Making pig tails for Filtek MK3 (1970's German EQ)

[Alistair]

Hi guys,
I was hoping someone much smarter than me may have a bright idea where I'm going wrong!  I've completed a few projects of this site, but haven't posted too much (I've been reading rather than talking!).  I've just got a little problem I can't find anything about searching on this site.

Over the past year I've bought about 5 Filtek EQ's, and successfully pig-tailed a few of them for use.  They're great, a real find.

I'm just having a little trouble with the MK2 and 3 EQ's I have.  The schems are here-

There's another schem file but it just shows the resistors needed for each frequency band etc, so it's got nothing to do with the pinouts.

From reading the schem and opening it up, I've figured out that-

Input cable- 2 and 22 (pos and neg), 21 and 3 ground/0v (I assume there are two grounds incase different consoles had different ground points, this would make the units a bit more versatile).

Out cable- 6 and 18 (pos and neg) 19 and 5 ground

Power input is on 14
Power ground is on 13

Chassis ground is pin 23

Internally pins 3, 5, 13, 19 and 21 are all linked (all 5 grounding points).  They are NOT linked to the chassis ground though.

I'm intending to make a little carry case for the 5 units and power them off a JLM powerstation, but in the interim I'm just using wall wart 24v power supplies.  I simply split the pos and neg wires on a power supply and send one to each unit.  This has worked really well on the other Filtek units I've had (Mk5, which are essentially the same unit but smaller and with a different pinout and Tuchel connector that is only 13 pins rather than 23).


So, long story short, I've wired all this up and with the unit in bypass, signal is passed through perfectly- which suggests that the inputs and output wiring is good.  As soon as I engage the unit, nothing but silence.   I've also experimented with linking the grounds to the chassis ground via a single wire from 13-23, but no change.  Unforunately, it doesn't have a power light so I can't tell you if they are powering up or not, but I'm thinking probably not.

Sorry to bug you guys, I was just wondering if you've got any ideas on where I might have gone wrong?

Thanks!

 

[mjk]

The red LED overload indicator will flash briefly (look in a darkened room) when the unit is turned on if the DC is connected to the correct terminals.

I'll need to check when I get home tomorrow how my MK3s are connected.

 

[Alistair]

Thanks, that would be fantastic.  I'm definitely not getting any flashes in the LED's, so I'm assuming I've done something wrong.  Hopefully it will be something obvious!

 

[Alistair]

Problem figured out- wired correctly, but 100% dead power supply!  Same supplier etc I used last time, but all of the new ones I purchased are dead.  Pretty frustrating!

 

[Tom.B]

Hello,
Can someone verify the pin outputs for the Filtek MK3?  I have the same schematics posted here, but having a very hard time making out the pin outs (especially the output).

For example, I see Alistair says the output pins are  6 and 18 - I can make out the "6" on the schematic, but cant make out if the negative output is "8" or "18".  I see if it is traced back to the output transformer, the transformer pins are "6" = pos Out and "9" is the negative Out (bottom side of the transformer).  I don't have the modules in my possession as they are in transit and I would like to begin making up my wiring harnesses already.  If I have to wait, I will just follow the pins back to the transformer when the modules arrive.

 

[culteousness1]

Hi Tom,

I recently racked a pair of these EQs for a friend of mine. I just followed the first drawing I found on Google:

If you gonna use shielded wires for hookup, make sure you only connect one side of the shield to the chassis to avoid a ground-loop.
Had it working from first power-up. Ah ja, Eingang refers to Input and Ausgang to Output  ;D

Cheers,
Carsten

 

[Tom.B]

Thank You Carsten.  Yes, Google is a wonderful tool.  You just have to type in the correct wording!
Got it, Thanks!

 

[flextone]

If you gonna use shielded wires for hookup, make sure you only connect one side of the shield to the chassis to avoid a ground-loop.

Sorry to revive this thread but I'm racking up Filtek modules for a friend (again) and wanted to ask:  Carsten, do you mean that you simply cut the shield wire on one side of the audio cable leaving it floating? Aren't the in/out transformers supposed to eliminate ground loop issues? 

 

[culteousness1]

That's correct. I connected the cable screen on one side to the chassis as written before.

Please consult Ruffrecords' Grounding 101 if in doubt: https://drive.google.com/drive/mobile/folders/0B_n67A1hN3qtR09CekNiSDM1N0k

Cheers,
Carsten

 

[flextone]

That's correct. I connected the cable screen on one side to the chassis as written before.

Please consult Ruffrecords' Grounding 101 if in doubt: https://drive.google.com/drive/mobile/folders/0B_n67A1hN3qtR09CekNiSDM1N0k

Cheers,
Carsten

Thanks for the link.

So I can simply leave the shield wires disconnected at the modules? Or is that asking for trouble and one should decide on lifting ground at either device inputs OR outputs only.  Making "directional" cables in other words.

I'm using balanced leads terminating them with TRS into a patchbay.

Cheers
R

 

[Aitd]

Hi Tom,

I recently racked a pair of these EQs for a friend of mine. I just followed the first drawing I found on Google:

If you gonna use shielded wires for hookup, make sure you only connect one side of the shield to the chassis to avoid a ground-loop.
Had it working from first power-up. Ah ja, Eingang refers to Input and Ausgang to Output ;D

Cheers,
Carsten

Hey! I have a pair of these BFE Filtek MK3a eq’s and a new purpose built rack from sonic world With power- I seem to be having a ground loop issue like the one you described… any ideas where to start? I’ve attached some photos of my rack and the way it’s internally wired. The only thing I’m suspect about is the small ground wire they have from 14 to 13 inside the unit to the connector. Everything else seems to match the pin out wiring correctly on both ends of the connectors.

I get the same 60hz loud hum in both modules.

Any help would be greatly appreciated- I really love these eq’s but can’t use them like this!! Seems like it’s a basic ground loop issue I just can’t quite figure it out!