the Poor Man 660 support thread

[AW_music]

What voltage are rated the caps used here, in the time constant mod ??
63V is enough ??

What are the bluebird timing mods?

I believe most of this is from bluebird with some other info from other folks (sorry, didn't note who wrote what):


The Main mod I wanted to suggest has to do with the time constants.

I just wasn't getting the flexibility out of the attack and release I wanted.

So I started off by adding a switch to change C4 (10uF) I used these values.
10uF, 6.8uF, 4.7uF, 1uF

I still felt like the attack knob wasn't changing the time constant enough.
I glanced over the original 670 schematic and realized it has a resistor in parallel with the time constant caps not in series that changes.

EDIT I'm sorry there are also resistors in series with the capacitors in addition to parallel. these would have an effect on attack time. EDIT

So basically I PUT (RV7) IN PARALLEL WITH (C4).

I put RV7 on a 5 position switch and used these values:

25K, 65K, 150K, 470K, and an open position (you could use 2 megs)

The higher the resistance the longer it takes the cap to discharge through it. longer release. the smaller the cap the shorter time it takes to fill up. shorter attack.

switching up the combination of the two makes for a lot of flexibility.


Voltage rating of caps:  there is no high voltage in this stage.  In my opinion you are fine with - let's say 63V.

I wanted to mention an easy way to get a good range of time constants without big changes is to just use the resistor values I mentioned earlier in parallel with the 10uf cap. You don't really have to change the cap value to get a good variation of release times. It has a lot more effect than the stock 10K pot in series with the 10uf cap.

I've scaled back to three caps. 10uf, 6uf, and 2uf.  Also using just three resistors in parallel with the caps. 68K, 470K, and 3m (or no resistor).  With those caps and resistors you can simulate the first three or four time constants of the real 670.

I've been using the 2uf and 68K in parallel setting the most. this is closest to the fastest fairchild setting. its great on bass drums vocals, just about anything. I'm sure its not the exact same because of the weaker sidechain but I'm loving it

I should also mention that I don't EVER use the Analag/Rowans original time constants because they are WAY too slow I used "Bluebirds" advise & set up a 2uf cap with various "switchable" resistors for release times. I think 68k, 180k & 470k then one position with just the 2uf (no resistor). My position 5 is blank for now & 6 is Rowans 10uf. These combination's work GREAT for vocal, bass... most things really.
Note to everybody: in Analag's design, the faster attack is with the 10K pot set at 10K... The lower it's value, the longer is the attack or to be precise the softer is the attack... The release time is function of the program which charged the network. More clearly, if the comp compress during a short time, the 10uF will be charged during a short time and the release will be quite fast. If the comp compress during a long time, the 10uF will be charged more and its discharge (release) will be longer... It is an adaptation with really interesting attack/release of the position 5 and 6 of the Fairchild.

The original design has far too long release times for my taste. I tried to measure the release time, got bored, went for lunch and when I came back the meter returned to 0vu. About 25 minutes i think.  (joking)

So, I took out c4, jumpered it and substituted it with different capacitors and resistors in parallel.

At the moment I have:
1u2 // 50k
3u3 // 100k
4u7 // 150k
5u6 // 1meg
6u8 // nothing
10u // nothing

Mind you, these are just values I had in hand. I installed them in order to start aurally tweaking the beast.  BOOM!!!  I haven't taken it to the studio yet, but listening at home I can easily see the poorman becoming my favorite compressor.

Beautiful compression action, especially with those short release times.


So based on what you explained (thanks by the way), my table:

Slow attack                                    Fast attack

      10uf  6.8uf  4.7uf  2uf  1uf  0.5uf
        None  2M  470k  150k  65k  25k

Slow release                                  Fast release

Bluebirds schematic can be found in this post:

http://www.groupdiy.com/index.php?topic=29056.msg369127#msg369127

Back to me.  I did a similar mod to mine based on Kevin's (khstudio) suggested values, which I've forgotten right now but maybe he'll chime in to mention them.  This TOTALLY transformed the compressor into something FAR more usable and flexible.  Even though I loved my 670 from the beginning, I REALLY love it now.

Cheers,
--
Don

 

[lolo-m]

What voltage are rated the caps used here, in the time constant mod ??
63V is enough ??

Yes, 63V is enough for the TC network...

Thanks to Rob's suggestion, I got my testing rig working.  I tested 16 NOS 6BC8 and have to say that there were 4 of them that had matching halves and lined up enough to call them a quad.

I then tested 16 NOS Russian 6N5P and the results were much, much better.  There were a dozen with closely matched halves and I could easily match those to make 3 matched quads.

I'm going to give it a try with the 6N5P tubes to see how the unit behaves with closely matched tubes.  I also want to check the heater current to make sure I don't stress out that circuit too much since the Russian tubes draw more heater current than the 6BC8s, .55A - .65A vs. .4A, respectively.

I was kind of disappointed to see how widely ranging the NOS American tubes were. 

Cheers,
--
Don

Sorry Don not to have aswered before but Rob did ...
I don't know if the widely ranging you've got with NOS American tubes is a matter of bad production or if the tubes you bought weren't from the same batch... And never forget that Americans are humans, and humans don't do perfect things  ;D .
Did you tried the PM670 with matched tubes ? I bet you'll find it a lot more interresting... Un-matched tubes means thump and by the way distortion.

 

[idylldon]

I don't know if the widely ranging you've got with NOS American tubes is a matter of bad production or if the tubes you bought weren't from the same batch... And never forget that Americans are humans, and humans don't do perfect things  ;D .

While all that's true, I think it has more to do with the fact I bought the tubes on ebay and some of them don't really appear to be NOS even though they were sold as such.  The matching quad I have in there now are all tubes from different mfgs.!

I also think that a lot of NOS tubes have been picked over for so long now the stock of good ones has almost been depleted with certain ones, though this probably isn't as true for the 6BC8 since it hasn't been in demand as much as say a 12AX7 and the like.

I haven't had the chance to try it out yet with the matched tubes but I might have some time today to see how it works.

Cheers,
--
Don

 

[dagoose]

Ok, decided to start working on my PM and so i added a seperate tranny for the second heater/slowstart and upgraded the caps t 3300uf. No i can get the voltages easy at 6.3v and less heat indeed.
I also modded the time constant caps and resistors though i didn't have enough caps to finish that, it's or really fast (2uf), or really slow (10uf) but that's just a matter of adding some extra caps in between. I really like the way it sounds now with the faster time constants! I really think the poorman can have some serious use now! 
I also ordered 6n5p's which are going to be matched.
I also need new 5687's but that is going to be taken care of as well.

The only thing bothering me is that when i add both 5687 sidechain tubes in there, (so stock) i can't zero the meter, it's pegging while with one sidechain tube it's no problem to zero it.
I tried an extra resistor in parallel but that didn't do much. 
I also noticed that the meters are interacting with different threshold settings which i read here before, even the channel not adjusting interacts with the other channel while not linked.
Is that because of the non matched 6bc8 tubes? Should i wait troubleshooting untill i have matched tubes?

 

[tekno808]

The only thing bothering me is that when i add both 5687 sidechain tubes in there, (so stock) i can't zero the meter, it's pegging while with one sidechain tube it's no problem to zero it.
I tried an extra resistor in parallel but that didn't do much. 

I had the same problem, the result was a bad 5687 ! ( JAN5687WB ) , i relaced with new national 5687 tubes , al problems gone !

below is the drawing i used for the zero VU adjust , i used 3.9k insteed of 3.6 k

Danny.

 

[skal1]

ok just got 4 new 24 step rotarys switches and have put the resistor around the switch , now last time a round i got confused with the connections to the switch so i am asking for a little help this time round.


on the  wiring guide  http://www.silentarts.de/DIY/PM660/PoorMan-WiringGuide.pdf


is the orange wire connected to pin1

is the brown wire connected to pin 3


is the red wire connected to the wiper.


thanks in advance


skal1

 

[radiance]

ok just got 4 new 24 step rotarys switches and have put the resistor around the switch , now last time a round i got confused with the connections to the switch so i am asking for a little help this time round.


on the  wiring guide  http://www.silentarts.de/DIY/PM660/PoorMan-WiringGuide.pdf


is the orange wire connected to pin1

is the brown wire connected to pin 3


is the red wire connected to the wiper.


thanks in advance


skal1

It seems you're referring to the time constant pot in which case your findings are correct.
But since you mention you got 4 I guess you'll be using them for gain and threshold duties right?

 

[skal1]

It seems you're referring to the time constant pot in which case your findings are correct.
But since you mention you got 4 I guess you'll be using them for gain and threshold duties right?

yes using the four rotarys for gain and threshold duties , are my findings are correct?

thanks again


skal

 

[radiance]

, are my findings are correct?

No.
Look again at the wiring guide. >http://www.silentarts.de/DIY/PM660/PoorMan-WiringGuide.pdf

As you can see there are more colors/wires involved at the gain and threshold pots.

Lets look at the gain pot and use the same numbers as mentioned in the poormans schematic.

Red wire is pin 1
brown and yellow wire are pin 2/ wiper
green and grey wire are pin 3

 

[skal1]

Thanks radiance,

just had a look at it again ,and everything is fine.



bless

skal

 

[dagoose]

6bc8 tubes suck big time...
You know why? today my 6n5p tubes came in and even without matching all of the problems i have with distortion, meter zero, meter response, meter interaction etc where gone instantly when i replaced them with the new tubes.
The Poorman really came alive this way and even with matched tubes (going to do that soon) it's a really great sounding compressor!

So drop your 6bc8/6bz8 tubes and get 6n5p tubes! They are even cheaper.. i know this has been said a couple of times before but now i know myself.

 

[idylldon]

So drop your 6bc8/6bz8 tubes and get 6n5p tubes! They are even cheaper.. i know this has been said a couple of times before but now i know myself.

With one caveat:  The 6N5P tubes draw more heater current, and since some of these builds seem to have PS issues due to an underspec'd power transformer, make sure you have enough headroom before plugging these tubes in.  From what I've been able to determine, 6N5P tubes draw 550 - 650 mA while 6BC8 tubes draw 400mA.  I'm not sure why there is a spread on the 6N5P tube heater current specification, and I haven't yet checked them myself, but if you get some that draw the higher current you'll be drawing over 1/2 amp more current than with the 6BC8s.  Even on the lower end you'll be drawing another 400mA, which just might push a marginal PS over the edge.

Cheers,
--
Don

 

[mitsos]

I've gotten some 6n5p tubes as well.. Haven't gotten around to this thing since.. but I'm excited to (maybe) finish it next month! have we hit 3 years yet?  :-[

 

[radiance]

6bc8 tubes suck big time...

No, they've just bigger tolerances compared to the 6n5p's. You'll see this when you start matching. Don't forget to match those 6bc8's as well just to see how big the tolerances actually are.

 

[dagoose]

6bc8 tubes suck big time...

No, they've just bigger tolerances compared to the 6n5p's. You'll see this when you start matching. Don't forget to match those 6bc8's as well just to see how big the tolerances actually are.

Yeah, i know but actually when i just put in other tubes without doing anything else and it works great right away to me the 6bc8 is just really bad.

 

[dagoose]

I have been matching tubes today and the 6n5p's are pretty close to each other. I also checked the 4 6bc8's i had and they where really all over the place like as if they where different types of tubes!

I have some questions about picking the right tubes even though i think i have things right.
What is more important, the matching between the 2 triodes in each tube or the matching between the 2 tubes in each channel and then crossing over (check the schem and seeing the crossover in the triodes)
Hard to explain actually..  ???

 

[radiance]

What is more important, the matching between the 2 triodes in each tube or the matching between the 2 tubes in each channel and then crossing over (check the schem and seeing the crossover in the triodes)
Hard to explain actually..  ???

The idea is that the total current draw of triodes 1 of both tubes is the same as the total current draw of triodes 2 of both tubes.

A cross match is when
tube 1 reads 3V and 4V 
tube 2  reads 4V and 3V
this is a rough example btw...

 

[dagoose]

What is more important, the matching between the 2 triodes in each tube or the matching between the 2 tubes in each channel and then crossing over (check the schem and seeing the crossover in the triodes)
Hard to explain actually..  ???

The idea is that the total current draw of triodes 1 of both tubes is the same as the total current draw of triodes 2 of both tubes.

A cross match is when
tube 1 reads 3V and 4V 
tube 2  reads 4V and 3V
this is a rough example btw...

Great! That was the way is was thinking indeed. 
I think i have some matched pairs then and already tested it and the compression and sound itself got indeed better. I could even hear it on my cheapo behringer monitors in my workshop.
A happy man! All i need is new 5687 tubes. 

 

[themagicmanmdt]

Greetings everyone!

Long time poster and lurker combined, however, I'm definitely not green to tubes, design, audiophilia and bridging the gap between audiophiles and recording engineers - with the dash of loving color if it means the sound is more affecting...!

I've scoured this post as much as I can, and would like to find a schematic of the PM660.

I'm aiming to have a stripped down version of the compressor, most likely without the soft start PSU (opting for a HV+ standby switch), without metering (for now, may add later, i enjoy recording with only my ears) and, depending on schematic, doing it entirely point to point (as I'm tired of dealing with crispy fried circuitboards in all types of gear).

Also, I'd like to experiment with independently varying the attack and release times instead of having preset 'constants' as much as possible, so I may try to seperate said switch into two seperate ones.

So, hey.

First -

Link to schematic?

I understand that SA and others have spend man and mind power bringing this incarnation to light, and if it's a matter of a contribution for those who made this happen for this community, I have totally no problem with that.

Groovy.

mt

 

[idylldon]

Link to schematic?

The schematic isn't public.  It was only given to those who purchased a PCB set.

Cheers,
--
Don