Questions about Matchless DC30 channel mix into one PI Grid

[psychepool]

I'm planning to make a Matchless DC30.
I don't like the fact that the DC30's FX Loop is assigned separately for each channel and that it is a passive loop.
In order to use only one FX Loop for two channels, the two channels must be mixed and sent to one output, so I searched for reference and found this circuit at here.

https://el34world.com/Forum/index.php?topic=23893.0

https://el34world.com/Forum/index.php?action=dlattach;topic=23893.0;attach=73688;image




I was thinking about adding reverb, so this circuit was a great referene.
Is there anyone who has ever made one using this circuit? I wonder if this is a circuit that works well. In theory, there doesn't seem to be any major problems, but I'm curious whether it actually works well without any special bugs.
Reverb is not an important consideration. First of all, I am curious about whether the mixing of the two channels occurs naturally.

Or, I'm wondering if there are better circuits for constructing something like this.
Looking at the DC30 Reverb model or the HC15 model, it appears to be configured to use only one FX Loop, as I wanted.
Have any of their circuit diagrams been made public?


Thank you

[PRR]

Welcome.

The two input paths are out-of-phase, so if you could get an exact 50:50 mix they would cancel-out. But the null is never complete, and there are sometimes useful sounds either side of the null.

[WimWalther]

I believe there's an error in that schematic. The junction of R12, 13, 14 & 15 should be a 4-way connection, not a jump.

Yes?

[psychepool]

Welcome.

The two input paths are out-of-phase, so if you could get an exact 50:50 mix they would cancel-out. But the null is never complete, and there are sometimes useful sounds either side of the null.

Thanks for your reply.

Why are the phases of the two inputs opposite? Is it because there is a cathode follower on one channel?

I'm not going to use both channels of this amplifier at the same time.
Basically, I plan to select the channel through the switch from the input. (Input from the unused channel leads to the ground)
Even if 4 inputs are used as in the circuit diagram, the channel inputs will not be jacked together like Plexi.
Is there a risk of an out of phase in this case as well?

Is there any problem other than what you mentioned?

I believe there's an error in that schematic. The junction of R12, 13, 14 & 15 should be a 4-way connection, not a jump.

Yes?

Someone mentioned it on the original page where this circuit was posted, so I know about it. In fact, of course, that location is usually connected, so I didn't realize it was jump until someone mentioned it. Thanks for your opinion!

[sluckey]

Is there any problem other than what you mentioned?

No. Fender has been mixing channels like that for a long, long time.

[tubenit]

I'll offer a thought for your consideration. I am NOT saying this is something you should do, but simply putting it out there as an idea.  I see no reason that this shouldn't work on your Matchless inspired schematic.

I've been "borrowing" half a dual triode and using it as a return on a psuedo kinda sorta active FX loop.  And then I use a mosfet as a cathode follower going into a tone stack as the "send" section of the psuedo active FX loop.  This has worked quite well for me and I'm very pleased with the results I've gotten.  I've tried numerous time signature effects pedal in this and all of them have worked to my satisfaction especially different delay and reverb pedals I have.

I like it also because I can put both a delay and/or a reverb pedal inside that loop. 


with respect, Tubenit

[psychepool]

No. Fender has been mixing channels like that for a long, long time.

Thank you. Not just circuits like Twin Reverb, but broadly speaking, the first stage of amplifiers like Tweed Baseman and Plexi is considered the same way.
If I'm not going to use Reverb, can I just skip the 150K behind the 150K/220K mix resistance?
If I want to connect the Reverb behind the FX Loop, should I connect the FX Loop behind the 150K/220K mix resistance and connect the Reverb with the 150K mix resistance between the FX Loop and PI?

I'll offer a thought for your consideration. I am NOT saying this is something you should do, but simply putting it out there as an idea.  I see no reason that this shouldn't work on your Matchless inspired schematic.

I've been "borrowing" half a dual triode and using it as a return on a psuedo kinda sorta active FX loop.  And then I use a mosfet as a cathode follower going into a tone stack as the "send" section of the psuedo active FX loop.  This has worked quite well for me and I'm very pleased with the results I've gotten.  I've tried numerous time signature effects pedal in this and all of them have worked to my satisfaction especially different delay and reverb pedals I have.

I like it also because I can put both a delay and/or a reverb pedal inside that loop. 


with respect, Tubenit

Thank you for your very good idea!

My question is, CH1 of Matchless DC30 uses 2 triodes in parallel for 1 stage unlike Vox's top boost circuit, what difference would it make if we used only one side?


Apart from the your answers, the additional question I would like to ask is does it actually mean a lot to install FX Loop on this amplifier.

The reason for connecting FX to the loop is to get a clean delay or modulation in a hard overdrive tone compared to connecting FX to the input, and I guess this amplifier gets most of the distortion by overdrive PI tubes or power tubes, and it's a situation where it takes overdrive at the back end of the delay or modulation anyway, so I wonder if it's that different from connecting FX to the input.

I'd love to hear from anyone who's ever used this amplifier, whether it's original or clone. Is it a big difference to connecting Fx to the input if it's plugged into the loop in an overdrive setup rather than clean or crunch?

[tubenit]

I can not tell what your question is ?    IF your question is does installing this type of design of a pseudo active FX loop impact the sound/tone ............... then the answer is yes it does in my opinion.


The extra triode used for the FX recovery can add some gain in the signal chain, so you may or may not want that in your amp?


I have used delays and reverbs between the guitar and the amp on the front end and in FX loops both passive and active FX loops.  I prefer delay and reverb in an FX loop. Just a personal preference and not necessarily "better".


With respect, Tubenit