[BradJudy]

I finished my PPA and STEPs this weekend (no case yet, I still have to order my Par-Metal). They both seem to work fine, except for a buzz the can't be heard until the volume is about half way up (and gets louder as you increase the volume further). It is present either when an input is attached or nothing is attached. It gets louder if I touch an input signal line (or even their insulated wires) and quieter if I touch an input ground. Touching the pot housing makes a slight noise, but doesn't increase or decrease the volume noticably (pot housing is grounded).

Unforunately, I set up the bias before I noticed the buzz - I'm not sure if it was there before or not.

Since it's sitting in the open, I wonder if it's just picking up RF. I tried turning off the lights, but that had no effect.

Some basic specs:

2x 637 1x 627 (I also have 8610s I can swap in)
8x 470uF 25V Cerafine
2x 5002 per channel
Alps 50k
RLED (10k) used instead of other LED options
No bass boost (S2 is jumpered)
Rest is pretty by-the-book (Tangent's instructions)

STEPs is by-the-books for 24V

Ideas?

 

[Megaptera]

Sounds like a grounding problem. Try touching a wire between the PPA's input ground and something big, conductive, and not connected to anything else, and see if that does anything. If not, try plugging the STEPS into a different outlet or power strip -- it sounds a bit like it might be a ground loop. Doublecheck all your groundings, basically, on both the STEPS and the PPA.

 

[Zemo]

I had a similar problem, wich was solved by tying the input ground to my chasis via the input jacks (make sure your steps isn't grounded to the chasis!). Since you have no chasis yet, I suppose you'll have to wait to try this one out!

-Z

 

[BradJudy]

Quote:

Originally Posted by Megaptera Try touching a wire between the PPA's input ground and something big, conductive, and not connected to anything else, and see if that does anything.

Well, I am basically big, conductive and not attached to anything else

(assuming I'm not touching any other part of the STEPs/PPA or my home electrical). As I mentioned, when I touch it, the buzz gets quieter (although doesn't go away completely).

Quote:

Originally Posted by Megaptera it sounds a bit like it might be a ground loop.

It isn't possible to have a ground loop with no input connected, is it?

 

[BradJudy]

Quote:

Originally Posted by Zemo I had a similar problem, wich was solved by tying the input ground to my chasis via the input jacks (make sure your steps isn't grounded to the chasis!). Since you have no chasis yet, I suppose you'll have to wait to try this one out!

Yeah, that test will have to wait a while.

 

[Megaptera]

Quote:

Originally Posted by BradJudy Well, I am basically big, conductive and not attached to anything else (assuming I'm not touching any other part of the STEPs/PPA or my home electrical). As I mentioned, when I touch it, the buzz gets quieter (although doesn't go away completely). It isn't possible to have a ground loop with no input connected, is it?

It's possible, just not as likely. All you need for a ground loop is to have some sort of voltage between two points on the ground -- then you get a current going, which adds noise. Doesn't matter if it's through one device or five; the electrons can't tell the difference. It's most likely to happen once you've got the amp connected to something, since there's just that much more ground, and it's possible there's a ground loop to the STEPS.

Might also be interference from the STEPS -- I don't know where my mind was when I first read your post, but I didn't realize the STEPS wasn't cased either. (Actually I nearly didn't realize the PPA wasn't cased, either -- space cadet today.) Can you jury-rig a different power source? Even a pair of 9Vs in series would give you an idea if the STEPS is causing the noise. If not, try moving the PPA closer to and farther from the STEPS and see if that changes the noise volume. (Obvious word of warning: don't move the STEPS unless you like exposing yourself to mains power.)

 

[jboehle]

See my recent thread titled "clone grounding problems". I was having exactly the same problems as you and then when I cased my amp up, it's dead silent.

I wouldn't worry about it too much until you can case it up. Then see what happens.

-Jason

 

[tangent]

I think you need a ground loop breaker. What worked in my very similar PPA is a 10 ohm 5W resistor between AC safety ground and amp input ground. This applies if you tied the AC ground to the case, which you should have, for safety reasons.

 

[ppl]

Quote:

Originally Posted by BradJudy Well, I am basically big, conductive and not attached to anything else (assuming I'm not touching any other part of the STEPs/PPA or my home electrical). As I mentioned, when I touch it, the buzz gets quieter (although doesn't go away completely). It isn't possible to have a ground loop with no input connected, is it?

Well your sure form a BIG antenna and the 50 or 60 Hz magnetic fields coming off all the ac-powered devises and wiring in your home transmit an ac signal plus the transmissions of CRT monitors and the like are directly into your Body and this can be easily picket up by audio gear just touch the hot input of any audio amp with your big old finger and you will hear an AC hum regardless of whether the amp is AC powered or connected to anything. Take this same amp into the wild away from AC and touch the hot input and you hear no hum just a click. Why because there are no AC signals for your big self to receive.

 

[BradJudy]

Quote:

Originally Posted by tangent I think you need a ground loop breaker. What worked in my very similar PPA is a 10 ohm 5W resistor between AC safety ground and amp input ground. This applies if you tied the AC ground to the case, which you should have, for safety reasons.

I take it this means you consider the best grounding to be AC ground to case and 10ohm 5W between AC ground/case and input ground. Do you feel this is better than doing the input ground to the case as Jason mentioned?

Unfortunately, I won't be able to try this until I receive my case, but I will pick up an appropriate resistor while I'm at the electronics shop.

Thanks

 

[tangent]

Quote:

Do you feel this is better than doing the input ground to the case as Jason mentioned?

If there's AC power within the case, yes. In fact, in some countries, it's mandatory.

 

[morsel]

Brad, please read the wiring considerations at http://elvencraft.com/ppa/ to address your problem. Also read the Rane Notes linked in the wiring considerations. Do not heed advice to AC ground your case, that is the worst thing you can do. While AC grounding of cases is in some circumstances warranted for electrical safety reasons, it is generally detrimental to sound quality unless balanced power is implemented, which is expensive and violates some electrical codes, so you might as well not AC ground the case to begin with.

 

[tangent]

Quote:

that is the worst thing you can do

Only if you don't value your life.

 

[BradJudy]

Hmmm...it would appear that despite being regularly debated, there is still disagreement on the best technique.

Since there are survivors from both POVs, I'm guessing neither technique is very dangerous.

How should input grounding work with multiple inputs? I am planning on having dual, switchable inputs. Would I ground the chassis to the input ground on the PPA, effectively switching which source was grounded to the amp chassis when I switch inputs? This seems more logical to me than not isolating the input jacks and grounding two different sources to each other (spells danger in my head).

I'm in the process of reading the Rane article which seems very interesting.

 

[morsel]

Whether single or multiple inputs, my answer is the same.

Quote:

Connect the case and pot housing to signal ground. This helps shield the amp from hum and noise. Most cases are tied to signal ground and/or AC ground. Do not connect V+ or V- to the case instead of signal ground as it will short the rail if it touches another case, cable plug, or other grounded conductor. Do not connect AC ground to signal ground or the case. This may cause ground loop problems.

All signal grounds are tied together via the audio interconnects. Unbalanced equipment that ties AC ground to the case and/or signal ground is a liability as it may cause ground loop problems. The goal of quiet unbalanced equipment is in direct conflict with the goal of satisfying AC grounding regulations. In the USA most unbalanced equipment is 2 prong. Making a device as small and low power as a headphone amplifier 3 prong is just creating a giant nuisance for yourself.