working fine again and it stays that way.
I checked voltages and they all seem right, any idea where this could be coming from?
I was thinking.. could it be that the 5534's don't like the 17v?

 

[Kingston]

5534 runs fine on 17V rails. The way it behaves now sounds like some cap, probably in the time constant network is connected wrong. Check your time constant networks.

 

[dagoose]

Please call me stupid... :
i recently did some experimenting for what i had to unplug the scamp board i because it was in the way of the trannies i was working on.. since then i didn't really test/use it, just put it back into the rack and it stayed there doingnothing.
I accedentily swapped the ''to attack'' and ''attack''.  :-\
Strange thing is that it is working quite ok in analag mode when you do that (time constant ofcourse not) but in scamp mode it doesn't.
I found out because when i tried to re-adjust the 0v on the attack i could try anything but it stayed 0v. Then i got suspcious and check the wiring.

It's up and running again!  ;D

 

[imo]

just getting back to my PM670 after a loonngg tour. Anyway, it looks like it has been a while since there was any action here, but i had a couple of questions.
1. The 75r resistor is connected to the anode side of the 4007's on the SCAMP board?
2. Where are R* and C*? Are you guys referring to to 'C-L' and 'R-L'? Then according to Chuck's diagram would you plug the time constant 2 pole switch to the R-L pads, with the 'brown' side meaning  pad of R-L that connects tothe left side of the 'to attack R' pads?
3. If you build the 2 pole switch with the 15 and use a DPDT switch as well, then you are replacing the 10k 'attack' pot with the 1st pole of the 6 position switch?

Just wanting to confirm as a lot of connections on this beast, and no comprehensive schematic.
Thanks
Ian

 

[radiance]

Ok, found some time for the poorman. I've read this whole thread, studied all schematics plus guide.
I'm figuring out what's the best way of implementing the time constant switch, or maybe switches.

One question: The "attack" pot does nothing when switched in "fairchild" (non analag) mode right?
The idea is to make your own time constant network by connecting various caps and resistors to the C and R terminals right?

Due to my lack of time the pauses in between working on this poorman are so long that I have to re-read all info every time.
Must be working for more than two years on this project. I keep saying to myself...enjoying the road is more important than the final destination...although it would be nice to eventually finish this project 

 

[radiance]

Is this thread still alive?

 

[loopermc5]

Is this thread still alive?

I'm also just getting to my scamp. Im going to use  switches with 2 decks so in each mode I have my seperate t.c's for each. i will also be wiring the release as a seperate switch. I got the board in and wired just need to complete the switches.

 

[tomcat]

Is this thread still alive?

I hope so ... will start my build next week ... hopefully

 

[radiance]

Is there maybe an updated schematic available? The one I have is dated 13-3-2009 and on that schematic it seems the attack pot is only working in analag mode.
I don't want a pot that's only working in 1 mode. More something like a big rotary switch with 12 presets (taken from both analag & Fairchild (scamb) mode).

 

[tomcat]

Have the same + wiring guide from 1.Jul 2009

 

[radiance]

I'm also just getting to my scamp. Im going to use  switches with 2 decks so in each mode I have my seperate t.c's for each. i will also be wiring the release as a seperate switch. I got the board in and wired just need to complete the switches.

Can you elaborate? Is the release switch done by different value resistors connected to the "R" terminal in the scamb pCB?

Also, will you be using the attack pot at all? Or just switching between different cap values in BOTH analag and fairchild mode?

 

[loopermc5]

well im going to combine jyrki3101 layout on page 7? of this thread and what Veermaster did here
http://www.groupdiy.com/index.php?topic=28274.0  I havnt actually sat down to figure out details yet but it's the basic idea of where i'm going

 

[radiance]

Re-read the whole thread (plus the pimp thread) once more and all's clear now.
One question though: is there a reason we should keep the analag mode at all?
In other words, is there anything special about the time constants from the analag mode or can we get these with the scamb mode as well?
Having these two mode's makes things unnecessary complex on the frontpanel if you ask me....

 

[loopermc5]

Re-read the whole thread (plus the pimp thread) once more and all's clear now.
One question though: is there a reason we should keep the analag mode at all?
In other words, is there anything special about the time constants from the analag mode or can we get these with the scamb mode as well?
Having these two mode's makes things unnecessary complex on the frontpanel if you ask me....

Thats the cool thing about it is you can just go nuts finding the  t.c's that work best for you. I kept the analag tc because I like it no other reason

 

[lolo-m]

Re-read the whole thread (plus the pimp thread) once more and all's clear now.
One question though: is there a reason we should keep the analag mode at all?
In other words, is there anything special about the time constants from the analag mode or can we get these with the scamb mode as well?
Having these two mode's makes things unnecessary complex on the frontpanel if you ask me....

I kept the analag mode as poeple asked for this... You can recreate it with the SCAB but it will be dificult and certainly never be exactly the same. Power to charge the caps in SCAB mode isn't the same than analag's stock sidechain.
Ps: Sorry not to be very active, but I started one year ago the hugest DIY work I can do. I bought an old factory build in 1850 and started to repair it to make a "huge" complex of 6 rehearsal places and my studio inside the 760 square meters I bought... I'm more confortable with hammer and concrete-mixer than with solder-iron at the moment  ;D ! To be honest, my body has never been that painfull...

 

[Kingston]

I built time constant networks so that in some of the range you can have roughly equal timing on both scamp and the plain mode. They don't sound the same at equal time settings because they have different attack and release shapes. Scamp has a much more abrupt discharge of the cap so even if calculations say "equal" they are not.

I would advice to keep both modes available for flexibility. Most of the time the plain mode is fast enough and sounds very "natural", say 2-4uF (medium attack) with 50k-150k in parallel (fast/medium release). With scamp it becomes harder to tell settings at that range apart as they will always be very fast.

Thanks lolo-m for the scamp board again, it really helps with flexibility.

 

[radiance]

For experimental reasons I have now the release resistors replaced with a 470K pot.
When doing clean compression I can't hear any fine adjustments but when things are a little distorting these fine adjustments are very nice to have for tone shaping.
Any reasons why I should NOT go for a pot instead of fixed resistors?