New Solid State FX loop source - $20

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Gainzilla
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Re: New Solid State FX loop source - $20

Post by Gainzilla »

Hey guys,

Sorry for missing all these replies. This is the same circuit as the mojo kit. It is also the exact board designed for use in the jet city 20hv amp, their 20 watt el84 based Marshall type circuit. It is designed to run off b+ voltage as per the rating on the IRF920 data sheet (safe enough for most amps).

I can also tell you that the 20hv also uses this board to add a fixed resonance to the amp. A front panel on/off switch connects via the 2pin connector. If you have an amp that doesn't have resonance, you can fly a nfb wire to and from the two side connections (FR, and FY), and connect a switch. If you have no need for this circuit, simply ignore.

Since Doug hadn't initially planned on selling these, they were fabricated for production with the two connectors, rather than through hole solder pads. The three pin connector is used for connecting the loop. Looking from the component side with the connections on top, the far left pin is connected to the treble pot wiper, and the far right pin connects to the master volume or PI input coupling cap. If you don't have this type of connector you can simply soled to the bottom of the board.

Since there is currently no documentation for these (the primary reason he hasn't listed them on his site), I offered to pull together a set of instructions. Feel free to lmk if you have any questions in the meantime.

Also, you'll notice mojo has added send/return controls to their version. The same could be done to this loop as well, if desired. Hope that helps!

Cheers!

- Bryce
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dorrisant
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Re: New Solid State FX loop source - $20

Post by dorrisant »

I still say the Mojo loop is different... Take a look for yourself.

Notice the absence of any TO-220 devices. Not trying to argue, just sayin'.
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Gainzilla
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Re: New Solid State FX loop source - $20

Post by Gainzilla »

That's true, and I did notice that. The boards themselves are also distinctly different. My understanding of things is that Mojo designed the loop, and then adapted the design for their own use. I haven't actually looked too much at the Mojo loop other than to note the clear board markings, optional trim pads, etc. The bypass switch is a nice option, but then, unless it's foot switchable I'm not sure how useful it actually is. :D
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Re: New Solid State FX loop source - $20

Post by dorrisant »

If you ask Miles... He says the circuit was stolen, not designed, by Mojo...
"Education is what you're left with after you have forgotten what you have learned" - Enzo
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Gainzilla
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Re: New Solid State FX loop source - $20

Post by Gainzilla »

I know Doug paid to have the loop designed, but beyond that I have no idea.
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dorrisant
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Re: New Solid State FX loop source - $20

Post by dorrisant »

Gainzilla wrote:I know Doug paid to have the loop designed, but beyond that I have no idea.
I believe you... That would explain the differences.
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Re: New Solid State FX loop source - $20

Post by Gainzilla »

Adding these here in case anyone needs them.

EDIT: Updated images with correct pin labeling.

Cheers!

- Bryce
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Last edited by Gainzilla on Thu Jan 19, 2017 10:31 pm, edited 2 times in total.
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MakerDP
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Re: New Solid State FX loop source - $20

Post by MakerDP »

Wow this is awesome. Thanks so much!

A $20 B+ powered effects loop is a fantastic find! I am going to order two or three next payday!
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Re: New Solid State FX loop source - $20

Post by sonicmojo »

Thanks for the source! I've been wanting to try one of these in one or two of my amps.
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Re: New Solid State FX loop source - $20

Post by iknowjohnny »

dorrisant wrote:If you ask Miles... He says the circuit was stolen, not designed, by Mojo...
Thats what i understand too, and the original is the $85 metro zero loss loop.... https://store.metropoulos.net/products/ ... x-loop-kit

Now wheres the link to this $20 one? I have tried 3 tube loop designs so far and all 3 changed the tone quite a bit so this is interesting to me because the metro look has been said by many to be totally transparent. But i see no link to this $30 version?

Also note that the metro has downloadable instructions with a chart showing what dropping resistor value you will need depending on B+ voltage. Something that i imagine will be critical to those buying the $20 one with no instructions !
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Re: New Solid State FX loop source - $20

Post by MakerDP »

see the original post in this thread. there is no link... you have to contact Jet City directly.
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Re: New Solid State FX loop source - $20

Post by iknowjohnny »

Gainzilla, can you ask him next time you talk to him what the optimal B+ is for the loop?
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Re: New Solid State FX loop source - $20

Post by Gainzilla »

I've added the schematic to the post with the annotated images above. We can look at the data sheets and components to tell us the operating voltage. :)

Correct me if I'm wrong, but...

IRF830 and LND150 are both rated at 500v Max
All the Resistors on the board look like 1w Metal Film
Can't read the voltage of the signal caps, but the one eCap on the schem is rated for 450v.

I would take a guess and say this thing could be safely operated anywhere south of 400v... The Metro loop says 300v is ideal, and the Mojo loop says "theirs" will operate safely between 150v-350v.

Where part of the Metro loop that makes it so transparent is the careful tuning of the voltages, the Mojo {EDIT: original post said Metro here} loop just says to connect after the last filter cap and drop resistor, which in most amps, should put you somewhere in that vicinity.

I have a 20hv and for what it is, I have no complaints about the loop. Sounds good with or without anything in the loop. Takes both pedals and rack gear well. That said, I've not compared the amp tone without the loop to see what it does to the tone. There are definitely ways to improve this thing, though, in the event you need to season to taste.

My general thoughts on this are its a relatively good loop for super cheap. If you know your way around the inside of an amp, you should be ok. At that price, though,I wouldn't expect much in the way of guidance or support. I'm offering to build the install guide as a favor, but I would look for that to be pretty generalized for most amps, with some specific info for Jet City amps.

Honestly, if transparency and preserving the original tone of the amp is critical to you, I would advise paying the $70 for the Metro loop for the peace of mind. You'll get super-detailed instructions allowing you to fine-tune the entire amp/loop as a system.

Hope that helps,

Cheers!

- Bryce
Last edited by Gainzilla on Thu Feb 23, 2017 5:37 pm, edited 1 time in total.
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Re: New Solid State FX loop source - $20

Post by iknowjohnny »

Hmmm....it's cheap but still i need to have reason to believe it's transparent, and i would never buy the metro because even tho i have seen lots of good reviews on it's transparency, thats a bit much w/o seeing for myself. $20 on the other hand is worth the chance but only if i have reason to believe it is transparent. Anyone posted reviews of jet city amps with that loop that u know of or any remarks about the loop anywhere?
Gainzilla wrote:I've added the schematic to the post with the annotated images above. We can look at the data sheets and components to tell us the operating voltage. :)

Correct me if I'm wrong, but...

IRF830 and LND150 are both rated at 500v Max
All the Resistors on the board look like 1w Metal Film
Can't read the voltage of the signal caps, but the one eCap on the schem is rated for 450v.

I would take a guess and say this thing could be safely operated anywhere south of 400v... The Metro loop says 300v is ideal, and the Mojo loop says "theirs" will operate safely between 150v-350v.

Where part of the Metro loop that makes it so transparent is the careful tuning of the voltages, the Metro loop just says to connect after the last filter cap and drop resistor, which in most amps, should put you somewhere in that vicinity.

I have a 20hv and for what it is, I have no complaints about the loop. Sounds good with or without anything in the loop. Takes both pedals and rack gear well. That said, I've not compared the amp tone without the loop to see what it does to the tone. There are definitely ways to improve this thing, though, in the event you need to season to taste.

My general thoughts on this are its a relatively good loop for super cheap. If you know your way around the inside of an amp, you should be ok. At that price, though,I wouldn't expect much in the way of guidance or support. I'm offering to build the install guide as a favor, but I would look for that to be pretty generalized for most amps, with some specific info for Jet City amps.

Honestly, if transparency and preserving the original tone of the amp is critical to you, I would advise paying the $70 for the Metro loop for the peace of mind. You'll get super-detailed instructions allowing you to fine-tune the entire amp/loop as a system.

Hope that helps,

Cheers!

- Bryce
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Gainzilla
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Re: New Solid State FX loop source - $20

Post by Gainzilla »

I don't really know of any reviews of the loop in and of itself, although there is a ton of buzz on the interwebs... Users wishing it was available for the other Jet City amps they own. It's hard to say what this loop truly sounds like because it come stock in an existing amp. Who's to say what the amp sounds like without it? Honestly, I like the sound, but I feel like there have been a couple times where I might've heard some slight return-stage distortion when running an effect level too high in the loop. Easily adjusted if using a loop with send/return levels. In that case I just turned down the output and was happy again.

I don't know man... I hear what you're saying... I'm about as picky about tone as it gets. For $20, you could buy it and try it. If you don't like it, you could probably re-sell for $15 or something. Or add your own send/return controls. Or use some of the tweaks from the metro loop to compensate for the loop now being in the circuit.

Part of me wonders if you're asking will my amp sound exactly the same with the loop in the circuit, or whether or not it colors the sound in a negative way. Truthfully, I don't think a loop exists that doesn't change the tone in some way. Plus, I mean, you're putting delays and shit in there, converting to digital and back, running through silicon... In that respect, everything about an effects loop will change your tone. That said, I can tell you is that I believe this is a good sounding loop that accommodates a wide range of signals "as-is." With a little bit of tweaking, some additional headroom and flexibility could be added. I'm personally adding one of these to my Jet City 100HDM. This amp has the typical SLO effects loop, which is weird and before the tone stack... The stock loop in that amp adds color and changes the tone of the amp. I'll be interested in comparing the difference, although, the tone will still be going through both buffer stages of the existing tube loop...

Anyway, the biggest recommendation I could make in the quest for tonal transparency is to make the loop parallel. Super easy, and you could add a wet-dry blend knob for total control of exactly how much of the original tone is there.

Does that help?

Cheers!
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