from Kevin about his Exodus amp
aghast at how the listening trial came out. It is so far from
the results of our installed user base that I immediately started
questioning the results.
is an absolutely HUGE installed user base of DIYers using the
Hypex amplifiers. The amp you used was nothing more than a stock
UCD-400AD built per the Hypex specifications. The almost universal
feedback we get from these amplifiers, not to mention our personal
experience using them at CES, building units for studios and using
them ourselves, told us that something was not right.
first thought was damage in shipping but then I remembered our
phone conversation about cables and it hit me like a ton of bricks.
I realized that you didn't use our single-ended to balanced adaptor
cables during the evaluation. There is no magic in our cables.
They are a simple twisted pair design with a shield. What is critical
is how you wire the input stage of a balanced amplifier. When
you failed to use our adaptor cables (as per our instructions
sent... shame on you!) for the evaluation you inadvertently introduced
noise at the input of the amplifier. I'm unsure of exactly how
much but my guess would be the neighborhood of 10db-20db. I'll
have the amplifier in question sent back here and do some quick
noise measurements with Praxis to illustrate my point.
Let me explain a little about the issues of adapting a singled
ended-source to a balanced load.
Hypex amps have true balanced input stages. To use them with single-ended
sources you have to tie the inverting input and ground reference
of the amplifier together to match the source ground reference.
Normally, you tie pins 1 & 3 of a typical XLR connector together
to achieve this. There are a couple of ways of doing that for
single-ended sources. I'll leave out the option of using transformers
(a great method) for brevity.
preferred method of converting a single-ended source is to use
an adaptor cable that ties the inverting input & the ground reference
together on the SOURCE end of the cable. In this manner you keep
ground currents that may travel on the signal ground reference
isolated to the source side of the connection.
second and less desirable option is to tie the analog ground reference
and the inverting input together just inside the RCA inputs on
the amplifier. The reason this is less desirable has to do with
grounding differences created in ALL unbalanced audio systems.
Currents DO travel through ground references and the less we have
flowing through the analog signal reference the better. Most OEMs
do this with a switch on the rear panel that allows the user to
select between balanced or single-ended inputs. The switch effectively
ties the ground reference to the inverting input when switched
for single-ended inputs. Our amplifiers do not use such a switch.
We provide XLR shorting plugs which short those pins if customers
require the less desirable conversion method.
all of our demo amplifiers we build adaptor cables that utilize
the first method of conversion. We do this because we want to
minimize the chance that someone will have a problem with background
noise due to grounding issues and we want to show off our amplifiers
in the best possible light.
the final analysis when you used your single-ended cables directly
into the RCA inputs without the proper XLR shorting plugs you
wired the input of the amplifier incorrectly. The result is very
predicabe... noise and hence the poor performance in your listening
I'll get you the Praxis measurements once I get the amplifier
about that. Had
I known that using a standard RCA (unbalanced) input was going
to cause a grounding problem then I would have certainly sought
a solution. As a mentioned before, and to be fair, I had to use
the same cables for all of the amps. It sounds like XLR shorting
plugs or a switch on the back panel when using RCA's will need
to be included with each amp.
look forward to re-evaluating this amp at a later date.
Park, TX 76367