DaveP

Re: EF85 Compressor from scratch
« Reply #20 on: August 30, 2016, 02:56:53 PM »
Sorry to disappoint, but I have decided not to go ahead with this project as it was.  (I have been asked to make a Fairchild 660)

I have been ill for 2 months now and have had time to reconsider, although I am now feeling back to my old self.

I am going to build another type of compressor instead that I find more interesting,  I will be able to use the same chassis etc.

I am usually determined to see things through to the end but in this case I have decided on something better.

Best
DaveP

« Last Edit: August 27, 2018, 03:20:43 PM by DaveP »
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tommypiper

Re: EF85 Compressor from scratch
« Reply #21 on: April 09, 2017, 03:05:57 PM »
Dave, your projects are always first class, educational, and fascinating.    (I think we need a Project Specific Discussions category for your builds alone.  "The Dave Channel.")  You are very generous to share all your development, research and thoughts and build progress reports. 

Glad you're feeling better.  Hope to read more about this soon.
Imagine a wet, slightly chilled from its gas release and decompression, with water droplets condensing, sucking surface tension, slowly sliding down the side, capped by a healthy virgin froth on top..

DaveP

Re: EF85 Compressor from scratch
« Reply #22 on: April 09, 2017, 06:14:08 PM »
Your post is very kind but undeserved, there are plenty of better builds than mine on this forum.

Perhaps where mine differ is that I'm crazy enough to show them in real time rather than after the event.  I find I need the added pressure to make sure they get finished.

I learnt a lot from the 660 project so I will be returning to this project next year after I have built a workshop inside my barn to work in. (my wife has evicted me from our spare room for being too untidy!)

Best
DaveP
Soundcloud: Delayed Action.

tommypiper

Re: EF85 Compressor from scratch
« Reply #23 on: April 16, 2017, 01:18:25 PM »
(my wife has evicted me from our spare room for being too untidy!)

Best
DaveP

Ha, I have to laugh.  I've been in the same state for years.  With no barn.  You're lucky to have a structure.  I'm hoping to build a workshop or erect a backyard shed. 

I've resorted to a flimsy card table in the yard with an extension cord for the solder iron.  Haul my project boxes out, unpack, paper weights against the wind, sunglasses against the glare.  You can only do so much when forever in picnic mode, with all your parts and tools scattered and perpetually stored in boxes....   :o
Imagine a wet, slightly chilled from its gas release and decompression, with water droplets condensing, sucking surface tension, slowly sliding down the side, capped by a healthy virgin froth on top..

DaveP

Re: EF85 Compressor from scratch
« Reply #24 on: April 16, 2017, 04:27:33 PM »
Quote
I've resorted to a flimsy card table in the yard with an extension cord for the solder iron.  Haul my project boxes out, unpack, paper weights against the wind, sunglasses against the glare.  You can only do so much when forever in picnic mode, with all your parts and tools scattered and perpetually stored in boxes....   :o
That is true devotion and it puts my troubles in the minor league  :-[

In the good old days the wife would have gone in the barn instead, but such is the price for reconstructed men, don't you just love 'em...... ::)

DaveP
Soundcloud: Delayed Action.

DaveP

Re: EF85 Compressor from scratch
« Reply #25 on: July 02, 2018, 02:10:04 PM »
I am resurrecting this project.
I sold most of my outboard recently, but feel the urge to record some more music.  I dropped it when I became ill, then a friend asked me to make him a Fairchild 660 and the project got shelved.

I have also finished the first of my monitor speakers, so they will both be ready soon too.

I thought I would share a few ideas about this new compressor in the meantime,  this is my new revised circuit.


I have been wanting to find a replacement for an inter-stage TX for some time.  I have made enough clones in the past so I thought it was time for something new.

All the stages in this schematic have been made in rough (hence voltages) but I have not put it all together yet.  The vari-mu stage can produce up to 30dB of gain reduction.

This design will be feed forward, by the way.

DaveP


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shabtek

Re: EF85 Compressor from scratch
« Reply #26 on: July 02, 2018, 05:02:58 PM »
looking forward to more high caliber design work
"really fine players do not use stomp boxes or master volume, they match the amp to the room and turn it up to 11.  Stevie Ray, BB King, Albert King, Duane Allman, Dicky Betts, Louis Armstrong"
   -CJ

Dmichel123

Re: EF85 Compressor from scratch
« Reply #27 on: July 04, 2018, 11:09:02 AM »
I'm gonna be watching this thread. The long-tailed pair with CCS will absorb the thump as well as an interstage transformer or choke?

alexc

Re: EF85 Compressor from scratch
« Reply #28 on: July 06, 2018, 02:51:07 AM »
Awesome Dave  ...  a resurrection  limiter ....    ;D      And feed forward - look forward to reading more. 

I have to say, I thought you had this nailed already, but oscillations can be a bug-bear to the finishing process, I guess.

All the best :)
I ping therefore I am

DaveP

Re: EF85 Compressor from scratch
« Reply #29 on: July 06, 2018, 03:22:45 AM »
Quote
I'm gonna be watching this thread. The long-tailed pair with CCS will absorb the thump as well as an interstage transformer or choke?
That is the hope!
The CMRR is supposed to be at least -40dB according to Morgan Jones.

The SA-39B does not have an interstage.  I made one of those with matched tubes and it worked fine, so I hope that this design will not thump either.  We shall see. :)

@alexc
Always good to hear from you mate!  A Resurrection limiter, I like that!

Best
DaveP
Soundcloud: Delayed Action.


scott2000

Re: EF85 Compressor from scratch
« Reply #30 on: August 01, 2018, 02:55:39 AM »
I'm not sure if this little thread was looked at but, PRR left some thoughts about the EF85..

Just in case it has anything useful for this.....

https://groupdiy.com/index.php?topic=30349.0

DaveP

Re: EF85 Compressor from scratch
« Reply #31 on: August 13, 2018, 03:18:15 PM »
Quote
I'm not sure if this little thread was looked at but, PRR left some thoughts about the EF85.
That was the inspiration for the project Scott. :)

I have finalised the design of the feed-forward amp which supplies the -ve DC. for the GR.



This is a three tube design, which basically uses the high gain of the pentodes to lower the output impedance with feedback.

The output Z is 100 ohms which is the same as a Fairchild.  A feedback design uses the audio output for this, a feed-forward design has to generate its own supply.

If you use a lower ratio OPT, you don't get enough impedance reduction, if you use a higher ratio, you don't get enough voltage at the output.  This compromise gets me 50V rms output which delivers -35VDC, all I'll ever need.  B7G tubes are used wherever possible to save space.  There are 12 tubes in all.

DaveP
Soundcloud: Delayed Action.

scott2000

Re: EF85 Compressor from scratch
« Reply #32 on: August 13, 2018, 06:29:39 PM »
I'm counting 11?? never mind.......



Need to wrap my head around the power supply a bit more...... but think I can figure it out  ...

Thanks for the revival!!
« Last Edit: August 13, 2018, 06:42:54 PM by scott2000 »

DaveP

Re: EF85 Compressor from scratch
« Reply #33 on: August 16, 2018, 05:10:36 PM »
This is the latest version of the power supply.

An elevated heater supply is not needed with the tubes chosen, the 6DK6 can withstand 300V between the heater and cathode, an unexpected discovery.  The EL86 can withstand 200V because it was designed for totem pole operation.  So the 170V output should be no problem.



All the main sections are now designed and will hopefully function together..............we shall see!

DaveP
Soundcloud: Delayed Action.

DaveP

Re: EF85 Compressor from scratch
« Reply #34 on: August 27, 2018, 03:44:21 PM »
The build has started!

I have made the power supply section in two halves.



This side has two 110V toroids with secondaries in series, so with a bridge rectifier you get around 340V.



This side has the heater toroid,  Caps and rectifiers.  All pre-wired for final assembly.
The heater rectification is done by two new SR1503 Solar energy diodes, these have very low forward drops,  Two 47,000uF caps complete the job with a 25W metal clad resistor in between. (not yet fitted)  The 12 tubes use around 4 Amps of DC.



This is how they will be orientated.

All for now
DaveP
Soundcloud: Delayed Action.

dustbro

Re: EF85 Compressor from scratch
« Reply #35 on: August 28, 2018, 12:46:11 PM »
Nice!! Can't wait to see this one complete

DaveP

Re: EF85 Compressor from scratch
« Reply #36 on: September 05, 2018, 05:03:25 AM »
Thanks Dan :)

The power supply section box is now finished.



I finalised the layout with no room to spare but it looks do-able from experience.



I take a long time over this part because of 3D implications, it takes a while to visualise the best possible layout.

Then it's down to the nitty gritty of cutting out those tube base holes.  Then I try to align the tubes (rotate) for the best orientation between them, so that they make connections easier, that comes next.

DaveP

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letterbeacon

Re: EF85 Compressor from scratch
« Reply #37 on: September 05, 2018, 05:22:17 AM »
Looking good!

How do you fix that mesh to the metal? With the rivets? And how do you make such a clean looking rectangular cut-out?

DaveP

Re: EF85 Compressor from scratch
« Reply #38 on: September 05, 2018, 07:44:05 AM »
Thanks Letterbeacon,

Yes, it's fixed with pop rivets plus washer.

The short answer is it's time consuming ???

You have to mark the outline as accurately as possible, then find the 45 degree spot for the drill to radius the corners.

I drill up progressively getting larger and push over to correct any misalignment until it reaches the line.

Best
DaveP

Then I cover the parts I want with masking tape and jigsaw to 1 or 2mm up to the line.  Then its all down to filing to the line.

Finally I wrap the file with emery paper and smooth it all off.  Sometimes I polish it with a rag wheel afterwards.
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mjrippe

Re: EF85 Compressor from scratch
« Reply #39 on: September 05, 2018, 11:36:48 AM »
https://www.amazon.com/Sheet-Metal-Nibbling-Nibbler-Cutter/dp/B00WFFZ2X8

Drill a 3/8" hole then use these.  It's slow, but takes less filing after.