M670 compressor

[EvilFuzz]

Gentlemans, so, what a final choice for the trafos?

Cinemag CMLI 10/600 for input,
Edcor XSM / Lund 1676 for out (and what is the best?)
Edcor WSM or XSM for SC? (and can I just reverse 600:10K for T4, or revers 10K:600 for T3?)

Another stupid question: Is it possible to use WSM 15k/600 | 600/15k for the IN/OUT/SC?

Thank you so much)

 

[stitch-o]

The XSM are fine enough to get going for SC, out
Id stick with designed values. There are lots of suggestions in this thread.
I'll report back on the Jensens for input once mine is up and going.
The recommended at Lundahls so Im sure those are exceptional, as well.

Once everything is sitting and working well, I might play with output transformer choice.

I have a few cap questions:
The release caps: what voltage rating is minimum?
The 10nF cap at the link switch-1n4007-1M resistor: is 50V ok for this cap pos?
Also, how egregious is subbing the HV rails 10uf's (off the 100r) with electrolytics?

I see C4 can be pulled and the attack-release switch leads can be wired there.

Heres the (Ithink) finished comp boards

Cheers!

 

[mdainsd]

Hello forum.

Im thinking of putting one of these together. I have the boards, but I think I'd rather do point to point.

QUESTION: Has anyone measured what the B+ supply current really runs at for these boards. The schematic has a total of 300mA  that's huge! Do these things really need more power than an original 670 with it's 22 tubes?

thanks!

 

[emrr]

Says 80mA for two in the original thread.  I measured one at 38mA, so that's in line.  Some 5687's were drawing double the expected current - don't know if anyone got to the bottom of that. 

 

[mdainsd]

Thanks EMRR! that helps a bunch. That will make the transformer issue much easier to deal with!

 

[Kingston]

The schematic has a total of 300mA  that's huge!

That's just the maximum the regulator can handle. I'm using it in lots of projects since it's cheap, reliable and generic - but never actually needed that much power.

 

[Kingston]

Also, how egregious is subbing the HV rails 10uf's (off the 100r) with electrolytics?

Of course you can do that. It's just my preference to have as little electrolytics in a project as possible. Less maintenance and worries.

 

[stitch-o]

Of course you can do that. It's just my preference to have as little electrolytics in a project as possible. Less maintenance and worries.

Cheers and thanks!

I'll start with the EL caps for space and cost constraints.
Im waiting on last 2 caps for release switch then onto completion.

THANK YOU KINGSTON for this amazing work!

 

[Kingston]

Just had a quick review of the schematic and I think those 2X 4K7 resistors on input transformer secondary might have been a typo. They should be more like 47K. If there's a center tap on the input transformer secondary the control voltage can be wired directly there with no need for these resistors - which is what I ended up doing after a few revisions.

 

[dagoose]

digging up an old one for now .  8)
I love my M670 the way it right now, kinda use it day in day out.
But one thing annoyes me is that I have a slight channel imbalance in level between L and R, about 0.3db which I want t get rid of.
The tracking itself is quite good, so the imbalance is consistent no matter how much you push it.
I tried chaning out some tubes but that didn''t really help so I suspect one of the transformers.

I was wondering what would be a good place to put a leveltrim (multiturn trimmer) to balance things a bit more

 

[dagoose]

digging up an old one for now .  8)
I love my M670 the way it right now, kinda use it day in day out.
But one thing annoyes me is that I have a slight channel imbalance in level between L and R, about 0.3db which I want t get rid of.
The tracking itself is quite good, so the imbalance is consistent no matter how much you push it.
I tried chaning out some tubes but that didn''t really help so I suspect one of the transformers.

I was wondering what would be a good place to put a leveltrim (multiturn trimmer) to balance things a bit more

Forget about it, found a nice place to add trimmers. In between the input tranny and the T-pad.

 

[EvilFuzz]

Who asked about P-t-P?
From dr. Weird laboratory... M660!

 

[EvilFuzz]

Sorry, something wrong with pics...

 

[shabtek]

Nice

Looks like fun

 

[EvilFuzz]

Nice

Looks like fun

Yeah, it's absolutely fun. Chassis from soviet  generator, trafos from DDR measuring equpment, other components from trash and garbage. But it works!)

 

[Script]

Love the inside and the overall approach  ;D

Personally, I'd probably buy some cheap but cool looking pvc sheets -- or how about some thin wood sheet (maybe withered cos from garbage  8) ) -- for use as faceplate with inspirational logo?

Many possibilities cos does not have to be aluminium e.g.

 

[Studio Mollan]

Old  topic but hopefully someone is still around.
I've just finished the build of this. Bought the parts ages ago but shelved it after people had issues with the PM660.
I got the Lundahls and everything is hooked up.  All voltages are cool and the unit passes audio. Sounds great but i struggle to get any real gain reduction going. I can get it to a maximum of 6dB with threshold all the way down and input all the way up. that can't be right so i have clearly done something wrong.
What levels can you expect out of the rectifier? I have the trimmer set to -4,5V and measuring the dc across the rectifier is max -5V. There should be a higher value DC there with input max and threshold all the way down right?
/
Emil

 

[Studio Mollan]

problem solved. A broken Edcor transformer. 3 out of 8 Edcors broken. Never buying them again.
Works fine now though! Great stuff kingston!

 

[duantro]

I've switched everything over to the full m670 schematic with -12vdc heaters, and the unit works great for 5 minutes, and then the -12vdc supply shuts down. I've used the lm338t in 220 format, and the heat sink gets piping hot. It's pulling 3a with lights, scamp, heaters, and bias. I have a thermistor controlled fan on my lid that isn't installed yet, but something seems to need addressed first. Perhaps a bigger heat sink, or attached to the back case panel? I have a 1"x1"x1" sink currently. Any thoughts? Do I need to go with the lm338k?

 

[Rob Flinn]

I've switched everything over to the full m670 schematic with -12vdc heaters, and the unit works great for 5 minutes, and then the -12vdc supply shuts down. I've used the lm338t in 220 format, and the heat sink gets piping hot. It's pulling 3a with lights, scamp, heaters, and bias. I have a thermistor controlled fan on my lid that isn't installed yet, but something seems to need addressed first. Perhaps a bigger heat sink, or attached to the back case panel? I have a 1"x1"x1" sink currently. Any thoughts? Do I need to go with the lm338k?

It's probably going into thermal shutdown.  How much voltage is across it input pin to output pin ?  The more voltage that is across it the hotter it gets and the less current it can deliver.  Looks at the data sheet there is a graph for this phenomenon.