Author Topic: Modifying series I stereo to mono (Read 342 times)

tdukes · « **on:** April 09, 2009, 12:14:12 PM »

Looking at this page.

It looks like what I need to do to convert a stero series I 1/4 jack to mono is:

1. remove violet wire from pin 8 to XLR 3.
2. remove orange wire from pin 4 to XLR 2.
3. add 20k resistor between pin 8 and XLR 3.
4. add 20k resistor between pin 4 and XLR 2.

Did I miss anything?

Todd.

JimmyJ · « **Reply #1 on:** April 09, 2009, 05:11:09 PM »

Almost... The 20k resistors are summing the audio signal coming from XLR pins 2 and 3. Connection point 4 on the 1/4 inch jack corresponds to the tip of your mono 1/4 inch plug so you want both resistors to connect to that point. When finished, connection point 8 on the 1/4 inch jack (corresponding to the ring of a stereo 1/4 inch plug) should NOT have anything soldered to it.

Make sense?
Jimmy J

tdukes · « **Reply #2 on:** April 09, 2009, 06:25:40 PM »

Yes it does. Thanks for seeing my mistake.

Todd.

tbrannon · « **Reply #3 on:** April 09, 2009, 06:43:20 PM »

Two 20k resistors = $2
One spare XLR jack in case you goof = ?

Having Jimmy Johnson as your online tech help = priceless

tdukes · « **Reply #4 on:** April 13, 2009, 06:46:39 PM »

Operation complete!

The only surprise was that the signals went to the 1/4 jack first and then to the XLR. So I removed the connection to the 1/4 jack and joined the two sections of wire and covered the joint with a little heat shrink tubing.

I am hearing a little phase shifting to the sound. I heard this before making the stereo to mono change but didn't mention it. Is this normal?

Todd.

JimmyJ · « **Reply #5 on:** April 16, 2009, 01:04:03 PM »

Todd,

It took me a minute to figure out what you meant here but I pulled the back panel off one of my old basses and now I know.

The bass' preamp outputs are orange and violet wires. These used to be connected directly to the 1/4 jack (connection points 4 &

and then short jumpers continued from there to XLR pins 2 & 3. This makes the mono 1/4 mod a slightly more complicated operation. You have a couple choices...

Quick and dirty would be:
1- Unsolder all 4 orange and violet wires from the 1/4 jack
2- Solder two 20k resistors to connection point 4 of the 1/4 jack (you should use some insulation on the resistor's leads - can be made by stripping some other wire and sliding the results onto the resistor's leads before connecting)
3- Connect the other end of one resistor to both loose orange wires, solder and insulate thoroughly. (Hey, I said it was dirty!)
4- Connect the other resistor to both violet wires and insulate that.

What you have done is tapped off the signal from both the orange and violet wires on their way to the XLR jack, summed the two signals and made a mono output. Doing it as above would not disturb the XLR but would leave you with a couple floating junction points that would make Mica scowl...

The more proper way would be to have the orange and violet wires go directly to pins 2 & 3 of the XLR and also have the resistors terminate at pins 2 & 3. The resistors then act as the new jumpers to get back to the 1/4 jack (summing the signals when they meet at connection point 4). If you want to do it this way I suggest you start with a brand new XLR jack and try to emulate the factory's use of shrink wrap.

As for your phasing question ... if you are used to hearing the bass in stereo there will be some slight cancellation when you make it mono but there should be no shifting as such. Be sure that the two preamp output signals are at no point connected directly to each other - without the summing resistors. This could cause some unusual audio gremlins as the two outputs would be effecting each other in strange ways. If you have done the mod correctly the outputs from your power supply should still be discreet stereo but the the sound of both pickups should appear when you use the 1/4 jack.

Hope this makes some sense - I almost know enough to be an Alembic repair guy...
Jimmy J

(Toby, that's funny!)

tdukes · « **Reply #6 on:** April 16, 2009, 06:19:37 PM »

Here is a picture of how it turned out.

The original orange and purple wires were a little short to make it to the XLR connector so I just removed them from the 1/4 connector and soldered them together. The solder joint is under the white shrink wrap. Next time I will remember to wipe the soldering iron off before using it to heat shrink the tubing.

That is also heat shrink tubing on the resistor leads. I might go back in and shorten the leads a bit.

Thanks for your help.

Todd.

JimmyJ · « **Reply #7 on:** April 16, 2009, 10:06:11 PM »

Hey Todd,
That's it! Nicely done! Maybe just bend those resistors slightly further into the cavity to get the leads away from the CONDUCTIVE silver paint.
But what about this phasing thing?
Jimmy J

tdukes · « **Reply #8 on:** April 17, 2009, 05:16:10 AM »

I heard the phasing sound a little last night when I was playing the guitar unplugged. This is a 6 string guitar, not a bass. I think what I may be hearing is the low E slightly being out of tune and the guitar being more resonant than my other solidbodies and having more sustain than my acoustics giving it a sound I haven't heard before.

It doesn't appear to be the electronics, it must be an acoustic sound that the guitar just makes. It is pretty subtle and getting harder to hear the more I play the guitar. Maybe its just in my head.

Todd.

JimmyJ · « **Reply #9 on:** April 17, 2009, 12:16:13 PM »

Hey Todd,

Yes, if the string is doing something acoustically then it's unrelated to the electronics, but of course the electronics will hear and amplify whatever is happening. I only really know about bigger strings (and one note at a time) but maybe it's an action thing or even your low E string going bad.

Anyway, nice work on the electronics. Enjoy your new standard-guitar-cable-friendly output!

Jimmy J

terryc · « **Reply #10 on:** May 12, 2009, 02:24:15 PM »

Jimmy J - apart from being a bass player of great renown..looks like you could put Dfung(our electronics theory wizard) to shame as well.