M670 compressor

[Nele]

Finetuning my unit and have some small questions:

- can I use Lundahl 5402 in stead of 1676? have a couple of those lying around.
- is it ok to use edcor xsm instead of wsm for trafo 3?
- if I want to use the scamp board I would need an extra powersupply of +/- 17V, right?

Thanks!

 

[Kingston]

can I use Lundahl 5402 in stead of 1676?

No. It doesn't work in the inverted (input) configuration with the 600-ohm source. And it doesn't work in the step down configuration as output transformer either. The vari-mu stage here has far too high output impedance for them. (5402 needs to be driven from very low impedance source)

is it ok to use edcor xsm instead of wsm for trafo 3

yes of course. WSM is smaller and has slightly better frequency response than XSM.

if I want to use the scamp board I would need an extra powersupply of +/- 17V, right?

I'm not perfectly acquainted with scamp, but you might be able to get away with just an additional +12.6VDC supply. It might be that +/- 12.6V has enough headroom. You can test this with an oscilloscope and probe if the scamp output clips.

 

[Nele]

Thanks!

Regarding the scamp: I'll first test to see if it's really needed. It sounds pretty awesome as it is without. First the psu rebuild...

 

[duantro]

I've ordered parts to attempt to implement the section of the B2+ from your PSU design, on my original PSU board. I think I can mount everything in place. I'm really liking how this thing is sounding as is now. As a recap I've done all of these PM board mods, EXCEPT that I still have heaters at 6.3, and haven't changed Q1. I also haven't changed r17, r18, and C3.

edit: Actually, I have ordered all of the parts for the new PSU except for the 12volt section. My existing PSU has been pretty stable, so I was just planning to change the B2+ section to have an adjustable range. I'll have the parts to do the whole high voltage side if needed though. I'm too green to know the benefits of running the heaters at-12VDC, as well as having to deal with the Scamp board voltages, which I really like having installed.

 

[Kingston]

A disclaimer since people seem to be veering into whatever directions at random.

Don't expect me to troubleshoot or help with the very likely issues when implementing things like this etc. misc. parts replacements that you happen to have in closets. There are other threads for that.

 

[duantro]

Kingston, or anyone else that knows, can you explain the reasoning or benefits of changing the heater voltages to your specs? Or any suggested reading that would shed some light on this? Not questioning your methods, just want to learn. Thanks for your time!

 

[Kingston]

Saves you building more than one low voltage PSU configuring it like that. Doesn't even need to be dual rail. That's the only reasoning. Optimisation and slimming down.

In fact you could simplify further and power both the trans-conductance stage and side-chain from a single 200VDC B+ supply.

 

[mitsos]

The original heater PSU was awfully wasteful.  Everything running at 6V when it could have very easily been run at 12V and half the current, and used a much smaller power transformer.

 

[warpierre]

At how many is tuned the HPF? I will set 3 switchable values..

 

[Silvas]

Hi Kingston,

I'm very curious about this PSU performance and i'm building the 250V section on veroboard to power a couple tube stages i'm playing with. Can i see your RMAA noise plot, just out of curiosity ?  I'm trying to get rid of even the last drop of ripple on my tube stages and i want to see how far i can go !

I've read this thread many, many times and being a succesful PM670 builder i find it fascinating (your design)

Best regards.

 

[Silvas]

Hi,

I have a new question : Edcor XS1100 at 4:1 (and 1:4)  might work here, right ? I'm tempted to build a proto of the Mu stage without the sidechain just to hear it !

Best regards.

 

[Kingston]

Sorry for not getting back earlier.

Hi,

I have a new question : Edcor XS1100 at 4:1 (and 1:4)  might work here, right ? I'm tempted to build a proto of the Mu stage without the sidechain just to hear it !

Best regards.

No, it will not work at all. Maybe there was a mention about LL5402 (of which XS1100 tries to replicate) but you need very low impedance to drive LL5402/XS1100 in any ratio/tap configuration.

As for your previous question, I don't have other noise plots apart from the ones from the first page. My multimeter resolution taps out way before this regulator to provide any meaningful data. The best I can get is 0.2mVAC from my Fluke 179 on any good PSU. But that just means the meter tapped out unfortunately. I have used the exact same high voltage PSU design on two other unrelated projects since and all I can say is your noise floor is as good as your overall ground configuration.

 

[Rob Flinn]

The original heater PSU was awfully wasteful.  Everything running at 6V when it could have very easily been run at 12V and half the current, and used a much smaller power transformer.

Not really understanding your reasoning here.  Since P= IV  the power used is the same whether you run at  12v or 6v.  Therefore the transformer would need to have the same VA rating.

 

[duantro]

The original heater PSU was awfully wasteful.  Everything running at 6V when it could have very easily been run at 12V and half the current, and used a much smaller power transformer.

Not really understanding your reasoning here.  Since P= IV  the power used is the same whether you run at  12v or 6v.  Therefore the transformer would need to have the same VA rating.

But it could be a lower amp rating at 12v, if I'm not mistaken. I've been looking for psu transformers to fully convert to this. Would a 3  amp toroid be passable?

 

[Rob Flinn]

If you double the voltage you halve the amps but the power is still the same P=IV.  For example 6vx1A is the same power as 12vx0.5A.  You spec the transformer on power rating, so if you needed a 30VA transformer at 6v you would still need a 30VA transformer at 12v because the Power required is the same.

 

[Kingston]

If you double the voltage you halve the amps but the power is still the same P=IV.  For example 6vx1A is the same power as 12vx0.5A.  You spec the transformer on power rating, so if you needed a 30VA transformer at 6v you would still need a 30VA transformer at 12v because the Power required is the same.

You are right of course.  He may have meant that regulation becomes less wasteful. But for me the reasoning for this configuration was simplification. Just one low voltage PSU rail and its regulator.

 

[Silvas]

No, it will not work at all. Maybe there was a mention about LL5402 (of which XS1100 tries to replicate) but you need very low impedance to drive LL5402/XS1100 in any ratio/tap configuration.

Got it.

You said "lots of substitution choice" so i'm thinking of using Edcor WSM 600:10K and 10K:600 for testing, then changing the input to sowter 4383 and output to LL1676, after everything's working as supposed.

I want to give this a shot with a mid-power sidechain amp based on LM1875.  Or maybe a switchable SS / tube sidechain using the original 5687 amp. I'm real curious about how this will affect attack and general compression behavior.

I want to build this for mastering, so i'll be needing stepped T-pads on the inputs.  Expensive but DIY-able.  Would you recommend something i can build for the T-pads ?

I'm doing a PCB for the PSU but the rest is going to be veroboard.

Thanks !

 

[mitsos]

The original heater PSU was awfully wasteful.  Everything running at 6V when it could have very easily been run at 12V and half the current, and used a much smaller power transformer.

Not really understanding your reasoning here.  Since P= IV  the power used is the same whether you run at  12v or 6v.  Therefore the transformer would need to have the same VA rating.

Of course, what we want to avoid here is waste in the form of heat from dropping voltage at double the current.  Remember the suggested 25W resistor, whose value had to be found in testing?  The trafo would also be easier to get/make since it wouldn't need 9A or whatever was suggested.  For those and possibly other reasons, the less current you have in your heaters the better.

BTW I've built Kingston's PSU for preamp use (just one regulated HV) it works perfectly for me.  The voltage multiplier is a hack, could be done so much simpler, but that's what came out at 3am. 

Anyway, been meaning to say thanks Kingston for sharing!

Sometime in the next couple of months I'll get my M660 going!

 

[arisebag]

Good evening,

does anybody have find a replacement for the Lundhal? It seems very difficult to obtain them.

I did all the modifications yet but keeping the edcors without CT... I had  sound first (at lower level due to the Tpad) but after the second attempt the sound began to distort a lot and now don't pass anymore. Maybe the edcors did not enjoy that...  :-[ And I still not have found Lundhals available....

Best regards.

Ari

 

[duantro]

Good evening,

does anybody have find a replacement for the Lundhal? It seems very difficult to obtain them.

I did all the modifications yet but keeping the edcors without CT... I had  sound first (at lower level due to the Tpad) but after the second attempt the sound began to distort a lot and now don't pass anymore. Maybe the edcors did not enjoy that...  :-[ And I still not have found Lundhals available....

Best regards.

Ari

I used the cinemag CMLI 10/600 transformer and really am happy with their sound.