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Princeton Reverb Hum / Noise with Tremolo

Discussion in 'Shock Brother's DIY Amps' started by jchabalk, Oct 24, 2020.

  1. jchabalk

    jchabalk Tele-Meister

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    I'm going to see if i can chase down this hum that's present in my tremolo. This may just be a direct result of the way that the trem works in this amp (by wiggling the bias).

    Overall this amp is really quiet. When i plug in i get a little bit of hum from the p90s in my guitar and it changes as i move the guitar around in relation to where the amp is. I'm not too worried about that sound.

    What i have here in the audio example is just the amp without anything plugged into it. The reverb and trem are enabled, i disable them each in the sound clip by putting a shorted 1/4" jack into their respective plug on the back of the amp, which is why you hear a couple of sounds when i disable them. (i swapped the standard RCAs with 1/4" plugs as part of the build).

    This sound clip with with the volume, reverb, treble and bass controls at 10 and the amp's been running for 5 minutes or so (it's warmed up).
    • 0-12 seconds: amp sitting idle, reverb + tremolo enabled (this is sound i want to understand / remove)
    • 13- 21 seconds: tremolo disabled, reverb remains enabled (pretty dang quiet)
    • 22-33 or so: reverb disabled (still nice and quiet)

     
  2. TwoBear

    TwoBear Tele-Meister

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    Is the chassis out of the cabinet and what kind of lights are around. It definitely sounds right at the low noise point and yeah it doesn't sound real great noise wise but if it's out of the chassis under a fluorescent or some kind of noisy light.... Is this your build and if so how's your lead dress?
     
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  3. Esquier

    Esquier TDPRI Member

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    It doesn't sound awfully noisy considering it's on 10! How often do you use it turned balls-out? If you added your guitar then you wouldn't notice it at all. Why play your amp with nothing plugged in? I have a home brew brown Deluxe that's hardly even "stable" and it makes plenty of noise if you even tap on the roof! But it sounds divine when turned up to 4-6 with guitar playing through it. I don't sweat it. It's probably down to a noisy tube. Mine that is. Maybe you could tune the bias differently, but really your Princeton sounds quite acceptable. It's not hi-fi gear, and even a nice stereo makes its noise when it's turned up to 10
     
  4. jchabalk

    jchabalk Tele-Meister

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    I should have mentioned, it is in the chassis for this recording and i do have shielding at the top of the cabinet. The only thing close to it is my variac and an incandescent bulb that i have plugged into the variac. But i'm in a city and there's definitely a lot of other stuff all around everwhere - but not within 5-10' of the amp.

    It is my build, the lead dress is pretty clean but i haven't gone in and started moving things around yet. It's built using the hoffman layout rather than the fender aa1164 layout.

    IMG_3472.jpeg
     
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  5. jchabalk

    jchabalk Tele-Meister

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    I was mostly doing this to isolate the sound mostly. I usually leave the amp at 7 or 8 and control volume using the guitar volume or how heavy i play. That sound is typically a bit lower but it gets annoying is all. I agree, when i'm strumming away it's a non-issue, playing softly it's there, and i usually have the tremolo running.
     
  6. Esquier

    Esquier TDPRI Member

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    Maybe if the bias was adjusted, the trem would be less "obtrusive". What's it biased to now, or do you leave that to "the Tech"?
     
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  7. King Fan

    King Fan Poster Extraordinaire

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    You've done a very nice job of documenting max hiss. Hearing it, I'd say yours has the *character* I would expect from this trem. Hard to judge the relative *volume* at actual PR settings. AFAIK very few people run PR V or T at 10, except Jim Capilongo, and he has tweaks in his setup.

    But I admit if it bugs you, it may be 'too loud' in a real-world sense. That is, of course, if it can be reduced. If not, we have to say it's not a problem after all. :D

    I forget from your other thread, but I agree with the above: What are the voltages on your output tubes (or better yet across the amp) and what is the % dissipation on your bias?
     
  8. schmee

    schmee Doctor of Teleocity Silver Supporter

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    So it's a home build? That info helps. I hear it as way too noisy in all modes. ... on 10 though?
    Especially the reverb up that high on Fender amps ......is always fairly noisy.
    It's a bit hard to see your grounding but it appears they are all collected on the buss wire at top and then go over to the cap can area? That's a no-no. You want you input and preamp grounds to be over near the input jacks for sure.
    The Fender layout isn't just something someone guessed at, it's tweaked to reduce noise.

    A recording with most everything at 12 oclock including reverb might help to compare...
     
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  9. Boreas

    Boreas Tele-Afflicted Silver Supporter

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    Have you tried it on a different circuit in the house? Have you played other amps on this circuit? In other words, have you ruled out a noisy A/C circuit?
     
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  10. King Fan

    King Fan Poster Extraordinaire

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    Hmm, yes, where do the grounds go? Trying to blow up the pic here...

    Hissy.jpg

    EDIT: Oh wait, it's per Doug Hoffman's layout... (upside down relative to the above).

    upload_2020-10-24_17-31-21.png
     
  11. King Fan

    King Fan Poster Extraordinaire

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    FWIW here's a pic of Doug's own build...

    upload_2020-10-24_17-37-6.png

    (Click on any of my pics here to enlarge.)

    I can't see his grounds (or yours) at the input jack, but it sure looks like he *doesn't* also connect his Marshall-style pot-back ground bus to the power amp ground bolt; as @schmee says, taking those preamp grounds to both the input jack ground and the power amp ground might not be so good...
     
  12. boredguy6060

    boredguy6060 Poster Extraordinaire

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    Nice work,
     
  13. jchabalk

    jchabalk Tele-Meister

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    Thanks for the replies - I pulled the amp from the cabinet and and spent a little bit of time with it this evening.

    I don't know why i had the pot-backs all tied to that transformer lug, it's something i did during the original build maybe 3 or 4 years ago. I removed that connection and just let it float - so the pots are tied together, along with the input jacks and the ground rail from the circuit board.

    I noticed that the reverb level has a lot to do with the sound. This isn't something i'd noticed before because i was disabling the trem and reverb. Tonight i left them both on - the trem intensity can be all the way up but if i turn the reverb down all the way the sound basically disappears. And i definitely don't run the reverb at 10 (more like 2-3).

    The bias was a bit cold (V5:19mv and V6:17mv), the plate voltage of V5 and V6 was 397VAC.

    I turned the bias up a bit (V5:22mv and V6:20mv). This didn't change much with the sound, it maybe sizzles a little more when the sound is cranked.

    I spent a little time poking around the reverb circuit but didn't find anything obvious. I'll see if i can try a different set of cables and a different tank tomorrow, i'm pretty sure i have another of each around here, and i'll start looking around for tips on reverb hum and shielding the tank. I'm all ears if anyone has some advice there too.

    I tied the ground back to the transformer lug just so i don't have a loose piece of wire floating around in the chassis, if i get to the bottom of this and don't need it i'll clip it off.

    I also played a bit tonight. With the volume on 6-7 and the reverb on 4 the sound still comes through pretty strong, but i only hear it when i'm playing quietly.

    This is mostly a curiosity for me - i'm just a home player who builds an app every once in a while and i've got a little extra time on my hands so i'm trying to get into the weeds a little on making what i've got a bit better.
     
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  14. jchabalk

    jchabalk Tele-Meister

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    Something i just noticed after poking around a little more wrt the reverb is that i have the ground from the Output Transformer secondary connected to the speaker jacks outputs, and then it continues to a bolt in the chassis near the jacks. I have the ground from the reverb transformer tied to that same bolt. The Reverb send/receive RCA jacks are just screwed tight to the chassis and have ~.6ohm resistance to that chassis bolt.
     
  15. Uncle Daddy

    Uncle Daddy Tele-Afflicted

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    I've just tried the same setting on my handwired PR and it sounds much the same. In the clip, the 0-12 seconds section in question sounds like resistor/tube hiss which is pulsing with the trem as it modulates. If I turn the volume on mine down to around 8, most of it goes away. If I turn the trem down to zero, it leaves the hiss without fluctuations.
     
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  16. Mongo Park

    Mongo Park Tele-Holic

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    I have a home built 6g2 with the exact same noise as yours.
    Here is the thread with some excellent advice. However this noise is inherently part of this style of trem, but I also think this style of trem sounds the best if you don’t get to OCD over this part of it. It is hard to tell from the recording how loud this noise is in a practical sense, I don’t think you will get rid of it chasing your grounds.
    https://www.tdpri.com/threads/6g2-build-trem-noise.935985/

    With all the fixes my amp still makes the sound you posted maybe not as loud it is hard to compare. Like above with a guitar plunges in and playing at a regular volume it is just fine. I have to turn the intensity to max to get that sound and don’t play it with it turned up to max. If I am out and I have the amp louder the ambient noise is louder than the whooshing sound.
    As an aside I added in another.02 cap to slow it down, which I like. I built it mostly to understand it as others will just buy a trem pedal.
    Good luck keep us posted.
    Cheers Ron
     
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  17. TwoBear

    TwoBear Tele-Meister

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    Cool it looks like you went with Xicon caps, no necessity to paying big money there. I'm sort of getting OCD... Did you say you changed the RCA's to quarter inch? I don't see them protruding into the amp, although what I'm really getting at is I think there is a design of maybe one of the reverb leads not being grounded... I'm not sure if I'm being clear but I think either the send or return has the ground interrupted at one end, like the inputs should also be, just there for shielding but to not create a loop. Also the Jack's all around should have the knurled washers that bite into the chassis when tightened down. I apologize if I'm telling you things you already know. Funny but I'm heading over to the pedals forum to talk about ground loop issues on something I just found.
     
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