Bridging two Threshold S/500 optical bias

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RobertS61

RobertS61

Member
Joined 2007
#1
Hi,

Is it safe and possible to bridge two Threshold S/500 optical bias (that's the latest version) by use of an Y adaptor to parallel the RCA signal from one channel, then connect to both L and R channels as input from one channel, then use the two of the Red speakers posts to connect speakers?
Like a S/1000 I think?

Thanks in advance,

Robert
 
#4
Like this:

https://www.diyaudio.com/forums/attachment.php?attachmentid=977094&stc=1&d=1629712715

F4 Manual text about mono-parallel configuration:
Mono Parallel Operation
In mono parallel operation, you can achieve up to 100 watts output into a 2 ohm
load.
The amplifier is driven by a single-ended source, through the two RCA inputs
in parallel. The easiest way to do this is through a male RCA cable going into one of
the RCA inputs with a jumper between pins 2 and 3 of the XLR input connector, which
parallels the two inputs. This jumper is supplied with the amplifier.
(No XLR on my S/500)

If you look carefully at the connector you will see tiny labels next to the pin holes.
For parallel operation of the two channels as one, you must connect the outputs left
positive to right positive either at the connectors themselves or by “bi-wiring” the
loudspeaker with two sets of cables. Remember that the positive outputs have a red
band.
The black banded output connectors are already connected together to ground, so you
can make this connection externally or not as you please.
 

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  • FirstWatt F4 Mono Parallel configuration.JPG
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#5
"Y adaptor to parallel the RCA signal from one channel, then connect to both L and R channels as input from one channel, then use the two of the Red speakers posts to connect speakers?"

Rephrased for clarity. Y adapter from output of Pre. Single Y adapter with L signal goes 1/2 to Left Input of amp, 1/2 to Right Input of amp. So, identical signal in to both amp boards. Connect speaker to both red terminals at output.

I never disagree with ZM, but I always like to learn more. I thought I had this stuff figured out... Clearly I am 😕

Two identical signals connected to the speaker terminals... am I wrong that there would just be no sound? There would/should be no voltage differential between the (+) and (-) speaker terminals. Thus, no inny outy movement of speaker cone. I've even had my coffee, so I am missing a critical element. Thanks!!!

Edited to add - The F4 article makes perfect sense to me if connected that way. If connected the way I described above, and perhaps what may have been originally intended, I don't think it would make music. Again, learning... so apologies.
 
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#7
I'm very bad with schematics so I present the back of a Threshold S/500 and can you point me out how I should connect the pre-amp and the loudspeaker to get a mono-parallel configuration?

I'm sorry for my stupidity but that's how I am in this matter.

It's not mine but the same:

Threshold S500 optical bias back.jpg
 

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  • Threshold S500 optical bias back.jpg
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#8
Y RCA to RCA cable

Y end to both RCA inputs on amp, sole RCA cable end to preamp RCA output

speaker neg to GND output on amp ( both GNDs are anyway connected - check with ohmmeter; if you don't have one, just put fat wire bridge between two Neg/Black outputs on amp)

fat wire bridge between two Pos/Red outputs on amp
speaker Pos to any of Pos?Red output on amp

that's mono parallel

*****************************************

for classic bridged configuration, one needs preamp with balanced outputs;

also , XLR to 2*RCA cable needed, one per channel:

XLR pin 1 is GND for first RCA,
XLR pin 2 is hot for first RCA
First RCA = Pos Rca
XLR pin 1 is GND for second RCA
XLR pin 3 is hot for second RCA
Second RCA = Neg RCA

connect cable XLR to preamp output
first cable RCA to Right RCA in on amp
second cable RCA to Left RCA in on amp

speaker Neg to left channel Red output on amp
Speaker Pos to right channel Red output on amp

GND is not involved with speaker
 
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#9
[special=]%[/special]
Zen Mod said:
Y RCA to RCA cable

Y end to both RCA inputs on amp, sole RCA cable end to preamp RCA output
Click to expand...
Which inputs? RIGHT - RIGHT or RIGHT - LEFT?
speaker neg to GND output on amp ( both GNDs are anyway connected - check with ohmmeter; if you don't have one, just put fat wire bridge between two Neg/Black outputs on amp)
Click to expand...
Speaker black terminal to amplifier black terminal? I will check ground with MM

fat wire bridge between two Pos/Red outputs on amp
speaker Pos to any of Pos?Red output on amp

that's mono parallel
Click to expand...
Okay that's clear

*****************************************

for classic bridged configuration, one needs preamp with balanced outputs;

also , XLR to 2*RCA cable needed, one per channel:

XLR pin 1 is GND for first RCA,
XLR pin 2 is hot for first RCA
First RCA = Pos Rca
XLR pin 1 is GND for second RCA
XLR pin 3 is hot for second RCA
Second RCA = Neg RCA

connect cable XLR to preamp output
first cable RCA to Right RCA in on amp
second cable RCA to Left RCA in on amp

speaker Neg to left channel Red output on amp
Speaker Pos to right channel Red output on amp

GND is not involved with speaker[/QUOTE]
 
#10
Like this. See attached for one amp.

L channel from pre => Y cable. Y goes to both left and right inputs on amp 1. Left Amp
R channel from pre => Y cable. Y goes to both left and right inputs on amp 2. Right Amp

Hook one speaker to each amp. Hook (+) speaker to either Red amp binding post and speaker (-) to either Black amp binding post.
 

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#14
HA HA HA - That'll teach me to open the .pdf after I convert it. I have no idea what happened. Blame it on software and/or dodoooooooness. :rofl: :rofl: Too funny. So very sorry Robert, but you hopefully got the idea of how it all should have gone together.

Still laughing.
 
#16
You won't believe I even repaired a Threshold SA/1 and Mark Levinson ML-3 in the past with a failing transistor in their circuit. I just can't get the picture right with these kind of things. I'm hopeless with it if it is not explained step by step. Should try to find out how it technically works so I can make a better mental representation of it.
 
#17
A very kind person on the forum made it "click" for me one day, so I'll try to convey how they explained it to me.

1. Speaker cone moves in and out based on the difference in the potential from the (+) to the (-) terminal. Generally, if the (+) terminal is more positive than the (-) terminal, then the cone moves outward... and the inverse is true for inward.

2. What I thought you were saying in post #1 was to hook the (+) and (-) of the speaker to both red binding posts. Perhaps I misinterpreted, but even so, it's a good illustration of why it won't make music.

See attached for a few things I had put together for my own understanding a few months ago along with an added pic of what I thought you were describing in post #1. Hope it helps with the technical understanding. Also fixed the wiring from the Y. 😀 😀

Cheers
 

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#19
ItsAllInMyHead said:
A very kind person on the forum made it "click" for me one day, so I'll try to convey how they explained it to me.

1. Speaker cone moves in and out based on the difference in the potential from the (+) to the (-) terminal. Generally, if the (+) terminal is more positive than the (-) terminal, then the cone moves outward... and the inverse is true for inward.

2. What I thought you were saying in post #1 was to hook the (+) and (-) of the speaker to both red binding posts. Perhaps I misinterpreted, but even so, it's a good illustration of why it won't make music.

See attached for a few things I had put together for my own understanding a few months ago along with an added pic of what I thought you were describing in post #1. Hope it helps with the technical understanding. Also fixed the wiring from the Y. 😀 😀

Cheers
Click to expand...
Thanks again. It's nice to have a forum where one can ask such a simple question and still get answer.
 
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