the Poor Man 660 support thread

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W DeMarco said:
Just wondering if anyone bought a spare PSU board to make two mono units and ended up building a single stereo.  I might need a new board if I cant work out the problems.
Click to expand...

since I get asked about spare PSU PCBs (no, I really don't have any left anymore) I will include a bunch with my next PCB order.
 
YeeHaw fellas, Big red is back in action.

Finally took the time to trace my psu voltages and found that R1, the 47 ohm 2 watter went bad after the big shock.  Swapped her out and voila, VOLTAGE!!!  Now I have to tweak a couple things and label the beast and throw it in a rack.  Question, my power resistor for the heaters gets unbelievably hot, way too hot to touch and the chasis where its installed gets really hot as well.  I figured its doin a lot of work but is it a bit much?

Thanks,

Silent, no psu board is needed any longer :p
 
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  :eek:

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

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

Thanks.

 
It's absolutely pointless to do full frequency sweeps when the unit is compressing. It's completely dependent on the speed of the sweep, and there are other factors depending on type of compressor as well. In PM670 the dual release makes it even more unpredictable (when sweeping).

Envelope follower, remember?

And the envelope of the sweep is useless information.
 
I don't totally agree with you but can see your point...
I've swept many comps & although they're all slightly different, they do stay within reason.
This thing is hitting the high mids & highs a lot harder than the low end... slow or not.

I also tested it normal & with a modified side chain... 2uf + 68k... which is pretty FAST!
Faster than the sweep I was running.

I did consider what your saying & can try "Individual tones" to see how it responds to different frequencies.

Look at the link I posted to see the roll off.
 
Picture this:

A quick sweep contains a lot of low frequency information. Those low frequencies quickly charge your envelope follower caps. When the sweep graduates to higher frequencies, there is less current to charge the caps, and they will start discharging. A cap discharge in your envelope follower means a release.

But PM670 has parallel release.

That -4dB you're looking at is the bigger one of the parallel release caps fully charged by the low frequency part of the sweep, I presume.

How long is your sweep, somewhere between 300ms to 1.5seconds? That shows on your graph.

Time to go mixing now. your unit works just like it's supposed to.

[edit]

wrote a couple of mistakes first time.
 
OK man... I just tried again but this time using a signal generator so I could "Slowly" go thru each frequency.

Same Results!!!

Once I hit about 1.5k, the compression increases.
At 2k to 3k I'm down about -2dB
At 4-5k on up I'm down about -3.5dB

Keep in mind, I tested my signal generator to ensure it was FLAT & even at ALL frequencies with no compression!

My compressor is compressing higher frequencies MORE than lower... period.
There's no disputing it.

can anyone else confirm or test this?

 
My compressor is compressing higher frequencies MORE than lower... period.
There's no disputing it.
Click to expand...
I didn't tested PM but your measuring is showing the response of the sidechain amp but in reverse. I want to say that SC probably has some bass roll off. That can be compressing character , if you don't like it that's the another story....
 
Moby said:
My compressor is compressing higher frequencies MORE than lower... period.
There's no disputing it.
Click to expand...
I didn't tested PM but your measuring is showing the response of the sidechain amp but in reverse. I want to say that SC probably has some bass roll off. That can be compressing character , if you don't like it that's the another story....
Click to expand...

I'm not saying I don't like it but I do notice a little too much high end loss when compressing... sometimes it comes in handy.

My point here it is to see if anyone else has the same results... if not, then I need to find out why mine is different.
IF other units built have the same response & this IS normal... then I may look into some "Side-chain Filtering" options.
 
I don't  know about other units but I don't think that you have less high end, it's just more sensitive to highs... try with some noise and check is the same or not... 
 
Moby said:
I don't  know about other units but I don't think that you have less high end, it's just more sensitive to highs... try with some noise and check is the same or not...  
Click to expand...

Yes I know... more sensitive to high end.
I thought I was being clear in my explanation.

Once again, just like my earlier "tube issues" nobody wanted to believe me until a few more builders had the same problem.
I'm not saying this IS a problem.
Until someone else actually does the same test I just did, we'll never never know & the speculating will continue.
 
Hey, got your message, very interesting.  Use pink noise rather than a sweep.  I've seen at least one compressor that wouldn't settle into a chartable response at all.    Also measure just the side chain amp as if it were the only amp to be tested, and see what it looks like.  Then you can attempt to intelligently gauge what's feeding the rectification and timing network. 
 
emrr said:
Hey, got your message, very interesting.  Use pink noise rather than a sweep.  I've seen at least one compressor that wouldn't settle into a chartable response at all.     Also measure just the side chain amp as if it were the only amp to be tested, and see what it looks like.   Then you can attempt to intelligently gauge what's feeding the rectification and timing network. 
Click to expand...

Thanks Doug,
I was going to test the side-chain Freq. response when I get done my session tonight.

The single frequency tests told me a lot but I will try the pink noise like you guys suggested also.
 
Kevin, you can try to add some capacitance on the transformer and measure. I think that can flatten a situation  ::)
 
stanz said:
Kevin,

Sounds like you fixed you PT issue. What was the final verdict?
Click to expand...

Nope... didn't fix the PT heat issues but I was about to test out a 6.3v 8A AC transformer on the heaters.
This is how I found the compression issues above. I felt I should test the noise & hum levels before & after the TX change & while testing for that, I ran some sweeps to see how the unit was responding to different frequencies.

I'm still running it with one tube in the side chain until I find a better PT option so I can run the "proper" 2 tubes in the side chain.
Although it works, I feel it may have been a little sweeter with the 2 tubes as opposed to 1.

BTW, I did test the side chain with 1 & 2 tubes in the SC... same outcome.
 
Hi Kevin,
I'm interested in your frequency response finding.

A question:
did you try to sweep just the side-chain amp?
and the results is the same [inverted now] bass roll-off?
 
I'm still running it with one tube in the side chain until I find a better PT option so I can run the "proper" 2 tubes in the side chain.
Click to expand...
I didn't notice or I missed that detail with just one tube. I think that 1 tube is not "happy" with 10K termination  :-\
 

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