GroupDIY

Project Specific Discussions => Dynamic Processors => Topic started by: DaveP on May 09, 2016, 07:41:44 AM

Title: EF85 Compressor from scratch
Post by: DaveP on May 09, 2016, 07:41:44 AM
I have finished the design and testing of the CV Amp.

(http://i1110.photobucket.com/albums/h448/DBPendrill/EF85%20Control%20Amp%202_zpsutkhaf4h.png) (http://s1110.photobucket.com/user/DBPendrill/media/EF85%20Control%20Amp%202_zpsutkhaf4h.png.html)

This uses a pair of 6CM7 TV tubes and it can output over a Watt of negative DC power into a 1k resistor in parallel with a 1uF cap.  These $3 tubes are essentially half a 6CG7 plus half a 12BH7.

They operate completely in class A with the Edcor TX and are at ~70% of maximum dissipation.  The feedback keeps the gain steady and brings the output resistance down to 100 ohms, the same as the Fairchild CV amp.

Best
DaveP

Title: Re: EF85 Compressor from scratch
Post by: ruffrecords on May 09, 2016, 12:59:38 PM
Completely OT, what drawing package did you use for the schematic?

Cheers

Ian
Title: Re: EF85 Compressor from scratch
Post by: DaveP on May 09, 2016, 01:11:49 PM
I hope you are over the worst now Ian and feeling better.

I have a template in MS Paint and just copy, cut and paste.

I made the component template from the original LA 2A schematic and have used it ever since.

I find it quite therapeutic, how weird is that ???

Best
DaveP
Title: Re: EF85 Compressor from scratch
Post by: DaveP on May 13, 2016, 05:08:55 PM
This is the power supply designed and tested:-

(http://i1110.photobucket.com/albums/h448/DBPendrill/EF85%20Power%20Supply_zpso8htr0ly.png) (http://s1110.photobucket.com/user/DBPendrill/media/EF85%20Power%20Supply_zpso8htr0ly.png.html)

This provides a basic supply for the control amp and a regulated supply for the signal amp.

The regulation sharpens the knee of the compressor.

All the transformers are toroidal, it's much cheaper to use several than buy specials to the same spec.

Best
DaveP
Title: Re: EF85 Compressor from scratch
Post by: vari-mu on May 17, 2016, 06:30:43 AM
 HI Dave , EF85 is a good choice for vari-mu compressor . I put a pair of EF85 Valvo 
into my compressor PV-670
and made the tests of work in extreme conditions:

Compression: 6 - 10 dB
Attack time : 0.2 - 0.4 msec
Release     : 40 - 60 msec

Pictures from the video:

(http://i63.tinypic.com/11jrm6d.jpg)

(http://i68.tinypic.com/330fejn.jpg)

(http://i64.tinypic.com/2qsur1c.jpg)

(http://i68.tinypic.com/2n3pec.jpg)

(http://i68.tinypic.com/2ztdkzb.jpg)

 Video is not an example of the sound,
but demonstration of the vari-mu compressor with tubes EF85 only.

 Excuse me, sound a right channel only.
Video here:
https://drive.google.com/file/d/0B5AYDQSv9pE1NG0xRDI4UjN5NVk/view?usp=sharing

  Vladimir P.
Title: Re: EF85 Compressor from scratch
Post by: DaveP on May 17, 2016, 10:44:25 AM
Hi Vladimir P

Thanks for your post, I am very impressed :)

It must have taken you as long to test and make the demo as it did to make the compressor!

I hope my effort sounds and looks as good as yours.

(I didn't know the President of Russia was a member of GroupDIY) ..............just joking ;)

Best
DaveP
Title: Re: EF85 Compressor from scratch
Post by: DaveP on May 25, 2016, 05:15:15 PM
I have been working on the design for the signal amp, this will be similar to the 660 with 4 tubes/side.

As I mentioned in the drawing board post, I have 10 x Siemens and 10 x Mullard EF85's to choose from so I set up a test to get relative data for them all.

I tested each tube with a 4.8k plate resistor and a 517 ohm cathode resistor, these values were chosen because they give 150V on the plate and 8mA current when the supply is 188V.  With 4 tubes the plate resistor is 1.2k (4.8/4).

What surprised me was the consistency of the Siemens production and the lack of it with the Mullards.  I should also say that each tube was tested with exactly 6.3V DC and the Siemens also had more consistent heaters as well, the Mullards needed much more adjustment every time to bring them to 6.3V.

(http://i1110.photobucket.com/albums/h448/DBPendrill/Siemens_zpsqgkkl5o2.png) (http://s1110.photobucket.com/user/DBPendrill/media/Siemens_zpsqgkkl5o2.png.html)
These are the Siemens test results and the tubes I chose for the left and right sides are shown with the combined currents and gains which both have to balance as well as possible.

These are the Mullard results
(http://i1110.photobucket.com/albums/h448/DBPendrill/Mullard_zpshg6cjjys.png) (http://s1110.photobucket.com/user/DBPendrill/media/Mullard_zpshg6cjjys.png.html)

You can see that compared to the Siemens tubes, they draw less current but have higher gain.

The gain figures were without bypass caps but with a cap they are all about 2.3 times greater.  Remember, they are triode wired with a very low value of plate resistor as in PRR's original post.

I set them up with 4/side and they balanced very well at quiescent gain and current.  I next have to test them through the range with negative grid voltages.

DaveP
Title: Re: EF85 Compressor from scratch
Post by: DaveP on May 29, 2016, 03:45:41 PM
I made one of my dangerous mock-ups with croc clips  :o with 4 tubes /side and although the gain and current draw were fine at idle, they went out of balance with increasing negative voltage on the grids.  There were also potential instability problems due to having over 24mA/V gm!  These are TV tubes remember.

I decided to start with a more practical approach with just a matched pair as this provisional schematic.  This is almost exactly as PRR's original post.  I have put a copyright sign on all my circuits because I don't want them ripped off by kit builders, but anyone on this forum can copy them for personal use.

(http://i1110.photobucket.com/albums/h448/DBPendrill/EF85%20Signal%20Amp%202_zpsepignzmd.png) (http://s1110.photobucket.com/user/DBPendrill/media/EF85%20Signal%20Amp%202_zpsepignzmd.png.html)

I am using just a 10k: 600 Edcor for the OPT at the moment, I have some other impedances on order to try.  Notice the way the OPT is connected, there are no coupling caps to charge and no current through the primary either, when in balance, which is virtually always.  This is definitely well within the 50V spec for this OPT.
I have tested the current versus the -Vg1 voltage in the following chart:-
(http://i1110.photobucket.com/albums/h448/DBPendrill/EF85%20Vg%20v%20Ia_zpsxvfkyx8y.png) (http://s1110.photobucket.com/user/DBPendrill/media/EF85%20Vg%20v%20Ia_zpsxvfkyx8y.png.html)

I have not yet tested the gm against current, but the gain and gain reduction are shown here:-
(http://i1110.photobucket.com/albums/h448/DBPendrill/EF85%20GR_zpsbd5jhvrc.png) (http://s1110.photobucket.com/user/DBPendrill/media/EF85%20GR_zpsbd5jhvrc.png.html)

This shows that 30dB of reduction is possible with -28V on the grids, pretty much as PRR predicted.  This has happened with about 8.4mA of idle current rather than 10mA as in his example, which should make the tubes last a little longer.

The gain is lower using the OPT direct coupled because there is a degree of negative feedback going on between the phases, the loss is more than just from connecting a 10k load.  I will be testing the frequency response with the other OPT's  later.

DaveP

Title: Re: EF85 Compressor from scratch
Post by: DaveP on June 06, 2016, 05:59:29 PM
I have finished a design for the signal amp and would welcome some expert comment.

The main issue turned out to be the need for a low output impedance to drive the output transformer to a decent frequency response.  I have used a direct coupled CF for each output and its flat from 20-20kHz.  If I had used multiple tubes, then the output impedance would have varied by too much under GR, this way it is constant at <100 ohms.

(http://i1110.photobucket.com/albums/h448/DBPendrill/EF85%20Signal%20Amp%203_zpsqknlqpea.png) (http://s1110.photobucket.com/user/DBPendrill/media/EF85%20Signal%20Amp%203_zpsqknlqpea.png.html)
I used a pair of excellent TV pentodes 6JC6A triode wired.  These frame grid tubes represent the state of the art in 1966 and give a gm of over 10 at half the maximum dissipation, the mu is 25 so this is where the low output Z comes from.

I have tamed all the grids of these TV tubes with grid stoppers to counter any parasitics, the FR drops slowly after 20kHz then picks up again at 50kHz drops and rises again at 100kHz, this from a $13.95 Edcor TX. 8)

There are no intermediate caps to charge and the 15mA of current has no problem with the output caps.  As PRR said, the voltage change with the GR tubes is only 40V, so the CF's can easily cope with this amount of movement, which is, in any case,  limited by the regulated supply.

Best
DaveP
Title: Re: EF85 Compressor from scratch
Post by: Winston O'Boogie on June 06, 2016, 08:49:20 PM
I like it Dave    :)   I've done similar with a pair of directly coupled cathode followers after the gain cell pair albeit using different valve choices.   Not much of value to say but, fwiw:

Won't probably sound or measure any better but you could lose a cap by trying it with just one 4.7uF between the OPT centre-tap leads?

I used squalid-state constant current sinks under the followers but... ?

Elevate the heater for the 6JC6's.

Protect the 6JC6's by limiting the grid to cathode voltage at turn on -    Zener. Neon. 

Edit:    Actually, looking at your schem., I would be tempted to try it with the cathodes directly connected to the OPT and then use a CCS  on the centre-tap...  Maybe another 6CJ6A? 

Anyway, just thoughts, looks good as is too, cheers.

Title: Re: EF85 Compressor from scratch
Post by: DaveP on June 08, 2016, 05:40:20 PM
Quote
I like it Dave    :)   I've done similar with a pair of directly coupled cathode followers after the gain cell pair albeit using different valve choices.   Not much of value to say but, fwiw:

Won't probably sound or measure any better but you could lose a cap by trying it with just one 4.7uF between the OPT centre-tap leads?

I used squalid-state constant current sinks under the followers but... ?

Elevate the heater for the 6JC6's.

Protect the 6JC6's by limiting the grid to cathode voltage at turn on -    Zener. Neon. 

Edit:    Actually, looking at your schem., I would be tempted to try it with the cathodes directly connected to the OPT and then use a CCS  on the centre-tap...  Maybe another 6CJ6A? 
I will try one cap and no caps as you say.

The heaters will be elevated on the 6JC6A's.

The grids come up slowly with the regulated supply which gives a soft start effect.

These are my provisional timings which were also used on the Group DIY comp.

(http://i1110.photobucket.com/albums/h448/DBPendrill/Timing_zpswvrh0urn.png) (http://s1110.photobucket.com/user/DBPendrill/media/Timing_zpswvrh0urn.png.html)

Any comments welcome

Best
DaveP
Title: Re: EF85 Compressor from scratch
Post by: DaveP on June 16, 2016, 04:44:33 PM
I have been working on the best OPT to use for the signal amp.

I tested a range of Edcor OPT's of various impedance and you might be interested to see the results.
These were tested with a common input voltage except the 600:600 which had square waves at that input level, I reduced the level for that TX until it was back to a clean sine wave, although the output level was fair, I don't think I'd like to run the amp into such a low load.  Output Z of the amp was ~100 ohms.

(http://i1110.photobucket.com/albums/h448/DBPendrill/OPTs_zpssamjao4v.png) (http://s1110.photobucket.com/user/DBPendrill/media/OPTs_zpssamjao4v.png.html)

I measured on the scope, the points where the voltage went -3dB in the top and low ends.  This rules out the 15k:600 and the 10k:10k as the top end starts to drop way too early.

The 2.4K:600 and the 10k:600 look promising.

Best
DaveP
Title: Re: EF85 Compressor from scratch
Post by: DaveP on July 18, 2016, 05:34:50 PM
This project has now gone live.

I started cutting the metal today.

(http://i1110.photobucket.com/albums/h448/DBPendrill/Start_zpswtif2guf.jpg) (http://s1110.photobucket.com/user/DBPendrill/media/Start_zpswtif2guf.jpg.html)

Gathering all the parts together.

DaveP
Title: Re: EF85 Compressor from scratch
Post by: DaveP on July 20, 2016, 11:18:21 AM
The front panel is now finished, this is the back view showing the tabs which connect to the rest of the chassis.
(http://i1110.photobucket.com/albums/h448/DBPendrill/EF85-2_zpssl9grkxs.jpg) (http://s1110.photobucket.com/user/DBPendrill/media/EF85-2_zpssl9grkxs.jpg.html)

I have just thrown in the meter to show what it will look like from the front.
(http://i1110.photobucket.com/albums/h448/DBPendrill/EF85-3_zps3fmepolx.jpg) (http://s1110.photobucket.com/user/DBPendrill/media/EF85-3_zps3fmepolx.jpg.html)

I have to print a dB scale for the meter.

The controls will be:-
Meter select, Attack, Release and Threshold.

Unashamedly right-handed, can't help that!

DaveP
Title: Re: EF85 Compressor from scratch
Post by: DaveP on July 21, 2016, 04:12:02 PM
Finished the chassis structure today.

(http://i1110.photobucket.com/albums/h448/DBPendrill/EF85-4_zpss9u1sa8e.jpg) (http://s1110.photobucket.com/user/DBPendrill/media/EF85-4_zpss9u1sa8e.jpg.html)

I still have to plan the layout and cut the tube base holes.  There is a transformer/rectifier module to fit on the chassis, this will be made from galvanised steel to reduce the magnetic field, toroidal transformers are used throughout.  I shall be using Merlin Blencowe's grounding plan for this project.

(http://i1110.photobucket.com/albums/h448/DBPendrill/EF85-5_zpsaonrhjqz.jpg) (http://s1110.photobucket.com/user/DBPendrill/media/EF85-5_zpsaonrhjqz.jpg.html)

The protective layer is kept on as long as possible.

There are 9 tubes and 7 transformers to fit in.

A little bit about the design.
It works like a smaller Fairchild and should have the same speed but with more variable timings for today's music.
It makes use of tubes at the pinnacle of tube development around 1960, especially high performance TV tubes.
The signal has only one capacitor in each half cycle and is not subject to feedback.  It could probably be direct coupled throughout, but slight imbalance could put DC through the primary so I opted to leave the caps.  I have gone for a tube regulator for ruggedness in the prototype, but if you are happy with silicon then you could use that.  But I have used the very latest Schottky diodes to rectify the heater supplies, they have around 0.3V Vf depending on temperature.  They are operated without heatsinks due to the very low load loading.  One supply is elevated to 140V to help the reliability of the regulator and the cathode followers.

Best
DaveP

Title: Re: EF85 Compressor from scratch
Post by: thomasdf on July 25, 2016, 05:44:54 AM
As usual Dave, I am AMAZED by your builds...! Next timing you will have to mold your knobs and craft your tubes to raise the bar a bit higher :)
Title: Re: EF85 Compressor from scratch
Post by: DaveP on July 30, 2016, 02:56:46 PM
Thanks Thomas,

I have not been up to any more work on the project as I am into my third week of bronchitis and I feel lousy.

All I have been able to do is ruffle a few feathers on the Brewery ::)

I am seeing the doctor on tuesday so maybe he will give me some antibiotics as it must be past the viral stage now.

Best
DaveP
Title: Re: EF85 Compressor from scratch
Post by: rock soderstrom on July 30, 2016, 03:11:31 PM
Arrgh, three weeks of bronchitis is not good... :( Get well, soon! Thorsten
Title: Re: EF85 Compressor from scratch
Post by: Winston O'Boogie on August 10, 2016, 04:38:00 PM
Hope your health is improved, take care Dave.
Title: Re: EF85 Compressor from scratch
Post by: DaveP on August 10, 2016, 04:51:08 PM
I managed to screw up my doctors appointment last week because I misheard the time the receptionist said (in French), I should have been there at 11.15 but I only caught the 15 and turned up when the doctors was shut at 3pm!!  Dickhead!

So I didn't get my antibiotics until a new appointment this monday and I'm only starting to feel a bit better today.  If this happens  to people in the near future when all the antibiotics are useless we will just die I guess.

Anyway, I have not been totally idle, I have been moving components around to finalise the layout.

Thanks for your concern

best
DaveP
Title: Re: EF85 Compressor from scratch
Post by: DaveP 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

Title: Re: EF85 Compressor from scratch
Post by: tommypiper 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.
Title: Re: EF85 Compressor from scratch
Post by: DaveP 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
Title: Re: EF85 Compressor from scratch
Post by: tommypiper 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
Title: Re: EF85 Compressor from scratch
Post by: DaveP 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
Title: Re: EF85 Compressor from scratch
Post by: DaveP 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.

(http://i66.tinypic.com/3329yfr.jpg)
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


Title: Re: EF85 Compressor from scratch
Post by: shabtek on July 02, 2018, 05:02:58 PM
looking forward to more high caliber design work
Title: Re: EF85 Compressor from scratch
Post by: Dmichel123 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?
Title: Re: EF85 Compressor from scratch
Post by: alexc 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 :)
Title: Re: EF85 Compressor from scratch
Post by: DaveP 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
Title: Re: EF85 Compressor from scratch
Post by: scott2000 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
Title: Re: EF85 Compressor from scratch
Post by: DaveP 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.

(http://i67.tinypic.com/b5r9eh.jpg)

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
Title: Re: EF85 Compressor from scratch
Post by: DaveP 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.

(http://i65.tinypic.com/2rhshew.jpg)

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

DaveP
Title: Re: EF85 Compressor from scratch
Post by: DaveP on August 27, 2018, 03:44:21 PM
The build has started!

I have made the power supply section in two halves.

(http://i64.tinypic.com/sdfkft.jpg)

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

(http://i65.tinypic.com/65a82q.jpg)

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.

(http://i65.tinypic.com/xmiqs8.jpg)

This is how they will be orientated.

All for now
DaveP
Title: Re: EF85 Compressor from scratch
Post by: dustbro on August 28, 2018, 12:46:11 PM
Nice!! Can't wait to see this one complete
Title: Re: EF85 Compressor from scratch
Post by: DaveP on September 05, 2018, 05:03:25 AM
Thanks Dan :)

The power supply section box is now finished.

(http://i63.tinypic.com/1zbyrzs.jpg)

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

(http://i63.tinypic.com/ayu3xj.jpg)

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

Title: Re: EF85 Compressor from scratch
Post by: letterbeacon 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?
Title: Re: EF85 Compressor from scratch
Post by: DaveP 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.
Title: Re: EF85 Compressor from scratch
Post by: mjrippe 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.
Title: Re: EF85 Compressor from scratch
Post by: letterbeacon on September 06, 2018, 05:47:30 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.

Thanks Dave. My metal-working skills leave a lot to be desired so this is very useful to know.
Title: Re: EF85 Compressor from scratch
Post by: DaveP on September 09, 2018, 05:26:55 PM
Got on well with it today.

The main part of the chassis is finished and major parts fitted.

(http://i64.tinypic.com/mcb6f7.jpg)

I made the RH side panel to keep it all rigid and attached the left side of the power supply section.

All the tubes seem to fit in OK along with some 15k:600 OPT's.

There  are three sections on that chassis, regulated power supply, Compressor amp and feed forward side chain amp.

(http://i65.tinypic.com/do19h4.jpg)

Next job is to sort out the earth busbar and the the tube heater supplies.  I will then be able to run the heater supply to the tubes and determine the value of the Al clad dropper resistor.  This has to be fitted before I can fit the rest of the power supply together.

All for now

DaveP
Title: Re: EF85 Compressor from scratch
Post by: L´Andratté on September 10, 2018, 05:15:06 AM
Thanks Dave. My metal-working skills leave a lot to be desired so this is very useful to know.

+1
I am planning out construction of my first real tube preamps (two of ruffrecord´s Classic Solo but  without pcb). I want to make them as old school as possible (except the rectifiers), so I have the search engine running hot on DaveP threads... ;D

Sorry for OT:
Are those Danbury transformers? Is it possible to get these screw-on shields somewhere? I use one for power supply and already know there will be hum if I go internal supply (preferred but not decided) and those should help a bit, right?



Title: Re: EF85 Compressor from scratch
Post by: DaveP on September 10, 2018, 11:17:10 AM
Quote
I want to make them as old school as possible
Well watch the next few posts carefully.

Quote
Are those Danbury transformers?
Yes, they were made especially for me by the guys who used to be at Danbury transformers.  They are not power transformers.

They were designed to be shielded input transformers and those covers were the smallest they could find.  But they are so beefy, it's possibly to use them as push-pull output transformers for 6SN7 type tubes.

Regarding your project, use toroidal transformers wherever possible, oriented with their axis at 90 degrees from other transformers and you should be OK.  Older "EI" transformers should be avoided  with "in the box power supplies", no-one wants vintage hum levels in the cause of authenticity.  Some old vintage designs have S:N levels of only -45dB.  No need to use a choke any more when you can get 12000 hour 180uF  or more caps.

Good luck
DaveP
Title: Re: EF85 Compressor from scratch
Post by: DaveP on September 13, 2018, 02:05:15 PM
The earth busbar is now finished and in place and so is the DC heater wiring.  You don't have to worry about wire dress like you do with ac twisted pairs.

(http://i66.tinypic.com/16iup21.jpg)

I have also fitted lots of Tag strips, you can't really calculate beforehand how many will be required, so best to make sure there are plenty spare to give you the most options for the layout.

(http://i63.tinypic.com/332ron6.jpg)

The 12 tubes seem to fit OK, I used B7G pentodes to save space, along with a 6AL5 and a 5651  voltage neon.

I will wire up the input socket before I fit the input transformers.

Now to light em up!

DaveP

Title: Re: EF85 Compressor from scratch
Post by: frederickalonso on September 13, 2018, 10:11:31 PM
Just WOW, respect!  :o
Title: Re: EF85 Compressor from scratch
Post by: EmRR on September 13, 2018, 11:03:50 PM
Looking good Dave!
Title: Re: EF85 Compressor from scratch
Post by: zamproject on September 15, 2018, 07:46:32 AM
As usual... f...ing impressive .

Best
Zam
Title: Re: EF85 Compressor from scratch
Post by: DaveP on September 15, 2018, 06:34:24 PM
I appreciate the support especially as some of you in NC have more important things to worry about :(

I fitted the heater dropper to give the tubes 6.3V @ 4.4 A, then I was able to connect up the other half of the power supply.

The chassis is now complete bar the faceplate.

(http://i66.tinypic.com/s6tye1.jpg)

The input is now wired so I fitted the Edcor IPT's,  the balance pot and the voltage regulator pot.

(http://i67.tinypic.com/67tfgl.jpg)

This compressor is designed for line level, so there is no step-up in the IPT's, they being 15k:15k.  I used this particular TX because the frequency response is flat, some of Edcor's other types have peaks in the top end which will probably make them ring.  As you can see, this one is pretty flat where it needs to be.

(http://i68.tinypic.com/4lred3.jpg)

I can now start adding the components and working out the layout.  Maybe I should say that this is an experimental design and I have no guarantee it's going to work as feed-forward, the side-chain will need careful balancing against the control amp. ???

Best
DaveP
Title: Re: EF85 Compressor from scratch
Post by: scott2000 on September 15, 2018, 07:32:01 PM
Looks amazing!! Can't wait to see how it turns out and if you make any changes along the way............

What is the metal box in the top of the power supply in the pic ????
Title: Re: EF85 Compressor from scratch
Post by: zamproject on September 15, 2018, 07:45:40 PM
What is the metal box in the top of the power supply in the pic ????

EMI/RFI line filter at main AC input.

Best
Zam
Title: Re: EF85 Compressor from scratch
Post by: DaveP on September 20, 2018, 04:36:40 PM
Here are some half-way through pics to give an idea of the point to point technique.  It's easier to mount components on turret boards, but you get much more connecting wiring with that method, which I don't like personally.  I like to keep wiring as short as possible in sensitive areas like input grids.

(http://i65.tinypic.com/25tkpyd.jpg)

It looks like chaos but the lead wires of each part are carefully bent and placed in this close-up.

(http://i63.tinypic.com/2qnphcp.jpg)

Looks better from this angle, I rarely do more than 2 hours in one sitting as you start making stupid mistakes.  It's a bit like a painting or a drawing, or a mix for that matter, much better to look at it with fresh eyes/ears the next day.

(http://i64.tinypic.com/rwjrwl.jpg)

This is how I avoid mistakes and mis-wires, I go over the schematic with a marker after each soldering.

Most of the sections left to do are on the front panel.

On the subject of soldering:  I use a 40W iron and wipe the tip clean on brass swarf in a pot before every soldering.  You never get a dry joint that way.

DaveP

Title: Re: EF85 Compressor from scratch
Post by: scott2000 on September 20, 2018, 04:48:45 PM
Wow..... I guess I knew it would be busy but this puts it in more perspective for sure! Nice!

What's that orange thing by the transformers???
Title: Re: EF85 Compressor from scratch
Post by: DaveP on September 20, 2018, 05:13:02 PM
It's a wire-wound 100 ohm pot used to balance the current of the EF85's.

It's not connected yet.

DaveP
Title: Re: EF85 Compressor from scratch
Post by: DaveP on September 30, 2018, 05:59:59 PM
I had it all wired up ready to go....................then smoke!  then Off quickly.
Just in case anyone thinks I'm smarter than I actually am.............HT input cap wired back to front.

Said cap swollen and about to burst.
(http://i65.tinypic.com/1z6rtki.jpg)

Any way, soon fixed and a salutary lesson to take more care.

All the components are now in place and voltages correct.

(http://i65.tinypic.com/ibick1.jpg)

The dropper resistors turned out to be 680 ohms and 560ohms, they are rated at 7 watts but the first one  emits 3 Watts, I'm not sure I want that amount of heat cooking the rest of the amp.  I will try to replace it with a chassis mounted Al clad type if I can.

Now the faceplate...............

DaveP
Title: Re: EF85 Compressor from scratch
Post by: scott2000 on September 30, 2018, 06:44:37 PM
Awesome! So weird I was just looking around several minutes ago and saw an old Hammond AO-33? chassis and thought of your project....It had 12 sockets exactly..... except only two of the 12 were 7pin.......the rest 9pin....


Congrats on the power up!!! Looks magnificent!!!!
Title: Re: EF85 Compressor from scratch
Post by: DaveP on October 05, 2018, 09:54:50 AM
I've finished modifying the Meter.

It started off like the one on the left, just an ordinary 1mA meter.

(https://preview.ibb.co/gtuAOe/Meters.jpg)

I removed the cover and the faceplate veeery carefully and scanned it into MS Paint on 300dpi resolution.

I also carefully removed the white paper under the mechanism.

Then I drew the new markers and erased the old numbers.  I used the DIN numbers that I had previously copied into Word.

This is where Paint shows up problems....It crashes!

The only way around the problem is to save your work after every action, otherwise it exhausts its memory.

When it was done I adjusted it to the correct size and printed it on buff paper.

I sanded off the original paint and used almost dry PVA glue to fix the new one on.

DaveP

Title: Re: EF85 Compressor from scratch
Post by: DaveP on October 05, 2018, 11:57:42 AM
Photobucket and Tinypics have gone off line, hence no other pics

DaveP
Title: Re: EF85 Compressor from scratch
Post by: DaveP on October 28, 2018, 04:44:15 PM
Finally finished the front panel

(http://i64.tinypic.com/opd55g.jpg)

This uses the same timings the forum agreed back when I made the GroupDIY 26C

I went to order more Letraset, only to find they have gone out of business!

I think I will have to get something similar from the US, from now on.

Now I only have to fit the front and make the base cover.

DaveP
Title: Re: EF85 Compressor from scratch
Post by: scott2000 on October 28, 2018, 05:14:20 PM
Woah...Nice ! Matches your monitors......
Title: Re: EF85 Compressor from scratch
Post by: scott2000 on November 16, 2018, 01:10:39 PM
Hi! Hope the build is going well in the home stretch!

May I ask what are these black wraps around the caps??? is it some specific holder??? or something else diy???

Thanks!!
Title: Re: EF85 Compressor from scratch
Post by: DaveP on November 16, 2018, 03:58:48 PM
Hi Scott,

Sometimes my time is not my own....you're married right?  Still lots to do renovating the house!

They are 18mm plastic cap clips from Farnell/Newark. Part no. 146-096

Best
DaveP

Title: Re: EF85 Compressor from scratch
Post by: scott2000 on November 16, 2018, 04:10:04 PM
...Yes married.....Broke the decade mark a few years ago ......

Actually cleaning up my garage in a minute and my chores will be done for today...... ;D

///scratch that....just remembered a couple of other things...lol

Thanks for the part! Looks better than 2 sided tape I've been using I  have to say :-[
Title: Re: EF85 Compressor from scratch
Post by: DaveP on December 08, 2018, 06:00:37 AM
I have an order for another V241-76 mic-pre, so I will have to take a break on this project for a couple of months.

Thanks for your interest and support and I promise it will be finished asap.

Best
DaveP