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

[lolo-m]

Moby, lightening fast, as ever  ...

Updated 1rst post with new wiring guide  .

 

[dagoose]

I'M in the middle of implemeting the scab-board in my pm670 and i was wondering about a few things.

Is it correct that the -17v and ground to the PM boards are both disconnected? i can imagine the -17v but the ground= earth or am i missing something here?

I dind't realize that the 10uf on the scam board is replacing one 10uf of the PM board.
I have wima's on the PM boards but i have a cheaper epcos poly cap (191-2948 RS) installed on the scab and so i'm wondering if it's better to desolder the wima and stuff it on the scab board.
It will be a bit harder and a lot more work because the wima's are a lot higher then the epcos caps and i have to put the scam board on a different place in the case. Now it fits above my XLR connectors with the transistors isolated mounted to the case. So.. will it make any difference if i use the epcos?

Is it a problem if i leave the discontunued 10uf wima on the pm board or shall i remove it anyway?

Can't wait to hear the scab mod! i only need some switches for the scab but i was also thinking of using the same switch as the bypass but with relays swithing in the 2 modes. you just need 12v to swith in the relay in scab or analag mode so 2x relay will do the job, will save some wiring.

 

[Moby]

I don't think there will be any difference between wima or epcos poly caps. This is sidechain and no audio is running through. Just DC time constant network. I will remove wima's and use it on some more critical place 
Regarding wires check the revised wiring guide.

Can't wait to hear the scab mod!

hehe, "SCAB MODE", sounds awful 

 

[Kingston]

Is it correct that the -17v and ground to the PM boards are both disconnected? i can imagine the -17v but the ground= earth or am i missing something here?

oh come on! read like the two posts before you!  :

 

[lolo-m]

I dind't realize that the 10uf on the scam board is replacing one 10uf of the PM board.
I have wima's on the PM boards but i have a cheaper epcos poly cap (191-2948 RS) installed on the scab and so i'm wondering if it's better to desolder the wima and stuff it on the scab board.
It will be a bit harder and a lot more work because the wima's are a lot higher then the epcos caps and i have to put the scam board on a different place in the case. Now it fits above my XLR connectors with the transistors isolated mounted to the case. So.. will it make any difference if i use the epcos?

As you can see I put a lot of holes to fit any 10uF cap you'll find  ... My answer is on the board ! But to be clearer and honnest, Silent Art says there's some difference (Wima's the best 10uF for him) but as Moby, I really do think that you won't hear any difference. We're in the sidechain, we're charging a cap with low voltages, slowly (audio spectrum is a really low frequency in electronics world  : ). So if the epcos fits better, use it  .

Is it a problem if i leave the discontunued 10uf wima on the pm board or shall i remove it anyway?

Well that's a waste to leave them, but that's better to leave them than to destroy the board  ;D. If you're not sure you'll manage to disolder properly the wima, don't do it and just strap it.

 

[dagoose]

you still definitely need the -17V wired to the main board! You will wreak serious havoc if you remove the connection.

It is used to bias the many tubes of PM.

Note that +17V is not actually required at all in a plain poorman. You don't really NEED relays and light, and meters. they are just luxury.

[edit]
ok... looks like i missed this (how could i..) and saved the wrong, old, wiring guide.  :-\
I think that after the weekend i will have it done!

now that I look at it, isn't there an error on the SCAMP wiring guide? the -17V connection is missing for the main board.

[edit2]

and ground!

Yes, there's two missing wires on the wiring guide  ;D. 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.

 

[SaMpLeGoD]

Hello,

Just some rookie's questions... what's for that two 4k7 trimmers on the SCamp board? How can I regulate them?
Thanks

Eddie  ???

 

[lolo-m]

Hello,

Just some rookie's questions... what's for that two 4k7 trimmers on the SCamp board? How can I regulate them?
Thanks

Eddie  ???

Hi Eddie,

Set the 2 PM660 boards trimmers as described in the 660 support thread.
Then, switch the SCAB in analag's mode.
Measure the voltage between the 2 pins of the SCAB "TO ATTACK-X" connector. Set the 4K7 trimmers to have 0 Volt there.
Here it is, the SCAB is set and ready to play in both modes  !!!!

 

[SaMpLeGoD]

Hi Eddie,

Set the 2 PM660 boards trimmers as described in the 660 support thread.
Then, switch the SCAB in analag's mode.
Measure the voltage between the 2 pins of the SCAB "TO ATTACK-X" connector. Set the 4K7 trimmers to have 0 Volt there.
Here it is, the SCAB is set and ready to play in both modes  !!!!

Hello Lolo!

Thanks for the explanation! I already did it!
I had a problem in on of my channels before I install the SCamp PCB, and I still have it with the board installed...
One channel compress, normally, althrough some strange behaviours in the extreme positions... but the other one, has some problem in the main board... still don't what what is happening...
With the new board (SCamp) I feel more the compression... but everything is still light to me... I didn't put that 75Ohm resistor that u said on your "pimpin' my pimp..." Will it rise my attcack to 0,4ms as I read? as long as I have some 2.2uF caps on it?
I really will love to have my compressor all working... but so far have some problems to solve...
Cheers,

Eddie  :-\

 

[lolo-m]

Thanks for the explanation! I already did it!
I had a problem in on of my channels before I install the SCamp PCB, and I still have it with the board installed...
One channel compress, normally, althrough some strange behaviours in the extreme positions... but the other one, has some problem in the main board... still don't what what is happening...

Hi Eddie !
I had a problem with one of my channels too, and I solved it changing finally the tubes. The PM660 handles mismatched tubes but not really mismatched tubes. If one of the 6BC8 isn't matched at all (with huge difference between the two triodes), you'll have really weird problems appearing in their grid bias (I can't understand why but it did on mine)!!! On one of my channel I had a few volts appearing between the legs grid resistor with no compression... I changed the tubes and now everything is good...

With the new board (SCamp) I feel more the compression... but everything is still light to me... I didn't put that 75Ohm resistor that u said on your "pimpin' my pimp..." Will it rise my attcack to 0,4ms as I read? as long as I have some 2.2uF caps on it?
I really will love to have my compressor all working... but so far have some problems to solve...
Cheers,

Eddie  :-\

With the 75 ohm resistor added, you'll have about 0,2ms with 2,2uF on the SCAB board and no other cap paralleled. To have those 0,4ms you're talking about, you need to have the 2,2uF on the board and another 2,2uF parralleled on the TC switch.
I really think the PM670 is really nutral. To ear the attack compression human ear needs a few ms, you'll ear only the release clearly with a really fast varimu.

 

[dagoose]

dammit... the scab board turned out to be a crap mod..  :-\
Both channels have distortion like hell, one channel is blown up in some kind of way (think the 6107 transistor, not sure) and everything is connceted the way it should..
Removed the c4, bridged it, removed r18, bridged it and removed all 4148's on the pm board but shouldn't there be some kind of bridge in there as well?

So far.. it sucks big time, i had a working pm670 but now it's dead.. 

 

[lolo-m]

dammit... the scab board turned out to be a crap mod..  :-\
Both channels have distortion like hell, one channel is blown up in some kind of way (think the 6107 transistor, not sure) and everything is connceted the way it should..
Removed the c4, bridged it, removed r18, bridged it and removed all 4148's on the pm board but shouldn't there be some kind of bridge in there as well?

So far.. it sucks big time, i had a working pm670 but now it's dead.. 

OUCH !!!
FIRST ANSWERS:
You don't need to make any bridge on the 1N4148 on the PM660 boards. Those diodes are now on the SCAB board.

SECOND SIMPLE QUESTIONS:
1°) The wiring guide only shows one channel. Did you do the mod on both ?
2°) The first wiring guide didn't shows the -17V link to the PM660 board...Did you wired it with the new wiring guide you can find on the first post of THIS THREAD ?
3°) check any shorts you could make with the solder on the SCAB (the pads are sometimes really close).
4°) Finally did you set the SCAB trimmers as described a few post earlier ?

This mod can't destroy the PM660/670 as nothing changes on the board. CV amplitude is the same,  voltages are the same, it is just a unity booster of the CV voltage.

 

[rrs]

Hello,

Just some rookie's questions... what's for that two 4k7 trimmers on the SCamp board? How can I regulate them?
Thanks

Eddie  ???

Hi Eddie,

Set the 2 PM660 boards trimmers as described in the 660 support thread.
Then, switch the SCAB in analag's mode.
Measure the voltage between the 2 pins of the SCAB "TO ATTACK-X" connector. Set the 4K7 trimmers to have 0 Volt there.
Here it is, the SCAB is set and ready to play in both modes  !!!!

Just checking if when measuring between the two attack pins the Attack switch can be disconnected (for easier measurement). I ask this because it was mentioned in the 660 support thread that all connections should be made when firing up.

 

[lolo-m]

Hello,

Just some rookie's questions... what's for that two 4k7 trimmers on the SCamp board? How can I regulate them?
Thanks

Eddie  ???

Hi Eddie,

Set the 2 PM660 boards trimmers as described in the 660 support thread.
Then, switch the SCAB in analag's mode.
Measure the voltage between the 2 pins of the SCAB "TO ATTACK-X" connector. Set the 4K7 trimmers to have 0 Volt there.
Here it is, the SCAB is set and ready to play in both modes   !!!!

Just checking if when measuring between the two attack pins the Attack switch can be disconnected (for easier measurement). I ask this because it was mentioned in the 660 support thread that all connections should be made when firing up.

Unfortunately, the SCAB and the PM board must be connected together to make this setting.

PS: I would suggest to connect the SCAB TC NETWORK switch on "R-X" connector or "C-X" connector.
    Analgs pot or switch will be connected to SCAB's "ATTACK-X" connector.

 

[rrs]

I only meant disconnect the "To Attack X" switch.
It's these two pins that should measure 0V between them right. Is it safe to disconnect the attack switch connector to measure the two pins?

 

[lolo-m]

I only meant disconnect the "To Attack X" switch.
It's these two pins that should measure 0V between them right. Is it safe to disconnect the attack switch connector to measure the two pins?

I don't understand what switch you're talking about  :-\. To me the SCAB "TO ATTACK-X" is a connector with 2 wires connected to PM660 "ATTACK" connector. There's no switch there.
This connector MUST be connected. The link is necessary to acheive proper setting.
The only switch I see is the "MODE" switch and it must be connected too to toggle the SCAB into analags mode (anyway, it wouldn't help to have this one unconnected).

Check back the wring guide and use the labels you see on it. I will answer more clearly to your questions  .

 

[rrs]

I only meant disconnect the "To Attack X" switch.
It's these two pins that should measure 0V between them right. Is it safe to disconnect the attack switch connector to measure the two pins?

I don't understand what switch you're talking about  :-\. To me the SCAB "TO ATTACK-X" is a connector with 2 wires connected to PM660 "ATTACK" connector. There's no switch there.
This connector MUST be connected. The link is necessary to acheive proper setting.
The only switch I see is the "MODE" switch and it must be connected too to toggle the SCAB into analags mode (anyway, it wouldn't help to have this one unconnected).

Check back the wring guide and use the labels you see on it. I will answer more clearly to your questions  .

Sorry I mean rotary switch. You have answered my question though tha the connection must be made when measuring this.

 

[rrs]

OK fired this thing up and got a very disturbing crackling sound? Switched off imediatly, sounded like something was shorting.

Did some searching arround. One thing I noticed was the LM7812 pin 2 and 3 both seemed to be connected to ground. Does this seem right or do I have a faulty component?

 

[Moby]

One thing I noticed was the LM7812 pin 2 and 3 both seemed to be connected to ground. Does this seem right or do I have a faulty component?

Pin 3 should be on ground but 2 no. Desolder the 7812 and check did you shorted 2 pin pad somewhere to ground and check 7812 too . I presume that you made some soldering mistake somewhere 

 

[rrs]

One thing I noticed was the LM7812 pin 2 and 3 both seemed to be connected to ground. Does this seem right or do I have a faulty component?

Pin 3 should be on ground but 2 no. Desolder the 7812 and check did you shorted 2 pin pad somewhere to ground and check 7812 too . I presume that you made some soldering mistake somewhere  

have disconected LM7812 and no short between 2 and 3. When 12 V is connected to meters and relays I can buzz with my multimeter pin 2 and 3.

powered up with 12V disconnected and still here the crackling sound. With no power to SCamp all is fine. All was fine before installing SCamp.

Let me know if anyone spots a problem here.