Div by 13 amp hum

[kgreene]

Hi,
I was wondering if anyone else had noticed that Divided by 13 amps have a very obnoxious hum, and if so, does anyone know of a solution???
I am currently trying out a model CJ-11 which I love the sound of other than I have to dial down the bass control to near 8 or 9 o'clock and the fact that it hums so much. A friend of mine has a model 13/29 which also has the same hum. In the past I have had this trouble with Dr.Z amps. I sure would like to get some technical insight into this if anyone has any.
Thanks!!

[rhinson]

Hi,
I was wondering if anyone else had noticed that Divided by 13 amps have a very obnoxious hum, and if so, does anyone know of a solution???
I am currently trying out a model CJ-11 which I love the sound of other than I have to dial down the bass control to near 8 or 9 o'clock and the fact that it hums so much. A friend of mine has a model 13/29 which also has the same hum. In the past I have had this trouble with Dr.Z amps. I sure would like to get some technical insight into this if anyone has any.
Thanks!!

post some good gut shot pics of the amp and maybe we can see something that needs correcting. rh

[Firestorm]

Also try to figure out if the hum is 60Hz or 120Hz. Two different sets of problems; two different sets of solutions.

[Kregg]

I have a 17/39 and it works fine.

Also try to figure out if the hum is 60Hz or 120Hz. Two different sets of problems; two different sets of solutions.

How does one determine whether it's 60Hz or 120hz?

Thanks,
CW

[fzfwyv]

Interesting thread. I have an FTR 37 that I purchased in December 2004. I think at this point Fred was still doing most of the building of the amps himself. I can say that my FTR is one of the quietest amps I've ever had as far as ANY noise goes. It's just flat out awesome.

A little later in 2005 I purchased an RSA 31. That amp was also dead quiet.

Last year I picked up a EDT 13/29. That amp had more noise than I liked and I ended up selling it. I also played the FTR 37 they had a Motor City Guitar a few times and I noticed that amp also had some noise that I didn't have with my amp.

I have no proof, but in my experience the earlier built /13 amps seems to be quieter than the more recently built ones. Could be a number of factors. I'm not smart enough to narrow it down though.

-Rich

[martin manning]

I have a 17/39 and it works fine.

Also try to figure out if the hum is 60Hz or 120Hz. Two different sets of problems; two different sets of solutions.

How does one determine whether it's 60Hz or 120hz?

Thanks,
CW

Use a 'scope. If you don't have access to one of those, the A-string 2nd fret (B2) on a six-string guitar is 123.5 Hz, and the A-string 2nd fret on a bass is 61.7 (B1), an octave lower.

MPM

[billyz]

I know that in the DR Z Amps with reverb, the Hum/noise was caused by a ground loop . The fix was too use an insulted rca jack and move the grounding point.

Could be a similar situation, does the hum go away or is reduced by removing one of the reverb tubes ?

[fzfwyv]

post some good gut shot pics of the amp and maybe we can see something that needs correcting. rh

I agree. I think Fred may have used some different components in later models. Can you post a couple gut shots?

-Rich

[selloutrr]

I've not experienced a hum issue from the Divided by 13 amps. If it's an issue you have experienced with several amps it leads me to question your power source. Does it tap on to a floresant light or some other kitchen appliance?

[rawnster]

I've owned two /13 amps (RSA 23, FTR 37). The FTR37 was WAY noiser than the RSA. It was a hissing machine. Did all the normal troubleshooting to lower the hiss. Finally I sent it back to Fred to take a listen. He called me and said that it was dead quiet. He said that he had the amp turned on at the moment and did not hear a thing. He called me a liar, and so I returned the favor. I know for a fact that it was noisy. I just told him to send it back to me. Got it back and promptly sold it. Mine was a late model 2007. Perhaps the earlier poster is right about the early models being quieter than the later models. I loved the tone, but couldn't handle the noise....and got tired of the sound man complaining about it too. I'll never buy another /13.

...just my experience.

[selloutrr]

NOT TO FUEL ANY FIRES, BUT A THOUGHT
it's unexcuseable to call a customer a liar, but i can see how things become heated in the world of music. it's very fueled on emotions anyway..
My bench power is setup with constant voltage transformers and isolated power. I have a far lower noise floor then most as fell as a steady flow of AC for stable test and measurement. I have one city power outlet for testing noise issues. I have had clients more then once with your same troubles you just discribed. it'll play clean on the bench and noisy at home the clients home. Live it's often from band power sharing common venue power or tapping into lights. Ground lifts don't always fix the issue. I'm not sure where you play but, bars are notorious for sharing band power with the dish washer and house lights. That's why tech riders say in bold DEDICATED AUDIO POWER MUST BE SUPPLIED!!!

[Alexo]

...so would a filtered IEC socket be the solution?

[selloutrr]

i'm not sure but it could explain the arguement between client and builder, as well as some of the similiar issues experienced between different amps, makes and models at the same location.


A friend had a similar problem last winter... he would be playing and all of a sudden his amp would get a loud buzz and hum but at my place it was silent and perfect. this went on for months on and off the bench open closed test after test, even a fight here and there. It turned out after I went to his house to check it out his practice room was on the same power as some of the swimming pool electronics. once we found a clean AC tap the amp was perfect.

[Structo]

...so would a filtered IEC socket be the solution?

That would help clean the ac power into the amp but do nothing for the rectified and filtered DC where you are probably getting the hum from.

[kgreene]

Hi guys. I was out of commission (sick) yesterday and didn't look at the responses, but thanks to everybody for your input, and let me answer some of the questions.
First, the hum/noise is predominantly 120 cycle with various other hiss and white noise overlaying it. It increases with both the volume controls, but more with the master. Even more dramatic increase comes with the pull boost on the pre-amp volume.
For comparison sake, my Bad Cat Cub IIR is plugged in the same power source and the amps are placed side by side; the Bad Cat is DEAD QUIET.
The Div by 13 is a model CJ11, which has no reverb, just volume (w/pull boost), bass, treble, and master volume. It is a combo with one 12" greenback celestion.
Unfortunately, I cannot take the amp apart since I have it home on a trial basis from the music store (which happens to be Motor City Guitar). I thought about calling Fred Taccone, but haven't done so yet.
The amp has a wonderful spank and warmth otherwise, so I'd like to find a solution. Overall, I think I prefer it to my Bad Cat.
What does anybody think about using a power conditioner? And if so, any recommendations on a specific model?
Thanks again for all the input.