M670 compressor

[duantro]

Hey Geoff004,
Did you also keep the same voltages as the pm670?

Sorry- missed this post.
I used the existing power section from the PM670 - no changes.  The voltages are exactly the same.

Personally my feeling is there is no need for a PCB with this project - other than a power supply (maybe).  It'd be easy to do point to point and is a great candidate for getting one's feet wet with a p-to-p build.  Or use and modify the existing PC boards as I did.
The changes of the M670 not only make for an easier build, they also make for a more useful unit.

Thanks Geoff004. That's what I'm planning, just was curious what you did.
I'm going to be able to mount all of my additional components on, or under the existing pcb.

 

[Kingston]

Not sure if this was mentioned here already, but 100-200VDC B+ to V1/V2 tubes makes a large enough difference everyone should experiment with the VR2 trim of the PSU. Or like me eventually put it under a switch. 200V has the cutoff curves working far more linear than 100V. Area around 100V is vari-mu like grandma used to make and "better on drums". 200V surprising sounds more like some very clean digital plugin compressors! And in a good way.


There's also a small difference on THD, which is lower with 200V since there's a bit more headroom.

I think I ended up with a switch of 120V and 200V. If one was to label the switch it would say "soft knee" (200V) and "very very soft knee, on a pillow" (120V).

It should be noted the switch also affects VU meter calibration which can be compensated with another switch pole. I didn't bother.

[edit]

forgot to mention the higher voltage also slightly increases maximum gain reduction (3-5dB). Adjust sidechain input accordingly when switching between settings.

 

[duantro]

Not sure if this was mentioned here already, but 100-200VDC B+ to V1/V2 tubes makes a large enough difference everyone should experiment with the VR2 trim of the PSU. Or like me eventually put it under a switch. 200V has the cutoff curves working far more linear than 100V. Area around 100V is vari-mu like grandma used to make and "better on drums". 200V surprising sounds more like some very clean digital plugin compressors! And in a good way.


There's also a small difference on THD, which is lower with 200V since there's a bit more headroom.

I think I ended up with a switch of 120V and 200V. If one was to label the switch it would say "soft knee" (200V) and "very very soft knee, on a pillow" (120V).

It should be noted the switch also affects VU meter calibration which can be compensated with another switch pole. I didn't bother.

[edit]

forgot to mention the higher voltage also slightly increases maximum gain reduction (3-5dB). Adjust sidechain input accordingly when switching between settings.

This is great info. I'll experiment here for sure. It seems that the original design could definitely benefit with a sharper knee, slight more gain reduction and better headroom. Sounds like a no brainer.

 

[Nele]

As for the 1N4007, sure a lower voltage drop diode can be used and I've certainly used some schottkys in another project in the past. But I can't detect any practical difference so a cheap one wins. 1m and 10nF are to dump the reverse recovery "snap" to ground. It might have very little practical effect and it's probably pointless with a schottky since they have ultra fast reverse recovery.

Now that I think about it, this is a place for an improvement indeed. I'll take out those reverse recovery hacks and select some modern schottky instead. The ancients needed this reverse recovery hack because their diodes weren't that great.

Might something like a 11DQ10 or MBR1100 work? Or even an UF4007? Almost finished hacking one of my channels.

 

[Kingston]

Might something like a 11DQ10 or MBR1100 work? Or even an UF4007?

I always use UF4007 in place of plain 1N4007. And MBR1100 whenever voltage if low enough. I only write 1N4007 to mean "generic high voltage 1A diode". Up to the builder to optimise further. I'm almost certain I used MBR1100 for the stereo link in the actual build. None of this affects sound in any meaningful way so it really doesn't matter either way.

Kingston, did you measure the attack time of your re-designed varimu? Sorry if you mentioned that before somewere in the thread.

Yes I've scoped it, attack and release. Just to verify that the rotary switches work, and they do. I haven't calculated the exact times from the scope images if that's what you wanted to know.

That 1uf setting rarely sees any use. It tends to get into "way too fast release"-distortion that is often heard in 1176, for example, but some people might find it usable.

 

[Kingston]

Yes I've scoped it, attack and release. Just to verify that the rotary switches work, and they do. I haven't calculated the exact times from the scope images if that's what you wanted  to know.

Yes, I'm interested in that values. I really need the fast attack time, mine PM is "boosted" with SCAMP and wonder will I loose some attack if I modify the unit.

The response doesn't change with anything I've done, which is certainly something I verified since. Only changes in sidechain would affect things in this area anyway, which you should already well know.

Since you're happy with your unit, why would you modify anything or even consider any changes? It seems you are consistently adverse to anything other than a stock PM670 so what are you even doing on this thread? There's already several threads for PM670, which seem perfectly suited to your requirements. You could stay there. I remember you had trouble understanding the specs on very first page of this thread and you basically refused to even believe there are any improvements even possible on the stock version. Would be futile to post more specs with that in mind. Which part of them will you ignore or refuse to understand?

[edit]

in fact, [expletive deleted to comply with forum rules]!  Nobody ever measured the specs for any variant of this project before. I've posted more data by now than is available on any of the historic projects that have been cloned thousandfold! I had forgotten I even posted additional specs to you personally in the first page. To which your response was to belittle the work just a bit more. Doesn't seem like you will ever be satisfied.

Next benchmark I have to run for you personally is charged by the hour (50 euros). You have all my details to make that payment. I will add charges for the previous suite as well. If your poorman is broken and want it properly serviced the same price applies, shipping, parts and services notes not included.

 

[gyraf]

Kingston,

You cross the "No Personal Attack" line here. This is by far our most important forum rule.

Please modify or delete.


Jakob E.

 

[duantro]

Not sure if this was mentioned here already, but 100-200VDC B+ to V1/V2 tubes makes a large enough difference everyone should experiment with the VR2 trim of the PSU.

Hey Kingston, I'm almost finished with all of these mods, just need time to wire the second low pass switch. In above quote, are you referring to the existing pm670 psu, rv2? I believe on pm rv2 adjusts 17 volts unless I'm missing something.
Cheers.

 

[Nele]

Not sure if this was mentioned here already, but 100-200VDC B+ to V1/V2 tubes makes a large enough difference everyone should experiment with the VR2 trim of the PSU.

Hey Kingston, I'm almost finished with all of these mods, just need time to wire the second low pass switch. In above quote, are you referring to the existing pm670 psu, rv2? I believe on pm rv2 adjusts 17 volts unless I'm missing something.
Cheers.

He means RV2 of the new powersupply which controls B2+.

 

[duantro]

Finished most of the mods. Sounds pretty damn good so far. Stil runnig pm psu at 136v would like to try to up the voltage do b+. Will take it to my studio in a few days. Here's a low res phone photo of my hacked boards undersides.

 

[Kingston]

Looks a lot like mine. A familiar wiring shape with the diode and those grid stoppers hanging loose. I recommend building the better PSU, or at least experimenting with a higher voltage option. It's relatively easy with analags version, too.

Don't forget to test the 50V option with an adequately sized heat sink!

[yes it's sacrilege, but... ]



Moby,

you didn't have to remove your post. Nothing to be ashamed of asking questions. I'm personally tired of handing out test suites like free candy and it surely will show. I might have been out of line with the above comments, but I'm also not going to spend four hours of my free time just to show you how some design detail works. You have all the test gear at your finger tips. It's the entry requirement to this thread. And surely you have at least one 2.2-10uF cap in your closet?

 

[duantro]

Looks a lot like mine. A familiar wiring shape with the diode and those grid stoppers hanging loose. I recommend building the better PSU, or at least experimenting with a higher voltage option. It's relatively easy with analags version, too.

Don't forget to test the 50V option with an adequately sized heat sink!

[yes it's sacrilege, but... ]

What is this 50V option that you are referring to?

 

[Nele]

Just finished my first channel and.. succes!! My 670 is finaly working! Even the meter is tracking well.. wow! Now on to the powersupply and channel 2..
Thanks Kingston!!! If you're ever in the neighborhood let me know and I'll buy you a beer or two, or 670..  8)

 

[Kingston]

What is this 50V option that you are referring to?

Again this new PSU I designed with the VR2 trim.

 

[mitsos]

duantro: Thanks for posting the underside pic! Still trying to find time to redo mine.. got a second channel PCB as a present from another member, so now I can do a 670!  ;D

Kingston, I didn't see this in the thread, maybe I overlooked it, but did you do the PSU on the old PCB or redo it completely?  I looked for pics of your comp but I didn't see any. 
thanks!

 

[duantro]

Ah, sorry, I should have checked your psu schematics first and I would have realized what you were talking about.
I ran more material thru my new "m670"  8) and it f***ing sounds great! Wow.
I'll try to mess with psu voltages when I get some free time.

 

[Kingston]

did you do the PSU on the old PCB or redo it completely?

I built it on a veroboard. It's not a mod of analag's PSU.

I've also used it on other projects since. Not the dual version, just a single stage. There's a development thread of the PSU somewhere in the drawing board.

 

[Nele]

There's a development thread of the PSU somewhere in the drawing board.

Here it is: psu-thread

 

[mikeyB]

I can't find it and it's late! - but i seem to recall the R.A.T. valve testing rig had various variable valve supplies for HT and other bias voltages - i'll keep looking for it - i know i got a paper copy somewhere as well! I think you could tailor it for current limit also.

 

[mitsos]

did you do the PSU on the old PCB or redo it completely?

I built it on a veroboard. It's not a mod of analag's PSU.

nice, I didn't want to try to mod the original PSU.  thanks for putting all this up, btw. My storage shelf will hopefully be a few pounds lighter soon..

There's a development thread of the PSU somewhere in the drawing board.

Here it is: psu-thread

thanks!