ASL UHC signature+Teac A-L700P failure

[CSMR]

I received my ASL UHC signature headphone adapter and connected it expectantly to my Teac A-L700P Class-D amp. There was a lot of noise from speakers and headphones. I have diagnosed the problem: the UHC left and right negative amplifer inputs are connected. For some amps this will be OK; others not. I confirmed that this is the problem by plugging in my speakers normally to the amp and connecting the negative terminals: same noise.

So in conclusion, the ASL UHC works only when you can link the negative terminals of your power amp. If you are careful you can test whether the UHC will work by connecting these terminals directly. It is understandable that the UHC has to connect the negative terminals, since the headphone has a common ground for both channels.
I doubt one could recommend putting the UHC in line with speakers, since the connection would become unbalanced.

The Teac is a Tripath amp, like the little Sonic Impact. The Sonic Impact is also said not to work well with the UHC. Perhaps they share the same problem, and the SI not having enough power and therefore clipping was a misidentification?
(One point about the Teac which may be relevant: the power plug has no ground.)

Grateful if more technically minded people could correct what I have said, or give the appropriate terms, and say on what amps joining negative terminals is not likely to be a problem.

 

[rickcr42]

if you have a floating ground (balanced) output amp and connected a common ground output device to it you are damn lucky you did not blow the amps output stage.

No passive "common ground" device such as headphone adapters (ALL) or hafler style surround adapters or even common ground speaker switches (most)should be used with an amp that does not have a shared ground output.

you are lucky to still have an amp

 

[CSMR]

Thanks for explaining this rickcr42.
It seems that's the problem with using this with the sonic impact too:
Quote:

Originally Posted by hottyson I used the speaker outs since the Sonic Impact Portable T-Amp lacks a headphone output. I also had to listen in mono using one chanel of the amp since the left and right chanels do not share a commone ground.

 

[blumenco]

I think that the ultrasonic noise is a problem, so what is the solution?

Ok, so it has been called a "filter" but all it really is is just a capacitor parallel to the binding posts.

it needs a larger value of capacitor across the binding posts. take off the old one and look at the value and try doubling or tripling it for instance. additionally, the resistor idea across the binding posts instead of in series with the positive would help.

OK THOUGH> I have read the eweitsman posts from the other si threads. I have read the warnings and value my hearing immensely... I do not want to debate. that said, Eliminating this noise issue whether or not it can cause hearing damage is important for being able to get this product usable by alot of people. I am not a business man, I am a diyer. I have no intention of selling anything. furthermore, since this noise is resonance at certain (probably lower, audible frequencies) it is giving higher harmonics at potentially high values. I have found in the concumer realm that speakers are rarely the devices that have frequency response issues, it is the electronics because companies filter the hell out of them (especially transistor stuff) to get rid of the last bit of negative feedback.

this thread is dedicated to SOLVING the noise issue by experimenting with it. something that SI obviously did not do to their product for this application. this is a simple freakin conversion to high impedance headphones and it will probably require some testing, etc.

therefore, unless someone has an oscilliscope proving the noise present, then we do not need to be discouraged on our quest to fix the problem. this is an experimental learning process and i claim to be expert of nothing. pleae, do not impede my learning process.

I read your simulation, eweitzman, BTW and it is most interesting. however, let us approach this thing with an oscilliscope and possibly even a HF microphone to see if those frequencies are ACTUALLY being produced. I have a freind in the physics dept. and i will see if he will let me use the stuff. it might take a little while though. if the thread dies or something, then i will post my results on a new thread.

Clark

I will go to rat shack and get some caps today... anyone else try any? take care to make sure it is ok to put two capacitors parallel over the same post.

 

[CSMR]

Another nugget of information here from occam:
http://www.audiocircle.com/circles/v...ic.php?t=16455

 

[rickcr42]

if this amp IS a balnced bridge or put another way has a floating ground output topology NO amount of noise filtering will help if the attempt is made to use the amp with a device that has a common ground.The negative side of both amps of the stereo pair will be in effect shorted together.A scenario that will not see that amp last long in the real world when it burns up.

there are the posible fixes for this thoug

1-RCL isolation network-no gurantees here folks

2-two ASL UPCs "floating" (one for each channel) and dual mono balanced wiring mod to the cans-pretty drastic measure just to use THAT particular amp