the Poor Man 660 support thread

[W DeMarco]

So I have decided to take my stereo unit and build two mono units instead.  I think the chassis was way to crammed for my taste. I have no room for scamp or slow start in there.  I already got rid of the hum that was all to much for use in the studio by seperating the 2 boards with some good distance.  Im still having some problems with the good channel but it seems to be small tweaks and another calibration.  Im hoping that theres a 2nd run so I can build another PSU.  My only other option is jummping the power to the 2nd chassis. 

Thanks for the help guys!

 

[[silent:arts]]

as said before I will soon have more PSU PCBs in stock.
give me a few weeks ...

 

[W DeMarco]

Sweet like money!!  Musta missed that.  Looking forward to 2 units now.

 

[geoff004]

Here's a picture of Undercarriage's unit:

There are still some issues with it.  The meters seems to be working well, and it seems that the headroom is better.
However there is distortion when compressing.  It varies how much on where the 'Attack' knob is set.  It's a 6 position switch with 5 2k resistors.  In the far left position the distortion isn't so bad but in any other position it gets to be a lot worse.  It almost doesn't make any difference where the threshold switch is set.
Both channels are consistent.
I tried 2 different sets of 5687s with and got identical results.
Any ideas?  things I should check?
thanks

 

[khstudio]

geoff004,

My unit distorts like that too & so does a few others that I've talked to on the phone.
It's NOT just distorting when compressing "Deep" into the curve either.  :-\

I will say that it is not drastic but definitely noticeable & too much on most mixes.

However there is distortion when compressing.  It varies how much on where the 'Attack' knob is set.  It's a 6 position switch with 5 2k resistors.  In the far left position the distortion isn't so bad but in any other position it gets to be a lot worse.

I noticed the same thing... I think it's due to the small cap releasing very fast.
It gets more distortion when the 10k ATTACK (Pot in my unit) is MAXED out in front of the 10uf Cap... this forces the smaller cap to work harder & adds to the distortion.

I have so much other work going on I haven't had much time to test or work on my unit lately but will be getting back to it.

Has anyone else checked their "Frequency while Compressing" ???

 

[W DeMarco]

Update

Ive had problems with my gain and threshold switches after fixing my psu so I figured I report on status.

This will attest to folks sayin check your interconnects!

upon install I wired my switches in mirror image due to me lookin at the wiring diagam as if it was knob side of switch out.  After I switched to the correct wiring I have good compression and gain.  In fact everything seems to be working pretty good 

Except:

In the 1st few positions of my threshold switch the vu seems to drop a bit on each turn of the switch.  Total drop seems to be about 1/2dB.  after I get 4 or 5 steps in it stays at that point.  It also seems to really compress hard around the 20th step(-10+dB) where the step before was only -5 or so.

1 way or another when dialed in to a good setting it sounds great!

Right now Im operating at 6.0 on heaters although I still need to upgrade after deciding to go with two mono units.  Hopefully this wont damage my tubes.  I want to use this bastard!!!

 

[lewilson]

You can run heaters at 5.8v with no trouble. 

 

[khstudio]

OK... I finally got around to some more testing on my unit.
I did try sweeping with "PINK Noise" & that looked pretty good to me.

Here is a sweep of the "Side-Chain" ONLY!!!
I disconnected the output of T4 (going to the Diodes) & reconnected a 4.7k LOAD resistor so I could see what JUST the side chain amp was doing... interesting stuff. I tested with both - a Single & 2 tubes in the sidechain.
The TOP line is RAW
The Top "Curve" is the "Single Tube"
The Bottom 2 "Curves" are the "2 Tubes" in the sidechain amp.
Notice the ONE tube has a better Frequency Response.  :-\

I also retested individual Frequencies again very meticulously & got the same results:
(See Post & Link to sweep Below)

Finally got my unit back up & running.  ;D

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.

 

[1954U1]

Mh.. throwing in some crude ideas..
maybe its a weak  wiring of the Edcor T4..
[you know, these tiny wires going to the pins.. it would not be the 1st time.. but it would be really strange in this case]
also, looking at the curves..  maybe the core has become magnetized?
or some internal leakage?

Anyway, do you have another spare Edcor to swap in and test?

 

[emrr]

okay, but would you say these charts are the inverse of the compressor action you saw earlier? 

The one tube response may be better than the two if the two are saturating the output transformer.  The one tube response is within the realm of a lot of vintage gear.  Though there is certainly better.

 

[khstudio]

okay, but would you say these charts are the inverse of the compressor action you saw earlier? 

The one tube response may be better than the two if the two are saturating the output transformer.   The one tube response is within the realm of a lot of vintage gear.   Though there is certainly better.

I'd say No, they're not an inverse which is confusing. I'm not sure if & how the "Time constant" section & components could effect the Frequency or even the loading of T4?

Also, when I said

I also retested individual Frequencies again very meticulously & got the same results:

I didn't mean the same results as THIS test but from the first "Individual Freq test" =
http://www.khstudio.us/DIY/PM670/PM LR Sweep.bmp

 

[[silent:arts]]

Kevin, what do you think is wrong with your unit ???
you liked the sound in a response before, what is wrong ???
the curves? the measuring? the sound?
I don't understand your issue

 

[khstudio]

Kevin, what do you think is wrong with your unit ???
you liked the sound in a response before, what is wrong ???
the curves? the measuring? the sound?
I don't understand your issue

Well lets see...
I built it stock & had problems so this led me to test & measure EVERYTHING.
At this point I have no choice but to run it with only one tube in the side-chain because of the Heat issues so before putting it in the rack I ran some sweeps & saw that my circuit was over-compressing the highs.
Everything I build I test to some degree to see how the Frequency response, noise, etc is... to make sure everything is running properly.

It doesn't matter if there's 1 or 2 tubes in the side-chain - I STILL get a little too much distortion even when compressing lightly which I don't care for but the comp is still usable & does compress & sound OK... but not quit good enough for full mixes. 

I don't understand why your angry??? 
This is a forum & I'm not only trying to learn but share my experience with this build.
Sorry to piss you off but I'm not just going to throw it in the rack & forget about it.

I can only be so much of a "Paint by numbers" builder... I've built a LOT of gear & this project kicked my ass!
What's the sense of building if I can't use it in the studio? I'm not saying this thing sucks but it could be better.

Kevin, what do you think is wrong with your unit ???

that's why I'm still working on it & posting here... I don't know. Maybe it's as good as it's gonna get???

you liked the sound in a response before, what is wrong ???

I do like this compressor & especially the "Way" it compresses but it doesn't seem totally up to par... especially on full mixes.
There's a reason WHY I'm still working on it or I would have sold it by now.

 

[emrr]

okay, but would you say these charts are the inverse of the compressor action you saw earlier?  

I'd say No, they're not an inverse which is confusing. I'm not sure if & how the "Time constant" section & components could effect the Frequency or even the loading of T4?

Your side chain amp actually exhibits a nice sort of hpf such as is good for keeping some low content from affecting compression.  So that part doesn't bother me, in of itself.  Now hookup the rectification and timing bits again, and measure from the same point with it all connected.  

If you did the original test again with pink noise, show us that.  Or do it if you haven't.  Pink noise won't be as relevant as real music, but certainly more than frequency sweeps.  

While the response test is hooked up would be a great time to select tubes for best balance/response. 

 

[khstudio]

Thanks Doug,
I'll try to do what you said tonight after my session.

BTW, I was thinking the same thing about the roll-off & low end content... that part & the new sweep didn't bother me as much as the 1 to 2 tube sweep & differences.

 

[[silent:arts]]

Kevin, you got me wrong.
I'm not angry.

Since measuring is a part of my day job I know how "wrong" some measuring curves can look sometimes.
I just wanted to know if you are only worried from the curves or if there is still any other issue.

 

[khstudio]

New Tests

Individual Freq Tones to show how the highs are more affected by compression(& in turn the output frequency of the unit.)
Approx 8 to 10 dB of Compression (which increases around 1k up)

This is a new Sweep Test:
BLACK = Raw Loop thru - Sound card
RED = No Compression - Thru unit
BLUE = Side-Chain ONLY, this time T4 fully connected (as per Dougs request) - signal taken from secondary.
PINK = Signal taken from output using ANALAG's 10uF (Stock Mode) - Approx 8 to 10 dB of Compression
ORANGE = Signal taken from output using 2uF @ 68k - Approx 8 to 10 dB of Compression

Harmonic Distortion Test @ 1k Approx 8 to 12 dB of Compression

 

[khstudio]

Kevin, you got me wrong.
I'm not angry.

Since measuring is a part of my day job I know how "wrong" some measuring curves can look sometimes.
I just wanted to know if you are only worried from the curves or if there is still any other issue.

Cool  ;D  My unit IS working again thanks to you!!!
Bear with me... I like to test the gear I build. Not necessarily as much as I have but I'm also trying to learn & try to tame down the Distortion issue.
I don't feel a lot of builders test their gear after building (or have the tools to)

 

[[silent:arts]]

the freq. response curves look fine to me.
I have build in the "THRUST" filter in my GSSL to get this compression curves ;D
the curve without compression looks like nearly any unit I measured with Edcor transformers inside.
but it is still in +/- 1dB specs (don't forget the scaling)

measuring distortion while compressing is nearly impossible, since compression is some kind of distortion.

mhm, I need mine back to do the same measuring (but I won't have time for this at the moment anyway )
however, it doesn't look bad - looks more like character ;D

 

[khstudio]

Really... the increased Compression from 1k up is normal?
I'm aware of filtering side-chains but I find it strange that the Side-chain Amp ONLY test doesn't show the same response I get at the output. ???

The "Time Constant" components obviously effect the response which I find VERY interesting.
This must be where the sensitivity to the higher frequencies occurs.
It's definitely NOT coming from the "Side-Chain Amp" itself from the tests I've done.
Could someone please explain how this happens? I'd like to understand this better.

I'd love to see some measurements from others units.

The Distortion is probably my biggest concern at this point.
Look at the "Harmonic Distortion" pic I posted... now that's "Character" & probably why I really like it on some things like Bass & some guitars & Vocals... but a little much on most mixes.