Having an issue with my Hiraga Super 30 Class A amp.
Had a small hissing sound, so rewired the signal in wires, and the speaker out wires. Also removed the speaker protection boards as I was concerned the small/cheap 12v transformer was causing the hiss. Redid the ground wires as well.
Now, I have a loud droning hum when connected to my Cary preamp.
With nothing plugged into the Hiraga, it’s virtually silent. When I plug my MP3 player into it, no hum. But, when I plug the Cary in, it drones like crazy.
When I plug the Cary into the Sony VFet amp, no drone. When I plug the Cary into my Adcom GFA 545, no drone.
What the heck us going on?
Any thoughts would be greatly appreciated!
P
Had a small hissing sound, so rewired the signal in wires, and the speaker out wires. Also removed the speaker protection boards as I was concerned the small/cheap 12v transformer was causing the hiss. Redid the ground wires as well.
Now, I have a loud droning hum when connected to my Cary preamp.
With nothing plugged into the Hiraga, it’s virtually silent. When I plug my MP3 player into it, no hum. But, when I plug the Cary in, it drones like crazy.
When I plug the Cary into the Sony VFet amp, no drone. When I plug the Cary into my Adcom GFA 545, no drone.
What the heck us going on?
Any thoughts would be greatly appreciated!
P
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Thanks!
Think I found the issue.
When I first built the Hiraga, I was using a Marantz 7T as a preamp. It has enough DC on the output, so the speaker protection was kicking in. So I put a cap on the input of the Hiraga to filter it out. I removed the cap when I rewired everything, as I wasn’t going to be using the speaker protection anymore.
My Cary was also showing some DC, and it benefitted from the cap being in circuit.
I was moving cables around, thinking it was a problem with the wires/connectors. Realized the amp works perfectly if only the left channel is plugged in. Right channel, and the hum/droning begins.
Pulled the Cary out and opened it up, switched the tubes left to right to see if it made any difference. Nope. Changed the rectifier. No change. Measured the DC on the outputs, and the right channel is seeing 96vdc (or somewhere in that neighborhood…) on the output.
That’s not right…
Odd that the VFet isn’t showing any issues. It’s the NPNtype Pass VFet from the DIYAudio lottery.Have not looked into why it seems to be fine and if the input is filtered?
Looks like I have a different problem on my hands. Have to figure out what is causing the Cary to be showing that much on the output. So thing ain’t right 🙂
P
Think I found the issue.
When I first built the Hiraga, I was using a Marantz 7T as a preamp. It has enough DC on the output, so the speaker protection was kicking in. So I put a cap on the input of the Hiraga to filter it out. I removed the cap when I rewired everything, as I wasn’t going to be using the speaker protection anymore.
My Cary was also showing some DC, and it benefitted from the cap being in circuit.
I was moving cables around, thinking it was a problem with the wires/connectors. Realized the amp works perfectly if only the left channel is plugged in. Right channel, and the hum/droning begins.
Pulled the Cary out and opened it up, switched the tubes left to right to see if it made any difference. Nope. Changed the rectifier. No change. Measured the DC on the outputs, and the right channel is seeing 96vdc (or somewhere in that neighborhood…) on the output.
That’s not right…
Odd that the VFet isn’t showing any issues. It’s the NPNtype Pass VFet from the DIYAudio lottery.Have not looked into why it seems to be fine and if the input is filtered?
Looks like I have a different problem on my hands. Have to figure out what is causing the Cary to be showing that much on the output. So thing ain’t right 🙂
P