M670 compressor

[zayance]

This is great for cutting traces, very sharp.....Japan Quality  ;D

http://www.conrad.fr/ce/fr/product/529613/Cutter-spcial

 

[bruno2000]

The bottom of those silentarts boards is very clearly laid out. It's easy to cut traces even if the board is populated already. I do this just by twisting a sharp knife tip at the trace. Dremel is a too powerful tool most of the time.

I have used a Dremel tool with a VERY tiny bit.  Worked great for me. YMMV.
Best,
Bruno2000

 

[Govinda Doyle]

Go Kingston!!
This is going to be an awesome compressor!!

 

[toolboxmuziq]

So - while I have no doubt that these things can improve performance on it's predecessor, it remains very close to it!

Along with the new features and the simplification of the psu design and build, it could well represent a real step forward in buildability and stability. And an incremental improvement in performance, tube and other matching issues allowing.

I would surely see it as a MkII version of the mighty and controversial PM660 (actual might may vary)

Fine, I'll keep this new proto to myself then, since it will always be just "MKII". A variable load DOA sidechain with threshold, which further simplifies the PSU and improves performance and safety, needs one less transformer, has an easy to use tube matching rig incorporated to it. But like you said "remains very close to the original". Since apparently all this design is as simple as "adding a cap" looks the folks here can take over. As a bonus I no longer have to shift through datasheets, calculate bias points and loads or measure a thing.

If only somebody had told me earlier it was this easy!

please continue the work that you have begun! I want a Fairchild compressor that actually does what a Fairchild does and is functional. Unfortunately the drip 670 is too expensive when you total the cost of everything. I actually found some great info on a guy who has actually started a company who remakes Fairchild  670's. He handmakes two different models mk1 and mk2. He has found a cool way to recreate the Fairchild sound without all the expensive parts. I'll upload the links and info he has on his units. He sales them for 4990£ and the are as I stAted hand made totally from knobs to the case to transformers. The only prob is that he is stationed in Europe and there is a wait time for construction and shipping

 

[Kingston]

I want a Fairchild compressor that actually does what a Fairchild does and is functional.

Then look elsewhere. This compressor has almost nothing to do with any Fairchild related design. Now that you mention it, M670 is a damn misleading name. It's only named that because it's derived from Analags 660 design.

Which also has nothing to do with any Fairchild related design.

Fairchild 670 is a bit more than gain reduction and sidechain sections that are separated with their individual I/O transformers. So is the M670. That's the only similarity. They sound very different.

Unfortunately the drip 670 is too expensive when you total the cost of everything.

It's still the cheapest option if you absolutely must have that old 6386 tube eating boat anchor. Historically accurate transformers - like those from Sowter - don't grow on trees either.

 

[Dylan W]

Kingston,

If you have time/inclination to run some program material or drum loops through the compressor, it might be interesting for us to hear what your design sounds like. Sound clips aren't everything, but they can give some idea of what a unit can do, and I for one am curious.

Dylan

 

[emrr]

I think the Tube Equipment Corporation SR-71 Blackbird is the best deal going in a Fairchild recreation, and given the option of building Drip or buying SR-71, I'll go SR-71 any day.  Once you count hours as dollars, I swear it's cheaper than the Drip.  It's the creation of our own Larrchild too, who has been inactive for a long time.  It's been in production for several years, at least. 

http://tubeequipment.com/?page_id=4

It's cheaper than this new one mentioned above, and it's all tube, smartly moves away from the 6386 to an appropriate sub. 

 

[Kingston]

Once you count hours as dollars

I don't value my time for personal projects and this is too easy to forget. Yes indeed, a tried, certified, tested and mechanically perfectly designed SR-71 comes out on top.

 

[MicDaddy]

Thanks Kingston for your insight and your comments throughout with regards to kit builders.  I am guilty, and your comments at first I took as insulting.  It has prompted me to find a new hunger for understanding of what it is that I'm building, which I believe is the premise for the forum so thank you for reminding those of us listening.

With that said I have a few, most likely mundane, questions:

With regards to your schematic, you have a dual pot(?) showing 25k on the secondary of T3 whereas the original had dual stepped attenuators at 15k.  What is the reasoning for 25k?  Are there any adverse effects when using 15k stepped attenuators with your redraw? (I already have Elmas built to 15k via log taper).

Which leads to the second question regarding your implementation of the 'FF' option.  You have a T-pad on the primary side of T1.  If I stick with stepped attenuators, the FF signal is untouched.  I believe you and EMRR have been discussing this some in this thread and a few others.  Honestly when some of you guys get talking it's so far above my pay grade I have a hard time keeping up.  From what I gather, FF might be 'unruly' in this configuration with stepped attenuators at the secondaries of T1 leaving the FF signal untouched at the primary side.  I suppose it's something I could try and if it doesn't work then it doesn't work, any insight would be appreciated. 

Still trying to wrap my head around your -12.6VDC heater scheme.

Also, I cannot find the post of ChuckD's relay power scheme, if you have a link or any insight into how this is implemented I'd like to take a look.  I believe what happens is that when/if the heaters go down, the relays disengage, and B+ isn't allowed to reach the plates... am I on the right path? 

Thanks in advance

I've got a 3rd hand PM670 that I've been holding onto for a few years now, your recent postings have stirred a fire to finish it.

 

[Kingston]

With regards to your schematic, you have a dual pot(?) showing 25k on the secondary of T3 whereas the original had dual stepped attenuators at 15k.  What is the reasoning for 25k?  Are there any adverse effects when using 15k stepped attenuators with your redraw? (I already have Elmas built to 15k via log taper).

Doesn't make a difference whether it's a total of 20-100k in this attenuator. Just needs to be "reasonably high impedance" and you interpret that as you please.  Simply use the dual log pot that is most available to you. 15k doesn't exist. Rotary switches are pointless here. You'll never be able to match the gain reduction of two channels perfectly enough to get any use of even 5% tolerance pots.

Also, I cannot find the post of ChuckD's relay power scheme, if you have a link or any insight into how this is implemented I'd like to take a look.  I believe what happens is that when/if the heaters go down, the relays disengage, and B+ isn't allowed to reach the plates... am I on the right path? 

I don't know about anything ChuckD has done but I've certainly implemented B+/heater fault protection in several projects. I've since found out heater faults don't exist. Don't bother with this. The way it works is that if heater 6.3VDC or 12.6VDC somehow dies (note, it never does), it also turns off a 5V or 12V relay that normally lets in all the B+ VAC voltage. Position is before the B+ rectifier etc PSU parts.


Feedforward option might be an acquired taste.

 

[prescott]

Very nice project!

Can't wait the PCBs!

Count me in for a stereo!

Congratulations Kingston!!!!!!!!!!!!!

 

[mikeyB]

With regards to your schematic, you have a dual pot(?) showing 25k on the secondary of T3 whereas the original had dual stepped attenuators at 15k.  What is the reasoning for 25k?  Are there any adverse effects when using 15k stepped attenuators with your redraw? (I already have Elmas built to 15k via log taper).

Doesn't make a difference whether it's a total of 20-100k in this attenuator. Just needs to be "reasonably high impedance" and you interpret that as you please.  Simply use the dual log pot that is most available to you. 15k doesn't exist. Rotary switches are pointless here. You'll never be able to match the gain reduction of two channels perfectly enough to get any use of even 5% tolerance pots.

Also, I cannot find the post of ChuckD's relay power scheme, if you have a link or any insight into how this is implemented I'd like to take a look.  I believe what happens is that when/if the heaters go down, the relays disengage, and B+ isn't allowed to reach the plates... am I on the right path? 

I don't know about anything ChuckD has done but I've certainly implemented B+/heater fault protection in several projects. I've since found out heater faults don't exist. Don't bother with this. The way it works is that if heater 6.3VDC or 12.6VDC somehow dies (note, it never does), it also turns off a 5V or 12V relay that normally lets in all the B+ VAC voltage. Position is before the B+ rectifier etc PSU parts.


Feedforward option might be an acquired taste.

Yes and no!
I've repaired 3 budget/medium priced valve condensor mics in the last 2 years. All used chinese ECC83 stock, all connected as 6.3V heaters. 2 of them had one side of the heater go open cct and the medium priced had both sides of the heater gone! So it does happen on the cheaper valves!

I've recently replaced the ht and main heater supply cap in a Tubetech summing mixer. Each channel uses 2 E88CC valves with heaters series connected to 12V and the output stage 82/83 connected as 12V heaters. Stock was russian made EH valves. looks like tubetech have no issue mixing the heater arrangements(they may select the 2 88's for similar current draw) A very nice build - by the way tubetech!

 

[duantro]

Thanks for doing this research and testing Kingston. The results look very good. I have ordered 4 Cinemag CMLI-10/600 transformers for inputs and interstage. I had a bunch of problems with failing/ broken wire on the edcores. My psu and regulated heater boards have been pretty steady, so I may keep it as is for now. When I get some time I will implement your schematic improvements. Can't wait to get this thing to perform!

 

[duantro]

Kingston - thank you for your time and effort in to this project.

I built a PM670 for a friend 4 years ago or so.  It never really worked well.  Balancing left and right wouldn't work with the attenuators I built and linked the 2 channels didn't really work together.
But the inherent sound of the unit was (is) great.
After some frustration with it (and some fried components) I picked it up from him the morning that this tread was started.

Anyhow, I kept the original power supply and added or removed things on the audio side according to the schematic posted on the first page.  I added 2 small boards built on cheap radio shack PC board.  One board has the 100R resistors and the 10uf caps.  On the other board I put all the components between transformers 2 and 3.  It's also got relays to handle the switching. 
Besides that I cut a bunch of traces on the PCBs and stuffed things where I could.  A couple things fit on the underside of the boards.  I did not change Q1.

The end result is really great.  Not much else to say.
I'll add that the stereo link works great and the meters track nicely too.
Thanks!

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

 

[tommypiper]

Just found this thread and so happy to see and it's been long overdue.  Kingston, thank you.  Seriously.  Thank you.  Please don't be discouraged by all the ignorant questions about 4.7 caps and sour attitudes.  Your work and sharing are deeply appreciated.

 

[duantro]

I've swapped out input transformers on one channel, as well as gain switches with a 600 ohm tpad, and this thing already sounds way better! Upper mids on edcores are real gritty and kind of harsh. The non center tapped cinemags are a lot smoother. I can't wait for some free time to finish this!

 

[prescott]

Is it possible that there will be PCBs for this project?

Looking forward to them

 

[Kingston]

I have decided I won't make PCB's for this after all. Except a more universal version of the PSU that I need for some of other projects as well. But that won't go public either. This project is much better suited to p2p than PCB's with all the tubes bolted onto a metal chassis.

I'm busy elsewhere in life (DSP/programming) and haven't got time for other big projects, let alone questions like "where's the BOM".

 

[duantro]

Kingston- you've already done the most important part by testing these mods and posting the schematics! I also cannot thank you enough for this. I know life gets busy, but hopefully you'll be able to drop by and make fun of some deserved , and probably a few not so deserved comments. ;D

Prescott- I'd advise either keeping an eye open in the Black market for people who regularly sell the PM670 boards in various states of gathered parts lots. Or as Kingston states, going point to point.

 

[geoff004]

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.