# Fender HRD: Hiss when something is plugged into power amp in



## Marion (Mar 29, 2016)

I bought a used HRD. It's loud so I decided to build a volume box. My first build. I hear a hiss whenever it's plugged so I thought i might have made a mistake building it or I used defective parts. I tried to isolate the problem and found out that it makes a hiss whatever pedal I plug in the effects loop. It hisses as soon as I plug something in the power amp in even of its just a cable. I tried different cables so I'm pretty sure it's not the cable. The hiss is not too loud and can only be noticed when I'm not playing but it's distracting. Also, the hiss doesn't go away even when volume and master volume are off. 

Is this normal? As I said I bought this used so I don't know if a new one has the same issue. 


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## Guest (Nov 6, 2017)

I recently picked up a '09 HRD. I haven't tried the fx loop yet.
I'll give it a go tomorrow to see if your problem is a design flaw or if it's your amp.


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## Distortion (Sep 16, 2015)

Little off topic but I had one on loan recently. I was using the foot switch between channels and it would give a click and some speaker thump when going from clean to OD channel. Also did it without the foot switch. Is that normal I don't think so.? annoying anyhow.


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## Guest (Nov 6, 2017)

Marion said:


> Is this normal?


I just tested my fx loop. I'm getting nothing.
Seems that my amp has a problem too.


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## Marion (Mar 29, 2016)

Distortion said:


> Little off topic but I had one on loan recently. I was using the foot switch between channels and it would give a click and some speaker thump when going from clean to OD channel. Also did it without the foot switch. Is that normal I don't think so.? annoying anyhow.


I get that too when amp is at low volumes. I don't get the thump past 4 on the volume. 


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## Marion (Mar 29, 2016)

laristotle said:


> I just tested my fx loop. I'm getting nothing.
> Seems that my amp has a problem too.


Sad to hear that but thanks for checking for me. 


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## jb welder (Sep 14, 2010)

How about you guys get a little more specific? 
HRD? does that mean deluxe and not deville? Which version, I believe they are up to III now?
Marion: the hiss with guitar plugged into fx return (guitar volume turned down) is louder than the hiss with guitar plugged into regular guitar input jack?
laristotle: if you mean no sound at all using fx return jack, can you start a separate thread?


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## Guest (Nov 7, 2017)

jb welder said:


> laristotle: if you mean no sound at all using fx return jack, can you start a separate thread?


I've never used a fx loop before until this thread popped up.
I did a little googlin' and apparently, the loop has to be set up before powering up.
I'll try this when the wife goes out shopping.


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## jb welder (Sep 14, 2010)

laristotle said:


> I did a little googlin' and apparently, the loop has to be set up before powering up.


If this is the case, it may be somehow related to Marion's issue.
Any links or references from the owners manual?


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## BGood (Feb 20, 2015)

laristotle said:


> I'll try this when the wife goes out shopping.


Good idea, because you could get a secondary hiss issue.


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## Guest (Nov 7, 2017)

Here's where I found the info about having the power off prior to hookup.
https://www.thegearpage.net/board/index.php?posts/9292917/



jb welder said:


> Any links or references from the owners manual?


The owner's manual is thin. 2 pages.


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## jb welder (Sep 14, 2010)

Ok, I think in that post, the suggestion of turning the amp off was just to avoid pops or thumps when connecting to the loop.
And maybe it would help protect the FX loop IC in this case. 

I think for both of you, the FX loop IC is where the problem is. 
It's designated as IC1 and located behind the preamp out jack. It is bypassed when the loop is not in use, which explains why both your amps work fine without the loop engaged.


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## Marion (Mar 29, 2016)

jb welder said:


> How about you guys get a little more specific?
> HRD? does that mean deluxe and not deville? Which version, I believe they are up to III now?
> Marion: the hiss with guitar plugged into fx return (guitar volume turned down) is louder than the hiss with guitar plugged into regular guitar input jack?


Mine is deluxe. Made in mexico but not Version III. It's not the guitar that I plugged into the power amp in. The hiss can be heard as soon as a patch cable (or any cable) is plugged in. The hiss doesn't go away even when the amp's volume and master volume are turned down. I'll try plugging the guitar directly tomorrow and see if there's any difference. 



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## nonreverb (Sep 19, 2006)

They won't as the Power amp input signal is inserted after the volume/master volume. Here's something to try....When you plug your guitar in, try turning the guitar volume off and see if the noise disappears.


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## alwaysflat (Feb 14, 2016)

Verify the U1 integrated circuit is the same part info as as in U2 location (TL072). It should be per the schematic above. If so, can swap them. U2 drives your reverb at the other end of the board.

Swap them or just put U2 IC into U1 and leave reverb empty for a quick test of your effects loop. 

It is a jfet op-amp so _some_ care should be taken for ESD protection, ground yourself before handling, do not touch the pins if you can help it.
Its not a mosfet so _acute_ care is less important. 
If you muck it up and damage pins, they can be carefully straightened. If you find your reverb is noisy - Order a couple anyway . I repeat TL072's are cheap. If you've never handled IC's before reach out for a buddy to help or check some vids. Orientation of the chip is important take a picture before you pull one out. Good references on the web to locate pin-1. 

Hope this helps.... / al
Watch this too and check for the hot spot ! ...


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## Marion (Mar 29, 2016)

nonreverb said:


> They won't as the Power amp input signal is inserted after the volume/master volume. Here's something to try....When you plug your guitar in, try turning the guitar volume off and see if the noise disappears.


I tested this and the noise disappeared. So what does this mean?


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## alwaysflat (Feb 14, 2016)

Could be EMI - good article here https://www.pedalsnake.com/blog/2016/09/noise-series-dealing-hiss/
You could check shielding on your guitar.
Could still be your cables, with volume down your guitar out shorts both the pickups and the external signal wire to ground level. Try short cables, no coils on the floor, not parallel to power lines.
The other electronic devices nearby like computer, tv, lighting (CFL, LED) etc., might be of interest.


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## nonreverb (Sep 19, 2006)

I'm going to attempt to answer each issue individually.

"I bought a used HRD. It's loud so I decided to build a volume box."
Can you detail what it is and it's components? Is it plugged into the speaker output?

"I hear a hiss whenever it's plugged so I thought i might have made a mistake building it or I used defective parts."
So the hiss disappears when it's returned to normal configuration?

"I tried to isolate the problem and found out that it makes a hiss whatever pedal I plug in the effects loop. It hisses as soon as I plug something in the power amp in even of its just a cable. I tried different cables so I'm pretty sure it's not the cable. The hiss is not too loud and can only be noticed when I'm not playing but it's distracting. Also, the hiss doesn't go away even when volume and master volume are off."

The only thing I can think of is it's the gain of the opamp buffer or it's bad. Since the hiss disappears when the volume on the guitar is at zero as you indicated, means that it can be controlled by grounding out the input. Opamps can behave that way when they're bad....besides, for the sake of a $2 part, it might be worth trying.


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