I’ve been doing some research into how to convert a stereo signal into a mono signal as I want to connect my decks (stereo rca out) or laptop (trs out) to my amplifier in bridged mode via xlr as this seems to be the easiest connector to hide the resistors. I’ve seen lots of different videos all suggesting seemingly randomised values for resistors, some saying you need to link the unused terminals on the xlr end and some not. Has anyone got any experience making cables like this and would be able to provide more clarity on how to do so
On my stereo to mono cables, I use 100 ohm resistors. The vaule is not critical, I selected 100 ohms because most solid state amplifiers have a 10 to 20 Kiloohm input impedence and 100 ohms is 1/100 to 1/200 of that so you only lose 1% of the signal. If you use SMD resistors you can hide them inside a jack, but if your amplifier dose have a XLR input, this is the easiest way. The purpose of the resistors is to avoid fighting between the left and right source or preamp outputs when a signal is only present on left or right channel; this will produce a nasty distortion. They are only needed when the source is designed poorly. Properly designed analog line outputs have provisions to avoid this issue, the output remains undistorted even when left and right outputs are electrically tied togheter. A low value series resistor don't harm the signal so I place it in the cable just in case.
Okay so the value doesn’t matter as long as the resistors are within the input impedance for the amp. I’m more thinking about making these amp saftey means rather than audio distortion as I’ve seen lots of people saying that running just a standard rca to xlr y splitter into the amp for long periods of time will cause greater (and unnecessary) amp wear. I also saw someone constructing a design that had a resistor wrapped round the 1st and 3rd pin of the xlr cable and was also touching the second pin on the way round. Is something like this needed?
Depends on the minimun loadimpedance your source is happy with. Amplitude loss is seldom a problem, but 1 channel feeding the other through 2 interconnected 2x100ohm resistors could be asking for troubles (unless you feed from from a "poweramp"). Remember, that in case of stereo, the signals are NOT the same, and each channels output receives also an input signal from the other channel (through the interconnection resistors). In case you dont know what is the minimal loadimpedance of your source is, i would suggest at least 2x1k
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I found bellow on the specs for the decks that I would be using to connect to the amp. If I build the cable for these specs would I be able to use the same one with an adapter to plug it into my laptop?
Looks like your source would be happy with a 10k load, so anything 100ohm, even 1k is a no no. Do you have info about the input of the amp you want to feed?
In your situation i would use two 4.7k resistors. Not exactly ideal, but should work as a good compromise
Is there a better solution than this I want these cables to last so would rather a more reliable solution rather than a compromise. Also would you recommend any of the ideas mentioned above like having an additional resistor or linking the 3rd and 1st terminal of the xlr bit?
Your given source and amp does not leave much choice, thats why i said compromise, a higher input impedance of the amp would have been preferable, but you have what you have, and don't worry, just about everything is a compromis one way or n other
The L and R cable coming from your source, each connected at the end (amplfier side》 to a 4.7k resistor, join the other end of the resistors and feed the connection of the two resistors to the paralelled inputs ( must be inputs of the same polarity!) of your amp and your done on the hot side.
In case the amp has a switch to paralell the inputs internally (2 ohm,880W) you would not need to join the resistors externally, you could just connect L to L and R to R with serial resistors that are then joined by the switch as paralelled mono amp or as usual 2 channel stereo amp with practically unnoticable degradation in performance. Important is, that the resistors are located close to the inputs of the amp.
In case the amp has a switch to paralell the inputs internally (2 ohm,880W) you would not need to join the resistors externally, you could just connect L to L and R to R with serial resistors that are then joined by the switch as paralelled mono amp or as usual 2 channel stereo amp with practically unnoticable degradation in performance. Important is, that the resistors are located close to the inputs of the amp.
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My amp does have a switch like this that allows me to swap between stereo, parallel and bridged mono. Based off your first paragraph I came up with the design below where both the resistors would be the 4.7kohm ones suggested. Would I need to tweak this design in any way as my amp has the switch mentioned on it?
The old Rane Note to the rescue:
Why Not Wye?
Dennis Bohn, Rane Corporation
RaneNote 109 written 1991; last revised 4/04
Splitting Signals
Subwoofing in Mono
Unbalanced Summing
Balanced Summing
Output Impedances
https://www.ranecommercial.com/kb_article.php?article=2106
Why Not Wye?
Dennis Bohn, Rane Corporation
RaneNote 109 written 1991; last revised 4/04
Splitting Signals
Subwoofing in Mono
Unbalanced Summing
Balanced Summing
Output Impedances
https://www.ranecommercial.com/kb_article.php?article=2106
Works for summing L+R into a mono. Btw, do NOT get temped to use much lower resistor values than 4.7k, lower values need a source that can handle it !!!
I’ve seen on the diagram like with a few others that there is a resistor of 20k value that seems to have very little explanation as to it’s purpose
Duely noted I will be keeping the values for the resistors around this level to keep my kit from breaking! And just making sure I want them summed on the positive terminal for the xlr for mono? Also I’m planning on making a similar cable to connect my laptop to the same amp. I’ve seen that the average output impedance for laptops is around 20ohms so would this require lower ohm resistors of around 10ohms? Because videos I’ve seen of people making similar cables said not to use resistors below 100ohms
Yeah that’s helpful if I was looking to do it on the xlr end what would I link 3 and 1 with?The diagram below shows the wiring at the XLR end. Perhaps it may help?
Tbone, In your case (because of the 10 times higher resistor values that have to be used) the resistors should be at the END of the cable so that cable capacitance is fed from the much ĺower source impedance instead of Zsource + Rserial. Use L and R cable BEFORE you combine the signals.
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Gorgon is this in the case of the dual rca to xlr or the 3.5mm trs to xlr cable? By end do you mean the XLR terminal which will go into the amp or the trs side which will go into the laptop?