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Author Topic: Tech 21 Power Engine 60 input hum  (Read 342 times)

dezmoduo

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Tech 21 Power Engine 60 input hum
« on: October 28, 2020, 12:53:13 AM »
I searched (googled) the issue and found https://www.ssguitar.com/index.php?topic=4118.0

So I bought a PE60 for a very nice price (red flag) that has a hum on the 1/4" input only. I've been using it with an BOSS ME-80 with success taking the mono out into a direct box and then into the lo-Z input on the amp.
  So silly me, I want to fix the hum. The amp works great in all other respects.  The amp is dead quiet when nothing is plugged in. Once a 1/4 " mono plug  is inserted, theres a hum, similar to tapping the hot/tip an open jack.  Using the xlr input is quiet as well.

  As an avid electronic enthusiast, I have built 3 fairly complex amps , recapped and modded my SF Bassman, with rewarding success. I have no scope at this point.



I benched the chassis to look for a blessed "easy fix". It didn't happen. What I did find on the 1/4" input jack was that is a "marshall" insulated type but appears to be a stereo jack. It's PC mounted and has 6 solder lugs into the board. The 2 closest to the chassis face have traces, the middle 2 have traces, and the last 2 go through the board but do not appear to have traces. I know it could be a multi-layer board but honestly looks single layer.  (I stopped myself from starting a big trouble shooting session because it was 11:45PM. I'll put fresh eyes on it in the AM.

  Could it be that the input is wired for a balanced  1/4" input? And that using a standard mono guitar jack is fouling the ground on the amp? I'm looking for a schematic, and will find the manual in my paper pile.
 The solder points look great but I'll tap them out a bit and check them with a meter to verify what I can.


From the manual
<<1/4” INPUT (*FOR INSTRUMENTS ONLY*)
Accepts 1/4” output of your pre-amp/processor or amplifier. This specialized input
features an isolation transformer to eliminate ground loops when using the Power
Engine 60 in conjunction with an amplifier. Be aware that this transformer loads down
passive guitar inputs. If you would like to plug your guitar directly into the Power Engine
60, either use an active guitar or any buffered type of effect pedal (Boss®, Ibanez®,
Tech 21, etc.) in bypass mode in order to drive the low input impedance of the amplifier.
*NOTE: DO NOT PLUG THE SPEAKER OUTPUT OF AN AMP INTO THIS
INPUT. Doing so may result in severe damage to the unit or your amp or both>>

Tomorrow is another day

Dez
NYC

phatt

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Re: Tech 21 Power Engine 60 input hum
« Reply #1 on: October 28, 2020, 07:16:15 AM »
My guess is that once connected to a preamp the hum should stop.
So,  Does the amp stop humming when the lead is plugged into a preamp?
I assume,,Any open lead will likely hum as there is no ground, the setup relies on the ground of a preamp.
Phil.

dezmoduo

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Re: Tech 21 Power Engine 60 input hum
« Reply #2 on: October 28, 2020, 02:14:19 PM »
phatt,
  All this is with completed connections all around.
I just reconnected the chassis in the cabinet and speaker.
With nothing plugged in there was a slight hum with the gain cranked. When I backed the gain down a bit, 15-20%, it was close to silent.  I set up my guitar/preamp volume down on the preamp, and then plugged the output 1/4" connection into the power engine. The hum was significant, as I had remembered it.

I tried some balanced 1/4" patch cords in that same connection and it was no worse  and no better.

What I did notice was that any slight nudge on the 1/4" connection jack, produced a change, a reduction/increase as I moved it ever so slightly.
I'm going to call this a "Faulty Jack"  or  "Failing Solder Point" at this point.  The PC board shows no signs of repair or replacement. All looks pristine.

I'm going to desolder & remove the jack and check it's integrity at the connections plus and faults to ground. It has to be this easy. The amp on the XLR input works flawlessly.

I'll update the post as I discover more.


Dez

dezmoduo

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Re: Tech 21 Power Engine 60 input hum
« Reply #3 on: October 28, 2020, 02:47:07 PM »
I'm calling it fixed.
With the assist from TEch 21 Support , and a couple of emails.

From Tech 21:
  <<Be aware the Power Engine 60 utilizes a ground independent transformer, which may pick up hum from the auto-switching power supply. Therefore, the XLR input of the Power Engine 60should be grounded. You can make your own grounding plug by modifying a male XLR connector by soldering Pin 1 to Pin 3 and inserting into the XLR input of the Power Engine 60 per the diagram below. NOTE: If you’re not into soldering, a Tech 21 grounding plug is avail-able for purchase. Please see our website Accessories page for details>>

I found the original manual, Celestion amp handle tag and the grounding XLR plug in a zip-lock bag from the original purchaser.

The PE amp is now as quiet as could be expected from any amp/effects combination.

It's done and on the slight chance that someone else has this issue, this post will turn up in a search and be of assistance.

Now onto my Yamaha G50-112ii    :lmao:
« Last Edit: October 28, 2020, 02:48:08 PM by dezmoduo »

Jazz P Bass

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Re: Tech 21 Power Engine 60 input hum
« Reply #4 on: October 29, 2020, 12:59:22 AM »
Thanks for winding it down.