Matchless DC 30 Single channel with reverb. Help!!!

Discussion in 'Shock Brother's DIY Amps' started by stinga11, May 23, 2020.

  1. stinga11

    stinga11 TDPRI Member

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    Greetings, I'm about to build a DC 30 for a friend. The project started as an Ac15 but has ended in another amplifier. The real Matchless DC 30 has a 470k resistor to ground before the phase inverter. But in my schematic I added Matchless Chieftain reverb. At the input of the reverb I have a 1M Grid leak resistor to ground so this makes me think, am I killing the signal twice? I considered removing the 470K resistor. What do you think?[​IMG]
     
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  2. Bitsleftover

    Bitsleftover Tele-Meister

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    Im very interested in this project.
    I’m not qualified to answer but while you wait for someone more knowledgeable to jump in....
    I’ve been thinking of doing a micro version of this for my next build. Im sure you’re aware, but what you’re building is essentially a Matchless Nighthawk Reverb. I’ve not been able to find a specific schematic but there must be something out there somewhere. I’ve been using the EF86 channel of the DC30 schematic like yourself.
    On my current Bassman Micro build, I experimented with different send and return locations for the one tube reverb I added. Regardless of where I placed the send, the one meg dwell pot remained very transparent. I found it was the return location that made the biggest impact on how intrusive the addition of the reverb circuit was.
    I also found that injecting the wet reverb into the PI like this had no noticeable effect on the dry signal at all. It was by far the most transparent way of adding reverb to my ears. The only reason I didn’t use that method on that build was that I wanted to keep the presence control which connects at that side of the PI. What I’m trying to say in long winded way is, I don’t think this reverb will drop your dry signal very much at all.
    All that said, from other EF86 builds I’ve read about on here, people almost always seem to be disappointed by the lack of gain. Because of that I think I’ll be giving the 470k a miss to start with. I don’t think the signal will be too much for the PI without it. I figure I can neatly add it to one of the effect loop send or return jacks later if I change my mind.
    Good luck with the build. I’d love to watch it progress if you decide to document it on here.


    Sent from my iPhone using Tapatalk
     
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  3. stinga11

    stinga11 TDPRI Member

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    Thanks for answering. The 470k resistor doesn't make much sense to me because before it there is only the volume potentiometer so I understand I can control the gain but as the original schematic has it I am concerned that it will lose some headroom. When this project is finished I will document it here.
     
  4. Lowerleftcoast

    Lowerleftcoast Tele-Holic

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    I believe the 470k is there because of the *send* of the passive effects loop. If the passive effect loop was not there the 470k would not be needed.
     
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  5. FenderLover

    FenderLover Poster Extraordinaire

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    I'd leave out the 470K and add it later if needed. I'd agree that gain would be negatively affected and there is only one gain stage to work with. The FX send is already ground referenced via the volume pot right before it, and the 470K is adding a voltage divider. Luckily there is a Master and that will let you get reasonable drive out of the preamp before setting the output level. You'll get a nice bluesy drive, but not really any crunch. A pedal out front is needed for that, which isn't a bad formula.

    Regarding the reverb, it works well. I have a Chieftain and there is plenty of verb there using both inputs of the LPTI as a mixer. If you need Dick Dale reverb, it will fall a little short, but I never come close to needing or wanting that much. The 1M and 500pF right before the verb driver is a filter that cuts bass from swamping the tank. You will see that in just about any spring reverb circuit.
     
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  6. FenderLover

    FenderLover Poster Extraordinaire

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    One more thing - you didn't ask, but I think the Master Bypass switch will have limited usefulness. Of course, that's for you to decide. :)
     
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  7. alathIN

    alathIN Tele-Holic

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    Very cool project and I will be following. You've got some of my favorite pieces in this.

    My first amp build was a Trinity TC15 which is very similar to this except it has another preamp channel and no reverb. The TC-15 made me a fan of the EF86 + rotary tone switch preamp channel and I included one in my current micro build.

    If you're shopping for transformers for this build you might want to look at the Trinity PT and OT, made by Heyerboer for exactly this kind of amp. https://www.trinityamps.com/product/trinity-tc15-kit/

    I'm driving myself crazy troubleshooting/tweaking the EF86 channel right now because if I make it more gainy I love the high gain sounds and if I make it cleaner I like the clean sounds. If I was to start over I might put in a DPDT switch and be able to flip between two different sets of plate and screen resistors.
    The Soviet era "Winged C" 6J32P is the most satisfying EF86 type I have tried. Unlike some Soviet tubes, it uses the same pin layout as its Western equivalent. It's livelier clean and smoother with high gain.

    I have also recently become an advocate of using power amp tubes as reverb drivers. I built a Weber ReVibe (the reverb part of which is based on the old Fender 6G15 standalone reverb) and uses a 6v6 or 6k6 as the reverb driver and it takes reverb to a whole new level.
    For my current 1W micro build I'm trying an EL84 reverb driver. The Fender Vibroking amps did this. I'm still troubleshooting this build but the reverb is glorious.
     
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  8. alathIN

    alathIN Tele-Holic

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    My TC-15 has this exact same post-phase inverter cut and MV layout and I can't tell the difference between MV at 10 and MV bypassed.
    I put Trinity's voltage regulation module in mine to have another option for loudness management. If I knew the MV was going to work so well I would not have bothered.
     
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  9. FenderLover

    FenderLover Poster Extraordinaire

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    You have confirmed my feeling about the Master Bypass switch, and that's to say that just because we can add a switch to just about everything doesn't mean we should.

    It's ironic how some folks complain about the Matchless Master volume circuit in their build, yet no Matchless owners complain about their amplifier. Mine certainly works just fine.
     
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  10. stinga11

    stinga11 TDPRI Member

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    Thanks, excellent explanation
     
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