the Poor Man 660 support thread

[elektrovolt]

Holger, your drum example sounds good. the original recording is also fine already. nice tight snare sound.
but the last 3rd sounds just that little bit thicker. did you modify the machine ? or is it just stock ? how much reduction did you do here ?

 

[Holger]

Elektrovolt, the drums are made with Toontrack Superior 2.
I did not modify the original build except for the slow start heaters.
IIRC I had some 5-6 dB of compression.
In the last third of the file both channels are compressing. The interesting part is the middle section where you can alternately solo left/right to get an impression what the compressor is doing, left is bypassed, right channel is compressed.

 

[elektrovolt]

ha, I already thought it would be drum software. the original sounds a bit compressed already. very much studio sound in there. those things are getting better and better. sorry, offtopic

I still have mine up for sale, but I still will be soldering some things on it. 'you have to solder when the iron is hot'

 

[ChuckD]

Trying to lower my noise floor in my PM670
Right now it has a humming that at 12'oclock is -70db but if I crank the Gain all the way it is -55dB which you can hear on quiet material.

Can someone tell me what is the difference between a Ground loop hum and Heater Noise?
Here is my plot:

As you can see the primary is 60Hz at -55dB  (Ground loop??)  
But then the Third order Harmonic is just as loud at 180Hz .

My heaters are AC unregulated.

Where should I start?

Thanks

Chuck

 

[mrclunk]

I had hum issues on the channel closest to the psu. I worked out that it was emf from the power supply, not a ground loop or the heaters. But you have a lot of extra wiring in there so possibly it could be a loop.
I ended up adding some steel shielding between the psu and right channel. Which reduced it alot.

Sounds to me like its picking up hum on the input section. The gain switches are vulnerable and quite close to your psu, also your balance and ms controls possibly.
One thing to try is moving the heater resistor (r15) to the back corner of your case.
If u pick that up (very carefully) and move it around inside your unit the hum may change.    
good luck and be careful!

 

[radiance]

Your heater voltage cables run very close to both your right input and threshold rotaries. Is the right channel worse than the left?
You might want to try turning those pm660 pcb's 180 degrees so the heater + psu wireing runs in the back of your unit.
Did you use the slow start heater PSU?
You can rule a groundloop out by checking your wireing. May I ask, how did you do your grounding? Did you connect all grounds to a single star ground point on the chassis, or did you run your grounds to the PSU from which you connected the ground to the chassis?

Oh, and something else, I saw you build your unit with UTC transformers. Are these only used for the MS en/de-coding part or are these used for T1 & T3 ...replacing the Edcors...

 

[radiance]

nice one Holger, good news what programs that btw?...

The screenshots were taken from Soundbooth which is part of Adobe's Production Suite.

Those screenshots use a lin frequency scale. Very hard to see whats going on in the lower region. Can you make some tests with a log scale maybe?

EDIT: I see that your scale is not really Lin, but it should be way more log than it is to give a clear view of the bass response...

 

[ChuckD]

Thanks for the replies guys!

So I already moved the heater Resistor to the back corner and glued it down. So I will have to get another one to move around and test.

No I did not implement the Slow start Regulators. Maybe I will give that a try.

Turning the boards might be a good idea to try So I will do that later tonight.
Also I may just make an enclosure for the PSU as well.


THe grounding is a big Star Ground on the case. I also sheild all the audio interconnects at one end into this same star ground.
The one thing that confuses is the Bypass Pcbs and the multiple grounds there. I will first have to go over these carefully.


Chuck

 

[mrclunk]

So I already moved the heater Resistor to the back corner and glued it down. So I will have to get another one to move around and test.

I wouldn't bother getting another one, the back corner is probably the best place for it.
I just found it handy to work out what the sensitive parts of the circuit are by moving it near them.

 

[ChuckD]

Sorry I forgot to comment on the UTCs

Yes I am using UTC A15 at T2 (main output) and T3 (input to the timing circuit).
I do not experience any of the distortion that others have spoken about.
I think the UTCs play a big role in that. If I can find any I will most likely trade out the 4 x  T1's  Edcors for UTCs or Triads some day. I did not do any matching of tubes either, I swear no distortion !

I can use this on a Rock/heavy master without any problems as I never crank it past 12 o'clock where the noise floor sits just below -70db.

However if I try to put it on a Jazz solo Piano then I can hear the noise floor.
So I still have some tweaking to do.

Chuck

 

[mrclunk]

cool!
I have a big sowter that i'm going to try in T3 position next week. Hopefully it'll get rid of the distortion i'm hearing on mine.

 

[jackies]

Yes I am using UTC A15 at T2 (main output) and T3 (input to the timing circuit).

Thanks for the clarification!
Now, what is the reasoning behind the choice of which transformers to upgrade?
Does sidechain transformer quality even affect the sound?
:

 

[mrclunk]

Does sidechain transformer quality even affect the sound?

I don't think so... well i hope not.
I'd like to use UTC Ouncer's here.  They're usually much cheaper

 

[radiance]

Replacing T1 & T2 would be my first choice.

 

[mrclunk]

But they (T1, T2) wouldn't effect the distortion we're getting under compression ???

 

[radiance]

But they (T1, T2) wouldn't effect the distortion we're getting under compression ???

Well, I think T2 does effect the distortion. T1 not so much...
Maybe best to replace T2 & T4...

Sorry I forgot to comment on the UTCs

Yes I am using UTC A15 at T2 (main output) and T3 (input to the timing circuit).
I do not experience any of the distortion that others have spoken about.
I think the UTCs play a big role in that. If I can find any I will most likely trade out the 4 x  T1's  Edcors for UTCs or Triads some day. I did not do any matching of tubes either, I swear no distortion !

When I think about this I wonder what Analag has used in his prototype..Did he wind those transformers himself as he also did in his huge tube compressor??
If yes, he probably would have made them very symmetrical, spot on...
Your UTC's are probably also spot on, very symmetrical transformers, hence why you both don't have distortion problems...
Just a thought....

 

[emrr]

The Gates Sta-Level input transformer is a single-ended type used PP with artificial center tap.    Balance is dictated by the input attenuator in both the Sta-Level and the PM660.  The output for the audio amp is more critical, but there are plenty of ways to achieve balance; chiefly through experimentation with various sets of tubes.  A 'perfect' transformer will require a perfect set of tubes.  An imperfect transformer will require a sympathetically imperfect set of tubes.  There's no simple winning recipe.  For instance, any set of power tubes matched in an instrument amp will likely not measure as matched when put into another amp, because of the tolerance of the transformer windings themselves.  Audible thumping is what you get from gross imbalance.  Any other general constant distortion is more likely headroom related. 

 

[mich]

When I think about this I wonder what Analag has used in his prototype..

- Edcors . ?

 

[[silent:arts]]

When I think about this I wonder what Analag has used in his prototype..

- Edcors . ?

Edcors!
he showed some photos some time ago.

 

[ChuckD]

Well I think it's the Edcor power transformer.
It seems to radiate way too much EMI.

I put 6 layers of Grain Orientated Steel  (transformer laminate) around all the UTCs in a cylinder shape and two layers around the Edcor power transformer. The 60Hz and 180Hz noise dropped 12db from -55 to -67. This is at max Gain.

Unfortunately I cannot move either as I have no room inside the case.
I think I will try a different transformer if I can find one.
After the labeling screw (see earlier posts)  up by Edcor and now this I don't think I will use them anymore. They are just too low quality in my opinion.

I don't suppose anyone has an extra power transformer out there?
I will try to make the shield better but I think swapping that out is the best.


Chuck