# Closed Circuit Booster Limiter: Feel the power of Mjolnir!



## jeffwhitfield (Jan 2, 2022)

In a video on Angus Young's rig, they talked about a rather important piece of equipment that appeared to be pretty critical to his tone: the SoloDallas Schaffer Replica, which replicates the preamp section of a Schaffer Vega wireless system. I was quite intrigued by this and wondered why this particular circuit was so important to folks like Angus. So I built a Closed Circuit and gave it a try.

It's an interesting circuit for sure. Doesn't appear to do much for drive pedals...but then again I haven't tried it with many. For many of the amp models I tried, it's a different story. It adds a bit of sparkle to them. It's almost like a boost of sorts with an added ability to compress things a bit. This combination does seem to add quite a bit of character to the amp. I can certainly understand why it would be missed if all you're using is a Marshall stack.

Question is: Are there any other boost circuits that are capable of achieving the same thing? 

in terms of design, since the original is called the Storm, I wanted something that fit the same bill. Was at first thinking about the X-Men's Storm...but that didn't fit really. So then I thought about the God of Thunder, Thor. Given that this is a pedal that is sort of an indispensable tool for some, naming it after Thor's hammer just seemed to work. Plus, it's just fun!


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## Preverb (Jan 3, 2022)

You seem to be building lots of pedals lately!  Do you end up keeping the majority of them? 

The white dot on the NSL32 is at the left lower side by the K?   I've got one of these partially started but then I realized I forgot to buy 2K resistors.  Sounds like it's most useful application is for ACDC style stuff?


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## jeffwhitfield (Jan 3, 2022)

Preverb said:


> You seem to be building lots of pedals lately!  Do you end up keeping the majority of them?
> 
> The white dot on the NSL32 is at the left lower side by the K?   I've got one of these partially started but then I realized I forgot to buy 2K resistors.  Sounds like it's most useful application is for ACDC style stuff?


Yeah, I’ve been doing a lot of building mainly as part of a study on different circuit types and the impact they have on a guitar sound. Started with distortion pedals, then overdrive, then fuzz. Also threw in a few modulation, delay, and other odd effects just for giggles. 

I have a handful that didn’t work out too well that are in my graveyard. About a dozen in archive boxes. Main collection is about a good two or three dozen or so. Haven’t really counted. Quite a few so, yeah, winding down and taking a break soon. Got two left in my queue and a few to debug. 

As for the NSL32, I did a search on the forum about this. One post talked about this and said the dot lines up with the K. The effect is really subtle. I don’t think it’s meant to be a super strong limiter. With both the gain and the limiter up you can definitely tell a difference. It knocks down the gain a bit when you dig into it. 

Useful for nailing an AC/DC tone..,but I think it’s useful as a way to add some sparkle to an already driven amp.


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## Preverb (Jan 3, 2022)

I am probably going to end up going through a similar process.  I really wanted a super lead style pedal but had ordered the M800.  I think there was a recent MIAB (Golden Falk) that might be closer to that.  It seems like I will end up with at least 10 different overdrives, preamps, distortions.  I think I should have ordered a few more modulation PCBs.


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## jeffwhitfield (Jan 3, 2022)

Preverb said:


> I am probably going to end up going through a similar process.  I really wanted a super lead style pedal but had ordered the M800.  I think there was a recent MIAB (Golden Falk) that might be closer to that.  It seems like I will end up with at least 10 different overdrives, preamps, distortions.  I think I should have ordered a few more modulation PCBs.


Ah, Plexi's! Those are all JFET based drives. The Acrylic Overdrive (Wampler Plexi-Drive) is another one that's similar. Strangely enough, I haven't built many. Only one I have is the AionFX Megalith (ZVEX Box of Rock) which is a MOSFET drive and uses BS170 transistors. Quite similar though. I might loop back around and build an Acrylic sometime. The ones you mentioned look interesting though.

I made my decisions based on certain mainstay pedals: Tube Screamer, Distortion+/250, Blues Breaker, DS-1, and others. Just went down the line of the most popular distortion and overdrive pedals and picked out some PCB's that were based on them.

Some surprised me in that I liked the inspired ones better than the original. The Irrlicht Overdrive (EQD White Light) was one of those. Felt more useable than the MXR Distortion+ / DOD 250 clone I built along side it. Sent the AionFX Aphelion to the graveyard due to the fact that the tone switch on it didn't do squat.

Once you get into fuzzes...man...that's a crazy dive with that one for sure.


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## sixxtus (Jan 16, 2022)

Very nice looking pedal ! This will be one of my next build !


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## Chuck D. Bones (Jan 16, 2022)

Nice build!  
I think what you're hearing as "sparkle" is the SVDS's ability to drive a cable with no high-freq loss.  The freq response of the pedal itself is pretty damned flat from 50Hz to beyond 20KHz.  What you will hear is a change in tone when the BOOST and LIMITER controls are turned up.  In this version of the SVDS, there is no filtering on the opto's LED current.  The Aion Gale has an optional filter cap in parallel with the LED.  Without the filter cap, the opto imparts some mild distortion on the low frequencies.  I put the cap in my build and I'm thinking of removing it.  YMMV.


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## jeffwhitfield (Jan 16, 2022)

Chuck D. Bones said:


> Nice build!
> I think what you're hearing as "sparkle" is the SVDS's ability to drive a cable with no high-freq loss.  The freq response of the pedal itself is pretty damned flat from 50Hz to beyond 20KHz.  What you will hear is a change in tone when the BOOST and LIMITER controls are turned up.  In this version of the SVDS, there is no filtering on the opto's LED current.  The Aion Gale has an optional filter cap in parallel with the LED.  Without the filter cap, the opto imparts some mild distortion on the low frequencies.  I put the cap in my build and I'm thinking of removing it.  YMMV.


That probably explains why Angus Young and others use it. Seems the boost adds just a little something to the tone.


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