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 Post subject: Feedback!
PostPosted: Sat Apr 06, 2019 3:02 pm 
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I’m really loving the tone of my Plexi build but I’m finding this amp really likes to feedback on either channel when the volume and/or volume and gain are up past 6 or so. Is this normal? I’m using a Les Paul with unpotted SD Seth Lover pickups. My 335 with ‘57 Classics will also feedback just as much. I can control the feedback with my palm on the strings but I can hear it coming through when playing open strings. I’ve tried different preamp tubes and another pair of power tubes as well. I’ve thought about increasing the cathode resistors on V1a and v1b to 1.5K each from the current 820 ohm each to reduce some gain. Any thoughts?


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 Post subject: Re: Feedback!
PostPosted: Sat Apr 06, 2019 4:41 pm 
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big room ?
small room?



distance from cab 4X12

all factors

Mine will feed back not usually on normal channel less I'm close to cab


Are you using VRM?


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 Post subject: Re: Feedback!
PostPosted: Sat Apr 06, 2019 8:44 pm 
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A bit extreme unless you are sitting beside it. Try 5751 in V1.

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 Post subject: Re: Feedback!
PostPosted: Sat Apr 06, 2019 10:50 pm 
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No VRM. 1x12 cab in a 12’x12’ room with a 15’ cord. I’ve got a 5751 here. I’ll give that a try.


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 Post subject: Re: Feedback!
PostPosted: Sun Apr 07, 2019 10:45 am 
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Sometimes, but rarely if you followed the layout, the OT primary wires need to be reversed (BROWN & BLUE).
If the 5751 does not do it, then you can try that.
The 5751 will reduce the gain BTW, so you may not want that.

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 Post subject: Re: Feedback!
PostPosted: Wed Apr 10, 2019 2:03 pm 
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I tried the 5751. It did raise the threshold for feedback but changed the bite of the amp. I’m learning to live with the feedback.


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 Post subject: Re: Feedback!
PostPosted: Thu Apr 11, 2019 7:35 am 
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You can try OT primary wires need to be reversed (BROWN & BLUE).
If the 5751 does not do it, then you can try that.

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 Post subject: Re: Feedback!
PostPosted: Thu Apr 11, 2019 4:25 pm 
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coco wrote:
You can try OT primary wires need to be reversed (BROWN & BLUE).
If the 5751 does not do it, then you can try that.


Thanks Stephen, I’ll try that one day when I get ambitious enough to pull the chassis out of the cabinet. If memory serves me, I may not have left enough brown wire to reach. On the upside, I can get enough feedback to keep Pete Townshend happy! Lol!


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 Post subject: Re: Feedback!
PostPosted: Fri Apr 12, 2019 4:20 pm 
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Played the amp a bit today. It’s really just the open low E string that gives the most feedback at high volume. The other 5 strings are much more manageable. An open low E will cause it to oscillate into feedback.


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 Post subject: Re: Feedback!
PostPosted: Sat Apr 13, 2019 3:41 pm 
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Before I had the VRM installed it would feed back in an 18 x12 room. back to the amp helped. or walked down the hall with a longer lead.

When i played in a much bigger basement didn't seem to have as much of a problem

im assuming your using the amp for all your gain or are you using pedals in front


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 Post subject: Re: Feedback!
PostPosted: Sat Apr 13, 2019 10:03 pm 
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sazafraz wrote:
Before I had the VRM installed it would feed back in an 18 x12 room. back to the amp helped. or walked down the hall with a longer lead.

When i played in a much bigger basement didn't seem to have as much of a problem

im assuming your using the amp for all your gain or are you using pedals in front


Yes, just using the amp for gain. Don’t get me wrong, I love how lively and responsive the amp is and the tendency to go into feedback and the ease with which it does so is part of that responsiveness; I was just wondering if anyone else was experiencing the same thing. It’s not a deal breaker by any means. My Trinity Tweed will also get a bit of feedback at high volume in the right situation but not as easily as the Plexi. The Tweed is more controllable. I have a 5751 in V1 on the Tweed and it sounds great in that circuit.


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 Post subject: Re: Feedback!
PostPosted: Thu Jul 18, 2019 3:50 pm 
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I solved my feedback issue. I bought a Boss WL-20 wireless system. I can crank the amp and by keeping some distance the feedback is gone. I literally have to stand 3 feet from the amp to bring on the feedback now. As a side note, I highly recommend the Boss wireless. No latency, crystal clear sound and no loss of tone. The range is more than enough and the freedom to wander around while playing is great. Yes, a longer lead would have accomplished the same thing but this is more fun.

Attachment:
1401CA02-3F64-4F5E-B24C-13B3DBFBA24D.jpeg
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 Post subject: Re: Feedback!
PostPosted: Fri Jul 19, 2019 9:00 am 
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That's cool. Expensive?

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 Post subject: Re: Feedback!
PostPosted: Fri Jul 19, 2019 9:59 am 
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Expensive? Yes and no. Cheap for a wireless system and considering what people pay for stomp boxes, etc it’s reasonably priced. But compared to a $50 cable? Yes, expensive.


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 Post subject: Re: Feedback!
PostPosted: Thu Dec 26, 2019 12:15 pm 
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Update. I finally got tired of the excessive hiss in the Normal channel and the continued propensity for feedback if I get too close so...

I pulled the chassis this morning and swapped the brown and blue OT wires to the opposite power tubes. They are now reversed in comparison to the layout diagram. The Normal channel now has much less gain and the hiss is comparable to my Trinity 5E3. There is now a noticeable difference in gain between the Normal and TMB channels. I must of been getting some sort of positive feedback the way it was previously wired. Stephen, I know this is what you suggested I try. Not sure why I resisted for so long.


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 Post subject: Re: Feedback!
PostPosted: Fri Dec 27, 2019 9:21 am 
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Interesting effect of swapping the wires though. All good?

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 Post subject: Re: Feedback!
PostPosted: Fri Dec 27, 2019 6:25 pm 
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Yeah, I guess? I played my Strat through it yesterday for a while. I now have to nearly crank the Normal channel to get it to distort with a Strat. Lots of clean headroom now. The TMB channel didn’t change much. I haven’t tried my Les Paul through it yet. The jury is still out. I’m surprised it made that much of a difference.


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 Post subject: Re: Feedback!
PostPosted: Sun Dec 29, 2019 6:16 pm 
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I just finished putting everything back the way it was. I think I’m loosing it. I don’t really notice much of a difference. Before I buttoned it back up I went over the lead dress and made sure everything was separated as much as possible. Maybe that improved the noise floor from what I was originally hearing. Who knows. Who cares. I’m leaving it alone. Still love this amp.


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 Post subject: Re: Feedback!
PostPosted: Sun Dec 29, 2019 8:21 pm 
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:thumbsup: :thumbsup:

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