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Almost finished most recent project, just need to clear up some channel switching issues.

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  • Almost finished most recent project, just need to clear up some channel switching issues.

    Dear MEF Wizards,

    I have spent the last two and a half years, on and off, putting together a circuit... just one of a few of my "ultimate amps". I have prototyped the amp three times now (tear down, rebuild with changes in circuit and components etc) and I nearing completion of my fourth prototype which I hope will be my final. However I am stuck on the channel switching circuit...

    The amp is two channels and incorporates a pair of 6V em relays.

    Until now I basically took the switching system from the Marshall Silver Jubilee amp, as seen here in this schematic -> Silver Jubilee Schematic @ The Tube Store website

    The two relays are just wired in parallel to switch at the same time, sharing that 2550 switching scheme. And it works for my purpose in my last prototype. But is it the best way to do it? I really want to build the very best amp I can and hope not to have to repair it in a year or two because I failed this one section of the circuit.

    I will attach a block diagram of the preamp section at the end.

    I had a custom transformer wound and in it is a 6.3V/3A winding specifically for the purpose of the two relays (instead of taking power from the heaters). My initial plans were just to use the existing switching system from the 2550 as is.

    To further complicate things, I am also thinking of adding one final, independent, relay for a gain stage switch in channel 1, should I do so also using this existing relay power supply? Plaguing questions indeed.

    Channel switching is quite new to me, this is only the second amp I have built to have switching (I built a 2550 once) - but this amp is not copied from any one schematic, rather at some level it's got some SLO/Dual Rec, some Marshall, some original stuff... and in all is a "unique" circuit... sort of

    My only wish is to make this switching circuit as simple and reliable as possible... If I can run three relays off of this single power supply, where TWO of them will be operated simultaneously, great. If I can only run two of them, that's fine too. But the question is always there in my mind... is there enough filtering? Etc etc

    Any help or insight you could offer would put me miles ahead, I've been stressing on this for about 8 months now!

    Thank you!

    Click image for larger version

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    "'He who first proclaims to have golden ears is the only one in the argument who can truly have golden ears.' The opponent, therefore, must, by the rules, have tin ears, since there can only be one golden-eared person per argument." - Randall Aiken

  • #2
    Originally posted by Gtr0 View Post
    Dear MEF Wizards,

    I have spent the last two and a half years, on and off, putting together a circuit... just one of a few of my "ultimate amps". I have prototyped the amp three times now (tear down, rebuild with changes in circuit and components etc) and I nearing completion of my fourth prototype which I hope will be my final. However I am stuck on the channel switching circuit...

    The amp is two channels and incorporates a pair of 6V em relays.

    Until now I basically took the switching system from the Marshall Silver Jubilee amp, as seen here in this schematic -> Silver Jubilee Schematic @ The Tube Store website

    The two relays are just wired in parallel to switch at the same time, sharing that 2550 switching scheme. And it works for my purpose in my last prototype. But is it the best way to do it? I really want to build the very best amp I can and hope not to have to repair it in a year or two because I failed this one section of the circuit.

    I will attach a block diagram of the preamp section at the end.

    I had a custom transformer wound and in it is a 6.3V/3A winding specifically for the purpose of the two relays (instead of taking power from the heaters). My initial plans were just to use the existing switching system from the 2550 as is.

    To further complicate things, I am also thinking of adding one final, independent, relay for a gain stage switch in channel 1, should I do so also using this existing relay power supply? Plaguing questions indeed.

    Channel switching is quite new to me, this is only the second amp I have built to have switching (I built a 2550 once) - but this amp is not copied from any one schematic, rather at some level it's got some SLO/Dual Rec, some Marshall, some original stuff... and in all is a "unique" circuit... sort of

    My only wish is to make this switching circuit as simple and reliable as possible... If I can run three relays off of this single power supply, where TWO of them will be operated simultaneously, great. If I can only run two of them, that's fine too. But the question is always there in my mind... is there enough filtering? Etc etc

    Any help or insight you could offer would put me miles ahead, I've been stressing on this for about 8 months now!

    Thank you!

    [ATTACH=CONFIG]54378[/ATTACH]
    I'm not sure I'd be switching the input side of the circuits. Switching between the outputs of the two channels and the two EQ circuits alone seems the most sensible. Now, if it was an effects pedal, there you do want to be able to take the circuit completely out for a hardwire bypass.
    Logic is an organized way of going wrong with confidence

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    • #3
      So I should feed both channels, splitting them where k1a would be and send one (or the other) to ground at k1b?

      Thanks
      "'He who first proclaims to have golden ears is the only one in the argument who can truly have golden ears.' The opponent, therefore, must, by the rules, have tin ears, since there can only be one golden-eared person per argument." - Randall Aiken

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