|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
174.3.131.191
So with my Jolida integrated used as power amp, I get a fair bit of buzz over the speakers.
Everyone is quick to say it must be a ground loop, even though the buzz is present without any other components hooked up.
So, I tried the ground zero, which is a nice product, that allows you to "match" and tie together all the ground potentials of all gear.
It did squat. Not even a change in "pitch" of the buzz/hiss at any of the 27 possible settings, which the instructions claim should happen.
Seems to me, that with all the chassis grounds still hooked up in 3rd prong of all the power cables, the effect of the ground zero would be bypassed?
Maybe all the third prongs need to be disconnected?
the instructions don't allude to this however.
Anyone else tried this ground zero box?
Follow Ups:
Might be helpful to distinguish between "buzz" which is most often 120Hz ripple (the output from the PS rectifiers which is "spikey", looks like a sawtooth waveform) and "hum" at 60Hz which is more sinusoidal (mains frequency coupling in). Ground loop problems result in "hum". Hiss and "buzz" are related to issues in the amp.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
I don't know how to describe it exactly...a buzz out of the woofer, mid and tweeter are higher pitch, but it is also saw-tooth sounding, so I guess hiss would be the wrong way to describe it.
One of the first things I tried was a cheater plug. did nothing.
They are new KT150 tubes, don't have a second pair of 12AT7's to try.
How do you isolate signal ground from chassis ground, and still have them both grounded?
Jolida 3502rc, can't seem to find the schematic
Edits: 08/29/16 08/29/16 08/29/16
"How do you isolate signal ground from chassis ground, and still have them both grounded?"
There are various schemes out there. One uses back-to-back diodes. The forward voltage drop of the devices act as a barrier to ground loop currents. With my DIY power amps I use a thermistor in parallel with a 1uF film cap. The cold resistance of the thermistor acts as a barrier (resistance goes toward zero gif there is a fault and real current) and the cap AC grounds the circuit.
You should make sure the ground connection in your amp isn't compromised. I had similar issues with one of my amps. I needed to scape (sand) the chassis under the ground lug to achieve a solid connection. A circuit that is not properly grounded will certainly "buzz".
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
I found the paint under the grounding post, cleaned that.
I found the power cord feeding the power condition was wired backward,
ie hot and neutral reversed, fixed that...
still the same buzz.
I think upon close comparison, the left channel is buzzing a bit more than the right, so I swapped tubes...still the same.
It buzzes less in integrated mode.
Do you have a scope? A DMM? If you do, see if you can trace back from the output and find where the noise enters the signal path. Also check to see if you have excessive ripple on the PS rails. If that is the case you could have a defective PS filter cap. An in circuit cap ESR meter works well for testing these. Good luck, these issues can be very frustrating. I know!
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
Thanks for the tips JKT, I don't have a scope, but maybe I can borrow or buy a used one. It's frustrating to find what you think must be the problem and it turns out not to be...
or maybe I'll have to bite the bullet and send it somewhere for repair.
Shipping kills
You might try posting this issue you are having on the DIY tubes forum here. Lots of inmates have more experience trouble shooting than I do.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
If you're getting the buzz with nothing hooked up to the Jolida (other than the power cord and speaker cables), just a couple thoughts:
Is the volume level of the buzz the same in both channels? If not, have you tried swapping tubes left-to-right to see if there is any change in the level of the buzz?
Have you checked the electrical outlet the Jolida is plugged into to be sure hot/neutral are wired correctly, and that a good ground connection exists? Even if things are wired correctly, it's possible that a connection to ground or neutral is loose or corroded. A cheap tester can help confirm this (link below if you don't already have one).
The buzz through your Jolida is NOT a ground loop. The Ground Zero will do nothing. There is a problem with the internal grounding or possibly a power supply issue with the Jolida.
Do not disconnect the third prong from your equipment, unless you have a death wish.
Dan Santoni
Paul McGowan said to lift the safety ground on their regenerator (p300) to lessen noise and the ground loop potential. Charles Hansen said safety ground is a noise antenna. Removing safety grounds in my biamped CJ system did much more more to improve sound than just get rid of a little hum from the ground loop that wasn't audible when music was playing anyway. I am happy to see a lot of new amps and powered sub's (designed) with a two prong IEC. Its about frickin time! Digital gear is mostly two prong and has been for some time.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
Charles Hansen said safety ground is a noise antenna.
Indeed he did but my recollection is that he suggested disconnecting or isolating signal ground from safety ground (earth) on the basis that the hazard posed by doing so was typically negligible in modern devices. Correct me if I'm wrong but I don't recall him ever suggesting that safety earth be disconnected from e.g. metal casework.
I agree with the basic idea - no signal ground in my audio system is connected to safety earth. The only way metal cases can rise to mains voltage is if isolating transformers fail by shorting secondary to primary. That's a very remote possibility but, should they do so, I'd expect the ECLBs to trip.
IMHO Blackdog is correct.
D
I don't have a problem with what you said. The risk is minimal though. I don't see it as a death wish. The system is unplugged when not in use. I've done other things I don't recommend like on an old NAD 2200 I took off the crap 16 gauge power cord and put on a good one wired direct to the transformer primary. This bypassed lots of stuff besides the switch and it was plugged into a switched outlet in a Monster Power device that would break the connection at 10A so a dead short would have safety but not its operating current. Again it was off unless I was right there listening. What a HUGE improvement it made.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
All the usual preliminary checks have been done before I posted.
Yes the noise is in both channels at the same volume, no matter where the pre volume is set, or even if the pre is disconnected. I do need to get the polarity checker yet though.
All the signal wire is bundled on one side, power wires on the other. looks OK.
I did find the grounding post, where the xformer, safety, and output signal grnds are all connected, have continuity with all the output lugs, both positive and neg.
I found this strange if not alarming, but maybe this has something to do with the output transformers. There is a wire from the board to the pos output lug, and a wire from the transformer to the same lug, per channel.
I also found paint between the grounding post and the chassis, which I removed.
This would be a fintastic amp if I could just the get hiss down...
all your help is appreciated
Now I'm confused...is it a hiss or a buzz? If it's a hiss, it's likely (but not definitively) tube related.
Do you have a cheater plug (3-prong to 2-prong adapter)? I'm not an advocate of running equipment with the safety ground removed, but on a temporary basis for trouble shooting it's worth trying. Try the cheater plug on the Jolida's power cord and see if there is any change to the buzz/hiss.
Blaackdog, advice taken.
Where would I begin to figure out the internal grounding issue in the jolida? I'd imagine there'd be several places to check.
If you're not getting a buzz with the amp used as an integrated, check the input wiring first. From there it's anybody's guess where to begin.
Remember there are lethal voltages inside. If you don't know what you're doing get professional help.
Dan Santoni
Well, i took electronics at tech school in 1986, so i remember a bit...
Took a look inside the jolida briefly to check the ground wires.
The Power supply, third prong IEC, and signal ground are all connected at the chassis grounding post. Seems OK so far
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: