the Poor Man 660 support thread

[analag]

24 steps is a matter of better fine tunability. 12 steps is fine as long as you measure 15K across the switch, no padding is needed. In 12 steps is what I'm using with no problems at all.

analag

 

[khstudio]

[quote author="analag"]24 steps is a matter of better fine tunability. 12 steps is fine as long as you measure 15K across the switch, no padding is needed. In 12 steps is what I'm using with no problems at all.

analag[/quote]

Thanks analag & Doug :thumb:

It's not needed right now but when you get a chance could you share with us how you set up your 2x12 switch?

Also,
What is the difference between the 600/10K and 10K/600 transformers?

I asked about the 10k:10k because my inserts on my boards are driven by TL074's... I may like to use the comp on them for some things & don't think the TL074's like driving loads lower than (aprox) 5k
+ I have 2 new Cinemag 10k:10k's I'm not using.

 

[analag]

On the input side 1:1 ratio will reduce sensitivity or push up the threshold that the compressor will react to too high, and if 1:1 ratio is also used on the CV amp, then the sidechain signal won't be enough to do any useful gain reduction.
It would work, but it would be able to really squeeze your audio.

analag

 

[khstudio]

I thought that might be the case, no problem :thumb:

 

[[silent:arts]]

[quote author="khstudio"]What is the difference between the 600/10K and 10K/600 transformers :?:

Aren't they the same thing... backwards??? :? [/quote]
this has ben asked many times before, here is the answer:
http://www.groupdiy.com/index.php?topic=28160&start=58

 

[khstudio]

Sorry I'm usually pretty good about searching but missed that one.

What's the difference between XSM600/10K and XSM10K/600?
Wouldn't it be the same if you just wire them in reverse?


reaction from Brian "busy" Weston at Edcor:

Brian Weston :
I am sorry that it has taken so long to get back. I have been on the production line all the time. The 600/10K and 10K/600 have the same turns ratio but different winding turns. The are designed for each secondary impedance. They can be used backwards but for best sound I would order the transformer you need.

Each impedance has a number of windings that works best for it. For instance lets say you are designing a 1:1 ratio transformer. If the impedance is low, say around 150 ohms you might have a number of turns that works very well. But if your impedance is 10K then the number of turn would be much higher. Even though they are both 1:1 ratio the number of turns is different.

This is why EDCOR offers different 1:1 ratio matching transformers for the different types of impedance. You could use a 600/600 in place of a 10K/10K and it would sound fine. But you could not use a 150/150 in place of 10K/10K It would not sound very good. 600 and 10K are very close in ideal number of turns. So they can be used in reverse. Hope this helps.

 

[cannikin]

I think these heatsinks will work for the USA peeps
Please check and confirm

http://www.aavidthermalloy.com/cgi-bin/stdisp_print.pl?Pnum=529802b02500g

mouser part number: 532-529802B25G

 

[guavatone]

BTW how many amps are these babies per ch?

 

[cannikin]

Brenbrue, volker, analag ---

Question #1: Is the 15-0-15V secondary on the PS XFMR for the relays? I've skimmed through the various threads but didnt find the answer.

If so, then if you aren't using relay/bypass boards you don't need this winding... Correct?


Question #2: I assume the Heaters off the PSU board are around 6.3Vdc. When you connect the heaters to the PM660 board.. does the 6.3Vdc go through any components on the PM660 PCB?

The reason I ask is because I'm going to mount the Tubes on the back of the Chassis (like the old days), so I'm hoping to run the Heaters directly to the tube sockets from the PSU board. I know, I know... its more work, more wiring, more connections, but more aesthetically what I want this unit to look like.

 

[[silent:arts]]

David,

#1) you need -17V for bias (like in the original, and this was answered many times before :green: )
with no relay board you need at least one 15V - 18V winding

#2) the heater is 6.3V, and is only provided to the tubes on the PCB

you want to do it point to point, am I right ? :green: :green: :green:

 

[cannikin]

Thought this would be good for people to have, I contacted Goldpt about switches and they graciously gave the resistor calculations for 15K.
That said, Goldpt doesn't make 15K but you can purchase a blank Switch from them and stuff it yourself. Not Cheap but they are nice switches and the hard part is done for you because the PCB.

These switches cost $108 each, although if you order 5 of them
the price falls to $97.20 each.

15K Calculation:

 

[cannikin]

[quote author="[silent:arts]"]David,
#1) you need -17V for bias (like in the original and was answered many times before :green: )
[/quote]

Thanks and sorry I missed that again :green:

[quote author="[silent:arts]"]
you want to do it point to point, am I right ? :green: :green: :green:[/quote]

exactly.

 

[[silent:arts]]

[quote author="cannikin"][quote author="[silent:arts]"]
you want to do it point to point, am I right ? :green: :green: :green:[/quote]
exactly.[/quote]
ordering 5 / 3 is then very generous :green:

 

[cannikin]

I'm curious if anyone has any intention of using audio transformers other than Edcor? if so "whatcha thinkin about using?"

 

[cannikin]

[quote author="[silent:arts]"][quote author="cannikin"][quote author="[silent:arts]"]
you want to do it point to point, am I right ? :green: :green: :green:[/quote]
exactly.[/quote]
ordering 5 / 3 is then very generous :green:[/quote]

I'm going to stuff the PCB as normal with the tube sockets and all components. I bought some surplus tube bases which I'll run wires to the chassis mount Tube sockets. So I have the option of plugging the tube into the PCB (for testing) or on the Chassis.

 

[Viitalahde]

EDIT: damned double posts!

 

[Viitalahde]

Regarding stepped attenuators..

There's just no way you need -62dB from an attenuator in your compressor. You're limiting yourself with that.

With the Analag opto, I went for -24dB total in both input and output at 1dB steps, which is way more than enough. I could've used 0.5dB steps, but no use for that.

For driving the sidechain I used 2dB steps which is fine too, and you can tweak the 1dB with the input attenuator.

 

[[silent:arts]]

the rotary switches

the first rotary switch is the "Input" or "Gain" switch.
dual deck is necessary, shorting preferred, and the more positions the better. over all resistance is 15K. matching the resistors for each step on both decks is a very good idea.
how to calculate the resistors ?

if you want it linear this is easy: 15000 / (number of positions -1) = single resistor in R
(you need (number of positions - 1) resistors of the same value)

you would better want it exponential (or log in potentiometer language).
it took some time to figure this out, but with some help I was able to do an Excell sheet to calculate the resistors for emulating a real log potentiometer.
fill in the desired steps you want: Log Pot to Switch Excell Sheet

you may want it in dB steps (like me). at the end it is a series attenuator.
my prototype has 18dB of gain, thus I will do one dB steps on an Elma, stopped to 23 steps, going from -4dB to +18dB.


the second rotary switch is the "Threshold" or "Compression" switch.
same as the first one, but the dB step attenuator doesn't make sense here. Lin or Log, your choice.

 

[[silent:arts]]

I'm off to this forum now, have to listen to a mastering a finish forum member did for me :grin: :wink: :green:

 

[Larrchild]

[quote author="cannikin"]Thought this would be good for people to have, I contacted Goldpt about switches and they graciously gave the resistor calculations for 15K.
That said, Goldpt doesn't make 15K but you can purchase a blank Switch from them and stuff it yourself. Not Cheap but they are nice switches and the hard part is done for you because the PCB.

These switches cost $108 each, although if you order 5 of them
the price falls to $97.20 each.

15K Calculation:

[/quote]

Those things are scary-good. They tracked like .2dB and were flat up to many megahertz!

I'd suggest hand-dialing the resistor values of the threshold pot. My Goldpoint version using a stock audio-taper needs more "in-between" points near the top. Next batch will be custom from them. That could just be my personal taste, but it's probably worth doing if you are not ordering a pre-made unit. Find the area you use a lot and spread it out a little. As Jaakko says, you can use 2dB on the output and 1dB steps on the input to get it anywhere you need, so they are probably ok as they are.

btw, I think my stuff is in his "hall of fame" over at the Goldpoint site.