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Trying to figure out if power amplifier is common ground or balanced/differential.


May 4, 2021
I'm receiving the Coda no.8 soon. I have a pair of RELs I wanted to pair with it using high level. I was told the Coda no.8 is a true balanced design. The manual isn't very clear to me. I see the words differential and balnced are mentioned in the manual but I don't know what it's referring 2. Trying to see if the black speaker terminal is ground or if it's live. If it's ground...I hear that referred to as "common ground". If it's not...then it's live though it's 180° out of phase(right?)..
If I get this wrong and hook up the Rels ground wire to the black speaker terminal...I could destroy the amplifiers. So I asked the manufacturer at Coda and he just responded with "The black is actually a system ground."
Is this the same as saying "common ground"?

"The Coda Continuum No. 8 amplifier is designed with the same level of thoroughness usually
reserved for the finest amplifier gain stages. Balanced interconnections are provided to take
advantage of the greater noise rejection they provide. Differential voltage gain throughout
provides exceptional rejection of external noise and contributes to the inherent DC stability of
the circuit. This allows direct coupling at the Balanced Inputs without servo circuitry. The unit
also uses output followers operating without feedback.
The front end is designed to provide a slew rate of 50 V/us without entering Class B operation
as is common in many other designs. This combined with excellent high frequency design
insures linear operation at high speed. The supplies take a very direct approach to high
performance. A top quality 3000VA toroidal transformer with independent and about
80,000 uF of total capacitance with very low ESR and inductance are used.
The current stage is capable of producing currents in excess of 100 peak Amperes with a
degree of linearity and speed which is not matched by other designs when producing only a
fraction of this current. This is achieved by the implementation of several distinct circuit
Each channel uses 20 individual output transistors with a combined power capability of 3600
Watts and 75 Amps with a bandwidth of 10 Mhz.
The bias section is designed to produce a precision transition with no abrupt changes in
distortion or output impedance."


Major Contributor
May 27, 2021
Yes, that would be a common ground (shared by the left & right channels and most-likely connected to power-line ground).

Normally "balanced" power amplifier outputs are called "bridged". The (+) & (-) speaker-outputs are both driven (with opposite polarity). And in that case the left & right speakers can't share a common connection.

Some stereo amplifiers have a switch that connects the inputs and inverts one channel. That puts it in bridged-mode. You connect the speaker between the two (+) outputs which are now out-of-phase. Then you can get at-least twice the power and often 4 times the power (in mono).

I don't know anything about those speakers but I've never seen a passive speaker with an actual ground. The (-) or black terminal is not (normally) grounded (until you connect it to the amplifier's ground). So usually it's no problem connecting any speaker to a bridged amplifier.

(You can't drive regular headphones with a bridge amplifier because the left & right sides share a common ground.)

Blumlein 88

Grand Contributor
Forum Donor
Feb 23, 2016
You can send the amp a test signal, maybe 400 hz at -20 or -30 db. Use an AC voltmeter to check voltage between the Red and Black speaker lead and then between Red speaker lead and the outer shell of the RCA plus. If you get the same reading both ways the black speaker lead is ground. If you get half the voltage on the Red speaker lead to RCA outer shell, then the output is differential.

If this isn't clear say so and I'll try some diagram or something.


Major Contributor
Forum Donor
Mar 16, 2016
Suffolk UK
You can also measure the resistance between the black terminal and the RCA shell. If it's a short circuit, or very near it, like less than 1ohm, then the black terminal is ground.


Rock Rabbit

Active Member
Feb 24, 2019
It seems GND
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