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PostPosted: Tue Apr 24, 2018 7:46 pm 
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Location: Chilliwack, BC, CA
I bought a headphone amp from a member on here claiming it to be brand new, impulse purchase blah blah. Anyways it's the Massdrop Cavalli Tube Hybrid amp and after inserting the tube, powering it on, connecting my 3.5mm-RCA cable to both my PC and my phone, there is no audio coming through my AKG 712 Pros. The headphones work fine with any other source at my disposal. Not the issue.

My phone audio port works. The 3.5-RCA cable works from both my PC and my Phone into my home stereo setup.

I've never used a tube amp before but the unit has it's proper functioning LED on while powered on, and the tube gets warm but there's no sort of glow coming off it, and when I power it off, there is a sharp sound that comes through the headphones, but no audio is being passed through the unit from the input to the output.

I opted for this amp because, forgive my ignorance, but my PC headphone output is already a DAC, my phone headphone output is already a DAC, so I didn't buy a separate DAC, since the digital to analogue is already being converted, is it not? I feel like I'm taking crazy pills because the seller is telling me that it won't work unless I have a separate USB DAC feeding into it...


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PostPosted: Tue Apr 24, 2018 8:27 pm 
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Location: kemptville, ON, CA
Turn the amp off and remove the tube. Make sure you insert it to match the pin pattern on the tube and socket. Then turn it on and try again.


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PostPosted: Wed Apr 25, 2018 2:05 am 
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Location: Fairport Beach (in Pickering), ON, CA
It seems like your amp is just that ... a headphone amp. I don't see any digital inputs just a pair of RCA inputs, so a DAC is required.

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PostPosted: Wed Apr 25, 2018 2:23 am 
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Tom_r wrote:
It seems like your amp is just that ... a headphone amp. I don't see any digital inputs just a pair of RCA inputs, so a DAC is required.


What he is saying though is that he is using a 1/8 inch to RCA analog cable from a headphone output. Not the best choice for sound quality, but it should be working that way.

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PostPosted: Wed Apr 25, 2018 3:24 am 
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Location: Toronto, ON, CA
Just wondering. If you're driving the amp from your computer or phone, do you have the volume set to max on the computer? My assumption is that it would not be line-level output coming from your soundcard, so you need to have the volume maxed out, and control the headphone volume via the amplifier...
As for re-inserting the tube, well yeah, you could try that, but the 6922 only has one way to go in unless you bent a pin or something...that being said, it could also be the tube itself is fried (though I'd expect there to be at least some noise in your headphones if that was the case).
B

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PostPosted: Wed Apr 25, 2018 6:44 am 
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Location: London, ON, CA
BSavvy wrote:
I bought a headphone amp from a member on here claiming it to be brand new, impulse purchase blah blah.

...... the tube gets warm but there's no sort of glow coming off it...


No glow most likely means bad tube or amp defect :idea: .


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PostPosted: Wed Apr 25, 2018 6:55 am 
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Location: Barrie, ON, CA
Before you spend time and money on tubes or anything extra for troubleshooting, call a local audio shop and see if they have an extra tube (that's compatible with yours) and a couple minutes to help you diagnose it. It's probably something very simple!


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PostPosted: Fri May 11, 2018 9:17 pm 
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Location: New York, NY, US
Sad to hear that! my advise would be to get in touch with a professional technician, if the tube is not glowing then you should make them check that first. Did you decided what to do? i mean about the seller, what does it say about this matter? maybe the unit got damaged during the shipping....

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PostPosted: Sat May 12, 2018 12:33 am 
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Joined: Wed Oct 20, 2010 6:55 am
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Location: Saskatoon, SK, CA
The unit, the power brick, or the tube is defective. Contact the seller.

Q: The unit ships with an Electro-Harmonix 6922, (6922EH) did yours come with that tube or another (cheaper) substitute? The E-H's are generally quite reliable.

Not all tubes glow (or glow brightly), especially small signal tubes like the 6922. Chinese manufacturers generally place an LED below the tube to create an unnatural simulated glow, but yours is a US-designed product by a competent engineer who (rightly) probably eschews such cosmetic foolery.


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PostPosted: Sat May 12, 2018 3:20 am 
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Location: Fairport Beach (in Pickering), ON, CA
Is there a Long & McQuade near you? Buy a cheap tube there.

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PostPosted: Sat May 12, 2018 3:50 am 
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Sounds like you have proven the source, and the headphones are functioning.

It is possible the tube was damaged during shipment, replace the tube.

If the tube is not the issue, then the amp/separate power supply is defective...

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Ohms

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