radiance

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #160 on: February 25, 2011, 05:56:37 AM »
I see the Fairchild time constants uses resistors in series with caps on two positions. Does this give a longer attack time?
"Knowing that you are dreaming, however, does not automatically guarantee full rationality.
Then again, being awake doesn't ensure good thinking, either." -  Lynne Levitan


lolo-m

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #161 on: February 25, 2011, 01:56:54 PM »
No, on position 5 and 6 the resistor just slow the release.
With Fairchild's TC network you have to think current. The current coming out of the SCamp charges the network. You'll see and understand that it will fill the smaller resistive element first (the smaller cap) then the most resistive element will make the cap's discharge. On position 5 and 6, there's an additional resistor+cap that will be charged by the current of the SCamp , then by the cap's charge and it have a really really long discharge. Honestly position 5 and 6 are nearly unusable now. They have a super fast attack time and a crasy long release (more than 2 minutes if I remember well). They were made to maintain the level whatever could happen in broadcast (mad DJ, poeple talking too loud or too low, sleeping engineer...) not to saturate the emiter.
I hope I've been clear enough  ::).
Hard to be a punk... But sometimes you have to...

radiance

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #162 on: February 26, 2011, 09:17:03 AM »
Thanks Lolo!

One more thing...is there a limit on how small the parallel resistance can be?
In the original Faitchild time constant section the smallest is 68K.
So, the smaller the resistor the faster the release time...why not make it even smaller, say 10K,  or even no resistance at all?
I like very fast release times ;-)
"Knowing that you are dreaming, however, does not automatically guarantee full rationality.
Then again, being awake doesn't ensure good thinking, either." -  Lynne Levitan

lolo-m

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #163 on: February 27, 2011, 02:19:43 AM »
I don't exactly know the limit for the parallel resistor but 10K is working for approx 20ms release time. I've got this setting in my TC network : 2,2uF // 10K.

...  or even no resistance at all?
I don't understand what you mean there but :
- No resistance (only the cap) will mean no release
- A wire parralleled to the cap will mean no attack and no release = no compression.

Another thing, if you want to slow the attack you've got a few options :
- you can use bigger caps : if you double the caps value you approximatively double the attack time or,
- you can use a little serial resistor added to the 75 ohm I forgot on the SCAB board (Read PIMPING MY OWN PIMP page 2). As it'll make the SCAmp output impedance higher, the caps will charge slowlier and attack time will be longer BUT be carefull with this resistor value as you create a voltage divider with the release resistor so the max compression will be affected.
Hard to be a punk... But sometimes you have to...

pacemaker

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #164 on: February 27, 2011, 05:40:20 AM »
hi lolo,
I'm currently building my PM670,
and i would like to put your scamp booster in.
not sure it's the right place,
but i can't find a thread for the boards only,
Was it a one shot run of boards or are they still available somewhere ?
best regards,
Francois

radiance

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #165 on: February 27, 2011, 06:37:43 AM »

- A wire parralleled to the cap will mean no attack and no release = no compression.


Strange, I had a 470K pot wired parallel to the cap and still got some compression when turned all the way cw which resulted in 0 resitance...well, maybe the resistance was 18R or so due to the pot being not very acurate...but still.
It did sound quite nice...I'll experiment some more with this.

Thanks again for chiming in on this old thread...
"Knowing that you are dreaming, however, does not automatically guarantee full rationality.
Then again, being awake doesn't ensure good thinking, either." -  Lynne Levitan

Kingston

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #166 on: February 27, 2011, 07:39:50 AM »
Are you sure you don't have the 221k resistor of the old time constant network still there?

radiance

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #167 on: February 27, 2011, 11:01:12 AM »
Are you sure you don't have the 221k resistor of the old time constant network still there?

It's still there yes...but that does not matter since the pot I use is parallel to that resistor as well is it?

..Or am I missing something?
"Knowing that you are dreaming, however, does not automatically guarantee full rationality.
Then again, being awake doesn't ensure good thinking, either." -  Lynne Levitan

Kingston

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #168 on: February 27, 2011, 12:39:18 PM »
Oh I see, close to 0 resistance. Don't know what is going on then.

lolo-m

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #169 on: February 28, 2011, 03:53:34 AM »

- A wire parralleled to the cap will mean no attack and no release = no compression.


Strange, I had a 470K pot wired parallel to the cap and still got some compression when turned all the way cw which resulted in 0 resitance...well, maybe the resistance was 18R or so due to the pot being not very acurate...but still.
It did sound quite nice...I'll experiment some more with this.

Thanks again for chiming in on this old thread...
You're right you may have some compression...
Looking at the schematics the 0dB point (6BC8 tube bias) is made with a cap parralleled to a resistor. The SCAmp if loaded with a shunt (0 ohm load) is charging the bias cap. This is why you've got some compression.

This is not really safe for the comp so avoid this by using a minimum of 4K7 in the TC network (about 10ms release with a 2uF cap). If you want to use a pot put a minimum resistor (4K7 or best IMO 10K serial to the pot). Every thing will be a lot more predictable that way  ;).
Hard to be a punk... But sometimes you have to...


lolo-m

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #170 on: February 28, 2011, 04:20:22 AM »
hi lolo,
I'm currently building my PM670,
and i would like to put your scamp booster in.
not sure it's the right place,
but i can't find a thread for the boards only,
Was it a one shot run of boards or are they still available somewhere ?
best regards,
Francois

Hi François !
The black market topic vanished for some reasons (I don't know).

First, like I said many times :
Have a working STOCK PM660/670. Test it, listen to it. If what you hear don't please you enough, PM me. There's a few SCAB boards left somewhere...

PS : Le bonjour d'Avignon, tu es où en France ?
Hard to be a punk... But sometimes you have to...

pacemaker

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #171 on: February 28, 2011, 08:46:51 AM »

merci pour tes conseils Lolo,
je suis a angers dans le maine et loire !
a bientot peut etre,
francois

dingo

Re: PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #172 on: March 14, 2011, 02:37:40 PM »
hello! :)
I am interested on scamp booster
I am building pm670
read all thread and...
would like to add the scamp booster option
are boards available? or maybe some etch file!
thank you!
dingo.

Moby

Re: [BUILd] PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #173 on: February 09, 2012, 11:11:32 PM »
Yes. Few left. please contact Lolo-m and I will send it to you .
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com

Freddy G

Re: [BUILd] PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #174 on: January 07, 2013, 10:19:19 AM »
I have a nicely working stock PM670. I have my scamp board stuffed and ready to go. I've read this thread a few times and am still completley confused about how to hook up the TC network. Verbal descriptions and theorys are going over my head!  Reading Chuck D's posts, I have similar questions. Really what I would like to see is a clear list of components for the TC network and a clear diagram on how to hook it up. I have Lorlin 2 pole, 6 position switches.
Help will be much appreciated!
PRR wrote:
Use #18 wire for rock-n-roll, #16 wire for classical.

Freddy G

Re: [BUILd] PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #175 on: January 09, 2013, 04:47:15 PM »
OK, I think I finally have a handle on this. I've been studying this switch from page 6:







I was so confused because I didn't understand the values...but now I see that the cap values are paralleled to make up the values as shown in the fairchild TC network.  And on the other pole of this switch I just couldn't figure out what the 2k resistors were doing and where did they come from? they are not in the fairchild tc schematic. Then it dawned on me.... that pole with just the 2k resistors is the Analag mode!..is that correct?
PRR wrote:
Use #18 wire for rock-n-roll, #16 wire for classical.

lolo-m

Re: [BUILd] PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #176 on: January 09, 2013, 07:26:46 PM »
I was so confused because I didn't understand the values...but now I see that the cap values are paralleled to make up the values as shown in the fairchild TC network.  And on the other pole of this switch I just couldn't figure out what the 2k resistors were doing and where did they come from? they are not in the fairchild tc schematic. Then it dawned on me.... that pole with just the 2k resistors is the Analag mode!..is that correct?
You're right. This switch is to get both modes on only one switch : analag's and fairchild's tc networks are on that switch.
I don't remember and don't have time to dig but it may need one more switch to toggle between the 2 differents modes...
Hard to be a punk... But sometimes you have to...

Freddy G

Re: [BUILd] PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #177 on: January 09, 2013, 07:32:03 PM »
I will likely not even use the Analag mode ....we'll see though
PRR wrote:
Use #18 wire for rock-n-roll, #16 wire for classical.

alexc

Re: [BUILd] PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #178 on: January 10, 2013, 12:34:39 AM »
Here's an novel use for the SCAmp pcb - I'm using it not in my poorman builds, but rather, in a diy franken build.

I had some neumann fader modules which I ripped all the transformers from.
The faders were discrete vca module type driving lowZ faders.
So I have taken the neuman discrete vca modules and am hooking them up to the SCAmp pcb as the sidechain.

Don't see why it won't work!

Am using this in a 3RU build with a pair of Tesla channel strips.

A combo of traffo/fet DI with Tesla early discrete/semi preamp+inductor eq and I'm adding Haufe active  transformer  main and  aux outs.

This will be the last of my franken-strips! 

All my parts used up then :)
I ping therefore I am

Freddy G

Re: [BUILd] PM660 / PM670 SCAmp Booster build and tips help thread
« Reply #179 on: January 10, 2013, 09:49:09 AM »


Hi,
Here is a build help thread for poeple who choosed to implement my SCAmp Booster on their PM660 or PM670. Just to save some time, let's call it SCAB (SCAmp Booster  ;D)

If you start filling the PM board, don't solder D1, D2, D3, D4, C4, R16 and R18. Put 2 wire links between C4 pads and R18 pads.
If they're already soldered, solder a wire link between the C4 pins and between R18 pins. I can't honestly say that's it is a good idea to dissolder C4 (even if I did) as it can endomage the PCB if not correctly done. Cut D1, D2, D3, D4 on the middle of the glass tube.

Just need to clarify...are you saying to remove R16? or to jumper it? In the Scamp wiring guide R16 is still shown.
PRR wrote:
Use #18 wire for rock-n-roll, #16 wire for classical.


 

Related Topics

  Subject / Started by Replies Last post
45 Replies
8801 Views
Last post October 24, 2018, 01:38:19 PM
by latosem
3 Replies
2376 Views
Last post May 25, 2011, 12:42:27 AM
by capnspoony
7 Replies
838 Views
Last post October 11, 2019, 05:42:16 AM
by mrclunk
8 Replies
1290 Views
Last post August 31, 2020, 01:43:53 PM
by milton99