Awesome project. For my first build , which I will try in the next year, I will certainly look into adding this. Will follow the experiences of others with great interest.
Your soldering skills are top shelf! I had Lee Jackson, of Metaltronix amplifiers in Austin Texas, build a tube buffered FX loop into my 1979 Marshall JMP 2203 head. It's awesome !
Your videos are a lot of fun to watch and super informative. I think some of us would be interested in your pcb design process. Specifically the pcb software design side of things.
Thanks Matthew. I very much like PCB design. I find it very enjoyable indeed. Its challenging and therein lies the attraction I think. I use Kicad for PCB design. I try to adhere to a few personal rules. They are: No trace right angles. Limit parallel trace lines as much as possible. Give V+ traces lots of space and make them as chunky as the layout allows. Signal and power traces on top layer, ground traces on lower layer. I dislike vias and have yet not had to use them, however I have nothing against them, just prefer not to use them as a challenge I guess. Position decoupling caps as close to opamp pins as possible. V+ and ground traces routed first to decoupling cap pin rather than straight to opamp pin. I try to limit traces underneath opamp if I can. I like to use sockets for opamps, and its important to have access to the ends of opamps so that they can be extracted. In that regard I keep the opamp ends clear of chunky components like capacitors that may inhibit extraction. Little things like that I guess. Thanks for question! Have a good one.
@@elams1894 I’m still learning my way through pcb design, so all of those are really helpful tips for me. I’ve been using Altium Circuit Maker since it’s free but i often hear people say they prefer KiCad. I believe KiCad also has a free version but I’m not sure. I’ve yet to try it, but I’m thinking of giving it a go. So far I’ve only completed a few small auxiliary relay boards for channel switching and a Boosting circuit board with many failures, but I eventually got there. Luckily the prototype boards are relatively inexpensive. Thanks for the reply!
I plan on building one some time in the future. I need a bedroom amp only thing I have right now is a Marshall Valvestate VS100. Would also love to have a JCM800 with a FX loop. Just need to get this thing going with a foot pedal for clean/dirty channel swapping and FX loop on and off.
"What kind of idiot am I?" Ask myself that all the time... Think of it this way, though... If you're smart enough to ask yourself that, you are not an idiot. "We know how stupid we are, therefore we're not stupid. We know how crazy we are, therefore we're not crazy." - Some old, wise guy -
I checked out the schem, very cool. Used a tube triode on the return to beef up the signal. That will do it. Much better. The old loop in the Laney AOR50 worked fairly well surprisingly, compared to the others of the day. Laney still strong in design, very nice!
I use a loop that was based off the Marshall loop. They were made by a company called Iron Sounds but are no longer making them. I’ve installed four and never had any noise issues. Switching the bypass switch on and off theres no difference in sound.
Thats great. Indeed there are some out there that perform well. It can be done, its just not an easy thing. Glad yours works well. Loops are great, they make one heck of a difference. Cheers!
Problem with almost all solid-state solutions is too-low voltage headroom on return. Notice weird Mesa graphic EQ circuit: not good-looking, but main point seems to be (relatively) high (negative) rail voltage. Hard to get around how much better a tube works, in otherwise all-tube circuitry designed to run at the limits. My approach -- caveat, haven't seen anyone else do this so maybe it's bad -- is to use passive resistor divider to produce the send (active buffer is unneeded and a waste here, 10k send impedance or so works fine), and then both halves of a 12ax7 for the return, each running gain of 10 or so with NFB, in series, so non-inverting gain of 100 overall.
Couldnt agree more. Tube driven is fantastic, however one has to factor in chassis realestate and power requirements to run an extra tube. Then the other niggle is that the signal then has to go into pedal silicon so a SS driven loop seems logical too. The return side is hugely problematic I find also. I can almost get the signal to parity on the return side with one opamp, however its just not quite there. In a series setup I would say there is no chance without distortion issues. That is why I have 2 x opamp stages for my return side. That works well for a split parallel signal and I find there is ample grunt, almost too much. With a tube driven FX loop, for sure you dont need SS buffer as the tubes cathode is low impedance. I think Laney uses both opamps (send buffer, return input stage) and then a triode on the return side to beef up the signal. So indeed you are in good company there. There are all sorts of things one can try and it sounds that you are right on on top of it. Bice one!
The difference between series and parallel; Eloquently put. Couldn't be more clear. (I know zero about this shit) The series approach doesn't make sense at all. Why companies would do something like that?
I'm not sure either G. I think it is mainly because it's the phase inversion easy fix. With everything in series, almost all pedal rigs will work. But the easy way is no fun at all. Ask a Mandalorian about 'Parallel' and they would all say together "This is the way"! 😂
