the Poor Man 660 support thread

[emrr]

Spend the money for some real Daven/Shallco and they won't fail.  Elma shouldn't either, can't say why they did.  Every old broadcast service limiter used rotary switches in path, and those were not allowed to fail.  I wouldn't use the cheapo's like Ural, but I have no experience with those failing either.  alexc appears to have no problem with them. 

 

[Kingston]

I had 4X of those Elmas on a build and all of them failed with the exact same fault: certain range was consistently losing contact. Pretty "awesome" stereo glitch and bubbling fx.

Similarly I have a quad Elma rotary as a stereo passive balanced attenuator and its just horribly glitchy. Never ever going to use them again and I've made it a point to remove all Elmas from within 100 meters of me for peace of mind and safety.

http://www.michaelkingston.fi/files/correct-and-accurate-rotary-switch-placement-and-handling.jpg

 

[alexc]

If I wanted to keep the stock attack time, but mod the release times, I could wire the TC network in parallel with the stock 10uf and just vary the resistors, is this correct?

For the background on the pm660 time constants mods .... https://groupdiy.com/index.php?topic=29056.20 describes the 'Bluebird mods'  which I think was the earliest ....

Basically the story is this :

- the pm660 is loosely modelled on the original fc660 which has a 'time constants' circuit consisting of a 'fixed part' and a 'variable part'  - they are parallel'd with each other across the rectifier bridge

- the pm660 'tc fixed part' consists of r17 (221K), c3 (0.22uF)  and r18 (120R)
- the fc660 'tc fixed part' consists of 220K and 2uF

- the pm660 'tc variable part' consists of 'attack pot' 10K rv7 and c4 10uF
- 'the fc660 'tc variable part' consists of a 2 deck rotary wired in parallel with 6 selections available

It can be said that the actual 'attack' and 'release' times are quite inter-related, the time circuit having both a 'fixed part' and a 'variable part';  so trying to seperate out the 'attack' and 'release' into two distinct controls is not really valid

ie.  a single control is probably warranted, as in the case of the original fc660.

NOW, the pm660 'attack' pot doesn't do all that much, and the 'single 10uF cap' is wayyyy long,  so many have gotton rid of all that and moved more towards the fc660 by using a single 'time constant' rotary switch of 6 positions and 2 decks.

[one can also simplify the original fc660 2 deck 6 position into a single deck switch]

BUT the question is 'do I really need the 10uF ?' (which is super long and not usable in some peoples opinion) was mostly asked *after* people (like me) had already soldered C4 into the pcbs. 

SO, I kept it in circuit -  they were expensive at the time!

Note that if one does desire the 10uF super-extra-long release time, it is too large to easily fit to the back of a lorlin; and further, there's not much space left in a pm670 to lay it down elsewhere, so best to use C4 

...

THUS my choice was to keep the on-board 10uF as 'selection 1' of a 6 position lorlin 2 deck switch with two decks : one for the caps, and the other for the resistors - basically the 'Bluebird' mods.

....

NOW  there's a number of ways to 'patch in' the 'time constant' rotary switch :

option 1

- one can short out the C4 cap if 10uF is not going to be used, and patch in the lorlin in place of the 'attack'  pot 
    ie.  rv7 connector pins 1,2  (pins 2,3 are linked on the pcb)

or

option 2 (my way)

- one can populate C4 cap and use it as the first selection ie. 'send' it to the lorlin -  this requires

      i) cut to the 'attack' rv7 connector pins 2,3 which are linked at the pcb 
    ii) link from rv7 connector pin 3 trace to 'top' of C4 trace ...  at back of pcb near the connector
    iii) wire rv7 connector pin 3 to position1 selection terminal of the lorlin cap deck
    iii) patch in the lorlin at rv7 connector pins 1,2

....

The easiest thing is option 1 - short C4, ditch 'attack pot' rv7 and use connector rv7 pins 1,2 to patch in a lorlin

Here's Bluebirds drawing    with a 2deck 5 positon rotary and his choices of the cap and/or resistors

..

Now the Lorlin switch has 2 decks on the back laid out as 2 half-circles of selection terminals with a pole terminal in the middle of each.

The pole terminals are to be connected in parallel ...  and that goes back to the pcb. (rv7 pin 2)
The selection terminals are soldered .. to 'one end' of  ...  the caps on one deck  ....  and resistors on the other deck

The 'remaining ends' of the caps *and* resistors are all wired together into a ring shaped 'cage' assembly ..
.  that 'common' ring is soldered up strong, and then a wire goes back to the pcb (rv7 pin1)

The lorlin layout is out there somewhere .... 

... insert pic ...
..

As to the  actual values :

- the cap can go from 10uF (very long release time) down to 0.22uF (very short), around 200V dc rated.
- the resistors generally from nil or 25K .. 500K ..  can be 0.5W

Now we know this 'time constant network' is also a 'filter' circuit for the output of the recifier bridge, it's a bit like a 'psu ripple filter'

The 'control signal' we derive from the rectifier bridge has a strongly and quickly varying 'dc' waveform (negative going) plus some 'ripple'.

The time constant network affects this ripple as well as dictating the 'timing' of movement of this negative going control signal (the desired end result of the sidechain amp).

Anyway, at the lower valued cap'n'resistor choices in play (fastest attack+release), it  is the 'least filtered' with  more ripple  - so one can use some additional resistance, in series and/or parallel to 'clean things up a bit'    ..  wrt to the phenomenon of 'control signal leaking into the audio signal'

It's hard to describe and easier to hear and see on a cro  Its a balancing act

Hence the sorts of choices made are .. like Bluebird has on his - the deck resistor starts low K, the deck cap starts high C  and each progress on the switch to high K and low C.

Actually determining the real 'timing' values in seconds or milliseconds and even microseconds is not easy .. it's a bit hit and miss and requires a more 'pro' level of skill and knowledge.

So, getting hung up on the specific times isn't appropriate until one has the measuring skill to verify.

One can do some rough calculations to best decide on the values and how they relate to reality.

Which is why trying to intimately map the pm660 time constants to the fc660 is a little apples-to-oranges. At the detailed level, the pm660 is only loosely based on the original, including in the control amp and thus the timing circuits.

One can go ahead and use the fc660  time circuit exactly if desired but probably makes sense to simplify a little.

In fact, I believe to correctly map fc660 times to pm660 requires more sidechain power than is available in in the mighty pm660 with its thunderous wastage of energy! Some people went on to make a pcb module to drive more power with transistors - they became known as the 'scamp' ers 

....

Fortunately, it all works out pretty well using the 'Bluebird' type mods.

I used 6pos dual deck lorlin, the decks in parallel  (fast to slow)

0.22uF, 0.5uF, 1.0uF, 2.2uF, 4.5uf and onboard 10uF on deck 1  //  in parallel with
      26K,    68K, 150K,330K, 470K and  Open Circuit  on deck2

which is, of course' also  in parallel with the on-pcb 'fixed timing' part as I described earlier.

Go ahead and calculate  ;D 

In practice, it will probably take a few attempts to get the timing that makes you happy. I used a resistance substitution box to find the rough R value for each of the C values while testing ....  that worked reasonably well

...

I find the setting I use most in middle of the pack - something like 1uF // 150K
Its fast attack (some ms) and a mid level 'release'something like 0.5s  at generous GR of -12dB or so.


It can release very fast but that does begin to get 'challenging' in the area of distortions of various kinds....

It has a very fast attack but that does begin to get 'challenging' in more subtle ways ....

----

Such is the magic  of big tube limiter design and construction  !!

 

[Holger]

I had 4X of those Elmas on a build and all of them failed with the exact same fault: certain range was consistently losing contact. Pretty "awesome" stereo glitch and bubbling fx.

Similarly I have a quad Elma rotary as a stereo passive balanced attenuator and its just horribly glitchy. Never ever going to use them again and I've made it a point to remove all Elmas from within 100 meters of me for peace of mind and safety.

http://www.michaelkingston.fi/files/correct-and-accurate-rotary-switch-placement-and-handling.jpg

Michael, just saw this, excellent...
Any other reliable 24 pos switches on the market except for the chinese ones?

 

[justinheronmusic]

What fuse should I use for this project?

EDIT: Found a link to this in this thread about 97 pages back, reposting for accessibility:

Hi,

Anyone could give the correct slow-blow fuse rating ?

thanks

Hi,

short answer - No.

Transformer VA rating will set the limit, so this number is easier to pick than calcluating and adding the current draw of all active an passive parts under load.

Assuming, you use a 6VA transformer, divide this VA by your mains voltage, giving 6VA/110V=0.055A. This transformer is maybe only 70% efficient, so multiply the 0.055A by (1/0.7), giving 0.078A. Nearest larger fuse rating will be 100mA. For the larger inrush current of a toroid you want this with slow blow/time lag characteristic. Fuse voltage rating is at least your mains voltage to prevent arcing when this fuse blows, so a 250V/100mA T (=slow blow) might fit for this example. Your transformer may/will be different, so do the math with your values.

« Last Edit: July 01, 2009, 08:40:28 AM by Harpo »

 

[alexc]

I use a 500mA slow blow fuse on mine, which is 240VAC 50Hz supply.

I also use a 750mA fast blow at times   

My Poorman have increased PSU capacitance on the dc heater as well as the HV, so the in-rush current can be significant on start-up.

You can just start out low and incrementally increase till you stop popping fuses on start-up 

 

[justinheronmusic]

What is the part number for the green terminal connectors?

 

[shabtek]

They are called Phoenix Connectors

While easy to connect to with screw driver I believe there is supposed to be a ferrule on the wire end for reliability. I prefer molex or similar plug type connectors. You will likely have to look at data sheets and measure pitch and hole size—it is a standard size thats needed.

 

[FarisElek]

Are pcb’s still for sale? I’m thinking of getting started on this.

 

[justinheronmusic]

Are pcb’s still for sale? I’m thinking of getting started on this.

I got mine off the black market a few years back, probably about 4 years ago. A few people still had them around - worth checking out. The build thread seems to be pretty dead for the most part, be warned.

 

[Rob Flinn]

Are pcb’s still for sale? I’m thinking of getting started on this.

]

Might have a pair for sale with PSU board and the transformer that was sold at the time.

 

[justinheronmusic]

Can anyone recommend a heatsink for the 10A Bridge Rectifier?

 

[justinheronmusic]

Progress Pic

Just finishing up and blew a fuse. As soon as the new one comes in I'll be rolling through R15.

If anyone has 6BC8 tubes they wouldn't mind selling me I would love to have some backups. Looking for GE & RCA.

 

[justinheronmusic]

Build is a success, stable, passes signal and compresses beautifully.

Using 1A 250v fuse here in the USA.

Heater is at 6.8v with 2 x 5687 tubes per channel. I'm using a .5R 50w heater resistor. 6BC8 tubes all sitting at 6.6v.

Using a single TC for now; a 1uf cap and 150k resistor in parallel. I have a 2.2uf and 350k resistor here in case I want to slow it down a bit, but it's fine for now. I will eventually put a 6 pos resistor ladder in paralell to vary the release time.

All Edcor transformers accept for T1 which is the Sowter, also using Rondo toroid for power. Not using bypass boards.

I'm not using matched tubes (All RCA 5687 & 6BC8 tubes), so there is distortion present. It's not bad! I hear it mostly in low frequencies, but I tend to saturate things and distort things down there anyway. This compressor has a character, and it's not a knight in shining armour. It's more like a knight in aged & oxidized nickel armour. Definitely beats using a plugin. I compared it to a Fab Filter Pro-L and the Shadow Hills Class A - both fantastic plugins. But the PM670 has more depth and seems to be doing more if that makes sense at all. More complex and doesn't sound like pro tools.

My only gripe is the metering. My meters dance when I adjust the threshold above 3 on channel 2 only. Adjusting threshold on channel 1 does nothing to the meters. I can live with it, but I would rather have more stability.

Will probably continue to hoard RCA 6BC8 & 5687 tubes and roll through them periodically until I find the closest quad by ear.

Thanks to Analag, Volker, and all of those who built and blazed the trails before me.
This build was the ship that I pulled over a mountain. This was my Fitzcarraldo.

 

[scott2000]

Nice work!

Let us know how the tube swapping affects this distortion you hear....

 

[[silent:arts]]

Congrats Justin  8)

 

[justinheronmusic]

Thanks guys. For me, this was a huge undertaking. It was the Fitzcarraldo of my DIY world! I never thought I would see the day.

I tried pulling two 5687 tubes but didn't like how it was affecting my release time - sluggish and not very musical. I put the 5687 tubes back in, and dropped my heater resistor back to .5 ohm (was using 1 ohm with only 2 5687 tubes).

I changed my time constant to 2.2uf & 150k. This allowed the transients to come through a little more while still sounding glued together, and oh boy does it sound ever so glued together. Coming from using plugin compression on the mix bus for the last few years, this has been a real nice treat.

Reading back in the thread there is a multitude of suspected reasons for dancing meters, but I don't believe anyone found out what it was; some say it was underpowered tubes due to the toroid, and some people said it was a problem with the tubes being mismatched. At this point, I don't believe I will spend any more money to find out. My workaround is to adjust the threshold of Ch1 using the meter for reference, then adjust the threshold of Ch2, then zero the meters, and then play program material through it and viola! I have a beautiful sounding compressor.

I received a new batch of 6BZ8/6BC8 tubes yesterday and dropped them in, and used my ears to find the best configuration. It's an improvement, but I am not sure if it was worth the extra money to find closer matches; if I had proof in front of me as to why matched tubes are oh soo important in this build then I may proceed in tube hoarding.  Though at this point I have no reason not to trust Analag's original statement about tube matching immunity for the 6BC8. I did drop RV3 down to -3.5v and that actually lowered my distortion quite a bit.

I think this compressor sounds fantastic. It's got a weight to it that sounds incredible when I run a full track through it. It's emotional, it's musical, and gives me something no plugin can come close to. The compression is so so smooth, it really puts the UAD Fairchild plugin to shame.

After I finish a few microphones I will work on a release switch for the 2.2uf, but I'm in no hurry. It's working quite well at the moment.

 

[FarisElek]

Thank you for the update! It's very good to hear and I'm starting this project. I do not plan on finishing soon. I'm hoping that through of the wealth of info here that I can piece this project together slowly.

The only thing is that I have a question about at this time is that I have a custom toroid that was part of a group buy and I can't find any information (other than the handwritten label) how to wire it. I tend to be very cautious with PSU wiring so I was hoping someone could shed some light on this particular toroid for me. Is this the Rondo? If so, I've read lots about "orange" wires, but this doesn't have an orange wire. Anyone know how to wire this for U.S. 120V?

Thank you,
Ryan

 

[justinheronmusic]

This doesn't seem like the Rondo toroid. The Rondo has his logo on it. I do believe he still sells it, you could ask him to make you one or take achance on this one you have.

In all reality you will probably be fine. Just remember to use .47uf - 1uf Polyprop in C6 on the PSU and x2 IRF840.

 

[wmarden]

So what are the best available switches to use on this project since the Elma's failed..? My 660 currently has the Elma's and I want to finish this project... I thought I'd ask vs. reading thru 163 pages of thread. Thanks in advance!