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  1. Replies
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    Certainly plausible, but unclear if the values...

    Certainly plausible, but unclear if the values are optimal (I would simulate it) or if it will achieve your OD tone goals.
    OD with spkr/OT is different than OD with R load. There are some prior...
  2. Ditto - although as an engineering exercise for...

    Ditto - although as an engineering exercise for switching heavy power/currents, the problem/solution has some value. I can't argue with the motivation either, but I wonder if given the part...
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    OK - thanks. So - the spec is for continuous DC...

    OK - thanks. So - the spec is for continuous DC - not AC voltages.
    That's comforting since I don't expect continuous large negative voltages.

    I still do wonder what happens if the spec is...
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    neg grid voltage limit

    I never paid much attention to the negative grid voltage limit in the 12ax7 specs. JJ and others spec -50V wrt to the cathode. Since many grids are AC coupled and some big signals can hit the cap,...
  5. Sure - why not? You describe one of many...

    Sure - why not? You describe one of many options that lead to shorter wires and simpler construction. Both are desirable (IMO) and yes, we have better methods, materials, and tooling than 50 yrs...
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    True - problematic, but many dual-channel scopes...

    True - problematic, but many dual-channel scopes allow A-B display so they provide a solution. The A and B channel probes can be connected to the two floating outputs, with their ground clips both...
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    Thanks - something like that seem to be...

    Thanks - something like that seem to be happening. The ripple freq appears proportional to current draw, but variations from 2ma to 20ma don't seem to impact the ripple presence. What does seem to...
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    Understood - I appreciate the links, a quick...

    Understood - I appreciate the links, a quick browse has already given me some useful ideas... thanks trobbins
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    Thanks for the suggestions... unfortunately, I'm...

    Thanks for the suggestions... unfortunately, I'm not versed in these circuits so I'm lost on how to implement any of it. That said, I'd be very open to seeing examples like your 12v supply (if you...
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    The grounds are connected on the PCB, so they're...

    The grounds are connected on the PCB, so they're not isolated. I can't hear 75KHz, but I can hear buzzing when it goes into ripple mode. The buzz seems to be the ripple freq. It's clearly a...
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    The freq varies - but it's below 100Hz. I've...

    The freq varies - but it's below 100Hz. I've scoped the input, it's clean (a bench supply).
    The ripple level varies as I adjust the output voltage or the input voltage (all tests with a fixed...
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    DC DC converter

    I recently played with one of those converter modules that are widely selling (got mine on ebay :tape:) that produces up to 390v DC from DC supplies. Here is a link to one example - they seem all...
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    I've been trying to understand this myself. I...

    I've been trying to understand this myself. I didn't know how things would turn out since AOT was an experiment. I have several theories, two of which I can argue from evidence so far. First is...
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    😎 thanks. There should be some clips and videos...

    😎 thanks. There should be some clips and videos on the HD site. GW has a whole show video. The 2x10 version combo is a beast. Fills a big room no problem. To be clear, the HD amps are only...
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    LT - I don't know of a filed patent. I can't be...

    LT - I don't know of a filed patent. I can't be sure, but I don't know of one.
    As for the PI tremolo - I designed a series of small cards for doing tremolo for an LTPI and a series of reverbs...
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    While I can't speak for GW, I can say this amp is...

    While I can't speak for GW, I can say this amp is a joint effort with me and GW.

    Also - since I've seen a number of posts that speak badly of GW, I suggest you listen to and play some of his...
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    I can't seem to upload it to the forum, but I'll...

    I can't seem to upload it to the forum, but I'll keep this link live for a bit.

    https://drive.google.com/file/d/1kPVTL_Ji5MnmR--NikyO_sbzswAayxZB/view?usp=sharing
  18. I think it's "all pass" NFB. It's not tuned to...

    I think it's "all pass" NFB. It's not tuned to produce an audible roll off. The amount of NFB does vary with the vol pot setting. At low volume, the NFB is also low (shunted to ground) so it has...
  19. The 5E3 doesn't usually have a standby sw. Does...

    The 5E3 doesn't usually have a standby sw. Does the 5R4 amp have a standby sw?
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    Just a comment on the neo Jensen. I have one and...

    Just a comment on the neo Jensen. I have one and I find it super clean - almost hifi clean.
    I'd vote for that alone making a big difference in tone and perceived headroom.
  21. Thread: LTPI balance

    by uneumann
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    2,201

    Well - seems transistors are still important for...

    Well - seems transistors are still important for such things. Thanks for that comparison.
  22. Thread: LTPI balance

    by uneumann
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    2,201

    Thanks - appreciate your comments, but really, I...

    Thanks - appreciate your comments, but really, I didn't design much of anything.
    If I can claim credit for anything, it's that I questioned why the Fender circuit didn't bootstrap the tail...
  23. Thread: LTPI balance

    by uneumann
    Replies
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    2,201

    Right - My spkr model does include some...

    Right - My spkr model does include some inductance/capacitance, but I don't recall where these models came from (maybe the Duncan site?) or exactly what the model is. I do know the model behaves...
  24. Thread: LTPI balance

    by uneumann
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    Bingo - you got it - that's a good way to phrase...

    Bingo - you got it - that's a good way to phrase it.
    Technically, the common mode signal could come from other sources too, but the spkr signal is pretty handy and works well for this purpose.
  25. Thread: LTPI balance

    by uneumann
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    2,201

    Perhaps we're using some terms differently. In...

    Perhaps we're using some terms differently. In post #26 I'm showing a NON-NFB example. Maybe there's confusion since the spkr signal still comes back to create the tail signal. Yes, that's a...
  26. Thread: LTPI balance

    by uneumann
    Replies
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    2,201

    So maybe this will help. Here is a basic non-NFB...

    So maybe this will help. Here is a basic non-NFB output stage. The input is 0.1v and the spkr signal is ~1.5v (both peak). The nfb input to the PI is grounded by a cap (C2 in this drawing), there...
  27. Thread: LTPI balance

    by uneumann
    Replies
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    2,201

    Yes - This pic shows sim traces for the cathodes,...

    Yes - This pic shows sim traces for the cathodes, V1 input and V2 input. The middle signal is the cathode signal and it's almost exactly the average of the two grid signals, as expected.

    52661
    ...
  28. Thread: LTPI balance

    by uneumann
    Replies
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    2,201

    Well - I found one flaw - maybe not fatal, but...

    Well - I found one flaw - maybe not fatal, but worth noting.
    In non-NFB amps, sometimes the PI is used as a mixer.
    In that case the V2 input produces positive feedback to the tail, making the...
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