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

[dagoose]

ok.. the board itself is working in analag mode.. but still not at scamp mode.
I think the 5534's are blown (they got hot with the weird voltages) but i don't have any in stock right now so i have to wait to get some.
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..

 

[lolo-m]

If you've got a TL071 (or OPA604 or any pin compatible opamp) it does work too (maybe a bit slower with a TL071).
Check again your connections of the +/-17V on both PSU and SCAB... If you use connectors there, it's sometimes difficult to be sure the connection is really good (it happened to me) and your previous voltage changes make me think about this kind of problem...

 

[dagoose]

Picked up some 5534's today and it's up and running!  8)
It sounds good, at least faster then the analag mode to my ears though i haven't really tested it yet but i'm happy with the result.
I used the bypass switch for in/out (2 relays and 2 pole switch), it now has bypassmode, analag mode and scamp mode so 3 steps and it works great and i didn't have to drill extra holes!
To make it more visible i added a red led to the back of the meter when in scamp mode so that it has a bit more like a red glow from behind. Not shocking but it adds something.  ;D

 

[lolo-m]

I glad to read this !!! I prefer this to your first post  !
Really happy you sorted out  !

 

[dagoose]

I will post some interior/beaver shots later on but it's already racked up now, it has to work hard today.  ;D
I was a bit sceptical at first mainyl because i didn't really understand what it was doing but now i do and it's so simple, i was really thinking the hard way.  :-\

 

[crisotop]

C3 on the main PM670 board is only used when in analag mode am I right?

 

[lolo-m]

C3 is used in both modes. Except if you don't want to use analag network at all, you need it. If you want both modes and stick to Fairchild network, use a 1,8uF. But trust me a 2,2uF is fine and doesn't make a real change in the release (and attack of course)  .

 

[crisotop]

that's all I wanted to hear (since a 2u2 is all I have at the moment

cheers lolo!
christoph

 

[khstudio]

Please forgive me for posting in 2 different threads but I'm not sure the main help thread gets enough visitors from complete builds.

Anyway...
Has anyone done any Full Frequency sweeps on their PM670 (with or without the SCAmp)
with & without compressing?

I don't have the SCAmp installed so mine is stock. I just did some sweeps & it looks pretty flat but when compressing it looks normal until it gets to about 1k - then it ramps down about -4 dB more or so 

http://www.khstudio.us/DIY/PM670/PM LR Sweep.bmp

If anyone has or could sweep their working unit... that would be GREAT!

Thanks.

 

[ChuckD]

Hey Lolo or anyone else

I am confused does the SCamp board use the same 10K Attack pot as the Analag version just making the time constants quicker?
Or do I have to have values for C* and R* in Scamp mode?

I am confused what to connect if I want to switch between both modes. The wiring diagram shows the R* and C* not hooked up but a 10K pot.

Also , this has been asked a few times, can someone put down what they recommend for values for both C* and R*?

Hey Thanks Guys!

Chuck

 

[lolo-m]

Hey Lolo or anyone else

I am confused does the SCamp board use the same 10K Attack pot as the Analag version just making the time constants quicker?
Or do I have to have values for C* and R* in Scamp mode?

I am confused what to connect if I want to switch between both modes. The wiring diagram shows the R* and C* not hooked up but a 10K pot.

Also , this has been asked a few times, can someone put down what they recommend for values for both C* and R*?

Hey Thanks Guys!

Chuck

The 10K pot is used only in Analag's mode....
C* and R* are the "a la Fairchild" TC network. If you want to have closer specs to the Fairchild use a 2 or 2,2uF as C* and copy the rest of the Fairchild TC network... Just don't forget that the 2uF and 220K of the Fairchild are already connected in the PM670 + SCAB.
Connect the switch mode as described in the wiring guide (one dual switch per channel)...
I hope I'm clear enough  ;D ...

 

[ChuckD]

No Sorry I still don't understand

to have closer specs to the Fairchild use a 2 or 2,2uF as C* and copy the rest of the Fairchild TC network... Just don't forget that the 2uF and 220K of the Fairchild are already connected in the PM670 + SCAB.

This statement seems to contradict itself.
So what do you recommend for the values for both C* and R*? For a True Fairchild? Can you just list the 6 values for me that may help a lot.

Thanks by the way for the quick response Lolo!

Chuck

 

[Moby]

Just copy the network from real F670. Or do your custom one if you want.Or read the PM pimp page....

 

[lolo-m]

Copy this network without R137 (it's already on the PM660 board) :

The network is composed by : R137, R138, R139, R140, R141, C109, C110, C111, C112, C113.

 

[ChuckD]

Thanks Guys

On the FC 670 schematic it shows C values and R values wired in series with respect to each other. Then each position is a R/C value put in parallel with the circuit.
With the SCAMP board it has two connections C* and R* that look simply in parallel with each other. Are the C* and R* already joined in series and then parallel WRT the circuit on the SCamp board or should I do that on the switch?

Do you have a schematic for the Scamp board that you could post? That would clear this up maybe.
Do you understand why I am confused?


Chuck

 

[lolo-m]

Looking at the Fairchild TC network:
- Consider that R137 is already on the PM660 board,
- C109 can be connected to C* on the SCAB board.
- The rest of the network will be on the switch connected on R* for example.

I originally put those footprints to let people try different possiblities of C and R in the TC network... I apologies if it's a bit confuse for some of us  ;D...

 

[ChuckD]

Lolo,

Thanks for the replies and patience !

I thought you said the C109 was already on the board?  But here you said to put it on connection C*
I really need to draw out this schematic I guess if you don't have one handy.

I will put the network as drawn on R* then But which side is which? In case I use electrolytics?
Hopefully I can clear this up for others. Or I am I the only one .... sorry if so.

Chuck

 

[ChuckD]

OK now I understand

1) On the Scamp Board C103 and C203 correspond to C109 on the FC670 schematic.
2) R17 on the Poorman Board Corresponds to R137 on the FC670 schematic.
3) Leave C* connectors empty.
4) Build the network in the FC670 Schematic by hand using a 2pole 6position switch connect that to R* connector.
5) The poles of the switch connect to the RED side of the wiring diagram while the shorted side of the network connects to the Brown Side.
6) If using electrolytics then the Negative terminal of the cap should go towards the Brown shorted connection


Is this correct?

Chuck

 

[lolo-m]

ChuckD spot on   ! You've got it perfectly right !

Here is SCAB's schemo :
http://pagesperso-orange.fr/NBNS-Studio/PM670/SCAMPBOOSTERdefinitive-sch.pdf

You can connect electrolytics as caps, but electrolytics are getting old quickly and unpolarised caps are not expensive when you're dealing with less than 63V (in our case it's max 17V). If you want to connect some lytics be carefull with polarity, the pin connected to the diode is the most negative pin.

 

[ChuckD]

If you want to connect some lytics be carefull with polarity, the pin connected to the diode is the most negative pin.

If this is true then my instructions (5&6) are Wrong?

Can you check it for me?

Chuck