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Project Specific Discussions => Dynamic Processors => Topic started by: synthi on November 29, 2005, 08:12:16 AM

Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on November 29, 2005, 08:12:16 AM
Hi People!
I just scored this beauty:
(http://img.photobucket.com/albums/v321/synthi/Chiswick%20compressor/vk1-comp_3.jpg)

It´s a very early VK1 compressor, Serial #14. I`ve told this design is based in the altec (emi) compressor.
The tubes are:
1x 5AR4
2x 12AT7
2x 6BZ7
2x 6AL5

I need to revalve and adjust the unit, the channels are not matched and the tubes about to die... just changed the 12AT7s (the only tubes I had) with a matched pair the channels are more equal in gain, but I`ll need to replace all the tubes.

the 5AR4 is the rectifier, no problem, the 6AL5s I think are sidechain rectifiers (?) and the 6BZ7 the variable mu tube :?:

I want to get a pair of matched pair for each but nobody seems to sell matched pairs of those, so:
-Can anyone sell me a matched pair?
-Or... I could get some of each (10-15) but what values must I look for match the vari-mu tubes (and rectifiers)?

Here is a link to the new compressor manual (almost the same thing, different trafos):
http://www.jivelive.com/chiswickreach/assets/images/manual2.pdf

Now here is some p*rn, the circuit is all point-to-point and seems simple enought to be useful from the photos:
(http://img.photobucket.com/albums/v321/synthi/Chiswick%20compressor/VK1-front.jpg)
(http://img.photobucket.com/albums/v321/synthi/Chiswick%20compressor/VK1-rear.jpg)
(http://img.photobucket.com/albums/v321/synthi/Chiswick%20compressor/VK1-bottom1.jpg)
(http://img.photobucket.com/albums/v321/synthi/Chiswick%20compressor/VK1-bottom2.jpg)
(http://img.photobucket.com/albums/v321/synthi/Chiswick%20compressor/VK1-detail.jpg)

Thanks!

Synthi.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: on November 29, 2005, 08:27:33 AM
Blimey - check out that tag board
Interview with VK
http://www.soundonsound.com/sos/jun04/articles/vickeary.htm
Original review
http://www.soundonsound.com/sos/feb00/articles/chiswick.htm
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on November 29, 2005, 09:02:59 AM
:shock:  So the phoenix is based  on the chi*wik! And also Vic Keary was the designer for my unit :)

I`ve found more info here:

http://www.thermionicculture.com/reviews/review_monitor_phoenix.htm

The 6BZ7 used in my unit seems to be a replacement for the original 6BQ7A, so I`m gong for a matched pair of the 6BQ7As. What about changing to PCC85 as mentioned in the article? is a direct sub?

Thanks!

Synthi.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: Viitalahde on November 29, 2005, 10:36:37 AM
Dare I say?

REVERSE

ENGINEERING

WANTED!!!

 :grin:  :grin:  :grin:

Nice photos!
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on November 29, 2005, 10:46:20 AM
hehehe :grin:

If anyone is going to R-Eng I can provide detailed photos at your request!
 :cool:

Thanks,

Synthi.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: on November 29, 2005, 12:02:53 PM
From that SoS Review
The Phoenix was the first of Thermionic Culture's products, and its design derives in part from the Altec 436 'vari-mu' compressor. This used 6BC8 triodes in a balanced (push-pull) configuration, but produced what Vic felt was unacceptably high distortion, so he improved the design during his time at Chiswick Reach, and it became known as the Chiswick Reach compressor (reviewed in SOS in February 2000; see www.soundonsound.com/sos/feb00/articles/chiswick.htm). However, the noise floor was still not as low as Vic wanted, and further development eventually resulted in Thermionic Culture's Phoenix compressor (see www.soundonsound.com/sos/apr00/articles/phoenix.htm). Some of the noise-floor improvement came from changes to the power supply, but some also came from a redesigned front-end which used a PCC85 valve instead of the Chiswick Reach's 6BQ7A. The PCC85 tube was designed for FM radio applications and hasn't been used in an audio application before; it requires an unusual 9V heater supply. However, all these cumulative changes brought the overall noise figure below -100dB, improved distortion further to 0.1 percent, and enhanced the general reliability of the compressor. Vic also improved the machine's flexibility and performance over the Chiswick Reach design with faster attack and release times. As this history shows, Vic is an inveterate tweaker, and still feels there are advances to be made with valve technology. He is currently experimenting with a different output valve for the Phoenix.

Title: Another vari-mu: Chiswik Reach Compressor
Post by: rafafredd on November 29, 2005, 11:08:53 PM
Quote
If anyone is going to R-Eng I can provide detailed photos at your request!


Man, it looks easy!

Come on!
Title: Another vari-mu: Chiswik Reach Compressor
Post by: CJ on November 30, 2005, 12:08:17 AM
Holy Cow I just threw out about ten of those BQ7's because I had so many of them!  Or was it BK7?

Also, 6AL5's out the wazoo, but Spain pays the shipping.

Andy is trying to get a socket that fits so he is cleaning out the house.

Dude, it's like, I couldn't see out the back window. I bought an HS-29 and a WeCo 111C and he "threw in" over 1000 tubes, in the boxes, yo.
 :thumb:

Don't feel sorry for Andy, his place looks the same, even after 5 or 6 carloads of stuff taken out. Barley even put a dent into that place. If there was a drive by, they would never find the bullets!
Title: Another vari-mu: Chiswik Reach Compressor
Post by: NewYorkDave on November 30, 2005, 09:24:48 AM
Too bad about those 6BQ7/6BZ7s: they're good for cascode amps--and so are 6BK7s, as a matter of fact. Let me know if you need to get rid of any more :wink:
Title: Another vari-mu: Chiswik Reach Compressor
Post by: ciminosound on November 30, 2005, 09:35:52 AM
It would be great to see the schematic for this. I have a bunch of the BC8, Bq7, Bz7. (They are listed as subs for each other in most books)

Curious about the Pcc85 though.  Isn't that a different heater Ecc*85? Ecc*85/ 6*A*Q*8? This tube type has been used in audio quite a bit.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: gyraf on November 30, 2005, 09:47:20 AM
I suspect that the tubes are the least esoteric things about this piece. I count at least five transformers / inductors.

Other than that, it looks pretty much like the prototype for my G10..  :razz:

Jakob E.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on November 30, 2005, 09:52:12 AM
There are 2 input and 2 output trafos, a mains trafo and the smaller one near the mains may be a 6.3V trafo?

Synthi.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: on November 30, 2005, 10:57:03 AM
I found this interesting...
The gain-reduction meters are not just VU meters modified for the task, but actually show the cathode current of the 6BQ7 gain-controlling valve. As the performance of these valves alters with age, it becomes necessary to trim the meter circuit, for which purpose a pair of electronic zeroing trimmers has been provided in the centre of the front panel

Transformer detail


substantial custom-designed devices, which apparently won't saturate below +24dBu, suffer only one degree phase error between 10Hz and 25kHz, and exhibit -3dB points only at 4Hz and 35kHz. Impressive beasts indeed, and fully shielded with mu-metal
published specifications quote distortion as better than 0.08 percent with +8dBu input level and 5dB of compression

And found this nice comment

Sowter transformers are used throughout Thermionic Culture's products ? both for audio and mains
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on November 30, 2005, 11:04:14 AM
Does anyoneone the contact info for the thermionic culture technical service or Vic himself?
in the website the only email is for the distributor...

Synthi.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: NewYorkDave on November 30, 2005, 11:05:30 AM
Quote

The gain-reduction meters are not just VU meters modified for the task, but actually show the cathode current of the 6BQ7 gain-controlling valve.


Big deal. That's how it's almost always done in "vari-mu" compressors.

Quote

substantial custom-designed devices, which apparently won't saturate below +24dBu, suffer only one degree phase error between 10Hz and 25kHz, and exhibit -3dB points only at 4Hz and 35kHz. Impressive beasts indeed, and fully shielded with mu-metal


Except for the mu-metal shielding, a $9 Edcor can meet those specs--at least in terms of maximum level and frequency response. I'm suspicious of that quoted phase shift figure, unless the xfmr was tested under some pretty un-realistic conditions.

I'm sure it's a fine compressor, and I'm not trying to piss on anyone's parade, but don't make the mistake of thinking that any given set of specs are remarkable just because the copy-writer wants you to believe that they are :wink:
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on November 30, 2005, 11:14:30 AM
Quote
Except for the mu-metal shielding, a $9 Edcor can meet those specs--at least in terms of maximum level and frequency response.

I'm sure it's a fine compressor, and I'm not trying to piss on anyone's parade, but don't make the mistake of thinking that these specs are remarkable just because the copy-writer wants you to believe that they are


Yes, I know, but the question is that would be a good vari-mu and seems to be easy enought to clone... or even improve!

Synthi.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: gyraf on January 04, 2006, 04:10:37 AM
Nice drawing, Olaf!!

 :thumb:

Jakob E.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: t-wurst on January 04, 2006, 04:42:18 AM
Just read this topic and my first thought was "Oh, looks like the Phoenix"!
Reading further this thought was proofed - funny  :grin:

I made some shots while Mr. Brauner himself (you know, this german microfone-guy) put his Weller-Iron in our Phoenix to change a defective switch. Try to upload these pictures soon. They´re using SOWTER xformer and Siemens Valves and the same "easy" point to point wiring - and the same housing...

Post pics soon
Title: Another vari-mu: Chiswik Reach Compressor
Post by: chrissugar on January 04, 2006, 05:36:33 AM
Are you sure the output transformer is 9745?
I looked at Sowter for this transformer and it looks totally diferent. I compared the 9745 pic with the third pic in your first post.

chrissugar
Title: Another vari-mu: Chiswik Reach Compressor
Post by: chrissugar on January 04, 2006, 05:47:04 AM
OK, now I'm confused.
If I do a search on the Sowter page it gives diferent picture, but if i look for the 9745 at "PRO VINTAGE" it looks like the transformer is an M6 with U clamp (like in your pictures).
Probably the picture at Sowter in search mode is wrong.

chrissugar
Title: Another vari-mu: Chiswik Reach Compressor
Post by: Viitalahde on January 04, 2006, 06:00:43 AM
Yep, nice drawing. Thanks!  :thumb:
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on January 04, 2006, 06:37:10 AM
Yes!  Thanks Olaf.

I just made some more hi-res closeup photos and spoted a couple of values, the Olaf work is great.

What I`m not sure about is the input transformer, I was told than in early version they used a small trafo (and seems to be the case with my VK1) that distorted with hi level signals.
If I send a 1Khz to at 0dBFS (+22dBm), with the input att engaged (-10dB) I need to set the gain pot (an attenuattor really, right??) past "6" I got nasty distortion, So with a quick calculations the thing is distorting with a +8dBm signal or so.
I think they used the 3575 in later units, so I think would be a good idea changing the original trafos with them...

Also, the input attenuation would be improved, any clues?

Also Looking to see your phoenix photos!

Thanks!

Synthi.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on January 04, 2006, 09:48:18 AM
I just emailed sowter support about the input trafos for the chiswick. I`m pretty sure the input trafo in mine is not a 3575, maybe same ratio but inferior specs ordered as a custom job for early works, and then sowter comes with the improved 3575 and they are using it now.

Would be interesting to know what trafos are used in the phoenix too.

I`ll let you know when I get a reply from Sowter...

Best Regards,

Synthi.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthpunk on January 04, 2006, 03:39:56 PM
the vk1 stopped using sowters years ago... they were replaced with massive, much higher quality ones, i think possibly sourced from Stevens and Billington.anything with sowters in it is either a prototype or so early as makes no difference- we were learning from every one we built!  the circuit linked to above must be an early one,  cos it is definitely different now... and its no longer true point to point- theyre now built on 'voyager board' - the dual row, 36 tag phenolic board from RS that the voyager space probe was built on.... the horrible birds nest point to point style was used on the first dozen or so.....

i know this cos i used to build vk1's when they were made in chiswick, after vic left, and before they started getting them built elsewhere.

i agree that it is a very pretty drawing! its nice to finally see it out there, ive been sitting on the schem for years, but i promised nigel (the guy who owns CR) that id never give it to anyone else...

a fine piece of reverse engineering! well done, olafmatt..

cheers,

rrrrich
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on January 04, 2006, 05:52:32 PM
Hi Synthpunk,

CW used the sowter for a bit more than a dozen for sure... Mine is #14  :wink:
Are they now using different output trafo or just changed the input? I think I read somewhere just the input trafo was upgraded...
Also, can you remember the specs and ratios for the trafos used in later revisions, Also, do you remember what was changed in later revisions? You know I`d like to upgrade mine...

Thanks,

Synthi.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on January 06, 2006, 08:36:40 AM
Hi People.

I did some research about the Vk1:

I emailed sowter about the trafos and they are really helpful! Brian Sowter spoke with Vic about the VK1, great. :grin:

Brian told they was dicussing about the saturation and the new trafos would be an improvement , but not a  solution... I know understand why:

I was checking the vk1 scheno vs the Altec and they are very similar. The VK1 is having the same behaviour than the Altec 436C, the stock -10dB pad is no enought for hot signals, and the output is really hot,  so I`m planning to add a 600omh stepped attenuator at the input and output. One of the things used in the pheonix compressor and later Chiswik models is having switchable 3 position pads for inputs and outputs, I think for correcting this.

Also looking how the input gain is implemented in the 436C and the Chiswik, the altec have the dual 50K pot before the trafo, but the vk1 have the dual 47K pot AFTER the trafo. It seems to be very crude in both designs, I`d like to have more precise gain control. Is there a more elegant solution than using dual pots here? NYD? CJ?

Thanks!

Synthi
Title: Another vari-mu: Chiswik Reach Compressor
Post by: Joechris on January 06, 2006, 09:04:48 AM
The Altec pot is also after the trafo. Use a resistor string pad instead.
Look at Davids Altec mod thread somewhere.
This is a great calculator:
http://homepages.tcp.co.uk/~nroberts/atten.html
jo
Title: Another vari-mu: Chiswik Reach Compressor
Post by: Joechris on January 06, 2006, 09:26:31 AM
So with a 2pole 12 way rotary, it could look like these.

Step 1, Attenuation = Infinity dB, Rx = 50000 ohms, Ry = 0 ohms, Resistor = 0 ohms.
Step 2, Attenuation = 35 dB, Rx = 49111 ohms, Ry = 889 ohms, Resistor = 889 ohms.
Step 3, Attenuation = 28 dB, Rx = 48009 ohms, Ry = 1991 ohms, Resistor = 1102 ohms.
Step 4, Attenuation = 24 dB, Rx = 46845 ohms, Ry = 3155 ohms, Resistor = 1164 ohms.
Step 5, Attenuation = 21 dB, Rx = 45544 ohms, Ry = 4456 ohms, Resistor = 1301 ohms.
Step 6, Attenuation = 18 dB, Rx = 43705 ohms, Ry = 6295 ohms, Resistor = 1839 ohms.
Step 7, Attenuation = 15 dB, Rx = 41109 ohms, Ry = 8891 ohms, Resistor = 2596 ohms.
Step 8, Attenuation = 12 dB, Rx = 37441 ohms, Ry = 12559 ohms, Resistor = 3668 ohms.
Step 9, Attenuation = 9 dB, Rx = 32259 ohms, Ry = 17741 ohms, Resistor = 5182 ohms.
Step 10, Attenuation = 6 dB, Rx = 24941 ohms, Ry = 25059 ohms, Resistor = 7318 ohms.
Step 11, Attenuation = 3 dB, Rx = 14603 ohms, Ry = 35397 ohms, Resistor = 10338 ohms.
Step 12, Attenuation = 0 dB, Rx = 0 ohms, Ry = 50000 ohms, Resistor = 14603 ohms.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on January 06, 2006, 11:00:43 AM
sorry I reversed the facts: the altec pot is after the trafo and the vk1 is before the trafo  :wink:

So I`m thinking now: input signal-->stepped attenuator-->variable T attenuator would be the solution?

ITOH, Thanks for the link for the calculator!

I see you post values for a 50K attenuator , its better than using 600ohm for both inputs and outputs?

Also I think I`ll need Balanced stepped attenuators and balanced variable T attenuator, right?

Thanks a lot friends!

Synthi.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on January 06, 2006, 11:56:56 AM
I think the output attenuator was in off position, but I`ll do some quick tests again....

More on this later today...

Synthi.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on January 06, 2006, 01:56:23 PM
Ok, tested:
 
Now I know the facts about the altec 436 operation, I`m feeding the unit with a -22dBFS (no pad) and -12dBFS (padded) and is working as it must.
I must pad the output at certain settings because it will over my AD sometimes, lot of gain inside really...
 
With an input at -22dBFS (0dBm), no pads, release to slowest, attack to fastest and threshold to "1" (minimun) I get unity gain with input level control at "3" (marked 1 to 11) and I get a digital over when level at " 9.8" but output is distorting when the level pot past "6" (about -6dBFS at the AD, compression meter reads -3.5dB compression). Now the funny part: If  I switch the OUTPUT pad "on", then I can go thru the entire range up to "11" without the distortion... (level "11": -11dBFS at AD, comprression 10dB)  
 
I`m using Apogee DA16--->VK1--->Mytek AD, all is calibrated and I tested: conecting the DA16--->Mytek AD, the ad converter is not distorting up to -0.04dBFS out from the DA16, so the AD is not overloading for sure. I`m using the RME digicheck for checking the inputs at the AD.
 
Its strange (at least for me) that the distortion goes by when I switched the output pad now that is clear that is not the AD who is distorting, so I think It could have something to do with output impedance being "better" when switching the output pad?
Also I noticed some phase isues, I think that would be becuase the input pots having variable impedance and the way attenuators are implemented... (?)
 
Also I have some thoughts about the best values for attenuation:
input attenuator: -22dB, for having a 0dBFS signal into 0dBm optimal operating level, or better having several values: -30 (for using the compressor as gain amplifier for coloring without compression) -22dB and -8dB for prosumer gear.
 
output attenuator: here the most steps the better for precise control, 6 steps is ok for interfacing with the AD or Professional gear. Seeing my tests, having 6dB attenuation would be enought for gear acepting +22dB signals, so 1 to 6 dB attenuation would be great, a better option would be 12 steps between 1 to 8dBs since some called pro gear can handle +20 max.
 
What do you think about this?

Synthi
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthpunk on January 06, 2006, 03:47:30 PM
both input and output TX's were changed- the new ones are about the size of a grapefruit, so a good deal bigger than the lychee sized original....

the original ones distorted on the low end, thats why they were changed.

and yer right, the first 20-30 or so had little tx's, not the first dozen.... if i remember right, i started building em from about number 18ish, till about number 30 ish, as a summer job between the 2nd and 3rd year of uni in the summer of 97..all the ones i built had little sowter tx's... some time after that they started being made out of house, somewhere in holloway rd, london.. i think they must have changed the trafos around the same time... chiswick reach studios themselves closed down in '99/2000, so its only the compressors left nowadays.. shame, it was a great place to record, and work, too!....

the output attenuator was also changed on the later ones, with more attenuation settings..


rrrrrrrrrrich

ps
Title: Another vari-mu: Chiswik Reach Compressor
Post by: NewYorkDave on January 06, 2006, 04:00:31 PM
It gets awfully confusing when you mix dBFS and dBM together like that, especially since everyone seems to have his own idea of how many dBM (or dBU) equals 0dBFS. The practice I follow is maximum level=20dB above standard operating level, therefore 0dBFS=+24dBM where S.O.L. equals +4dBM. But I know that there are others who only consider 18dB of headroom to be necessary, instead of 20.

I recommend that for the purposes of this discussion, since we're talking about an analog device, we stick to dBM (or dBU if you prefer).
Title: Another vari-mu: Chiswik Reach Compressor
Post by: Larrchild on January 06, 2006, 04:56:19 PM
To add to the confusion, the headroom @50 hz is different than the 20 hz spec. Sowter's site says to subtract some db's @ 20 hz.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on January 06, 2006, 05:12:15 PM
Quote
The practice I follow is maximum level=20dB above standard operating level, therefore 0dBFS=+24dBM where S.O.L. equals +4dBM. But I know that there are others who only consider 18dB of headroom to be necessary, instead of 20.



I know lot of people from USA use the smpte standard of 0dBFS=+24dBM , we EU people mostly use 0dBFS=+22dBM

Sorry if if its confusing....

Synthi
Title: Another vari-mu: Chiswik Reach Compressor
Post by: Lukpio on January 06, 2006, 08:03:28 PM
BTW if I remember correctly, ADATs used +18dBu as 0dBFS and old Mitsubishi digital multitracks used +19dBu=0dBFS.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: bernbrue on January 20, 2007, 04:17:01 AM
Hi Synhi,
I followed this thread for a quite long time now and I think the VK1 could be a very good DIY project. Here are a few questions:

Did you manage to repair and setup your VK1?
Is the schematic that was published here correct, does it work?
Have you got further information of this beast?

Maybe we can start a nice DIY project out of it. Frank (nrgrecording) has already made a pcb layout from your schematics. I'm just making a BOM for this project.

Regards
Bernd
Title: Another vari-mu: Chiswik Reach Compressor
Post by: bernbrue on January 20, 2007, 05:43:12 AM
Hi Olaf,
I would like to invite you to our German forum. You may contribute a few things to our thread. Look here please:
http://techtalk.te.funpic.de/index.php?topic=166

See you
Bernd
Title: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 20, 2007, 06:26:42 AM
I currently fiddling with this circuits 6AL5 side chain adding it to a BA6A, its working nice giving me more control over the limiting.

Question what is the thumps switch meant to do ??????????????
Is that switch on one of the pots ????? and why ????????


Thanks people........................Gary O.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: synthi on January 20, 2007, 07:13:32 AM
hi Bernbrue,

Yes, I have my vk1 woring, and sound awesome!

I was driving the unit too hard, lower levels ans all is fine. This is because the trafos used, later they changed the trafos for hotter levels, but I`m also recording lower levels now so is not a problem anymore...

Also as olaf pointed, they changed the tubes to ecc85.

I kweep mine unmodded but would be great DIYing another one for playing with.

The thump switch engage a very slow attack, usefull for percussive sounds.

I`m sorry I can read german so would be great if you can move the Vk compressor here again!

Hare you planning to fab the PCBs? NGR where are u!? :thumb:

Synthi
Title: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 20, 2007, 08:58:11 AM
Thanks for the thump explanation I have increased the attack pot value on my version, it seems to be giving me that slower attack without the switch.Im experimenting with the CCA Electronics LA1D side chain circuit

IV added the 100K pot from the LA1D to give me a kinda ratio/threshold thing seems to do similar job as the daul 47K pot in the chiswick,its hard to tell as I have all the side chain stuff breadboarded across my desk with wires running into BA6A limiter, I might leave out the threshold daul 47K pot from the Chiswick out after further tests, Im also gonna have a switch to choose between Chiswicks variable control and BA6A s Daul release time.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 20, 2007, 10:14:30 AM
Thanks Olaf, this is all so interesting Im not very good with even basic electronics sometimes, I need to learn much, I think I can understand this tho, I also left out the 15K before the 68K would that give me slightly faster attack ??????
By the way I have now wired in the 6H6 Diode valve from the BA6A instead of 6AL5 and im feeding it from the the BA6As OD3 regulator valve via a 100K pot like in the LA1D

http://www.gyraf.dk/schematics/CCA_LA1D_Limiter.gif

Should I lower the attack pot back to original 220K then ????
how about 100K pot in place of the 68K thump resistor & the 15K ?????

By the way so far its all sounding rather good better control than original BA6A two releases but would like it to run best it can & also understand what each part is doing

many thanks.......................Gary O.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: [silent:arts] on October 08, 2007, 12:04:08 PM
I think there should be just one simple rule:
don't bother anyone with pm's or emails about projects.
everyone can ask questions in the forum if he has problems, but if someone shares he is not responsible for everyones problems in understanding the circuit or building it. that's it.

this said: I have build this compressor, and Olaf did a great job doing the reverse engineering and the PCB layout. :thumb:
bothered with the arguments he told us I understand why he decided to took all the documentation all off.

and: I understand it even more since I'm bothered with stupid questions via pm or email about projects I have build. ask in the threads, somebody will answer. if not, find the answer on your own.

that's it :!:
Title: Another vari-mu: Chiswik Reach Compressor
Post by: volta on October 08, 2007, 07:14:48 PM
Quote from: "[silent:arts
"]I think there should be just one simple rule:
don't bother anyone with pm's or emails about projects.

and: I understand it even more since I'm bothered with stupid questions via pm or email about projects I have build. ask in the threads, somebody will answer. if not, find the answer on your own.

that's it :!:


I have a better rule.
Don't post or share if you don't want to be "bothered with stupid questions " from us stupid DIY'ers here on this forum.
It's human nature to ask questions.
Who better to ask than the person posting the working project?
This forum is used for exchange of ideas and questions.
If you don't want to be open for "stupid questions" don't post.
Go open a company and sue us for posting your brilliant godlike works of art. :evil:
Title: Another vari-mu: Chiswik Reach Compressor
Post by: [silent:arts] on October 09, 2007, 04:35:32 AM
Quote from: "volta"
This forum is used for exchange of ideas and questions.
:thumb:
correct. ask in the forum so everybody can learn.
we would not see so much working GSSLs etc if all questions would have been alsked to Jakob in privacy.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: peterc on October 09, 2007, 04:54:16 AM
I have to agree with silentarts on this issue.

The number of silly questions one gets w.r.t a project is high, & I would say that 80% have already been discussed in previous posts.

It is always a pleasure to help out newbies but sometimes people are just really lazy & not willing to put in some effort. Not referring  to anyone in this thread, I've never dealt with any of you guys!

Peter
Title: Another vari-mu: Chiswik Reach Compressor
Post by: volta on October 09, 2007, 02:16:06 PM
Quote from: "kubi"
Honestly Volta, I don't see your point. What else are you asking for?
Today most of the people successfully finished their clones, the project is closed, the files removed. You are late.


Drop the condescending tone.
I haven't pm anyone about this project.It's the arrogance and lack of patients that's disturbing to me.Words like "bothered with stupid questions"
I don't think there is such a thing as a "stupid question" when you are trying to learn something.That's my point.
 
Early bird gets the worm.
Like they say in Russia,Owellski.....
Title: Another vari-mu: Chiswik Reach Compressor
Post by: jensenmann on October 09, 2007, 03:22:43 PM
Quote from: "volta"
Quote from: "[silent:arts
"]I think there should be just one simple rule:
don't bother anyone with pm's or emails about projects.

and: I understand it even more since I'm bothered with stupid questions via pm or email about projects I have build. ask in the threads, somebody will answer. if not, find the answer on your own.

that's it :!:


I have a better rule.
Don't post or share if you don't want to be "bothered with stupid questions " from us stupid DIY'ers here on this forum.
It's human nature to ask questions.
Who better to ask than the person posting the working project?
This forum is used for exchange of ideas and questions.
If you don't want to be open for "stupid questions" don't post.
Go open a company and sue us for posting your brilliant godlike works of art. :evil:


None of the initiators of the VK1 Project posted here because exactly this reaction was expected to happen. For that reason nobody can blame them for nothing. It was never intended that this project becomes public. Nobody wanted to share.

But for all of those who want a VK1 clone:
Get yourself a VK1, trace down the schematic, design a PCB, find out which iron to use, which meter to use, get your costom mainstrannie done, make up your mind how to calibrate that beast, build it, test it, enjoy it. It´s as simple as that.
Title: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on February 13, 2008, 04:46:26 PM
I was told by tube guru ECC85 is not vari mu ??? just had a google comes up as vari mu there as here too...ah well ..Iv just soldered up a version of this limiter birds nested it on tiny 6 by 5 inch piece of ali, borrowed a 1:4 input tran & OP tran from Sowter the one for a BA6A seems to be working well...goin to tart it up a bit then try other transformers I have


Thanks
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: SUPERMAGOO on December 13, 2008, 06:37:07 PM
   please reactivated this thread. was very interesting  :o. you have to be patient and always will be no stupid question. I did many stupid question  :'(
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: SKJGProject on October 11, 2009, 01:25:42 AM
another bump.....any chance for more details about the clone?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: penguin on October 11, 2009, 09:39:13 AM
ur email ?
EDIT: many request for this hidden info...

here is the link for download.. 7 days... 100 downloads...
zip file contains everything you need..

https://www.yousendit.com/download/Z01QRFFVQXA3N0R2Wmc9PQ
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mitsos on October 11, 2009, 09:48:21 PM
zip file contains everything you need..
wow... you can say that again. thanks for sharing. Just wish this project was more open for discussion  :(
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: olafmatt on October 14, 2009, 08:02:32 AM
Why don't you just link to this one?

http://purusha.smokinggunrecording.com/XVXDY/
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mitsos on October 14, 2009, 08:53:51 AM
Another interesting link. Is this the comp that the thread about purusha's copying was about?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: olafmatt on October 14, 2009, 09:15:20 AM
Another interesting link. Is this the comp that the thread about purusha's copying was about?

Cood catch, that's the one. So everybody just make a few "for your firends" who buy them for 3000,- USD on Gearslutz.

Quote from: Purusha
Hi Olaf,

just a friendly question  :wink:

I will be honest with you. I build a few units a year for some local friends who have studios. So naturally I would rather have a pro made PCB than a home etch. No intentions to show this to anyone on the forums!

Is there any way to get the gerber file for the VK-1 PCB?
I think I would rather have a few boards made by a fabric.

You have my word that no one will ever find out about this. Maybe I can even help you one day with some front panels or cases.

Regards, Purusha
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mitsos on October 14, 2009, 10:50:47 AM
Another interesting link. Is this the comp that the thread about purusha's copying was about?

Cood catch, that's the one. So everybody just make a few "for your firends" who buy them for 3000,- USD on Gearslutz.
Well, since we have your authorization....   ;)

In case the little winky guy isn't clear, I am kidding of course...  I don't think that Purusha's post ever saw the light of day before. I think it's good you posted, there were quite a few people who had no idea what the heck was going on with the thread silent:arts (I believe it was him) started about purusha copying a comp. So you are the one who did the rev-eng and layout? Good to know. Btw, this must have been the same comp someone posted a picture of but promptly deleted since it was supposed to be secret (a year or two ago)?  I remember the thread, I barely had time to read it and poof! it was gone.

Thanks for posting these details. I know volker took some flak for "complaining" about someone copying a project that the "owner" wasn't openly complaining about.  Obviously Purusha lied about his intentions, and now at least it's in writing.

That said, I hope you'd consider bringing this project back to DIY-land. I guess it's already there since, many people must have downloaded the files Penguin posted (I too asked for a copy) BUT, at least for me, it would be cool if there wasn't the rotten feeling of this project being cursed.... I still think most people are here to learn (or at least attempt to electrocute themselves). Just a thought.  Thanks for reading.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: SIXTYNINER on October 15, 2009, 12:05:17 PM
ur email ?
EDIT: many request for this hidden info...
here is the link for download.. 7 days... 100 downloads...
zip file contains everything you need..

https://www.yousendit.com/download/Z01QRFFVQXA3N0R2Wmc9PQ

Hello checked link
but no docs available ,
it is "xpired"?
tanks
 :-[
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: kambo on January 01, 2010, 03:33:28 PM
i finally finished this baby as P2P,  ;D
but its not the original circuit anymore
its something between altec436C meets urei 175b...
i call it 4375 for now...

for people with PCB pdf files: i dont know if he pcb has some errors, but p2p is pretty easy for this....
and original circuit works fine.... on pcb heaters looks odd to me... rest is easy to check, if you wanna use PCB...

due many mods/changes my P2P is in a mess right now...
when i get time, i will update some news, but in a different thread... as this is no more what the title says anymore
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 01, 2010, 03:49:52 PM
Would be interested to hear more I have messed with some DIY vari mu & am doin so now & had a little play with this circuit tho bit of confusion about correct tube to use it sort of worked.....Ive since been thinkin about the similar 436C circuit.

Thanks
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: kambo on January 01, 2010, 09:06:07 PM

i will be back  ;D
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: flaheu on January 02, 2010, 04:59:35 AM
Kambo ! Nice !

I've got all the parts to make a compressor like this, I've got all the docs, but because someone said it's not correct, I'll follow this thread and hope you're gonna share your schematic and your mods.

cheers
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 02, 2010, 02:54:33 PM
Ive just wired Up my version of this compressor for education myself purposes... as follows sowter Input Tran 1:4 250K daul ladder pot grids of ECC85 output tran a BIG  expensive Sowter meant for BA6A no output pad.....its sounding good....tried a Sowter 6:1, 9050 worked but distorted a bit, gonna try the recomended Sowter 8650 output tran........also noticed a different schematic than I worked from with 290V Ht extra capacitors different resistors feeding threashold pots & a balances pot for ECC85 plates & couple other differences , gonna try these changes out too
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: syn on January 03, 2010, 10:13:11 AM
...also noticed a different schematic than I worked from with 290V Ht extra capacitors different resistors feeding threashold pots & a balances pot for ECC85 plates & couple other differences , gonna try these changes out too
any chance you could share this schemo?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 03, 2010, 10:32:39 AM
Its already here Olafmatt posted both schematics and lots of useful info its near the bottom of 3rd page
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: syn on January 03, 2010, 11:09:39 AM
thnx, I have that. I thought something "new" has surfaced. to avoid post (http://www.groupdiy.com/index.php?topic=37018.0)ing twice.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: rocketattack on January 12, 2010, 09:40:28 AM

I bought two PCBs, Cases, and VUs for this a while ago but never got around to building them. I'm going to get rid of them and post them in the black market. PM me if you're interested.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: diyfanatic on January 12, 2010, 10:01:21 AM
becarefull, pcb seems to have some errors...purusha inside!! :P
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mulletchuck on January 17, 2010, 10:55:53 PM
diyfanatic, does the Schematic contain errors?   
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: tommypiper on January 17, 2010, 11:57:21 PM
i dont know if the pcb has some errors, but p2p is pretty easy for this....
and original circuit works fine....
Which "original circuit" are you referring to?  The Altec, or the Chiswick schematic in the previous links?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: kambo on January 18, 2010, 02:19:21 AM
both... i have no idea how original Chiswik schematic tho...
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: diyfanatic on January 18, 2010, 08:06:42 AM
diyfanatic, does the Schematic contain errors?   

sorry I can't tell, not that I won't!
just refering to another thread where it's seem that the layout have some errors...
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: stitch-o on January 18, 2010, 08:24:12 AM
There is def something un-funky with that layout....
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mikeyB on January 18, 2010, 09:57:23 AM
 >:( yeh - i'm one of the "unlucky ones" that bought kit (3 kits actually :o) from Tat - plus all the sowter iron + mains transformers - spent f**kING months trying to sort these but not much joy! I know that Tat pulled a fast one but I (and many others) bought the kit in good faith and spirit of the GROUPDIY forum.
I've no wish to turn this into a commercial project - just want to finish something that best part of £2000 spent on. I don't expect help posted here but if anyone would be kind enough to help via pm it would be massively appreciated.
With many PLEASE-THANKYOU-PLEASE in advance - mikeyB
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: diyfanatic on January 18, 2010, 10:41:02 AM
it's a shame...£2000  >:(
may I ask how much for the pcb?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 18, 2010, 11:11:32 AM
2000 pound !!!!! may I ask what did you spend that amount on ?

I havent been following this PCB story I gather some bugger sold u PCBS that have errors.......Im sorry to hear that >:( thats sh*tty......but moving on can you not fix or work around the errors, I recently point to pointed a mono version of this mainly from junk total cost prob 100 quid there not much to the circuit, in total labour I reckon it took less than a day, ok its not pretty and I made short cuts but it works great... now I no that I might tart it up a bit, as I did it as an experiment.

I wish you luck if I can help let me no.

Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Nele on January 18, 2010, 11:19:57 AM
the errors I know of is that Tat's pcb was single sided and the design is double-sided..
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mitsos on January 18, 2010, 11:39:00 AM
If the schemo is correct (as kambo says above) then the quickest way to fix the PCBs is to throw them away and put this together P2P.  I haven't compared the schemo and layout, but I don't see how purusha could have messed up a board that was given to him finished.  Did he try to add stuff/features/mods and messed that up? Should be easy to fix if purusha would tell people what he "modified."

ALSO, have you tried posting at purusha's forum? People keep posting here, but fixing this board would be better handled at HIS forum. He should own up to his mistake and devote some time to fixing it.
www.diy-racked.com/

There you can ask him directly what he modified so you know which part of the board needs correcting and can focus you efforts there. good luck, it sucks to have so much $$ sunk in a non-working project...
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mikeyB on January 18, 2010, 12:11:11 PM
2000 pound !!!!! may I ask what did you spend that amount on ?

I havent been following this PCB story I gather some bugger sold u PCBS that have errors.......Im sorry to hear that >:( thats sh*tty......but moving on can you not fix or work around the errors, I recently point to pointed a mono version of this mainly from junk total cost prob 100 quid there not much to the circuit, in total labour I reckon it took less than a day, ok its not pretty and I made short cuts but it works great... now I no that I might tart it up a bit, as I did it as an experiment.

I wish you luck if I can help let me no.



Hello gary o - 6 channels of sowter iron in and out - 3 mains txs - 3 pcbs - 3 cases - pots/switches/meters/caps/connectors etc-etc-etc - yep - all high qual components - best part of 2k!!
Thanks for the offer of help - I may have to take you up on that one - cheers
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 18, 2010, 01:48:06 PM
Yeah I see MikeyB sorry I re read yr message and saw you went for 3 units.......good news is its not hard to point to point this thing all is not lost sounds like the boards are no use then as mitsos says throw em aside.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: djn111 on January 18, 2010, 02:58:41 PM
Hi,

I think the only thing missing on the boards is the heater supply of the tubes, I have pictures of both versions, and it is clearly show, easy fix with some wire twisted together.

DJN
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mikeyB on January 18, 2010, 04:47:47 PM
thanks for the tips guys - sorted on the heater wiring - it's more to do with biasing of the valves/meter set up and trimmer settings -
still on it!! Might soon get the chance of getting my hands on the real thing!! - that would help immensley!!
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: tommypiper on January 18, 2010, 05:30:07 PM
Did he try to add stuff/features/mods and messed that up? Should be easy to fix if purusha would tell people what he "modified."

ALSO, have you tried posting at purusha's forum? People keep posting here, but fixing this board would be better handled at HIS forum. He should own up to his mistake and devote some time to fixing it.
www.diy-racked.com/

There you can ask him directly what he modified so you know which part of the board needs correcting and can focus you efforts there. good luck, it sucks to have so much $$ sunk in a non-working project...


AFAIK, Purusha got an early version of this PCB which was reverse engineered and put together by someone else and some bugs may have still been in the PCB at that time.  It was a two layer board, and Purusha sold it as a one layer board, omitting the heater traces.  He otherwise did not make any mods AFAIK.  I believe Purusha would love to offer fixes, but does not know what they would be, because the original PCB designer and he have had a major spat over the incident.  Silent Arts has a long thread here discussing this situation and I don't think it needs to be revisited.  For those who missed the drama, that should explain the situation for you.  Because of this drama, those who may have figured out solutions to the PCB are reluctant to post them or even share them via email or PM (as I have tried in private discussions)...

The Chiswick schematic that is being circulated along with Purusha's PCB appears to be authentic, and should work on its own, AFAIK.  I'd love to hear some confirmations on that, as I am building it....

Purusha's PCB appears to be the same as the Chiswick schematic, with a couple minor value changes which should be easy to spot, AFAIK...

The big problem in this situation is that we feel our hands our tied in discussing the Chiswick schematic... which shouldn't be the case.

I feel very sorry the dispute (between Purusha and others) happened.  I hope the parties can find a way to move on.  It puts innocent buyers who trusted the forum and offerings from its members into a compromised situation without any support.  This is unfair to innocent forum members who had no knowledge of the dispute or its background and got caught in the middle of other people quarreling.

Guys, life is too short. 
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: syn on January 18, 2010, 06:00:37 PM
Why someone doesn't  just rent the real thing, we split the cost and the schemo? What is the point in talking about it every-now-and-then? Why don't we just do it and let  the past go by. The thing is not biased properly- it works- but it has problems. Why don't we just forget about what was before, and start a new build? Even those who have parts will not loose much, maybe not even PCB- it can be edited (traces). I think fix is simple- like proper biasing.
Please.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: tv on January 18, 2010, 06:11:55 PM
>>>> i only wanted to show this poor guy that diy is not all about money.

http://www.youtube.com/watch?v=dqiOpePmnl0
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: kazper on January 18, 2010, 06:24:25 PM
If you read from the beginning of this thread the hole deal was based off a member here who had got a deal on one and posted many internal pictures of it. That started the whole ball rolling and it's where the reverse engineered schematic came from and eventually a pcb you all know the rest of the now so called folk story...

It's generally seen as unfair that the project became a hush hush, but life itself is not fair. I do feel for those who paid for a bummer PCB and kit, I was even offered it myself. In all it is what it is.


Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 18, 2010, 06:35:41 PM
Wow that Zappa guy has some mustash !!!! I bet he could be modded.......shave that off & he would get more HF response from his vocal chords...

Anyway heres my little baby mono version of this compressor as I say its an on going experiment so dont laugh she made out of junk but sounds sweet Psu & in/out transformers live in other boxes


(http://thumb4.webshots.net/t/71/71/3/38/18/2598338180103387484tBosOp_th.jpg) (http://entertainment.webshots.com/photo/2598338180103387484tBosOp)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mushy on January 18, 2010, 07:32:08 PM
Any shots of the guts, Gary?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: djn111 on January 19, 2010, 03:43:28 AM
Hi Gary,

Looks good, many of my tube amps start out like that, but if you don't mind me asking you used the schematic of P-you now who ?

I like your workbench as well :-)

DJN
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 19, 2010, 10:19:15 AM
Mushy il take a shot of the underside tho il prob have the safety police on my ass.....lots of hazards there.......DJN, I used the schematic from the beginning of this thread , I think its gone now but it & another slightly different schematic and some other info are here on page 4 I believe, as I said I not been following the PCB story staying out of that I just wanted to see how this thing sounded , mine is different in the following ways ...I used my own simple external PSU provides 295VDC 12.6VDC & 6.3 ACV ....my input tran is Sowter 1:4 a higher ratio and a 25K attenuator dual ladder type, that lead me to changing the side chain resistor values so I had better threshold control, I have the balance pot fitted ......as in what I guess is the revised schematic, I tried the extra capacitors from the revised schematic but dont seem to make audible difference, maybe some1 can tell me what they do ....Im goin to disconnect the feedback resistors to see if I get dirtyer sound and maybe have a switch there.....so really this thing is just a Altec 436C with a few tweaks emi tweaks I read somewhere .....I was going to make a 436 for fun, do you think It would sound much different than this maybe with the original input tube??????...... not that I dont like this thing....Iv read bad things about the 436 but then wonderful things when emi ed ......call be a pervert but I think I want some filthy distortion.......
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: penguin on January 19, 2010, 11:04:11 AM
il prob have the safety police on my ass.....

we will protect you  ;D wont we guys 8)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 19, 2010, 02:16:14 PM
Cool thats better now I feel unsafe again....

Its a little rats nest very small maybe even a threws nest

(http://thumb4.webshots.net/t/64/764/2/71/8/2163271080103387484OfPmDp_th.jpg) (http://good-times.webshots.com/photo/2163271080103387484OfPmDp)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mushy on January 19, 2010, 02:32:19 PM
I didn't see nuttin out of the ordinary in dare...   ;)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mitsos on January 19, 2010, 03:28:26 PM
Hey Gary, um wow, I thought my wiring was messy!  ;)

would you mind posting the schemo you used? It'd be interesting to compare to the other one.

cheers
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mulletchuck on January 19, 2010, 04:00:40 PM
Is this compressor a DIY version of
(http://www.manleylabs.com/images/pro2001/mslchp.jpg)

???   

Total noob here trying to learn what a vari-mu compressor is, and that was the first link returned in google.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on January 19, 2010, 04:12:51 PM

loooks good gary o ,

hey  gary o  have you a circuit of your 295v psu what tx did you use current / va.

i built 1 changed e**85 4 p**85 works a treats. what did you set the  grid bias to on the vm tube.


skal1


 


Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 19, 2010, 06:52:09 PM
Mushy you would if you put yr fingers in there :)

Mitsos this is kinda neat for me ....I might post areal mess for you to laugh at......The schematics I used are in a link in this thread on page 3 Im not sure if they are the best ones out there, you may already have better ones, as I said this thing is basically a Altec 436 isnt it .......I changed a couple a things to suit the parts I had to hand, if you read my last few posts youl see i changed couple a things.....I dont really no what Im doing so i learn by doing

Ska1 not sure about grid bias can you elaborate for me as I say Im a little green on electronics theory .

Mullet that is a vari mu limiter but not the one we on about.....check the meta for lots info on vari mu limiters
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on January 20, 2010, 07:25:31 AM
I'm about to start building one of those VariMu's from Purusha. As far as I can tell the PCB's were fine, there's an additional document explaining how you need to place the tube heater wiring yourself. Then it should work just fine. Do any of you truely know of another fault in the PCB?

kind regards,
Maarten
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: stitch-o on January 20, 2010, 07:43:58 AM
I have heard from a very reputable source that this build/layout
(and he made 3 of these comps) gave only about 2dB of compression...

I was seriously thinking of doing one of those Purusha special boards but instead, I think
I'll (like Gary, cheers for the pic!) build a pair of 436s in a box, make them
stereo linkable and tweak them out a bit. Or maybe a modified PRR?

Unless, that is, the VK1 gets fixed with confirmation.

Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on January 20, 2010, 02:34:16 PM
I have heard from a very reputable source that this build/layout
(and he made 3 of these comps) gave only about 2dB of compression...


duppy know who fee frighten


skal1
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on January 22, 2010, 06:04:47 PM
any know the cv of this forbidden project , idle and when under compresion .


thanks

skal1
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Jim50hertz on January 23, 2010, 04:13:32 AM

[/quote]

duppy know who fee frighten


skal1
[/quote]


So, think the duppy has a correct copy of the schematic, that we can fix our problem pcbs, and compress our days away?  ;)

Peace,

Jim
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: stitch-o on January 23, 2010, 07:23:45 AM
(http://i48.tinypic.com/14lu4vm.jpg)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: jackies on January 23, 2010, 07:40:27 AM
 ;D
Indiana Jones and the Limiters of Destiny!
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on January 23, 2010, 10:35:46 AM


duppy know who fee frighten


skal1
[/quote]


So, think the duppy has a correct copy of the schematic, that we can fix our problem pcbs, and compress our days away?  ;)

Peace,

Jim
[/quote]


well if someone would be so   kind enough to shed some light on the errors , that would be nice , but i think the victims will have to bite the bullet or buy/build a  436c and work  out the problems from their.

skal1
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: ChrioN on January 23, 2010, 12:05:24 PM
why not do pcbs for the 436c instead?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: stitch-o on January 27, 2010, 10:25:37 AM
why not do pcbs for the 436c instead?

You should nudge Nadege
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mitsos on January 27, 2010, 11:03:17 AM
why not do pcbs for the 436c instead?

You should nudge Nadege
did anyone ever test those boards?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: ChrioN on January 27, 2010, 11:25:04 AM
So it has been made?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mitsos on January 27, 2010, 12:11:16 PM
So it has been made?
looks like it.. search for nadege 436 and you should find the thread. The links don't work directly, I had to cut and paste them.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: stitch-o on January 27, 2010, 02:45:16 PM
Maybe this will get me outta a few years of purgatory tho I'm pretty sure this isn't the VK1, it might provide
the basis of a good 436 mod:
(http://img130.imageshack.us/img130/2825/436cmods.jpg)
(http://img641.imageshack.us/img641/6020/altec436maybe2emimod.jpg)
(http://img651.imageshack.us/img651/5529/altec436maybe3emimod.jpg)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: syn on January 27, 2010, 05:33:12 PM
stitch-o thank you.how about bigger schemo?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: stitch-o on January 27, 2010, 06:30:09 PM
stitch-o thank you.how about bigger schemo?

(http://img189.imageshack.us/img189/2825/436cmods.jpg)

If anyone makes some boards, I'll take a couple  ;D
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: djn111 on January 28, 2010, 03:18:39 AM
Hi,

I think someone already did, use google and you will find them :-)

DJN
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Nele on January 28, 2010, 05:32:32 AM
why do you guys want a pcb..? the number of components is so low and the layout so simple you could easily do it p2p.
being someone who stepped into the purusha/vk1 trap I might just give it a try.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: stitch-o on January 28, 2010, 07:27:32 AM
why do you guys want a pcb..? the number of components is so low and the layout so simple you could easily do it p2p.
being someone who stepped into the purusha/vk1 trap I might just give it a try.
I have plenty of P-T-P projects cooked and cooking but when you have 3 kids, a full time job engineering/producing
and piles of freaking projects already piling up (not to mention a full time working mama/girlfriend), spending hours designing a point-to-point layout is the last thing I can deal with, time-wise.
Why do you have to ask something banal like this?
And I've googled a lot. There is nothing.

Wow, I thought people might be appreciative of this info...  ???
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Nele on January 28, 2010, 07:43:18 AM
oops.. sorry. no bad feelings meant.  :)
I was just wondering. I'm also a big fan of pcb's but I'm also lazy ;).
This just seems like a pretty simple project to p2p. I'll see if I can draw up a layout with turrets.

cheers,
corneel
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: stitch-o on January 28, 2010, 08:36:16 AM
oops.. sorry. no bad feelings meant.  :)
I was just wondering. I'm also a big fan of pcb's but I'm also lazy ;).
This just seems like a pretty simple project to p2p. I'll see if I can draw up a layout with turrets.

cheers,
corneel


Now I am the one who is appreciative.
Thanks Corneel!  ;D

edit: gotta stop posting before my morning cup of coffee...
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Jim50hertz on January 28, 2010, 08:41:44 AM

This just seems like a pretty simple project to p2p. I'll see if I can draw up a layout with turrets.

cheers,
corneel


Yay!  As a Tat PCB buyer like yourself this'd be most cool...  Much thanks  :)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: djn111 on January 28, 2010, 10:43:55 AM
Hi,

You did not google right, send me a pm, where you want the files.

DJN
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mitsos on January 28, 2010, 10:58:02 AM
please post here.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mulletchuck on January 28, 2010, 03:40:51 PM
Djn, upload the files to the group Gmail account for all to share  :)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on January 28, 2010, 03:58:14 PM
where i can not see it


skal1
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: djn111 on January 28, 2010, 04:24:32 PM
Hi,

Sorry can't do I am not the original designer, so pm and you get them

DJN
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: electrochronic on January 29, 2010, 12:31:10 AM
DJN

PM box is full ?

Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: jackies on January 29, 2010, 12:42:26 AM
 ::)
Oh cmon already people!
Anyone here used a computer before?
All you have to do is to go to Nadege's photobucket album and view pictures on the photobucket site.
How difficult is that?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: electrochronic on January 29, 2010, 01:09:38 AM
jackies

same files, Nadege and DJN ?

not sure since I have not seen DJN's
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: jackies on January 29, 2010, 01:39:42 AM
I'm pretty sure DJN was referring to Nadege's pcb design.
Let him correct me if I'm wrong.
Title: Dangers of the Altec compressor
Post by: KickBack on January 29, 2010, 02:10:23 AM
Hi

I am like a real oldster, and I have worked on lots of tube gear.

I have a pile of info stuck up there about tubes.

I also have Modded a lot of tube gear and discovered thier dar and dirty secrets. That altec Compressor has a serious flaw. The original tube, the 6bs8, is one of a series of tubes, 6bs8, 6bz8, 6bk7, 6bq7, 6aq8, and a couple others that have the ability to be controlled by varing the grid bias.

Vary-Mu is kind of misleading because any tube varyies Mu or gain some with bias change. Most tubes are fairly stable and gain is a function of grid and plate resistors, plate voltage, and screen voltage.

Thes 6 Volt dual triodes were designed for tuners. RCA comes out with a new TV set and designs the 6bc8. Then GE comes out with thier latest and designs the 6Bz8 etc. and a whole series was done up. Then years later the why and other types that relate is lost.

The problem with these compressors is this. I have run into this when working on Vintage gear and just more secrets lost in time. This compressor was sent out with tested, special versions of  the first tube. The balance in the two triodes as to gain is critical because if the gain is off, then one side of the output stage drives too hard, and the compressor "Thumps", and sometimes oscillates.

Even old guitar amps came with special versions of tubes, so they do goofy stuff sometimes when using new versions.

The solution to making this a stable, and very decent compressor, is to use a pentode-triode type, like a 6GH8, 6Bl8, 6AN8, 7199 etc. the pentode as first gain stage, the triode as phase splitter. Then the gain control voltage goes back to the pentode, and the signal is split very balanced, so no funny Bizz Mit the Thumpys or other fun.

You can use the same socket, just change out the dual triode.

Again, 6bc8,  6bz8, 6bk7, 6bq7, 6aq8, 12ay7, 12au7, 6bs8, 6bc8, and 12at7 are all fairly close in specs, and used original for some tuner and some audio circuits. 12au7, 6bk7, and 6bq7 are the warmest sounding.

I had a studio send two of these to me about six years ago freaking out, and I found that, since they were used mostly for PA systems for schools, they never had to deal with complex signals, so the imbalance does not cause much of a problem, and in schools or other PA use, the thumps get lost as no low end in these systems.

Title: Re: My first rerlp, Altec
Post by: KickBack on January 29, 2010, 02:31:18 AM
I meant 6bc8.

The changes made to the 6bc8 stage are ways to try and correct the imbalances when the gain of the two triodes changes, but the tube itself, if not the right version of this tube, will not have the same plate curves for each triode.

Also, back then, companies made special versions of tubes that solved their design problems.

Fender this with amps they made before they had adjustable bias. I have to tweak older Fender amps to bias them as they were original sold with 6v6, 6l6 etc. tubes that biased up with thier circuit.

This also happens because the cathodes of the 6bc8 are tied together. About 100 to 330 ohms in series with each kathode would make the two triodes more stable. The gain fall off, slight, can be taken up with 56K plate resistors.

Also plate to grid negative feed back, crosscoupled, would improve it's compression action.

Best of ruck :D
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: djn111 on January 29, 2010, 02:46:03 AM
Hello,

Yup you are right :-)

DJN
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on January 29, 2010, 09:20:15 AM
Hi there Kickback you real oldster hehe who seems to no what he is talking about unlike my self which is why Im here to learn, got some questions for you or anybody else.....

Kickback I dont no if you have seen the chiswik schematic that is here

http://purusha.smokinggunrecording.com/XVXDY/1schems.pdf

Youl have to forgive me my knowledge is patchy

Iv made a point to point version of this with a few little changes Im just trying to learn and end up with a nice sounding compressor for my vocals and mines is workin great Im happy but would like to learn more and maybe improve.......

Im using Ecc85 daul triode seems to work well.....

Kickback your saying a pentode wired as triode would be better ?? I dont dispute , want to hear more, I no theres plenty vari mu circuits that do that...

Doesnt the 1K pot between the first tubes plates tune out imbalances ??

Ive seen altec schematics with an added pot between the first tubes cathodes, Is tha a further improvement ? or do we only need the plates balanced?

The tubes used for the Altec/chiswik including my ECC85 are not true vari mu tubes I have read ......wouldnt it be better to use a tube that is, maybe octal 12SK7?

Kickback you said about the pentode as phase splitter ? does that mean we dont need centre tap on input transformer ?

Also plate to grid feedback cross coupled ? I think I understand plate to grid feedback.....as in Chiswiks 12AT7 output tube......

What is cross coupled ??

were you talking about feedback on the gain reduction tube ???

Questins questions questions sorry Im just very hungry to learn I believe in this little altec circuit and Abbey road did not that Im a fan.....I DIYed a RCA BA6A had Sowter make transformers specially for me the thing is great and so it should be its much more complicated I love it its sounds great its sounds different to thicker bass heavy to the Altec chiswik circuit but on vocals  its doesnt sound worse just different thats why i think this thing is great, punches above its weight.

Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: electrochronic on January 29, 2010, 01:42:14 PM
Kickback

Thanks for that explanation , very informative.

So 6BC8 or the listed dual triodes should be sub'd for a pentode run as both a Pentode/triode and triode/inverter.

Curious, When you mentioned special tubes made for design challenges, how would one of these tubes be marked ?
Or would they just have a special silkscreened part number and no tube number designation, like ex:12at7. Kinda of like some unidentifiable transistors you find on power supplies, and other proprietary circuits with special part numbers on them that do not cross to any standard industry part numbers.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: KrIVIUM2323 on February 04, 2010, 12:07:19 PM
Quote
Kickback your saying a pentode wired as triode would be better ?? I dont dispute , want to hear more, I no theres plenty vari mu circuits that do that...

Just take a look here: http://www.manleylabs.com/techpage/TBAR.html

The fact is that pentodes tubes can be divided in 2 kind: sharp cutoff and remote cutoff. By nature the second group (remote) are well suited as varimu because they have control grids of uneven spacing (the grid is 'tight' in one end and 'more spaced' in the other). When the bias is large the transconductance of the tube is small limiting the gain of the amplifier hence varying transconductance: varimu by nature when connected as triodes! ;)

6ba6 and 6sk7 are eg of remote cutoff tube, 6sj7 and 6au6 are eg of sharp cutoff.


Quote
Doesnt the 1K pot between the first tubes plates tune out imbalances ??

It does but for small imbalances, said 5% max. For larger ones it can't. This is the reason why pairing is so important in this purpose.


Gary O could you measure the consumption of your kind of Vk1? I would like to know how many milliamp a channel is using in pratctice. Thanks in advance.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on February 04, 2010, 03:49:59 PM
Very very interesting, so KrIVIUM2323 you seem to now a lot about these things compressor i mean, anyway can you tell us what would be the max gain out of the 12at?* to drive the cv to -30v  just query something in my head.


 skal1
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: KrIVIUM2323 on February 04, 2010, 04:41:27 PM
Quote
you seem to now a lot about these things compressor

I'd love to know much but i'm like many in here: i'm learning!  ;)

Quote
anyway can you tell us what would be the max gain out of the 12at?*

No i can't... because i don't understand the way the gain stage is working! ... it's not entirely true indeed as i understand how it work but not the math behind (to compute it theorically)  ;D
But... we've got an output attenuator of 30db so i would say 30db for the gain stage...

 For the moment, what i noticed is that the arrangement (anode straight to primary of center tapped output transfo with B+ at center tap and common cathode resistor for both half of 12at7) really looks like a power amp output stage. In fact it's almost the same with others varimu designs.

And... by looking at 12AT7 datasheet it make sense: typical gain of classA with 250V anode Voltage, cathode resistor of 200 ohms (470 ohms driving 2 cathodes in // is approximately 220ohms for both no?) give an amplification factor of 60 ( 35db gain). If we take out 5db (feedback r103/102) which is aproximately 15% negative feedback it seems ok...at least for me! ;D


So :
Quote
to drive the cv to -30v  just query something in my head.


I won't be surprised that the treshold 47k log / 18k resistor// with 6al5 cathode input in both sides can take 15v each side which after rectification by 6al5 sum to give 30V. I'll try maths but here again i don't know how to make them...

 But 30V for driving the gain reduction stage seems a lot to me. I was more expecting something in the 10V range...  ???

How did you get 30V Skal1? Assumption ? Math? I'm curious too as this is something i ask for myself too.  
(edit: after reading a post from PRR it seems that we could expect something in the range of 1db/volt for cv/gain reduction stage here: http://www.groupdiy.com/index.php?topic=1509 )
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on February 04, 2010, 05:40:17 PM
yes that seems right , so if i was to measure an 436c with out the 6al5 in the socket  , just using it like a line i should be see 30 dB ->
  Voltage-ratio = 31.6228
  Power-ratio = 1000
 hum.

so that means just over 15v a side at 6al5 , so what does 30 Voltage-ratio equate to in ac after the blocking caps ?


after 6al5  you should expect at lease a good cv , yes  ;D well if you built that thing you would not see anything in that  ::)


skal1

 



Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: KrIVIUM2323 on February 04, 2010, 06:23:30 PM
Quote
so if i was to measure an 436c with out the 6al5 in the socket  , just using it like a line i should be see 30 dB

A little less as in 436C the output tube is a 6CG7 and it has an amplification factor of 20 so a gain of 26db. But are we talking about 436C or VK1?  Even if it's the same kind of topologie/schematic there is some change between the two designs... ;D


Quote
so that means just over 15v a side at 6al5 , so what does 30 Voltage-ratio equate to in ac after the blocking caps ?


In fact it's not really 15v from the ac signal: i've read somewhere that 6al5 need a minimum voltage of 45v to begin conduct so it's more 60v from any sides of the output which is 'seen' by 6al5 input. If cv is 30V it means 30db gain reduction... HIGH GR!
I never use comp with such high gr!...  ;D

Quote
after 6al5  you should expect at lease a good cv , yes   well if you built that thing you would not see anything in that  

CV is comp/threshold dependent so it depend what you do with your comp settings...
What do you mean? About Vk1? Purusha did crap we all know that... but Olaf did a pretty good job as far as i can see. Anyway if i built one i'll go P-T-P not pcb. And with the right kind of tube!
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on February 04, 2010, 06:29:29 PM
pray tell...


skal1
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: KrIVIUM2323 on February 04, 2010, 06:37:30 PM
Quote
pray tell...

? Excuse me english is a foreign language for me i don't understand.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on February 04, 2010, 06:46:46 PM

In fact it's not really 15v from the ac signal: i've read somewhere that 6al5 need a minimum voltage of 45v to begin conduct so it's more 60v from any sides of the output which is 'seen' by 6al5 input. If cv is 30V it means 30db gain reduction... HIGH GR!
I never use comp with such high gr!...  ;D

[/quote]

hummm  so basically what you are saying is the 6al* needs to see 45 ish ac volts at the anode to start conducting and then some more to give you that useful cv so if your output craps out at this point cv is weak, yes, so work on your cv sig.


skal1
Quote
pray tell...

? Excuse me english is a foreign language for me i don't understand.

hey ,it just means {tell me what is right kind of tube!}

skal1
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: KrIVIUM2323 on February 04, 2010, 07:02:36 PM
 ;D tube: 6BZ7!  :P  I must take a look at datasheet but i think using ***85 need some mod from schematic // the original tube.

Quote
hummm  so basically what you are saying is the 6al* needs to see 45 ish ac volts at the anode to start conducting and then some more to give you that useful cv so if your output craps out at this point cv is weak, yes, so work on your cv sig.


Well in fact i'm not sure... i may say something stupid  ??? Don't know have to search where i think i've read that... Because when i look to 6al5 datsheet it don't make sense at all!!!  ::)

Well from datasheet each section with an input (ac) signal of 15v rms will produce a dc output signal of approximately -16,8/17v for a load resistance of 15000 ohms (aproximately). And as far as i understand there is a 10v drop at 60 milliampere current on plate.

Humm. I need to think about that! And by the way i did understand a sentence i've read telling that 'thump modify the impedance of the gr/cv path'! Great! :D

PS: Skal1 check your pm please.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mikeyB on February 24, 2010, 05:58:51 AM
Couple of things - I asked in another thread about trimming out differences in diode halfs ie 6AL5 - if imbalanced will produce ripple on control voltage causing distortion in varimu stage - so can this be trimmed - will try this when i get chance.
More of a design question - tube currents should be matched- right? In the chiswick output stage there is a trimmer in the cathodes to balance current but in the front end there is a trimmer in the anode resistor circuit - could this be changed to a cathode balance trimmer as in the output - or would it cause problems in setup/operation - just thinking of safety point of veiw when dabbling!
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on February 24, 2010, 07:58:44 AM
Kr1v sorry I forgot you wanted me to measure the consumption of my mono chiswik type cpmpressor ? you want me to put milliamp meter in series with the B+ ? I gotta wire the compressor up Im on the case also Miha if yr here il measure the CV voltage for you
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: rotation on February 24, 2010, 12:05:51 PM
Yeah, i'm here, please check this out. I measured this myself and my max input to 6al5 cathodes was 8V and it put out -8V max at anodes. Meter and daw shows max 8dB of compression at this conditions.
If i took away 100k FB resistors things get better, IIRC there was max 12dB GR.

Another member tried to add some DC to cathodes (like on many other comps where cathodes are connected also to B+ through divider or whatever that is) of 6al5 and nothing changed, he also got max 8dB GR. Than he tried adding more ac to cathodes of 6al5 and he couldn't get more than -8VDC at anodes of 6al5, no matter how much DC was at cathodes. I hope i'm stating this correctly, maybe person who told me this will jump in because he also tried to add 436's SC..

Miha

p.s.: we better move this to Altec436 thread because discussion is related to other compressor and there are also posts from PRR. It was good discussion there and it would be a shame to divide it in several threads.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: KickBack on February 26, 2010, 03:08:33 AM
Hi

I have re-built several of the Alter 436 compressors. I have worked on gear from the 1920's on up.

I used to service recording studios in LA in the 1970's and 80's. 

A. My solution to the 436 was to take the 6bc8 out and use a 6gh8, 6an8, pentode to split-phase inverter to kill the imbalace problem in the dual triode, unless a special 6bc8 from Altec. Control the grid of the pentode, cap couple to the triode phase inverter.

B. Put another 6al5 in parallel to lower the voltage drop, or feed the Dc into a op-amp to get more DC gain.

C. Use op-amps to make a voltage follower and just forget the 6al5.

6bk7, 6bq7, 6aq8, 6bz8, 12at7, and a few more do the same as the 6bc8, and have different grid control curves.

You can try another dual triode in the front end.

The gain stage works like this.

These tubes were used for TV tuners so they have the ability to "variable Mu" or gain more than standard tubes.

The -DC from the 6al5 lowers the gain of the dual triode. The 6al5 needs a certain amount of AC to "Turn on" as it has a operating curve, and that is the threshold. When the AC on the primary of the out trans, (higest voltage point as the line out trans steps down), is high enough, then -DC comes out of the 6al5 and lowers the gain of the 6bc8.

The problem with this circuit is that the 6bc8 from ALTEC was made special for this bad circuit. If there is any imbalance in the gain of the two triodes, then the drive to the 6cg7 is off, and the compressor "thumps" or worse.

This guy was designed to go into a PA system with no response below 350 Hz so you never heard it at your local high school when the principal was chatting away.

 
You have to really spend a lot of time studying all the tubes made to get some ideas as to how they were used.

i can post some circuits, let me know.


Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: gary o on February 26, 2010, 06:59:40 AM
Hi Kickback thanks for your knowledge I wpild love to see your circuits Im sure other will want to see them too I would be very interested in see a schematic of how you would wire up a penrode to split the phase and kill the inbalance......Am I right in saying some other older vari mu limiters used this like the RCA BA6A ?

Thanks
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on February 26, 2010, 08:18:16 AM
Me too  ;D

skal1
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: KrIVIUM2323 on February 26, 2010, 09:41:02 AM
Hi everybody.

Gary, I think Kickback is refering to pentode because some of them are remote cutoff and do well in comp job (when triode connected). For the phase splitter take a look at RCA's BA21A. The first stage of this preamp run single ended and the 6072 second half is used as a phase splitter. This is the way to go: first tube GR and second a phase splitter (or first triode and second one in case of a dual triode tube). This is convenient for mono unit for stereo you still need matching for two channels (and from the rca Ba21A manual you need a selected tube for this task, but it deal with very low voltage as preamp so need of hi spec, in comp i think i'ts not that crucial)  .  


Quote
Kr1v sorry I forgot you wanted me to measure the consumption of my mono chiswik type cpmpressor ? you want me to put milliamp meter in series with the B+ ?

Yeah that would be nice.

Quote
unless a special 6bc8 from Altec.

Kickback you have already stated this before. In what are 6bc8 from Altec special? Pairing of some spec (transconductance and paired triodes i suppose) or something else?


PS:Gary could you backup and clean your PM box as it's full and cannot be accessed anymore.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on April 18, 2010, 06:30:58 PM
I have heard from a very reputable source that this build/layout
(and he made 3 of these comps) gave only about 2dB of compression...

I was seriously thinking of doing one of those Purusha special boards but instead, I think
I'll (like Gary, cheers for the pic!) build a pair of 436s in a box, make them
stereo linkable and tweak them out a bit. Or maybe a modified PRR?

Unless, that is, the VK1 gets fixed with confirmation.



I've just finished mine and it rocks 100%. There are no faults or flaws and it sure does more then 2dB of compression! Check http://www.diy-racked.com/diy-talk/viewtopic.php?f=12&t=98 and www.tubefreak.com/varimu/

Kind regards,
Maarten
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: ChrioN on April 18, 2010, 06:50:22 PM
Nice build! And scratched up panel. But I wouldn't expect anything less from our friend tat  :)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on April 18, 2010, 06:54:48 PM
Nice build! And scratched up panel. But I wouldn't expect anything less from our friend tat  :)

Scratching is all my fault. Tat delivered a flawless case/pcb and with the docs it was not so hard to build. Finished version is cleaner inside, with all cables tied together.

Maarten
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: SIXTYNINER on April 19, 2010, 03:28:58 AM
nice unit !
any picture about the "jewel" ?
6t9r

Nice build! And scratched up panel. But I wouldn't expect anything less from our friend tat  :)

Scratching is all my fault. Tat delivered a flawless case/pcb and with the docs it was not so hard to build. Finished version is cleaner inside, with all cables tied together.

Maarten
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on April 19, 2010, 08:06:23 AM
Something like this? Found it at a local store, uses a small push in light bulp and (this one) runs on 6V from the heaters. On start-up the light slowly fades in, which looks really nice.
(http://www.tubefreak.com/varimu/jewel.jpg)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: SIXTYNINER on April 19, 2010, 09:42:55 AM
...yeah , cool jewel light..

how many compression db , from the vk1?
20?

6t9r
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on April 19, 2010, 10:08:53 AM
No, no 20dB GR with my version. But maybe if you take out the negative feedback circuit you'll get there. But if you REALLY want 20dB of GR, maybe a varimu is not the type of GR you want. It does amazing compression between 1-5dB, nothing I've heard/used comes close to this type of compression. Between 5 and 10dB GR it really depends on the audio and the settings, how it will suit the audio. Check the samples on my site www.tubefreak.com/varimu. The drms3 files have fast, slow and the modded extra slow attack, which I like a lot. There's also a file with 10dB of GR in the 'drums' files.

I'm gonna mod the attack & release times some more. For mastering I like some longer attack times and some shorter release times. Don't care much for how the time values compare to other units (=way off!), the mods are done by taste and needs. With a few additional mods this thing is gonna be even more killer, especially the longer attack times are a real bonus. And the high pass filter is so sweet, really opens up the music and an absolute must for the way I use it. Really can't live without a HP filter in a compressor. Don't know why and how others encountered troubles with the VK1 project, mine works flawless and sounds killer.

Kind regards,
Maarten
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on October 15, 2010, 05:38:01 PM
I've added a specific page regarding this project on my website www.tubefreak.com  It's filed under Effects & Rackgear.

Kind regards,
Maarten
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: SKJGProject on May 14, 2011, 11:16:01 PM
are there any options for the sowter 8650?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: SKJGProject on May 19, 2011, 07:23:57 AM
....and is it possible to use a 1/2 mA meter with the clone?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on May 19, 2011, 08:09:30 AM
The 8650 is not a problem, I've made mine with it. All the docs are here that explain it. http://purusha.smokinggunrecording.com/XVXDY/

As for the meter, 1/2 mA ain't a problem either, it's just a matter of using a different resistor for R106, VR100 or Rmeter. Don't know exactly which one, but there is enough info in the lab regarding this. And otherwise it's just trial and error.

Maarten
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: syn on May 20, 2011, 02:02:02 AM
Hi Tubefreak
                  have you measured noise on your unit? Any figures?
Cheers
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: SIXTYNINER on May 20, 2011, 06:06:11 AM
hey "Marteen"
please the "docs" you used for build your "vari-mu"
are all correct or they content some error?

I've made mine with it. All the docs are here that explain it.
http://purusha.smokinggunrecording.com/XVXDY/
..........................................ise it's just trial and error.
Maarten
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: SKJGProject on May 20, 2011, 07:00:39 AM
there is no "error" there is only one side of the pcb missing which contains the heater and stereo link traces but you can connect them manually
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on May 20, 2011, 07:32:43 AM
Yeah I did some measurements, but didn’t write them down. Noise was below 90 dB iirc, the input pad has a slight influence on the freq response, overall the freq response was flattering flat (small smile curve). Biggest influence are the Sowters and NOS tubes imo. They impart a sonic improvement that is very subtle but can really transform a cold digital source to something more lifelike.

Did a mastering job a while ago where the artist only used a software piano. It sounded fake, clearly not a recorded piano. With some minor EQ and running it through the Varimu, the whole staging changed for the better.

Regarding the faults, PCB and docs are fine, just wire the heaters below. There is a clear image of how to do this.

Maarten
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: syn on May 21, 2011, 04:31:25 AM
Maarten,
               mine is sounding fine too, but I have a bit more noise than I like ~-80dB-Aweighted.
Thanks for sharing the info, now I'm sure it's up to transforemer placement and/or grounding  (it's 50Hz hum).

Cheers
Milos
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on May 21, 2011, 10:52:43 AM
That could indeed be the cause. Just did a test with some tube swapping and without calibrating I easily got -97dB.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: JdJ on October 20, 2011, 11:20:01 AM
Tubefreak - did you end up just using the Conrad meters, or did you replace them?  I wasn't sure when I read about the mounting difficulties on your site.

Best,

Josh
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: SKJGProject on October 20, 2011, 11:41:03 AM
i'm still in the middle of the build....i was lucky to buy some original thermionic 1/2ma meters
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: 3nity on October 20, 2011, 11:57:07 AM
this one seems a nice build.
without knowing i almost have all the parts.
i have the T-pads, input transformer, turret board and tubes.

The only thing im looking on this side of the world its the output transformer...PP Triode to Line output

Anyone ?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on October 20, 2011, 04:07:57 PM
It took some extra time to mount them properly. Eventually it worked out ok and the meters haven't caused any troubles since.

The input pad is a nice tip/trick btw, it changes the frequency curve slightly and can be a nice way to add some thickness. The whole unit saved the day on a sterile and harsh sounding track by reshaping the highs.

Killer unit, highly recommended.
Maarten
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: prescott on January 05, 2014, 06:34:27 AM
Hello!

I've built this comp too 2 years ago.
I cannot make it good...

It eats the transients, and cutting the high freqs in some way.
I also have a PM670 which is much more better, no problem with that one.

I tried the mods you wrote on your site, but didnt changed these problems.

If this topic will wake up, I will send some material into the comp to show the result.
Maybe you can help me finding the solution.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on January 05, 2014, 07:28:44 AM
Please post some wavs. It would be handy to post one in bypass, one with te comp engaged and no compression and one engaged with compression.

What type of in- and output transformers and tubes are you using?

The unit is indeed a bit slow and doesn't work with all material. Sometimes is does wonders sometimes it doesn't.

Kind regards,
Maarten
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: TonyMN on January 08, 2014, 12:46:49 PM
Here's the one I completed about 6-months ago. I love it. It makes almost everything sound awesome.

http://www.moddefecation.com/images/crcomp/Chiswick%20Reach%20Coffin%20Vari%20Mu001.JPG

Here's More:
https://www.facebook.com/media/set/?set=a.566584430101894.1073741831.478520652241606&type=1&l=71a5846419
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on January 08, 2014, 05:33:52 PM
 :) :)nice TonyMN very nice , whats that HFmod thing about
cheers

skal
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on January 08, 2014, 06:03:46 PM
On the 'normal/white' DIY case the switch is on the rear. It selects the high pass filter for the side chain. Looking at the pics, we both come to the same setting.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on January 08, 2014, 07:20:00 PM
yeah get now ;)

skal
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: prescott on January 09, 2014, 05:58:34 AM
I use Sowters, as it was in the BOM,

For more about the tubes, and sound samples I will post in a short time.

Thanks!
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: prescott on January 09, 2014, 06:58:16 AM
Can someone upload somewhere the original Purusha docs please?
The old link doesn't work any more.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: TonyMN on January 09, 2014, 12:39:57 PM
Sure.

www.moddefecation.com/CR_COMP.rar

otherwise you could use the wayback machine.

https://web.archive.org/web/20100725153918/http://purusha.smokinggunrecording.com/XVXDY

Hope you get it working.

- Tony
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: AErige on January 09, 2014, 01:15:29 PM
Hey tony,
did you paint your frontpanel by hand? not sure since I can see what seems like a silkscreen mask in your pic here (https://www.facebook.com/photo.php?fbid=566586713434999&set=a.566584430101894.1073741831.478520652241606&type=3&l=71a5846419&src=https%3A%2F%2Ffbcdn-sphotos-f-a.akamaihd.net%2Fhphotos-ak-prn1%2F1556376_566586713434999_96135634_o.jpg&smallsrc=https%3A%2F%2Fscontent-b-ams.xx.fbcdn.net%2Fhphotos-ash3%2F1535372_566586713434999_96135634_n.jpg&size=1280%2C960)...looks pretty nice.

Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: TonyMN on January 09, 2014, 02:26:33 PM
Hi,

Thank You. Yes, I silk screened it using a Yudu machine. Which I do not recommend to anyone. There are better ways to silkscreen. The lettering came out ok, but not as good as I wanted.


Prescott, I used a 100 ohm trim pot for VR103 (schematic). The BOM calls out for a 10k. (DC balance)

- Tony
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: dmp on January 09, 2014, 02:57:17 PM
Mine sounds great with the HPF on, but motorboats with it off. Tried the balance trimmers to no avail. Do I need better matched tubes?
Anyone else been through this?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: TonyMN on January 09, 2014, 04:12:23 PM
Hi DMP,

I guess I would check to see if it's wired according to the 1SC.pdf. It sounds as if a cap might be shorted somehow in the off position.

- Tony
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on January 09, 2014, 05:30:39 PM
hay lads i confused about how to calibrate they thing the process makes no sense to me , please help..

cheers

skal
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: dmp on January 09, 2014, 06:08:53 PM
Quote
Hi DMP,
I guess I would check to see if it's wired according to the 1SC.pdf. It sounds as if a cap might be shorted somehow in the off position.
- Tony

Pretty sure it is. And it motorboats in the lower positions, not just off. There is a very low frequency oscillation through the sidechain I think.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: TonyMN on January 09, 2014, 06:53:15 PM
Hmm, I'm just guessing here.

Is this on both channels (stereo) or is it different for one or the other channel(mono)?

Have you tried different tubes?

Are all your Sidechain caps rated for 250v+? A faulty cap?

Also you could wire the SC Backwards (Swap A for B and vice versa) so that the switches are after the caps and they are not getting blasted with the b+ voltage every time you switch. I'm not sure what the contacts are rated for.

- Tony
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: dmp on January 10, 2014, 10:20:24 AM
Quote
Is this on both channels (stereo) or is it different for one or the other channel(mono)?
Yes both channels

Quote
Have you tried different tubes?
No, but I think that I should.

Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Tubefreak on January 10, 2014, 03:23:23 PM
Just to let you know: just did a mastering job on some electro type of music and the Vari Mu was too slow to maintain the punch in the kick even with all compression off. And mine is fitted with premium NOS tubes and Sowter transformers. Api2500 and a vintage Philips compressor did the trick with this song.

With rock, the varimu is a godsend.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: analogica on January 20, 2014, 03:10:40 AM

 Hi fellas,

this is what mine does, there is a huge cut on highs from 5 K, and abit happening also on lows, some armonics appear on mids so the sound gets weird. Not sure about the transients, but the loss of air is noticible and not nice.

I went for maarten mods, sowters and same tubes...(not matched, at least by me). Is there any solution to this?

This pics are on bypass, and On with 0 compression. thanks fellows!

http://tinypic.com/view.php?pic=2ewnpci&s=5#.UtzXhhDFLIU (http://tinypic.com/view.php?pic=2ewnpci&s=5#.UtzXhhDFLIU)  bypassed

http://tinypic.com/view.php?pic=kco088&s=5#.UtzZDRDFLIU  ON

http://tinypic.com/view.php?pic=35ing35&s=5#.UtzZZhDFLIU (http://tinypic.com/view.php?pic=35ing35&s=5#.UtzZZhDFLIU) White noiz, comp ON
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: analogica on January 20, 2014, 03:14:43 AM
I mean :o ;D ;D ;D ;D ;D.....tubes not tested by me, I dunno if they are matched, both channels seem to behave the same...
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mikeyB on January 21, 2014, 09:23:34 PM
Here's the one I completed about 6-months ago. I love it. It makes almost everything sound awesome.

http://www.moddefecation.com/images/crcomp/Chiswick%20Reach%20Coffin%20Vari%20Mu001.JPG

Here's More:
https://www.facebook.com/media/set/?set=a.566584430101894.1073741831.478520652241606&type=1&l=71a5846419

Hi TonuMN
Hows the bump-thump-crush implemented and whats the lo/mid/hi FD?
i'm guessing the -7dB is an input attenuator?
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: TonyMN on January 22, 2014, 04:04:34 PM
Hi MikeyB,

The -7db is the input attenuator. The Bump is the regular setting, the Crush is the thump setting on the others and the thump is somewhere in between those two (I forget the exact resistance).

The lo/mid/hi FD switch is just a switch that selects a different resistor for r102 and r103. So Low-FD would be off/no connection, Hi-FD would be 100k, and Med FD 470k. This was just an experiment and I've only used in the Low-FD (off) setting so far.

- Tony 

Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on February 03, 2014, 11:28:01 AM
can a kind soul , give me the the voltages at the node of 470 ohm resistor of 12at7 and the cathode of the 6bz7 please .

cheers


skal
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: ilfungo on April 23, 2014, 11:56:33 AM
Hi
I'm starting to build this comp and need some info:
Can i use for input transformer Marinair t1148?

"
T.1448 Line Bridging Transformer. Designed specifically to isolate equipment with previously unbalanced input arrangements, this transformer may be inserted without serious loss of level.
Rated impdances: 10,000/2,5000 : 9,600/2,400
Nominal Ratio 1+1: 1+1
Primary Pins 2-4, 3-5
Secondary Pins 7-9, 8-10
Screen pin 6
Rated max input: +20 dBm (above 40 Hz)
Distortion: <0.1% (above 40 Hz)
600 Ohm source, 9K6 load <0.01%
Square waves (10 KHz, 9K6 load) No overshoot, no ringing
(Avoid stray capacity across secondary)"

There is a cheap alternative for output transformer that work?

For main transformer(toroidal)?
http://www.don-audio.com/g-pultec-power-trafo-sec-220v-9v-5V???

THANKS!!!
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: ilfungo on April 24, 2014, 10:00:12 PM
??? :(
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on May 29, 2014, 05:40:34 PM
can a kind soul ,measure  the the voltages at the cathode of 12at7 and the cathode of the 6bz7/ ecc8* please , no compression.

cheers


skal
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Dr Gris on May 30, 2014, 01:22:12 AM
Done.

//M
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Dr Gris on June 02, 2014, 05:40:03 PM
Done!


Best
//Magnus
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: ilfungo on June 02, 2014, 07:09:56 PM
No prob...
Thanks!!!
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: ilfungo on June 09, 2014, 04:05:34 PM
Hi
I'm at the end of the of VK1 construction
but I have a problem with the output pad ....
the attached diagram is correct?
I do not know why but from the position 0 dB to -5 I have about 20 dB of difference
I double checked a thousand times the resistors but it's all right ...
Thanks
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: ujszaszyistvan on July 20, 2014, 06:15:45 AM
Hello dear experts including Master PRR
Can I have some questions?
It is about the 12AT7 output stage of the Tubefreak/Chiswick VK1
Please forgive my english...its not my mother language

At the moment I havent got a Sowter 8650 push pull transformer.

I have a Neutrik line transformer that can handle line driving up to +24 dBm, it is 10K:10K.
I know the Neutrik transformer not a 10K:600  but my soundcard has 1M input impedance.

Can I use my Neutrik NTL1 10K:10K line transformer for an output stage a la resistance coupled with 100K plate resistors sitting in the 12AT7 anodes and 470 ohm cathode resistors coupling with a 10mF capacitors?
By the ampbook calculator I would get 34.66 dB and 9.83K output impedance.


Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: Dr Gris on July 31, 2014, 11:29:08 AM
And done...

best
//M
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: ilfungo on August 04, 2014, 03:37:49 PM
Thanks Dr Gris!!!

From some pictures I've seen that The Phoenix use as output trim  stereo 4K7 pot between secondary of transformer and output XLR...
There is also a resistor in series with a + between pot and XLR output ( seems 430R).
Can someone explain?
Impedance?
Thanks!!!
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: JayDubrek on August 13, 2014, 02:33:40 PM
So I'm having a slight issue on this... R14 6.8k resistor keeps burning out on my right channel. Using a 2 Watt resistor here...all voltages on both channels check out fine. Any ideas....probably missed something dumb...this connects to the center tap of the output transformer. The trannie measures out fine and can't trace any shorts anywhere.... Dodgy 12AT7 maybe? Hmmmm
Jay
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: skal1 on August 29, 2014, 06:58:07 PM
seems you are pulling a lot of current through R14 6.8k, have you check out  vr103, R7 ?  these maybe shorted out, have a look...


skal
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: JayDubrek on September 02, 2014, 06:21:34 AM
Yep, it was a short. Couldn't see the wood for the trees, or in this case the valve base for the wires! A tiny sliver of wire had bridged pins on the valve base. This is a PTP build, not the PCB that has been discussed on here. Voltages all good now.  Just need some time to test with audio.
Cheers
Jay
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mrkrawn on October 09, 2014, 06:38:54 PM
hi people
i buy this toroid from donaudio
http://www.don-audio.com/power-trafo-sec-220v-9v-5V

 i 've wire it in serie like the picture on website.
orange and grey together.
I put L on yellow N on purple like the picture.
When i put my multimeter between purple and yellow without 230v it detect a short.
I think if i put the 230v my fuse will blow
I find that strange
Maybe i did something wrong or these transformers are faulty i don't know
if someone have the same transfomer please can you explain me
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mrkrawn on October 14, 2014, 02:26:23 PM
Problem solved by put a bigger fuse like 500ma
Now work perfect :)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mrkrawn on December 12, 2014, 10:16:12 PM
Hi everybody

 i start to build this great diy compressor
i will remove the R102 and R103 resistors.

I just want to know if i need to put a jumper or just remove these résistors

Thanks :)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: petermontg on March 05, 2015, 06:01:57 AM
I have been slowly chipping away at one of these past few months. Still a bit to but getting there.....

(http://i457.photobucket.com/albums/qq298/divinemothercrumbles/DSCN0431_zpsrocex618.jpg)
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: JayDubrek on March 05, 2015, 08:36:08 AM
Looking good Peter! Any internal pics?
Jay
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: petermontg on March 05, 2015, 11:47:15 AM
Looking good Peter! Any internal pics?
Jay

When 100% I will post up the gut shots.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mrkrawn on March 09, 2015, 06:45:13 PM
Hi
anyone know what's the goal with  the dc balance trimmer?
Nice  big box peter where did you get it?
thanks
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: petermontg on March 10, 2015, 09:35:05 AM
Hi
anyone know what's the goal with  the dc balance trimmer?
Nice  big box peter where did you get it?
thanks

Adjust your DC offset.

The case is from modushop. I tend to use these as if you dont want the front panel they will give you a discount and the rear panel is easily drilled.

Frank in NRG CNC cut and engraved the FPD file for me.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mrkrawn on March 20, 2015, 01:53:05 AM
Hi
anyone know what's the goal with  the dc balance trimmer?
Nice  big box peter where did you get it?
thanks

Adjust your DC offset.

ok Peter thanks
and what the good value for DC offset.

The case is from modushop. I tend to use these as if you dont want the front panel they will give you a discount and the rear panel is easily drilled.

Frank in NRG CNC cut and engraved the FPD file for me.
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: mrkrawn on April 23, 2015, 09:44:56 PM
Anyone know where connect the sidechain input jack.
should i connect it to the 6AL5 pins 2&7?
Thanks
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: echoplex on March 03, 2019, 02:40:40 PM
super old thread.. I know.
but has this ever been a DIY clone project?
can I still buy PCBs and case anywhere?

cheers
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: ilfungo on March 04, 2019, 11:08:59 AM
Hi echoplex
I've bought the PCBs time ago from
Tat Purusha.
I don't know if are still for sale, can you try contact him...
ciao
Title: Re: Another vari-mu: Chiswik Reach Compressor
Post by: dustbro on March 05, 2019, 08:07:18 PM
can I still buy PCBs and case anywhere?
I have an enclosure / PCB / and toroid transformer. PM me