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post #1 of 21 Old 06-23-2020, 02:51 PM - Thread Starter
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Humm, no FAQ on hum

I've run into a strange and very annoying 60 Hz hum/buzz coming out of my L and R front speakers. Go to YouTube and search for 60 Hz hum to hear what it sounds like. (I need more posts here to use links) To me it sounds more like a buzz. It lasts exactly 10 seconds and returns about every 3.5 minutes. At other times there is a very faint buzz, inaudible unless you put your ear right up to a speaker. This has risen its ugly head since I incorporated an Adcom GFP-565 stereo preamp dedicated to CD and phono. I have a Yamaha Aventage RX-a840 home theater receiver for all other signal sources.

SETUP (if relevant): The preamp's bypass outputs are connected to a 2 channel power amp which drives the main speakers, the receiver's pre-amp outputs are connected to another 2 ch. power amp which drives the rear speakers, to another power amp for the center channel (using only its right channel) and to a powered subwoofer. I have a Y connector connected to L and R "lab" outputs of the preamp, and another Y connector at the subwoofer to accept signal from both the preamp and the receiver's subwoofer output. I intended this setup to allow the subwoofer to be used for both 2 ch. audio from the preamp as well as for home theater from the receiver. I connected the receiver's pre-amp main L/R outputs to the preamp's aux inputs. When listening to 2 ch. audio I turn off the receiver. When listening to other sources (e.g., DVDs, satellite TV) I set the preamp to aux and the volume control to roughly unity gain. I don't use the receiver's power amp outputs for anything.

All electronics are Adcom except the receiver, an OPPO CD/BluRay player, and a Cambridge phono-pre-preamp. The main and center channel speakers are Gallo Reference Strada 2s.

I've done my best to keep interconnects away from power cords. All power cords are connected to dedicated, grounded circuits.

The episodic hum/buzz occurs regardless of the source and regardless of whether the receiver is on or off. However, switching the preamp to an inactive input (tuner, tape) eliminates the buzz. It didn't occur before I changed the setup to accommodate the preamp. Adding the preamp produced a major improvement in 2 channel audio and I don't want to give that up. Now if I could just swat that damn buzzing bee...
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post #2 of 21 Old 06-23-2020, 08:57 PM
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The fact that you say it's a 60Hz hum would indicate that it's a ground loop problem.
Adding the Adcom GFP-565 looks like it may have been the change that caused it. See if it goes away if you revert the system back to its preexisting state, including where everything was plugged in before.
The fact that it lasts 10 seconds, goes away, then returns on a periodic basis is interesting.

See if you can get everything plugged into the same electrical circuit, which generally resolves a ground loop.
If the problem persists, you may want to check the subwoofer forum for ideas on how to address the symptom.

The GFP-565 may have a grounding problem inside the unit itself. You may want to contact their support for tips to diagnose.

Quote:
Originally Posted by bigdancehawk View Post
I've run into a strange and very annoying 60 Hz hum/buzz coming out of my L and R front speakers. Go to YouTube and search for 60 Hz hum to hear what it sounds like. (I need more posts here to use links) To me it sounds more like a buzz. It lasts exactly 10 seconds and returns about every 3.5 minutes. At other times there is a very faint buzz, inaudible unless you put your ear right up to a speaker. This has risen its ugly head since I incorporated an Adcom GFP-565 stereo preamp dedicated to CD and phono. I have a Yamaha Aventage RX-a840 home theater receiver for all other signal sources.

The episodic hum/buzz occurs regardless of the source and regardless of whether the receiver is on or off. However, switching the preamp to an inactive input (tuner, tape) eliminates the buzz. It didn't occur before I changed the setup to accommodate the preamp. Adding the preamp produced a major improvement in 2 channel audio and I don't want to give that up. Now if I could just swat that damn buzzing bee...
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post #3 of 21 Old 06-23-2020, 09:49 PM
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Originally Posted by bigdancehawk View Post
...It lasts exactly 10 seconds and returns about every 3.5 minutes....

Sounds like your pre-amp is being affected by the WiFi antenna on your Yamaha receiver. (I bet turning off the power switch of the receiver does not turn off its WiFi)
To test this theory you could either remove the receivers WiFi antenna or just unplug the receivers power cord to see if your buzzing problem goes away.
If removing the antenna solves the buzzing problem, but you need internet access, you can try connecting the receiver to the router with an Ethernet cable.


I'm still perplexed by your RCA cable connection description regarding the use of Y-connectors.
Outputs should never be connected to outputs, but you seem to do this twice:
- once with the "Lab" outputs of the pre-amp that go to the sub.
- again at the subwoofer input to connect the pre-amp and receiver together.

You've described almost all the other components in your system except for the powered sub, so I'm not sure what to suggest.
If your sub has both, an LFE input jack and a stereo left/right pair of input jacks, you should connect the receiver to the LFE jack and the pre-amps "Lab" outputs to the stereo left/right pair of input jacks with a pair of cables.
Whatever you do, you need to lose the Y-connectors because shorting outputs together is the wrong way to go about creating a mono signal.
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post #4 of 21 Old 06-24-2020, 05:57 AM
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Is there one source which, if you disconnect it, the hum goes away? One easy to check for ground loops is to run a wire between the ground terminals of the source and your amp, then pull out the RCA connector part way, so that the center pin is connected but not the outer shield (doing this without the ground wire I mentioned will produce a horrible hum).
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post #5 of 21 Old 06-24-2020, 10:36 AM
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Intermittent noise or hums are typically from timed or short use external sources.


water well pump
window air conditioners
fridge
freezer
light dimmers
... and lot's of other things.



If you can’t explain it simply, you don’t understand it well enough – Albert Einstein
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post #6 of 21 Old 06-24-2020, 12:39 PM - Thread Starter
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Originally Posted by Ratman View Post
Intermittent noise or hums are typically from timed or short use external sources.


water well pump
window air conditioners
fridge
freezer
light dimmers
... and lot's of other things.
Ha! We bought this house not too long ago. It's equipped with a sump pump--something we've never had before. I thought that was it for sure, but alas when I unplugged it the noise remained.

Here's what's so strange: the intervals between the buzzing are almost always exactly 3.5 minutes and the buzzes last exactly 10 seconds. It's not light dimmers or the fridge--they don't cycle on and off at those intervals. We don't have any window air conditioners. I unplugged the freezer to no avail. I'm now going to unplug all charging devices one at a time, starting with the robot vacuum cleaner.
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post #7 of 21 Old 06-24-2020, 12:44 PM
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Perfect/consistent "timing". Coincidence? Nah....
You have something that "cycles" and injecting noise. Of course, that's just my opinion.



If you can’t explain it simply, you don’t understand it well enough – Albert Einstein
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post #8 of 21 Old 06-24-2020, 02:28 PM - Thread Starter
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Quote:
Originally Posted by stereo2.0 View Post
Sounds like your pre-amp is being affected by the WiFi antenna on your Yamaha receiver. (I bet turning off the power switch of the receiver does not turn off its WiFi)
To test this theory you could either remove the receivers WiFi antenna or just unplug the receivers power cord to see if your buzzing problem goes away.
If removing the antenna solves the buzzing problem, but you need internet access, you can try connecting the receiver to the router with an Ethernet cable.


I'm still perplexed by your RCA cable connection description regarding the use of Y-connectors.
Outputs should never be connected to outputs, but you seem to do this twice:
- once with the "Lab" outputs of the pre-amp that go to the sub.
- again at the subwoofer input to connect the pre-amp and receiver together.

You've described almost all the other components in your system except for the powered sub, so I'm not sure what to suggest.
If your sub has both, an LFE input jack and a stereo left/right pair of input jacks, you should connect the receiver to the LFE jack and the pre-amps "Lab" outputs to the stereo left/right pair of input jacks with a pair of cables.
Whatever you do, you need to lose the Y-connectors because shorting outputs together is the wrong way to go about creating a mono signal.
No antenna. The receiver is hard wired to the router via Ethernet cable.
The subwoofer is an Acoustics MJA pro50. It has left and right low level inputs. One of these also serves as a mono input. The high level input is a balanced XLR female.

The preamp doesn't have a mono or subwoofer output. The Y connector on the preamp is to combine L and R output to make a mono source for the subwoofer. Steve Hoffman said you can do this to get a mono signal out of a stereo turntable. LINK At the subwoofer, I didn't think I was combining two outputs, just allowing the subwoofer to get signal from either the preamp or the receiver's sub output. But you've prompted me to do some research on this and it seems Y connectors aren't a good way to combine two signals, but rather for splitting a single signal. With both the receiver and preamp on, it looks like I've been combining their signals.

HERE is a device that supposedly converts stereo to mono. Part no. 50-20795. What do you think?

Last edited by bigdancehawk; 06-24-2020 at 02:52 PM. Reason: add part no.
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post #9 of 21 Old 06-24-2020, 02:31 PM - Thread Starter
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Originally Posted by Ratman View Post
Perfect/consistent "timing". Coincidence? Nah....
You have something that "cycles" and injecting noise. Of course, that's just my opinion.
You're exactly right, but I can't figure out what it is.
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post #10 of 21 Old 06-24-2020, 02:40 PM - Thread Starter
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Originally Posted by philpoe View Post
The fact that you say it's a 60Hz hum would indicate that it's a ground loop problem.
Adding the Adcom GFP-565 looks like it may have been the change that caused it. See if it goes away if you revert the system back to its preexisting state, including where everything was plugged in before.
The fact that it lasts 10 seconds, goes away, then returns on a periodic basis is interesting.

See if you can get everything plugged into the same electrical circuit, which generally resolves a ground loop.
If the problem persists, you may want to check the subwoofer forum for ideas on how to address the symptom.

The GFP-565 may have a grounding problem inside the unit itself. You may want to contact their support for tips to diagnose.
Thanks! I may start by running a simple stereo system setup with just the preamp, a power amp and speakers. No subwoofer. If that produces hum the culprit has to be the preamp or its interconnects to the amp picking up a stray signal from somewhere. After that, I'll try reconnecting everything back the way it was before, as you suggest.
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post #11 of 21 Old 06-24-2020, 02:44 PM - Thread Starter
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Quote:
Originally Posted by MTVhike View Post
Is there one source which, if you disconnect it, the hum goes away? One easy to check for ground loops is to run a wire between the ground terminals of the source and your amp, then pull out the RCA connector part way, so that the center pin is connected but not the outer shield (doing this without the ground wire I mentioned will produce a horrible hum).
I had all the same sources connected to the receiver and there was no hum, but I'll try disconnecting both the CD player and the turntable from the preamp. Are you suggesting I should run a ground wire from the CD player to the preamp or the power amp?

Last edited by bigdancehawk; 06-24-2020 at 02:46 PM. Reason: correct tense
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post #12 of 21 Old 06-24-2020, 02:48 PM
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Originally Posted by bigdancehawk View Post
You're exactly right, but I can't figure out what it is.
I'd suggest a troubleshooting technique that may help...


Disconnect all stuff. Reintroduce one component at a time.
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post #13 of 21 Old 06-24-2020, 02:50 PM
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Originally Posted by bigdancehawk View Post
Are you suggesting I should run a ground wire from the CD player to the preamp or the power amp?
Give it a try. It shouldn't be necessary, but it can't hurt.



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post #14 of 21 Old 06-24-2020, 02:54 PM - Thread Starter
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Originally Posted by Ratman View Post
I'd suggest a troubleshooting technique that may help...


Disconnect all stuff. Reintroduce one component at a time.
Makes sense.
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post #15 of 21 Old 06-24-2020, 04:09 PM
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Makes sense.
I thought so.
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post #16 of 21 Old 06-24-2020, 06:59 PM
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Originally Posted by bigdancehawk View Post
...The subwoofer is an Acoustics MJA pro50. It has left and right low level inputs. One of these also serves as a mono input. The high level input is a balanced XLR female....
HERE is a device that supposedly converts stereo to mono. Part no. 50-20795. What do you think?

I looked up the manual for your sub and confirmed the two (left/right) line level RCA inputs that you mentioned. These two inputs will solve your Y-connector problem at the subwoofer end.
Just connect your receivers sub cable to the left (or right) sub input, and then plug the sub cable from your pre-amp into the remaining input. They won't interfere with each other this way.
(FYI: the high level input connector is actually a Neutrik Speakon connector, not an XLR connector. Just mentioning it in case you ever decide to buy one)

That still leaves the problem of having to mix the pre-amps Lab outputs together without using a Y-connector.
I can't recommend the MCM Custom Audio 50-20795 stereo-to-mono signal converter because it uses transformers to mix the signals together.
Transformers have a tendency to roll-off the response at the deepest frequencies, and subwoofers only operate at the deepest frequencies.
Without any specifications to guide me on its capabilities I just don't feel comfortable recommending that product.
If you can find or make your own cable that uses resistors to isolate the Lab outputs before joining them together to one cable that goes to the subwoofer, that would work just fine.




Does your pre-amp sit close to the receiver?
If it does I still think you should try my earlier suggestion of unplugging the receiver while listening to your pre-amp to see if the timed buzz problem goes away. (It still sounds like a nearby Wi-Fi transmitter problem to me)
If unplugging the receiver does eliminate the problem, then you can then try obtaining some clip-on ferrite cores and attaching them onto your pre-amp input cables to see if that will also silence the buzz.
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post #17 of 21 Old 06-24-2020, 07:22 PM - Thread Starter
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Originally Posted by stereo2.0 View Post
I looked up the manual for your sub and confirmed the two (left/right) line level RCA inputs that you mentioned. These two inputs will solve your Y-connector problem at the subwoofer end.
Just connect your receivers sub cable to the left (or right) sub input, and then plug the sub cable from your pre-amp into the remaining input. They won't interfere with each other this way.
(FYI: the high level input connector is actually a Neutrik Speakon connector, not an XLR connector. Just mentioning it in case you ever decide to buy one)

That still leaves the problem of having to mix the pre-amps Lab outputs together without using a Y-connector.
I can't recommend the MCM Custom Audio 50-20795 stereo-to-mono signal converter because it uses transformers to mix the signals together.
Transformers have a tendency to roll-off the response at the deepest frequencies, and subwoofers only operate at the deepest frequencies.
Without any specifications to guide me on its capabilities I just don't feel comfortable recommending that product.
If you can find or make your own cable that uses resistors to isolate the Lab outputs before joining them together to one cable that goes to the subwoofer, that would work just fine.




Does your pre-amp sit close to the receiver?
If it does I still think you should try my earlier suggestion of unplugging the receiver while listening to your pre-amp to see if the timed buzz problem goes away. (It still sounds like a nearby Wi-Fi transmitter problem to me)
If unplugging the receiver does eliminate the problem, then you can then try obtaining some clip-on ferrite cores and attaching them onto your pre-amp input cables to see if that will also silence the buzz.
This is great info. Thank you very much. Yes, the preamp sits on a shelf immediately above the receiver. I'll do as you've suggested and let you know the result. FYI, the wi-fi transmitter is roughly 16 feet away.
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post #18 of 21 Old 06-24-2020, 08:46 PM - Thread Starter
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Originally Posted by stereo2.0 View Post
I looked up the manual for your sub and confirmed the two (left/right) line level RCA inputs that you mentioned. These two inputs will solve your Y-connector problem at the subwoofer end.
Just connect your receivers sub cable to the left (or right) sub input, and then plug the sub cable from your pre-amp into the remaining input. They won't interfere with each other this way.
(FYI: the high level input connector is actually a Neutrik Speakon connector, not an XLR connector. Just mentioning it in case you ever decide to buy one)

That still leaves the problem of having to mix the pre-amps Lab outputs together without using a Y-connector.
I can't recommend the MCM Custom Audio 50-20795 stereo-to-mono signal converter because it uses transformers to mix the signals together.
Transformers have a tendency to roll-off the response at the deepest frequencies, and subwoofers only operate at the deepest frequencies.
Without any specifications to guide me on its capabilities I just don't feel comfortable recommending that product.
If you can find or make your own cable that uses resistors to isolate the Lab outputs before joining them together to one cable that goes to the subwoofer, that would work just fine.




Does your pre-amp sit close to the receiver?
If it does I still think you should try my earlier suggestion of unplugging the receiver while listening to your pre-amp to see if the timed buzz problem goes away. (It still sounds like a nearby Wi-Fi transmitter problem to me)
If unplugging the receiver does eliminate the problem, then you can then try obtaining some clip-on ferrite cores and attaching them onto your pre-amp input cables to see if that will also silence the buzz.
Correction: the preamp sits 2 shelves above the receiver. The middle shelf has the BluRay/CD player and a DirecTV box.

I unplugged the receiver, leaving everything else the same, including both Y connectors. I almost lost track of time listening to music. No buzz whatsoever. JD Lang, Bizet's Carmen Suite and Prokofiev. It was the best sound this system has produced to date. WTF?
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post #19 of 21 Old 06-25-2020, 06:33 PM
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Originally Posted by bigdancehawk View Post
...I almost lost track of time listening to music. No buzz whatsoever. JD Lang, Bizet's Carmen Suite and Prokofiev. It was the best sound this system has produced to date. WTF?

That's great, you've narrowed down the problem to the Wi-Fi radio built-in to your Yamaha receiver. (Remember, Wi-Fi relies on transmitting signals as well as receiving them)
Even without an antenna being attached, it seems like your receiver is doing an automatic search for other Wi-Fi equipment every 3.5 minutes by sending out signal bursts that are strong enough to be picked up by your Adcom pre-amp.


Maybe you could look through your receivers manual to see if there is a way to shut off the Wi-Fi.
If you can't turn the Wi-Fi off you could look for a screw cap that fits the Wi-Fi antenna jack but is sealed (and doesn't have a center pin) to prevent the signal from leaking out.
Otherwise you'll have to separate the components further apart until the noise goes away, or invest in some split ferrite cores that you can clamp around the Adcom's cables.
(you said earlier that the unused inputs on the Adcom didn't have this problem, so it's your cables that are acting like antennas)

Good luck.

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post #20 of 21 Old 06-27-2020, 11:16 AM - Thread Starter
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Originally Posted by stereo2.0 View Post
That's great, you've narrowed down the problem to the Wi-Fi radio built-in to your Yamaha receiver. (Remember, Wi-Fi relies on transmitting signals as well as receiving them)
Even without an antenna being attached, it seems like your receiver is doing an automatic search for other Wi-Fi equipment every 3.5 minutes by sending out signal bursts that are strong enough to be picked up by your Adcom pre-amp.


Maybe you could look through your receivers manual to see if there is a way to shut off the Wi-Fi.
If you can't turn the Wi-Fi off you could look for a screw cap that fits the Wi-Fi antenna jack but is sealed (and doesn't have a center pin) to prevent the signal from leaking out.
Otherwise you'll have to separate the components further apart until the noise goes away, or invest in some split ferrite cores that you can clamp around the Adcom's cables.
(you said earlier that the unused inputs on the Adcom didn't have this problem, so it's your cables that are acting like antennas)

Good luck.
Great info--thank you very much and thanks to everyone for their advice.
Exactly right: the Adcom preamp was picking up the signal. Your idea of using ferrite cores on the preamp's cables led me to detach them one at a time. When I disconnected the cables from the CD player the noise stopped. I took a closer look at the cables and they both had small holes from our destructive cat chewing on them. So I replaced the cables and now the noise is gone for good. Hallelujah!!
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post #21 of 21 Old 06-27-2020, 11:27 AM - Thread Starter
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Quote:
Originally Posted by stereo2.0 View Post
I looked up the manual for your sub and confirmed the two (left/right) line level RCA inputs that you mentioned. These two inputs will solve your Y-connector problem at the subwoofer end.
Just connect your receivers sub cable to the left (or right) sub input, and then plug the sub cable from your pre-amp into the remaining input. They won't interfere with each other this way.
(FYI: the high level input connector is actually a Neutrik Speakon connector, not an XLR connector. Just mentioning it in case you ever decide to buy one)

That still leaves the problem of having to mix the pre-amps Lab outputs together without using a Y-connector.
I can't recommend the MCM Custom Audio 50-20795 stereo-to-mono signal converter because it uses transformers to mix the signals together.
Transformers have a tendency to roll-off the response at the deepest frequencies, and subwoofers only operate at the deepest frequencies.
Without any specifications to guide me on its capabilities I just don't feel comfortable recommending that product.
If you can find or make your own cable that uses resistors to isolate the Lab outputs before joining them together to one cable that goes to the subwoofer, that would work just fine.




Does your pre-amp sit close to the receiver?
If it does I still think you should try my earlier suggestion of unplugging the receiver while listening to your pre-amp to see if the timed buzz problem goes away. (It still sounds like a nearby Wi-Fi transmitter problem to me)
If unplugging the receiver does eliminate the problem, then you can then try obtaining some clip-on ferrite cores and attaching them onto your pre-amp input cables to see if that will also silence the buzz.
I wired the subwoofer as you suggested, thus eliminating the Y connector. It worked like a charm. It never occurred to me that I could connect different sources to the L and R inputs.

Now if I could just find or make the thing from your diagram I can eliminate the other Y connector.

Anybody need a couple of high quality Y connectors?
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