the Poor Man 660 support thread

[[silent:arts]]

I now have a unity gain noise floor of -79dBu and -78dBu. Bypassed it is -83dBu each.
50Hz and 100Hz all below -90dBu now.

The Poorman 670 is now officially my quietest unit yet with respect to mains noise.

 

[analag]

I'm sure Analag is referring to the non-working units only.

No, Analag is refering to the PSU schematic, which has been made public after several people had PSU Failures.
PSU's in working and non working units are all the same so it's only a matter of time/luck before a failure will occur.

Did you do the actual design?

Failure...I have the oldest unit and it ain't failed yet. Simply use the voltage dropping mod I provided and all will be well. No luck needed.

Another thing, if the initial PSU schematic & design works well, why is it that all of a sudden Analag strongly suggested to replace C6?

In my unit C6 is .47uF and as you can see it's quite easy to be a typo. My B+ filters are 330uF so 220uF is good. If the B+ going into the regulator is kept to a minimum the heat of the MOSFets will also be much less. Apparently the PSU's that fail have a pre-regulated B+ of more than 350V, so the mod is to keep the voltage at a safe level.

 

[radiance]

Thanks again Analag.
So what do you suggest? I've had no PSU problems so fare. Should I replace C6?

 

[alexc]

Another 8hrs or so of use in my studio. No probs at all.

I am trying out different tc networks. The bluebird mod is now 2x 6pos switches
with 0.22uF, 0.5uF, 1.0uF, 2.2uF, 4.5uf and the onboard 10uF on one switch and
26K, 68K, 150K,220K, 470K and OC on the other, in place of the stock series 10uF and 10K pot.

I am using mostly a parallel 220nf and 26K. It's very fast release - maybe 0.25s or so.
Not sure of the attack, but it seems moderately quick.
The responsivess is there all right. Just fantastic.

The release varies nicely with switch position.
The attack varies with the other, but also slows down the release.

So I will probably pick the combos I like and put on one 2pole switch.

Then try  lolo's scamp before deciding how I'll end up.

I get some distortion when using more than 10dB or so of GR.
It actually sounds really good for elec guitar. I back it off to around 6dB or so for bass.

This is with no matching at all of 6BC8's. I have 4 only.

So I'm making up another with some mods, for use in one of my frankenstein channel strips
which will double as a tube matching rig for a bunch of 6BC8s and 65NP.

Hopefully that will improve the depth of GR with less distortion and make it more usable
for different sources.

For guitar though, it really is outstanding. The crunch I get with a high input level
and deep compression is simply the best I have used. Needs a fair amount of
external make up gain tho. Maybe an additional 6dB at the mixer.

Also trying to figure out how to display the attack and release times in daw like some others
have done. Any suggestions? I mean - how to turn on/off the GR without touching the
input signal or knobs.

Anyway - all in all, fun and games for someone with way too much time on my hands!

 

[alexc]

So - more playing thru the Poorman and comparing the channel with the original time constant
network and the channel modded with Bluebirds network.

I definately get a lot less distortion using the unmodded network when in deep compression
(more than 10dB GR) than the modded channel with fast settings of 220nF+26K parallel.

As I increase the time constant with the modded network I also get less distortion as it all slows up.

So -just wanted to say that the stock unit is not overly distorted at typical setting.

I think whatever mod I do, I will retain the original network.

(Still don't hear any difference in the stock Attack knob tho' )

Still lovin' it. The most telling thing is that I've been playing the guitar for many hours
at a go using it. Always a good indicator of a great unit for me.

Just makes me want to play thru it .. more. 

 

[analag]

Thanks again Analag.
So what do you suggest? I've had no PSU problems so fare. Should I replace C6?

You can omit C6. Audiophiles do as they think it makes the regulator more sensitive to the hum frequency, which affects the sonics in some way. Try it without it. 

 

[analag]

So - more playing thru the Poorman and comparing the channel with the original time constant
network and the channel modded with Bluebirds network.

I definately get a lot less distortion using the unmodded network when in deep compression
(more than 10dB GR) than the modded channel with fast settings of 220nF+26K parallel.

As I increase the time constant with the modded network I also get less distortion as it all slows up.

So -just wanted to say that the stock unit is not overly distorted at typical setting.

I think whatever mod I do, I will retain the original network.

(Still don't hear any difference in the stock Attack knob tho' )

Still lovin' it. The most telling thing is that I've been playing the guitar for many hours
at a go using it. Always a good indicator of a great unit for me.

Just makes me want to play thru it .. more. 

You made my day  .

 

[pacemaker]

Hi analag,
i am now building the PSU for the proorman,
i have some spare 220uF 350V,
is it possible to use them for C1 and C3
or do i really need some 400V caps ?
regards,
Francois

 

[[silent:arts]]

Francois,

250V AC rectified will give you roughly 350V, use 400V caps in the place of C1 & C3

 

[dagoose]

Right now i'm using the tubes and transformer as an extra heater in the studio because it's freezing something like -6 degrees celclius right now.. i'm also happy with my d-aoc andand pultec though they produce just a little less heat. brr... i love tubes!  ;D

 

[[silent:arts]]

tube sound is even warmer in winter if you have the white christmas edition PCBs ;D ;D ;D

 

[dagoose]

tube sound is even warmer in winter if you have the white christmas edition PCBs ;D ;D ;D

hmm.. i have the regular ones..

 

[letterbeacon]

This is the support thread for the PM660, but is there a thread or information anywhere where the PM660 design is compared with the Fairchild 660?  How close are the two designs?  Has anyone been lucky enough to compare a PM660 with a Fairchild 660?

Will there be another run of PCBs at any point?

Thanks!

 

[[silent:arts]]

...
Will there be another run of PCBs at any point?
...

I do not have any plans for another run.

for your other questions:
the PM660 shares the topology of a fairchild 660.
however it is not a clone. different tubes, different transformers, and so on.
some people like it, others are disappointed - I would say because of the name.

while most people won't have played with a real 660, they are awaiting "magic" just because of the name.
to be honest I'm tired of this. and I know I'm able to destroy your recording / mix with the real original either.
I have tried this with success  ;D :

 

[letterbeacon]

;D

Thanks very much!

 

[radiance]

I replaced the four 1000uF caps on my slow start heater PSU with 3300uF 16V (panasonic I think) caps which DO fit the PCB.
I also swapped out R1 for a wire.
I now easily get the required 6,3V (I had to trim down from something like 7,4V) and a ripple of 5mV.
Somehow it seems there are less weird knob/meter interactions after I did this mod.

The hour of finishing this unit is neigh...I'm now experimenting with time constants.

 

[crisotop]

Hi analag,
i am now building the PSU for the proorman,
i have some spare 220uF 350V,
is it possible to use them for C1 and C3
or do i really need some 400V caps ?
regards,
Francois

Read a couple of pages back - when using the groupbuy custom-wound torroid I (and others) have nearly 390V before the regulator. So 400V is just enough, better buy 450V caps.

best of luck with that beast,
Christoph

 

[dingo]

hello!
I am building the pm670
searching for some 5687 tube
I have found some JJ ECC99 RF Double Triode Can be used instead of 5687?
dingo.

 

[Kingston]

hello!
I am building the pm670
searching for some 5687 tube
I have found some JJ ECC99 RF Double Triode Can be used instead of 5687?
dingo.

Not on the PCB. It has a different pinout. If you build point to point without a PCB then sure, it's close enough.

 

[dingo]

thanks!!
kingston