5E3 odd "ring modulator"-like slight distortion?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by shakti, Apr 15, 2019.

  1. shakti

    shakti Member

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    I built a 5E3 about a year ago, but between all my amps have not been able to give it as much time as I should. As cool as it is, it didn't knock me out and I have been having a love/hate relationship with it. I built it mainly for a Neil Young type sound, and it certainly does that sagging, pumping, farty type of Neil Young distortion.

    But I am thinking something's not quite right. Now I should add that my favourite amps are Hiwatts, and you would be hard pressed to find something more unlike a Hiwatt than a Tweed Deluxe. But I really do think it is lacking in its clean tones. I know it's not supposed to have a lot of headroom, but mine just never gets *really* clean and when it does (by rolling back the guitar volume), it still sounds lacking. I have never tried another 5E3, but judging by soundclips there is a slight, odd distortion in mine which shouldn't be there.

    The sound I am talking about is a very low grade almost ring modulator-like distortion. Some notes are more plagued by this than other. It is worse with humbuckers, but it's noticeable also with single coils. I can hear it virtually right from the start, gets gradually slightly worse as I get to about 2 or 3 on the volume. After that it seems to become *less* noticeable, probably because the other (and wanted/intended) distortion of the circuit takes over. Rolling back the guitar volume cleans it up, but it doesn't get as clean as I think it should, and sounds lacking for want of a better term. It also seem to be lacking a little in dynamics.

    I have built close to 20 amps over the years. I tried meticulously to make the grounding and lead dress good, but it was my first tweed-style build and there may be ways to improve it. I used Jupiter red caps, carbon comp resistors and high-quality RIFA filter caps. All stock values (15uF filter caps). CLassictone transformers, and an early 70s Jensen Vibranto speaker (close to C12N). I am using old stock tubes, 12AY7 in V1 and 12AX7 in V2. I have tried it with stock rectifier, GZ34 and another which I forgot the name of. Tried 6V6s and 6L6GCs. No difference really, it's always there.

    Any suggestions to what this could be? I would be guessing insufficient power supply. Could it be this bad even with stock values? It sounds like particularly bad ghosting, but the amp doesn't have any hum to speak of.
     
  2. pdf64

    pdf64 Member

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    A bad HT cap (or connection to them) at either the reservoir or screen grid nodes, can have that effect.
     
  3. HotBluePlates

    HotBluePlates Member

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    There's no good way to diagnose distortion remotely. We'd have to hear/test it.

    I've previously over-tightened the speaker mounting bolts, and caused a slight fuzzy distortion that was only on lower notes at lower volumes.

    Could be oscillation, could be loose grounds, could be cold solder joints, could be wrong cathode resistor value, could be a bad tube, could be a cabinet rattle/buzz due to a loose part or cracked wood. Could be a lot of things.

    Unless you're able to apply a known test signal, reproduce the sound & scope through the circuit to see where the signal gets weird, I don't know how to tell you to proceed. Perhaps others have some clever ideas (and I entirely believe someone might).
     
  4. shakti

    shakti Member

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    Thanks for your input guys! I know, it's not easy to diagnose this without clips, photos or oscilloscope traces. I have got an oscilloscope but I just don't have much time to troubleshoot these days, things are just so busy in the spring with all the stuff I have to do outside.

    I know it's not the tubes, speaker or cab, have tried it into a 4x12 and it's the same. I also don't think it's blocking distortion, it's not that kind of clamping/gated type of distortion you get from blocking distortion. The amp does do that kind of thing too, but that's the nature of it as you turn up loud, and that's the Neil Young type effect that I want.

    It might be some kind of oscillation, but the more I think about it, there more I am thinking I must look hard at the power supply and particularly the filter caps. If I have a bad connection or if I even managed to miswire it this might lead to these kinds of symptoms; kind of starved for power - it has volume but no definition or clarity with this slightly wobbly ring modulated overtone.
     

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