the Poor Man 660 support thread

[cannikin]

[quote author="Larrchild"]
btw, I think my stuff is in his "hall of fame" over at the Goldpoint site. [/quote]

I didn't realize that was your gear.... wow.... hows it doing in the market?
its amazing unit!

 

[Larrchild]

Well they look great and I sell every one I build, but they are a painful build, lol. I have spent quite a while redesigning for mass production, while retaining elegance.

It's all packaging changes these days. Schematic has remained the same for years.=)

It's good to make things that people other than you can build, or you become a prisoner to your own idea, ha!

Bring on the CNC robots!

BTW, I meant to say the output attenuator could remain stock, but the input might benefit from 1dB steps as Jakko said.

 

[fazeka]

Hi Analag (or anyone else who may have an answer),

I read somewhere that Fairchild when building the originals removed the diode bridge from the Simpson VU meters, essentially making them DC milliammeters:

Fairchild 670 meter thread

My question: can I use my pair of Simpson model 127 1 mA DC milliammeters instead of VU meters for the PM670?

Best,
Chris

 

[emrr]

[quote author="[silent:arts]"]the rotary switches

the first rotary switch is the "Input" or "Gain" switch.
dual deck is necessary, shorting preferred, and the more positions the better. over all resistance is 15K. [/quote] 15K ohm per section? or total? I'm assuming per section, meaning 30K measuring both sections

my prototype has 18dB of gain, thus I will do one dB steps on an Elma, stopped to 23 steps, going from -4dB to +18dB.

Ah, good info. 18 dB total gain. So, 1 dB steps gets you below unity gain. And for those asking about low noise tubes, that's the amount of maximum possible gain you are worrying about in regards to noise contribution.

Regarding the sweet spot of the 'Threshold' switch; it appears then that a low level audio signal could receive an 18 dB boost in the audio amp, plus whatever boost is available in the side chain amp for driving compression. So, if you put a typical +18 dBm FS signal into the unit, how much might one wish to turn down the input, and likewise compensate with the side chain gain? Or, is the side chain fully capable (I imagine so) of knocking down the gain below the clip point successfully? Those are the questions for all to consider (when second guessing the designer :razz: ). I imagine (22) 1 dB steps on each is more than enough to wrangle the signal several different ways.

Sorry to make more work so early; figure I'd throw out these musings to help folks get a grasp on what these attenuators do, and how it relates to their systems. I'm used to dealing with things like Collins 26U's and Gates SA-39's with 2 dB/step input and output ladder attenuators and 55 dB wide open gain. They have fixed thresholds, so the input attenuator is the whole deal, and the output is for setting recorded level. It's normal to run that variety at -26 input and -24 output; that won't apply to this design.

 

[seavote]

could this setup work? done for 15K?

http://www.penguinlovers.net/audio/Attenuator.html

 

[codered]

Earlier on in the thread,SilentArts was suggesting checking out the audio path in the original schematic.I was kindof stuck in the first step trying to figure out which transformers are used for the M-S seperation. :sad:
Then I moved on to the attenuators-the original used a bridged T configuration and we are using a regular potentiometer but just stepped and the dual deck is for the dual mono operation.The idea behind using the rotary switch is to have good tracking between the channels by choosing closely matched resistors.Could anybody tell me if my understanding is correct.

 

[guavatone]

I would be willing to sell folks some of those Elmas if we had enough orders. Maybe someone can fab the PCB.

 

[outoftune]

what size case will work best for the pm660? is 2U enough or is 3U necessary?

 

[tommypiper]

[quote author="cannikin"]I'm curious if anyone has any intention of using audio transformers other than Edcor? if so "whatcha thinkin about using?"[/quote]

David, yes, I'm hoping to experiment with a Lundahl (don't know which one yet) for the inputs. I hope to compare them to the Edcors in the same chassis and then decide. I'll stick with the XSMs for output.

But my build progress is pathetically slow, I don't know when I'll have time...

What about you?

 

[cannikin]

I think I might do sowter or cinemag on input, and Heyboer on the output. Not sure though... also depends how much $$ I have at the time of purchase

 

[emrr]

[quote author="codered"]
Then I moved on to the attenuators-the original used a bridged T configuration and we are using a regular potentiometer but just stepped and the dual deck is for the dual mono operation.The idea behind using the rotary switch is to have good tracking between the channels by choosing closely matched resistors.Could anybody tell me if my understanding is correct.[/quote]

I am assuming these are dual attenuators for PP circuits, located on the secondary of the inputs, center tap to B-/ground; look at the input pot on an Altec 436B or C.

 

[[silent:arts]]

[quote author="emrr"]I am assuming these are dual attenuators for PP circuits, located on the secondary of the inputs, center tap to B-/ground; look at the input pot on an Altec 436B or C.[/quote]
exactly
:thumb: :thumb: :thumb:

and yes, 15K each deck

 

[tommypiper]

[quote author="cannikin"]I think I might do sowter or cinemag on input, and Heyboer on the output. Not sure though... also depends how much $$ I have at the time of purchase[/quote]

I hear you on the $$ front... plus lack of time... and we don't even have boards yet.... I am getting the Edcors so I'll have them in any case, they're cheap and may be useful elsewhere if I don't use them all...

Do you know which Sowter, Cinemag and Heyboer models you're thinking to try?

 

[Vas]

[quote author="tommypiper"][quote author="cannikin"]I think I might do sowter or cinemag on input, and Heyboer on the output. Not sure though... also depends how much $$ I have at the time of purchase[/quote]

I hear you on the $$ front... plus lack of time... and we don't even have boards yet.... I am getting the Edcors so I'll have them in any case, they're cheap and may be useful elsewhere if I don't use them all...

Do you know which Sowter, Cinemag and Heyboer models you're thinking to try?[/quote]
hi there!
i was wondering for edcor alternatives too!
and i have some spare sowters(dla2a leftovers it seems they sould work!)
anyway,any info appreciated!
best regards
b.

 

[Jonkan]

Any more info on the pcb connectors needed for the project? And the heater resistor?

Im trying to buy components before the pcbs arrive, and at the same time pick up some forgotten parts for my d-aoc. If possible, id like to save on shipping costs ordering at the same time.

If not, thats just fine too, im just wondering.
I can wait. :green:

/J

 

[cannikin]

[quote author="tommypiper"][quote author="cannikin"]I think I might do sowter or cinemag on input, and Heyboer on the output. Not sure though... also depends how much $$ I have at the time of purchase[/quote]

I hear you on the $$ front... plus lack of time... and we don't even have boards yet.... I am getting the Edcors so I'll have them in any case, they're cheap and may be useful elsewhere if I don't use them all...

Do you know which Sowter, Cinemag and Heyboer models you're thinking to try?[/quote]

I'll probably use the Sowter 4383 La2a inputs or CInemag CMMI-8C. I'm having Heyboer Build me 2 more outputs (because I already have 2). Not sure though I might go with input Edcors due to $$ flow. To me this project is the "BIG Kahuna" so I might as well blow out the cash and get expensive transformers....

 

[emrr]

You guys postulating the use of other iron might wish to consider whether or not the Edcor center-taps are integral to every position, or not. We haven't seen it.

 

[cannikin]

[quote author="emrr"] consider whether or not the Edcor center-taps are integral to every position, or not.[/quote]

time for cannikin to learn something new. :thumb:

Doug please explain more of what your thinking...

 

[emrr]

Only that one must plan for other iron having center taps, in the absence of knowledge concerning their usage in this project. For instance, the Sta-level doesn't use CT iron on the input, nor does the 436A. But the 436B and C do, as do most other PP limiters. We don't know what's going on here yet.

 

[[silent:arts]]

CT is used on both 10K/600, but not on the two 600/10K