Build Thread:VECA MS (VCA comp)

[knight84]

Hi,

I was thinking of buying a Serpent Audio kit then saw this unit. Now, I may be dragged to this. The picture was very explanatory IMO. But just wanted to confirm If the 3rd position has absolutely the balanced weighted M-S field?
If so thats great. Also I would like to see that with a comparison with a real SSL unit. If not possible showing all possibilities on a stereo bus would be great as well. 

 

[Gustav]

Hi,

I was thinking of buying a Serpent Audio kit then saw this unit. Now, I may be dragged to this. The picture was very explanatory IMO. But just wanted to confirm If the 3rd position has absolutely the balanced weighted M-S field?

It doesnt. The 6th position is to GssL weighting (more M than in turbo mode). Everything else is more S/less mid going down. The drawing was meant to illustrate that.

If you want a setting with the theoretical weighting flat, you can calculate the values ( 0,5 gain for M, 1 for S).  You have that type of design control at your disposal just by changing the resistor values that program gain before the M/S decoding.

In real life application, in my experience, the math doesnt matter too much, since the output and balance of the respective processing chain depends on what you put in.  Just set it so it sounds good to you, and remember, in this unit, the M/S processing is only split in the SC detection.

The solution I ended up with is -1M +3S for each step left. It gives a good flow to the dial in my experience.
You could also sub the switch for a pot (or two pots) for infinite settings.

Gustav

 

[knight84]

That sounds convincing. Another question, what is the blend knob for? Does it work like a wet/ dry mix knob ?

Barbaros

 

[Gustav]

what is the blend knob for? Does it work like a wet/ dry mix knob ?

Yes, thats what it is.

Gustav

 

[knight84]

what is the blend knob for? Does it work like a wet/ dry mix knob ?

Yes, thats what it is.

Gustav

Thanks a lot. And by the way congrats for the design or innovative expansion of the design I should say maybe I will give my order as soon as a friend travels to Danmark.

 

[XAXAU]

Hey Gustav!

I asked a while back what the stall switch does? Also, is it possible to put a pair of Lundahls on the output? Noob here, been trying to read the schematics but can´t figure it out.  8)

 

[Gustav]

Hey Gustav!

I asked a while back what the stall switch does? Also, is it possible to put a pair of Lundahls on the output? Noob here, been trying to read the schematics but can´t figure it out.  8)

Stall is a fixed attack/release setting. Values given for a levelling sort of setting, but you can vary them or do something else entirely.

No footprint for Lundahls, if thats what youre asking.

Gustav

 

[XAXAU]

Hey Gustav!

I asked a while back what the stall switch does? Also, is it possible to put a pair of Lundahls on the output? Noob here, been trying to read the schematics but can´t figure it out.  8)

No footprint for Lundahls, if thats what youre asking.

Thanks! Yeah, sort of. I was just wondering if there was an easy way to put the Lundahls at the output?  Maybe the question is too noobey for you?

 

[Gustav]

Hey Gustav!

I asked a while back what the stall switch does? Also, is it possible to put a pair of Lundahls on the output? Noob here, been trying to read the schematics but can´t figure it out.  8)

No footprint for Lundahls, if thats what youre asking.

Thanks! Yeah, sort of. I was just wondering if there was an easy way to put the Lundahls at the output?  Maybe the question is too noobey for you?

Or maybe I am too noobey to understand the question!?

Theres no footprint for an output trafo, and imo, theres no need for one either. Of course, if you feel the unit will not perform to your liking without, you can omit the 1646, exchange it for a wired in 5402 and make a few, small adjustments. There is no PCB footprint or drop-in solution, though.


Gustav

 

[kustohm]

Hi everyboDIYers!

A question about the tantalum capacitors:

In the PCB the polarity is printed but on the tantalum themself...no polarity...
Same lenght for both legs, no + marked, only value.
Can you help me please?
Thanks

 

[Gustav]

Hi everyboDIYers!

A question about the tantalum capacitors:

In the PCB the polarity is printed but on the tantalum themself...no polarity...
Same lenght for both legs, no + marked, only value.
Can you help me please?
Thanks

I answered your mail about this.

If you send a mail during the weekend, please be patient and at least wait for the nearest weekday before sending it again.

Gustav

 

[kustohm]

Hi,

I am just finishing my Veca, everything looks OK.
Just 2x IC's 5534 remaining instead of the 2x 5532 marked on the PCB...I don't know if it's almost the same  but I put them instead of 5532.
I checked the secondary before everything: was good.

But: I turned on the Veca... R10 burned! The first one (on the left between the 2 1000µf on the top of the PSU section).


Somebody could help me please?
In advance thank you!

 

[Gustav]

Just 2x IC's 5534 remaining instead of the 2x 5532 marked on the PCB...I don't know if it's almost the same  but I put them instead of 5532.
I checked the secondary before everything: was good.

You can't replace 5534 with 5532. You can usually use Google to clear out such issues in five seconds if you have doubts.

Gustav

 

[kustohm]

Just 2x IC's 5534 remaining instead of the 2x 5532 marked on the PCB...I don't know if it's almost the same  but I put them instead of 5532.
I checked the secondary before everything: was good.

You can't replace 5534 with 5532. You can usually use Google to clear out such issues in five seconds if you have doubts.

Gustav

OK, thanks Gustav.
Unfortunately you put this 2x 5534 instead of the 2x 5532 on your kit, did you think there's an issue with my R10 burned?
I precise that I've not done the mod you explain in the "errata" PDF file concerning -12v...

 

[Gustav]

OK, thanks Gustav.
Unfortunately you put this 2x 5534 instead of the 2x 5532 on your kit, did you think there's an issue with my R10 burned?
I precise that I've not done the mod you explain in the "errata" PDF file concerning -12v...

Mail me about the IC, and Ill get the correct ones out to you (Probably from a  kit packed before the revision, and I forgot to change them)

And yes, putting in the wrong IC can certainly result in a burned 10R. Unless you left it on for quite some time, its probably not dead, but I can include a 10R resistor, no problem.


Gustav

 

[TwentyTrees]

Hi all!

As there hasn't been much feedback on the VECA so far, I wanted to just jump in and say that this is a really fun build and an amazingly flexible compressor. I also wanted to share some of the things I encountered when building mine in the hope that it may help others. I decided to go for this rather than the standard GSSL for the built-in side chain and blend features, as well as the (unique?) mid/side side-chain emphasis – and Gustav has done a great job of bringing all that together into a unit that shares a lot of DNA with the GSSL but is very much its own beast.

I finished building mine over the weekend (still got a bit to do on the aesthetics!), and was surprised and delighted when it worked first time and nothing blew up. I was particularly surprised as I made a few modifications to the design, so the chances of everything working straight off the bat seemed pretty remote (of course, the sensible plan would have been to build the thing first, verify it was working, and then investigate mods – what can I say, I like to live dangerously...). I should note that the fact I carried out mods isn't a reflection on Gustav's design, which as I say is excellent – rather, I know how I like to use compression so wanted to make as flexible a toolkit as possible.

As well as an extra 1.5:1 ratio, I added a bunch more side-chain filter options, a whole load more attack times, and pots for variable attack and release (selectable from the A/R switches). Details at the end. I spent a long time doing my homework, and many hours reading various posts around here, so huge thanks to the whole community for being so giving in sharing info and expertise. The fact that this all worked first time is testament to everyone else's hard work as much as my obsessive research!

I was a bit worried that the additional ratio and other mods might upset the delicate balance of the compressor, so following advice I found around the place (referenced below) I switched a couple of resistors out for trim pots and set out the  details here in case anyone else is thinking of doing similar:

• R100: this 2K resistor calibrates the meter, and I switched it out for a 5K trim pot (which I pre-trimmed to 2K)
• R101: this 120 K resistor trims how the ratio is applied at a given point on the threshold (as far as I understand it!), and I replaced it with a 100 K resistor plus 200 K trim pot (pre-trimmed to 20 K) in series
• R4 & R21: these 1K resistors manage the control voltage fed to the left & right channel VCAs from the compression section of the board. In practical terms, they control the range of the ratios - if you increase them above 1K, the ratios  bunch up (ie, 2:1 might be more like 3:1 and 10:1 might be more like 8:1), and if you decrease them, the ratios spread out (so 2:1 might become 1.5:1, 10:1 might become 11:1). After extensive experiments, and much twiddling of the 200K trim pot above, I reduced these to around 900R each by strapping a 16 K and 20 K in parallel with each (based on what I had lying around - not elegant, but it works).

Calibration took a while (mostly experimenting with R4 and R21), but after making the changes above, and tweaking the trim pots (using the SB400 calibration guide and the posts by regularjohn, MikeClev and jwhmca linked below), I was able to get the ratios almost spot on:

• 1.5:1 gives an increase of 6.3dB on 10dB input increase, therefore 1.56:1
• 2:1 gives an increase of 5 dB, so 2:1
• 4:1 gives an increase of 2.5 dB, so 4:1
• 10:1 gives an increase of 1 dB, so 10:1

Given how long it took me to get to this point, I will happily accept being very slightly out on the 1.5:1 ratio!

All in all, it's been a great experience from which I've learned a huge amount, and I can't wait to start using the VECA in anger. My thanks to Gustav, and to all those whose good ideas and hard work I have benefited from here. Now to tidy up the wiring, cut down the pot shafts, and sort out the front panel (where did I put that walnut sheet..?).

Cheers,
Andy

===============
Full list of mods:

• Additional ratio: 1.5:1 (see link below for details)
• Additional attack times: 5 ms, 15 ms, 20 ms, 50 ms, 100 ms (using 41.2K, 124K, 165K, 412K and 820K resistors respectively)
• Switchable variable attack, between 0.1 and 30 ms (250K log pot in series with 820R resistor)
• Switchable variable release, between 0.1 and 1.2 sec (1M lin pot in series with 180K resistor - both paralleled with 47uF tantalum cap)
• Side-chain filter frequencies: off, 40Hz, 60, 80, 100, 120, 40, 160, 180, 200, 250
• And the meter LEDs change colour from amber to white when the compressor is bypassed!

===============
Calibration links:
Calibrating the GSSL (regularjohn)
http://groupdiy.com/index.php?topic=40883.msg507502#msg507502

SSL clone compressor ratio measurements (MikeClev):
http://groupdiy.com/index.php?topic=944.msg535243#msg535243

GSSL 1.5 ratio mod (jwhmca):
http://groupdiy.com/index.php?topic=49854.0

SB400 calibration - at the end of the Build Guide
http://groupdiy.com/index.php?topic=40971.0

 

[Gustav]

I made a few modifications to the design
http://groupdiy.com/index.php?topic=40971.0

I am so honoured you found it worth putting this amount of time and effort into it. Thanks for sharing, and modding, and showing the design actually holds up to that level of scrutiny Your work is a great example of adding a true level of DIY to a ready-made project!

Hope it serves you well!

Gustav

 

[TwentyTrees]

Thanks Gustav! Between the VECA and my MS PQ76, I'd say my master bus is pretty much ready to rock...

 

[tata]

ive just built a VECA, everything seems to be fine - but im not too happy with the Blend control, as is.
id like to get smoother / more even blend behaviour - is this the place for a W-taper pot? would that help?
also id like to get rid of the level drop when Blend is active.

im planning to do a new front PCB for it, to make it fit a 1U rack, and being able to do/add some mods.
im very intrested in using pots instead of rotary switches, adding a dual color LED for Bypass/Action, and id love to look into the "true bypass" mode too - it seems unit is not passing audio when turned off (by design).

im happy with the VECA in general - it sounds gooood and was fun to build.

 

[Gustav]

ive just built a VECA, everything seems to be fine - but im not too happy with the Blend control, as is.
id like to get smoother / more even blend behaviour - is this the place for a W-taper pot? would that help?
also id like to get rid of the level drop when Blend is active.

Unfortunately, I have no idea how you would implement the W-taper and achieve a throw to your preference. Hopefully someone else (smarter than me) can help with that.

I took care to make sure the blend was unity (no compression, blend in and 100% "clean". Any processed signal added, and level will depend on your make-up gain setting, of course.

Unless you are talking about a minor difference (0.2dB ish), I would suspect some error here if you are not seeing unity under described conditions.  In fact, you should see a level bump (not drop) in the center of the pot, where signals are summed. Check the schematic, its as simple as changing the resistor controlling gain to the opamp doing the summing, if you want to change the level.

"true bypass" mode too - it seems unit is not passing audio when turned off (by design).

The bypass is true, but my logic is to have relays "default" to the path they will be used most. So, no voltage to activate the relay = relay in default = relay switched into the signal path.

I have later learned that some have a preference to have the default path to bypass, since the unit will carry the signal when its turned off. I honestly never thought of that (grew up in patch bay environments). You can do a few cuts and add a few wires to the bypass relays to reverse this behaviour to your preference. Let me know if you need help with that!

im happy with the VECA in general - it sounds gooood and was fun to build.

Goooood to hear

Gustav