the pimp / mod the Poor Man 660 thread

[buschfsu]

buying caps for my PM670 and purusha case (6 selections for TC)

trying to understand this and so far i have...

Slow attack                                     Fast attack

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

Slow release           Fast release
EDIT: had release descriptions backwards based on this bluebird quote...
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.

as i understand it putting these in parallel on a switch means that these six combinations are possible?  do these combos match what i have for descriptions above?

 

[lolo-m]

buying caps for my PM670 and purusha case (6 selections for TC)
trying to understand this and so far i have...

Slow attack                                     Fast attack

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

Fast release Slow release

as i understand it putting these in parallel on a switch means that these six combinations are possible?  do these combos match what i have for descriptions above?

Will you use my mod ?
If you do, you'll get approx 0,2ms attack with a 2uF; 0,4ms with a 4uF. Release is the R*C...  If you want longer attack times, I've got tips but it doesn't belong to this thread....

 

[buschfsu]

trying to understand it first.  so are you saying the attack time is not related to the paralleled 'RV7' resistor subs and the 'C4' cap subs?

 

[lolo-m]

trying to understand it first.  so are you saying the attack time is not related to the paralleled 'RV7' resistor subs and the 'C4' cap subs?

In analag's network it is more or less. I mean the attack is given by C3 charge more than by the C4's. Electricity is like water, it fills quicker a small glass (C3) than a big one (C4) especially if you reduce the throat of the bottle (RV7+R18) to fill the bigger one (C4)...
Of course the caps are charged in parallel so changing C4 for a smaller value will change a bit the attack time but C3 is 45 time smaller than C4 stock so...

 

[buschfsu]

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

is accurate?  obviously there are other factors at work as well.

 

[Kingston]

I've been experimenting with 6K4P's all weekend.

I didn't want to end up with oscillation with some quick slap-on-wire-only tests, so I built a very sturdy adapter from each 9-pin socket to two 7-pin sockets using turretboard/bus-wire/sockets combo for each 6bc8 position.

I looks quite impressive actually, I should take some pictures.

Anyway, I was able to match these even better, quite perfectly actually, since I wasn't stuck with dual triode halves. I bumped B+ up to 165V and set the trimmers to 5,5V each (just a quick test, I'll optimise later). It allows about 22dB maximum gain reduction, and more headroom. Of course I had to experiment with more B+ for more headroom, but less maximum gain reduction. 190VB+ would allow around 15dB max gain reduction, for example (tested quickly)

I don't know why some people said earlier 6K4P is not a good fit for poorman, and why it was suggested only about 6dB gain reduction would be possible. 6K4P is a brilliant fit actually. It cuts the unusable distorted ranges available with the 6BC8, basically fixes gain staging. 6BC8 is simply not capable of 40dB gain reduction in this circuit, so why even have that much range available? It just sounds bad.

6K4P makes a much more balanced set up with it's wider grid curve and it's no longer easy to make poorman a distortion generator. VU meters now display much more usable information, instead of sitting "buried" whenever something compresses.

And the sound, obviously the the 6K4P at higher B+ compress a bit different than 6BC8. To me, this sounds more like the big brother and its variants, more controlled somehow.

I did say that 6BA6 (and so 6K4P) is not suitable in the PoorMan. The grid voltage swing needed to have -10dB of effective gain reduction is far more than 12Volts.
How did you check the gain reduction ? With the Vumeter or with a real Gain meter ? Did you use the SCAB or stock Sidechain ?

But I agree on one point, the 6BA6 sounds cleaner than the 6BC8  .

I don't know why you keep saying that. Did you test yourself, or just read some datasheets? I'm using the VU meter to read the gain reduction obviously. It acts the same in compression, or when used with the tube matching rig. 14V = about 17-20dB gain reduction at 160V.

I wonder what's a good way to beef up the sidechain for more voltage swing? Would be interesting to run the tubes closer to the edge.

OK, it's time to end some unopened project. I'm working with another member on a prototype based on 6BA6... The voltage swing needs to be a lot more important with this kind of tube than with 6BC8 or ECC189. For example in our prototype, the -20db gain reduction need a CV of -40V and -10db is around -20V, both referenced to the grid voltage for 0db gain reduction.
That would mean in the PM670 a CV swing from -5,5V to -45,5V to get -20db of GR...
The vu resistor have to be choosen well to track correctly the gain reduction. The movement is showing you some compression but maybe not the real amount of compression.
As my prototype use different resistors values and different transfos, I will try tomorrow in the PM setting but I'm quite sure you can't get -22dB without a huge voltage swing... But if it is, that's a really great news  ;D !

It is definitely possible. I do realise the VU meter is not a perfect measurement, but I know I'm in the ballpark with it. I can hear it. If it was compressing less than 10dB it would be near invisible and hard to tell because of the extremely soft knee of the grid curves. Remember, I have no Scamp yet.

I can hear it compressing like mad at max settings. It sounds gorgeous. Just like with the 6BC8 and variants, but no distortion.

Remember I only chose tubes that would go to about 18-20dB reduction at -14V grid. About one quarter of my sets could do this. Another quarter would not even hit 10dB at -14V.

 

[lolo-m]

It is definitely possible. I do realise the VU meter is not a perfect measurement, but I know I'm in the ballpark with it. I can hear it. If it was compressing less than 10dB it would be near invisible and hard to tell because of the extremely soft knee of the grid curves. Remember, I have no Scamp yet.

I can hear it compressing like mad at max settings. It sounds gorgeous. Just like with the 6BC8 and variants, but no distortion.

Remember I only chose tubes that would go to about 18-20dB reduction at -14V grid. About one quarter of my sets could do this. Another quarter would not even hit 10dB at -14V.

Now I understand better how your setting can work that way ! 6K4P seam to have more diferences between curves than the 5749 (6BA6W) I tested.
And I agree it is a lot more easy to match single triodes than dual triodes. Well matched triodes are a huge improvement in terms of distortion and attack times.

 

[Kingston]

6K4P seam to have more diferences between curves than the 5749 (6BA6W) I tested.

Yes. I have 5 6BA6 meant for another project but I quickly checked (with your matching rig) just how "equivalent" they are to 6K4P. They all fell in the "higher quadrant" of the 6K4P sets, with only one barely going under 10dB with -14dB grid. None could be matched with the "steep curve" 6K4P's I'm using.

 

[lolo-m]

6K4P seam to have more diferences between curves than the 5749 (6BA6W) I tested.

Yes. I have 5 6BA6 meant for another project but I quickly checked (with your matching rig) just how "equivalent" they are to 6K4P. They all fell in the "higher quadrant" of the 6K4P sets, with only one barely going under 10dB with -14dB grid. None could be matched with the "steep curve" 6K4P's I'm using.

That's what I always thinked for 6BA6 use ! But I was sure (and I was wrong) the 6k4p was a close equivalent of the 6BA6. But obviously, it isn't !

Just because I'm curious, how did you wired the 6K4P ?

PS: If you plan to use the SCAB, you'd better change the 5532 for OPA604 and power it with +/-24V rails. It'll give you more compression headroom in SCAB mode especialy for the peaks.

 

[Kingston]

That's what I always thinked for 6BA6 use ! But I was sure (and I was wrong) the 6k4p was a close equivalent of the 6BA6. But obviously, it isn't !

Just because I'm curious, how did you wired the 6K4P ?

Well it is "an equivalent", but 6k4p has more ranges it seems. Or maybe they are equal but we just haven't tested enough 6BA6 batches.

From some other thread: Safe triode mode for 6BA6 is : pin2 tied to pin7 and pin5 tied to pin6 (lewilson:Yes, this is exactly how mine is. )

I wired it like that. Actually 6K4P cathode is hardwired to grid 3 (and screen) so it's even easier (pins 2 and 7 internally connected).

PS: If you plan to use the SCAB, you'd better change the 5532 for OPA604 and power it with +/-24V rails. It'll give you more compression headroom in SCAB mode especialy for the peaks.

I had not thought about Scab headroom. hmm. This might be a bit difficult since my power supply might not be able to provide +/-24V rails. I will experiment.

 

[lolo-m]

I had not thought about Scab headroom. hmm. This might be a bit difficult since my power supply might not be able to provide +/-24V rails. I will experiment.

Don't bother... Try to set the +/- voltage as high as possible with stock PSU with some margin for regulation and you'll be fine.

 

[inputoutput]

New trafos Mounted! a pair of vintage Chicago trafos (BIH 1) on the input T1. 600/50K (Thought they were 1:1 ratio, but now I'm not sure anymore. Anyone?)  On T2 theres a pair of LL1676


Before and after :


Edcor :

New Trafos

------------------------------



Edcor :

And here with the new Trafos

It should be taken into consideration that a lower ratio on the inputtranny gives a lower volume in - which is more gentle on the rest of the circuit. But interestingly enough, the output volume was almost as loud.




With full Gain I now have virtually no noise or hum. Only a modest 60Hz peak at -96dBu on right side and a -106dBu on left side.



As for the sound, the results are self explanatory

 

[radiance]

So are these 40Hz and 2K test signals (sine's) we're seeing here?

 

[inputoutput]

sinustones. The results looks kinda the same in all frequencies.

 

[inputoutput]

Stumbled upon a page with sample testrun through the Analogue Tube AT-101 (Fairchild 670 Recreation). http://ronansrecordingshow.com/2010/06/analogue-tube-at-101-the-fairchild-670-recreation/  Hope Ronan Chris Murphy, who run the site, and the musicians at play, thinks it's ok that I borrowed his soundsamples.  I ran the files through the PM670 to see how it came out.  This is just a fast run-through.  Don't make a review out of this, cause there are so many factors at play....! Compared to the wonderful AT-101 I would say that the Poorman tightens the bottom end, and the midtone sounds harder. 

I have been using the PM670 A LOT throughout the last year, with great joy,  mainly because of its uniqueness.  The clue is to know what it's good at, and what not.  Like, if you run a clean piano piece through it will probably sound nothing but horrible, but a more low-fi'ed piano track might sound just wonderful (as long as the inputgain is not set to high.)

Here are the files (one with bypass, one PM670 and one AT-101) http://www.kaada.no/DIY/PMSHOOTOUT.zip

 

[Ronan Chris Murphy]

Hope Ronan Chris Murphy, who run the site, and the musicians at play, thinks it's ok that I borrowed his soundsamples.  I ran the files through the PM670 to see how it came out.  This is just a fast run-through. 

Hey, that is cool that you did this. You definably have my permission, For those that are just going to download the files here and do not visit my site, I just want to acknowledge the musicians on the samples who I did not pay anything for the use of their music in the shoot out:

In order the audio samples contain clips of:
Jibilian/Setar http://www.garyjibilian.com
Tay Zonday http://tayzonday.com/
Terry Bozzio http://terrybozzio.com/
Kathleen Blackwell www.kathleenblackwell.com

 

[opacheco]

A lot of money, time and effort. I have enough tubes to re-tube it three times. As much as I love it, I wouldn't build another one...too much work.

Analog,

I see your proyect....man that is incredible!!...Do you have info or Instruction in order to do a unit like this(your own instructions)??
How about the sound?

Thanks a lot for your time.
Opacheco.

 

[analag]

This was built and fine tuned years ago and as for the sound, I took it to the NY group meet and the guys rather liked it a lot  . It  would be a combination of PCB and point to point wiring. Power and output transformers would have to be custom. It's a big project but the sound is worth it I suppose.

 

[opacheco]

This was built and fine tuned years ago and as for the sound, I took it to the NY group meet and the guys rather liked it a lot  . It  would be a combination of PCB and point to point wiring. Power and output transformers would have to be custom. It's a big project but the sound is worth it I suppose.

Analog, Thanks for you response!

Do you have the schematic that you used for it?....how about the internal pics, do you have some internal pics?

Thanks for your time
Opacheco.

 

[analag]

I have go dig around to find the internal pics. These are all I could find. I took the second pic about five years after I built the thing.