the Poor Man 660 support thread

[mrclunk]

elektrovolt,
i had the same problem and i'd blown the ifr840's. I had also soldered in an incorrect resistor on the PSU. I forget which one now... When i changed out the ifr840 i also replaced all the little transistors. Sorry i can't be more specific, don't have my documents with me.
good luck

 

[radiance]

was just about to write....replace both IRF840's......when I read mrlunk's post 

 

[elektrovolt]

thanks guys. I already replaced one IRF820 with a 840, so I have two 840s now. I will get two more tomorrow, if they still have them at radio twenthe. we'll see...

OH ****, I really must hurry with this machine, the Drip 175 pcb just came in today

 

[elektrovolt]

replaced both IRF840's - - -

nothing !  :'(

EDIT: ok, now it is working ! the meter goes up and stays there. all voltages correct... meter at zero... warming for a few minutes...

connection to the soundcard... ok, working somehow. not really compressing. and then: BAM ! a spark, I thought it was somewhere at the back of the pcb (transformer 2 + 4 side) or at the transformers. sound craps out, again the same **** !

 

[[silent:arts]]

have you checked the PSU transformer?
which one do you use?

 

[mrclunk]

Bummer
I'm sure i had the same problem. I've my notes today.
I replaced Q1, Q2, Q3, Q4, Q5.
Also i had an incorrect resistor at either R6, R7 or R5.
It was defiantly one of the resistors between the pairs of heatsinks, i remember that much.
Lift a leg and double check them. I'm not sure if this was the cause of my irf's blowing but certainly reduced the HT output voltages.


Also i think i read here that you should only power up the PSU with the audio boards (or at least one) wired in.
Perhaps someone can elaborate on that...

Hang on in there man, its worth it!

 

[elektrovolt]

Volker, I am using a toroidal transformer from Bernd. voltages there are OK.
Mr Clunk, I already replaced the resistors there, but not the transistors. they aren't available here, have to order them from conrad. and again some IRF's..:|

I read about connecting it first before powering up, that is what I did. never powered it up without connecting

 

[ChuckD]

Thanks to Analag , Volker, Lolo and Frank!
Big thanks to Frank who spent so much time with me getting this panel exactly correct. We spent so long getting the Big F correct!

10 transformers total
Full M/S switching as per the original design. I built my own boards using relays.
Used LoLo's Timing network to get actual Fairchild timing.  I still can switch to Analag's timing but it is fixed at 5K for now.

Input stage uses UTC A15  to Edcors
SC input is UTC A15  to Edcors.


One Issue : the Left meter seems to read more compression then the right, I am not sure that the circuit is compressing as meter says. I think they are equal but the meters might be different. How can I tell??
Still need to tweak a few pots but it is working and sounding great!

Chuck

 

[mrclunk]

What a beast!

 

[tommypiper]

Excellent excellent!    Congrats.

Sorry you moved to SoCal.  Would have loved to get together and hear it in person! 

 

[radiance]

Very nice Chuck!!  Where did you get those big stockly pointers (meter bal zero bal) from?

replaced both IRF840's - - -

nothing !  :'(

EDIT: ok, now it is working !

Just curious...why did it not work straight away?

I sugest you re-read all your post in this thread. You might see a patern emerge...If I remember correctly you once had a working unit, well...at least a unit that did not blew the PSU. Somehow you've changed something that caused the PSU troubles.

 

[Kingston]

but it's blatantly not Fairchild recording equipment corp long island city L.N.Y Model 670.

I just don't see the point of cloning the front panel of a piece of equipment THAT much different to the insides.

I would barely understand if you had actually built a fairchild 670 clone with that panel, but this is an entirely different design!

 

[stitch-o]

I just don't see the point

because it looks freakin cool.
+ front panel design is an art all it own.
This homage is a very impressive tip'o'the hat.

Nice box, Chuck!

 

[inputoutput]

very impressive!!!! Holyshit x2

 

[tommypiper]

You used the Edcor PS transformer!  With no heating or PS problems?  Unlike KHStudio who never figured his problems out?  Voltages fine?  How is noise?

Wonderful job.  

I have a million questions, like...
Where'd you get the box/case?
The front panel and its hinges?
Did you have the case painted?  Or it comes like that?
Is the panel lettering painted?  Is it by silk screen?  Where did you have it done? 

Great design.

 

[ChuckD]

Box I drew in Adobe illustrator and had a sheet metal shop make it for me, about 100 bucks.

The Front panel I used several front shots of the Fairchild from google search and knowing the General Radio knob size, since I have those, I scaled the photos to actual size. From there I was able to redraw the panel in adobe illustrator. Then I gave it to Frank who engraved it for me after translating it to his own FPE type format. This took a considerable amount of effort, especially getting the fonts just right.

The hinges are here:
http://www.hardwaresource.com/Store_ViewProducts.asp?Cat=1829

The case was powder coated in a Gun-metal gray colour. I should have gone lighter to be more like the original but oh well.

The knobs are not Stockly. The original Fairchild used General Radio knobs. I collected them on ebay over the years.

I haven't noticed too much heat yet. But I haven't run it for long periods yet either. As far as noise I think it is pretty clean. I make my own hookup wire from OCC wire braided by hand then shrink tube, then Solder wick shield, then shrink tube again. Then all the shields are connected one end only to the star ground. I started doing it this way with Volker's D-LA2A and noticed it made a huge different in noise. Plus I put the transformer outside of the case this time.

Chuck

 

[Kingston]

The mid-side relay switching network is a nice touch. Great to see it's easily doable. I presume those are DPDT relays, but why 6? In the schematic there are 10 single pole switches, ie. 5 DPDT relays...

I have a similar PCB in the works, but with added relay switches for feedback/feedforward/external sidechain, and sidechain high pass.

 

[alexc]

Hi Chuck D

Wow    Man 8)

 

[ChuckD]

Kingston,
Although I disagree with your previous harsh words on it not being a Fairchild I will be a good sport

Here is the M/S network

There was one connection that I had to use a jumper shown in the layout.
pm me if you want the BRD for Eagle CAD.

Chuck

 

[Moby]

Mikko, if you need that board I can add that to the list