Dennis Had Inspire Amps

[Ruleof72]

Originally Posted by Analog Addict

I communicated with Dennis and he said take the three prong cord and a pair of pliers and break off the ground plug, which is the bottom round prong. That is floating the ground.

He them said to take the now two prong plug and flip it over so that it is oriented in reverse from the normal orientation when it has three prongs. This is called reversing the polarity. Now test the amp and see what happens.

Ok, I removed the ground plug and oriented the plug reverse in the outlet. I had no interconnects connected, just the speakers. When I turned on the amp I got the same result, an audible hum from the speakers after about 10 seconds of the amplifier being powered up from cold. The loudness of the hum dropped (after about 30 minutes of the amp being on) to a level that was still just audible if I place my ear within a foot or so from speaker but not so loud that I can hear it from several feet away.

Any ideas?

[bearcity]

Originally Posted by Ruleof72

Ok, I removed the ground plug and oriented the plug reverse in the outlet. I had no interconnects connected, just the speakers. When I turned on the amp I got the same result, an audible hum from the speakers after about 10 seconds of the amplifier being powered up from cold. The loudness of the hum dropped (after about 30 minutes of the amp being on) to a level that was still just audible if I place my ear within a foot or so from speaker but not so loud that I can hear it from several feet away.



Any ideas?

The anecdote comes to mind where the man goes to the doctor and complains his arm hurts when he wiggles it a certain way and the doctor’s response is “don’t wiggle it that way.”

Not sure why you have your head 1’ from the speaker?

[Ruleof72]

Originally Posted by bearcity

The anecdote comes to mind where the man goes to the doctor and complains his arm hurts when he wiggles it a certain way and the doctor’s response is “don’t wiggle it that way.”

Not sure why you have your head 1’ from the speaker?

I agree, having to get within 1' from the speaker to hear a slight hum isn't worth worrying about. It's the fact that for the 1st 30 minutes or so (until the amp is warmed up) the hum is audible from my listening position about 8 feet away. That doesn't seem normal but this is my 1st tube amp so I have no reference point to know if it's an issue or not.

[Analog Addict]

Originally Posted by Ruleof72

I agree, having to get within 1' from the speaker to hear a slight hum isn't worth worrying about. It's the fact that for the 1st 30 minutes or so (until the amp is warmed up) the hum is audible from my listening position about 8 feet away. That doesn't seem normal but this is my 1st tube amp so I have no reference point to know if it's an issue or not.

Have you tried different tubes? And perhaps I missed it, but what kind of speakers are you using, and what's their efficiency?

[Ruleof72]

Originally Posted by Analog Addict

Have you tried different tubes? And perhaps I missed it, but what kind of speakers are you using, and what's their efficiency?

Yes, I've tried the 6SL7 and the 6SN7 input tubes. The SL7 seemed a bit noisier. I also tried the 5U4 rectifier and it was basically the same as with the 5AR4. I don't have another set of KT88's to try. In all cases the loudness of the hum seems to go down once the tubes/amp are completely warm.

I have Tekton Enzo XL towers. Efficiency is ~92-94.

[Analog Addict]

You don't need to use KT88s. You can use 6L6s, 6V6s, and even 6F6s. I'd use a 5V4 with 6L6s and a 5U4 with the others

[Ruleof72]

Originally Posted by Analog Addict

You don't need to use KT88s. You can use 6L6s, 6V6s, and even 6F6s. I'd use a 5V4 with 6L6s and a 5U4 with the others

My plan is to try some other power tubes but for now all I have are the KT88's. I will give a longer listen with the KT88/5U4 combo and see if that makes a difference.

Based on everything I've tried, is the hum coming from the power, the transformers, the tubes or some combination?

[FloridaBoy]

Originally Posted by Ruleof72

My plan is to try some other power tubes but for now all I have are the KT88's. I will give a longer listen with the KT88/5U4 combo and see if that makes a difference.

Based on everything I've tried, is the hum coming from the power, the transformers, the tubes or some combination?

What does your entire system consist of? I have 3 Inspire amps and none of them have that issue with 99db speakers.

[FloridaBoy]

Originally Posted by Bombadil

I noticed that listing. It is a little tempting. Not much of a jump in power from my Inspire but would be running the output tubes more in their optimal range than in mine, where they are pushed to their max.

I sent you a PM from AC.

[rmlowz]

I am considering getting a Inspire 45 amp,
I have Klipsch K402 horns, I have a Universal Inspire and a SET KT 66 Inspire that I have been having a lot of fun with. What do my Inspire friends think how a 45 Inspire will sound with the K402s. Is this the route I should be taking?
Rich