the Poor Man 660 support thread

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[quote author="Gachet"]Threshold question:

I was planning to build the same attenuator for both treshold and input(12 steps log).But after reading this topic I think i will go for a 3K fixed resistor (lowest treshold I suppose), combined with a 12 steps 1K per steps.

Is that a good idea ?[/quote]


No idea; have no bench tests yet. We don't know the operating point.
 
[quote author="emrr"][quote author="[silent:arts]"][quote author="emrr"]Probably needs diode isolation to keep time constants from shifting with parallel connection.[/quote]
does an original 670 have one ? :wink:[/quote]
No, but every other stereo linked vari-mu does, or it ignores the shift. There is a good amount of commentary about this in other vari-mu threads.[/quote]
but this thread is about the poor man, isn't it ?
don't get me wrong, but I think we should put all suggestions, mods etc to an extra thread.
we already have 25 pages here.
it is DIY, you have a lot of experience, feel free to mod the design.
but we have a lot of not so expereienced members in this thread, and my thinking is they could get confused with all the options / mods etc discussed here.
let them build it like it is, if they feel to need any mods they can do later.
 
There's been no mention of the linking to date, and it's not on the schematic. I was avoiding addressing it until it was brought up. I consider it relevant to making dual mono and stereo operation match in timing. The Fairchild fails to correct for this, for better or worse. As is, in the original design, if you toggle between linked and unlinked the time constants will double/halve because of the nature of paralleling networks. We do not have the complexity of time constant switching found in the Fairchild, so it's not as if I'm suggesting we alter something that already mimics exact original operation. We don't have mention of any exact time constants with the PM. As far as I can tell the only thing possibly changed by addition of diodes is the need to overcome the diode voltage drop through additional drive on the threshold control. Hopefully that explains my thinking, and I shall mention it no more.
 
Doug, I understand, and your suggestions and thinkings are welcome.
My thinking is just: we should start another thread for pimping, and leave this one for the "building by numbers" support.
 
PLEASE don't stop discussing the Stereo LINK :!:

Doug,
Since you seem to be pretty knowledgeable with this stuff I think you should start the PM670 MOD's Thread. That way you can man the first pages links & info. I'd start it with this Stereo Link idea. I for one am interested!!!

Volker has been pretty good at keeping the links (on page one) updated & will probably add the MOD Link also. :wink:
 
[quote author="[silent:arts]"]Doug, I understand, and your suggestions and thinkings are welcome.
My thinking is just: we should start another thread for pimping, and leave this one for the "building by numbers" support.[/quote]

Understood. How to get the 'option' questions to start in another thread, though?

I noticed the AC and DC threshold adjustments on page 8 of the Fairchild 670 manual. At a glance I would assume RV3 and RV6 are to be adjusted to match, and are equivalent to the single DC threshold control in the original. I don't believe Analag has weighed in about this to date.
 
[quote author="no-fi"]Anyway - in that case, I'll see what I can find around here in the range of 10uF parts... otherwise off to TAW, and more international postage.[/quote]
It would help us in helping you to have a more precise location than the one currently in your profile. From your earlier mention of AU$ I'm guessing 'somewhere in Oz', right? I believe RS carry EPCOS polypropylenes which may or may not fit the footprint on the PCB*. Then again, knowing RS int'l shipping will look cheap in comparison.

[quote author="no-fi"]As for the reason I'm asking about switched sidechain circuit components already.... well, I've already done $100 in shipping, so if I knew I might want a bunch of 4 & 8 uF caps in the future, and they had to be high voltage (ie, I also had to order the 10uF Wimas) well, I could order them all at once... [/quote]
Are there any tube projects that tickle your fancy, like the MILA, the One-Bottle or the G9? 4..10uF output caps are quite useful in many SE tube line output stages.

JDB.

[*] From what [silent:arts] has written I gather that any 10uF polyprop cap that fits the PCB will do. This excludes the Solen Fast and similar (large) cylindrical caps, and I would personally be wary of no-name Shanghai Specials. It doesn't have to be a WIMA, if you find a polypropylene film part from EPCOS, BC, Panasonic or AVX that has a similar footprint it should work Just Fine. You can get the footprint by measuring the slkscreen on the PCB, or from the WIMA datasheet.
 
[quote author="emrr"]How to get the 'option' questions to start in another thread, though?[/quote]
http://www.groupdiy.com/index.php?topic=351648#351648

[quote author="emrr"]I noticed the AC and DC threshold adjustments on page 8 of the Fairchild 670 manual. At a glance I would assume RV3 and RV6 are to be adjusted to match, and are equivalent to the single DC threshold control in the original. I don't believe Analag has weighed in about this to date.[/quote]
You might have answered your question yourself.
analag will coment this someday, but I have a feeling he is "on vacation" for a new design right now. we will see.
 
[quote author="jdbakker"]
It would help us in helping you to have a more precise location than the one currently in your profile. From your earlier mention of AU$ I'm guessing 'somewhere in Oz', right?
[/quote]

you're right.

Sinney, oztraya. maaaaate!
:)

Are there any tube projects that tickle your fancy, like the MILA, the One-Bottle or the G9? 4..10uF output caps are quite useful in many SE tube line output stages.
Click to expand...

I was thinking maybe a pultec passive EQ, (or a pair of them!! :)

that would make 2 compressors (solid state and tube) plus 2 eqs (solid state & tube)

then maybe I'll give DIY a rest for a little while, and learn to use everything!

[*] From what [silent:arts] has written I gather that any 10uF polyprop cap that fits the PCB will do. This excludes the Solen Fast and similar (large) cylindrical caps, and I would personally be wary of no-name Shanghai Specials. It doesn't have to be a WIMA, if you find a polypropylene film part from EPCOS, BC, Panasonic or AVX that has a similar footprint it should work Just Fine. You can get the footprint by measuring the slkscreen on the PCB, or from the WIMA datasheet.
Click to expand...

hmmm.. ok, in that case, I probably need the big WIMAs... apart from huge 400V solens, I can get something locally, made by a company called farad - http://farad.net - but I guess that would count as a "shanghai special"... and apart from these, 10uF polypropylene caps are pretty light on the ground.
 
[quote author="no-fi"][quote author="jdbakker"]
It would help us in helping you to have a more precise location than the one currently in your profile. From your earlier mention of AU$ I'm guessing 'somewhere in Oz', right?[/quote]

you're right.

Sinney, oztraya. maaaaate![/quote]
Ah yes, the first and only place where I've ever seen a sign at a park entrance saying Please walk on the grass.

[quote author="no-fi"][quote author="jdbakker"][*] From what [silent:arts] has written I gather that any 10uF polyprop cap that fits the PCB will do. This excludes the Solen Fast and similar (large) cylindrical caps, and I would personally be wary of no-name Shanghai Specials. It doesn't have to be a WIMA, if you find a polypropylene film part from EPCOS, BC, Panasonic or AVX that has a similar footprint it should work Just Fine. You can get the footprint by measuring the slkscreen on the PCB, or from the WIMA datasheet.[/quote]
hmmm.. ok, in that case, I probably need the big WIMAs... apart from huge 400V solens, I can get something locally, made by a company called farad - http://farad.net - but I guess that would count as a "shanghai special".[/quote]
They're pretty much the poster child for Shanghai Specials, yes. [I needed to reformat the URL as http://www.farad.net , BTW]

[quote author="no-fi"]apart from these, 10uF polypropylene caps are pretty light on the ground.[/quote]
If you're just looking for an inexpensive way to check whether the circuit works before ordering the WIMAs (/while compiling a larger WIMA shopping list), those parts should work OK, as would Polyethylene/Mylar film caps or (in a pinch) low-ESR bipolar electrolytic capacitors. They may not sound the same as the Real Deal, and the heat from the tubes may shorten their life considerably, but it should work nonetheless.

JDB.
 
this will stay secret :wink:
no, for sure analag will explain the function of the trimmers sooner or later.
or follow emrrs post, seems logical.
btw, the prototypes work without tweeking the trimmers

if you mean the trimmers in the PSU:
they are for +12V [not so important] and -17V [very important]
 
another question.

I was looking at the 4700uF cap specs recommended in the BOM from mouser, and these parts have a ripple current of 1480 mA.

Now, these caps are being used to filter the rectified heater supply for all the tubes... which is nominally 6A.... so... for a possible ripple current of 6A, are these caps well enough specced? or do we need to go looking for much more heavy duty caps?

Alternatively, is it possible to do away with rectifying and filtering such a large amount of power, and run the tube heaters on AC, like is shown in the fairchild schematics?
 
[quote author="no-fi"]another question.

I was looking at the 4700uF cap specs recommended in the BOM from mouser, and these parts have a ripple current of 1480 mA.

Now, these caps are being used to filter the rectified heater supply for all the tubes... which is nominally 6A.... so... for a possible ripple current of 6A, are these caps well enough specced? or do we need to go looking for much more heavy duty caps?

Alternatively, is it possible to do away with rectifying and filtering such a large amount of power, and run the tube heaters on AC, like is shown in the fairchild schematics?[/quote]

First, the official parts list doesn't list a Mouser part #.

I would expect most caps to have fairly similar ripple profiles. Or at least not appreciable difference.

Single cap stage filtering with far less capacitance on an SA-39 is enough to get the input stage effectively silent, as compared to AC feed. And that's with much more finicky tubes, IMO.

I'm sure you could do fine with AC on the filaments.....other than the board layout designed for DC. I guess you could cut traces and play with the black art of hand-wired filament layout.
 
[quote author="emrr"]
I noticed the AC and DC threshold adjustments on page 8 of the Fairchild 670 manual. At a glance I would assume RV3 and RV6 are to be adjusted to match, and are equivalent to the single DC threshold control in the original. I don't believe Analag has weighed in about this to date.[/quote]

RV6 has an equivalent in the Fairchild, and is not the DC threshold setting. The Fairchild manual offers no clues I've noticed yet as to adjustment. RV3 does not exist, and may effectively be the DC threshold, implemented another way.
 
[quote author="emrr"]
First, the official parts list doesn't list a Mouser part #.
[/quote]

OK. sorry. I was in a hurry and didn't check the exact supplier name I typed.

you probably realise I meant the farnell part, right?

I would expect most caps to have fairly similar ripple profiles. Or at least not appreciable difference.

Single cap stage filtering with far less capacitance on an SA-39 is enough to get the input stage effectively silent, as compared to AC feed. And that's with much more finicky tubes, IMO.
Click to expand...

I think you're talking about ripple voltage in the circuit here... thats not what I was asking about - I was asking about the capacitors ripple current.

A capacitor's ripple current rating, for an electrolytic cap, is a rating of something the cap can stand... a bit like voltage or temperature... It's something you need to stay under. Essentially looking at the current continually going in and out through the cap's ESR gives you an idea of how much power is dissipated in the cap. too much than the cap can handle, and you get an unhappy cap...

Now, these caps we're talking about have a ripple current rating of about 1.4A.... which might be a bit below the amount of ripple current they'll experience in this design.... which will be 6A, from what I've read pn the heater current requirements... So I am worried may cause them to fail very fast.... does anyone have any comment on this?

I'm sure you could do fine with AC on the filaments.....other than the board layout designed for DC. I guess you could cut traces and play with the black art of hand-wired filament layout.
Click to expand...

well, it does sound like it could be fun...
:)

hmm..... maybe if all else fails.
 
I'm planning to try another way to get the different voltage needed for the pm 670 in case edcor never invoice me...

I've found a transfo 9V 5.56A Is that suitable for stereo unit?
Can use 2 toroidal trannies :
230 to 2X15 and 2X12 to250
Like in G9

Thanks :grin:
 
shoot Edcor a email direct.

Parts are the following numbers...


PW670 is power transformer also know as XPWR063
The PW670 is a group buy discount price.

NM670 is the Audio transformers as know as 4x 10K:600R XSM, and 4x XSM 600R:10K
The NM670 is also a group buy number.

Why your ordering think about other projects like NYDave's Reamp 10K:150R etc..

With the One rate box, for $30 USD you can get a decent amount of stuff in there (not sure on power transformer) but you should try and take advantage of shipping.

I just placed a $350 order with them last week, I've been holding out for a long time.

Kaz.
 
[quote author="kazper"]
With the One rate box, for $30 USD you can get a decent amount of stuff in there (not sure on power transformer) but you should try and take advantage of shipping.

[/quote]

I just got my edcor package in Australia on monday (1 x 670 kit and 1 x PSU transformer for the 670)

I can confirm they ship these together internationally for the basic "box" cost (ie it cost me no more shipping to send the PSU transformer with my audio transformer kit on top of what they were going to charge just for the audio transformers) - but my shiping was US$40.

and tell you what - it's a damn hefty PSU transformer!!
:)
 

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