Kriton:

Yes, I might try the Lexi out, if that is cool with you!

Tis very cool with me.  Heck...  last year I had a Crown K2 out on loan, I've currently got an EV Dx38 out on loan and I've got a dbx 5dbx that has been out on loan for over a year now....what the heck is one more item?  I've got your pick of 6 dogs if you'd like to borrow some of them 

Just let me know if you want me to bring it to the office or if you'd like an excuse to come out and pick it up at the house.  I'll even bring the remote.

Trey Cannon:

I always suggest using the 4 ohm taps no matter what the speaker says it is. If the amp expects a 4 Ohm load and gets an 8 Ohm load it will be even happier. Your not going to hurt a thing.

Thanks for this info Trey. I have been using 4 ohm taps for a while but couldn't remember why. This was info I received when I first joined this forum. Next time you are in town give us a call. Its about rib time again. 

Trey loves tubes 

He loves the breaky sound NOS tubes make when he pretends they are skeet with his shotgun....Fling!

Don Richard:

Ah, the Dodds are amps, driving the line arrays.

Equipment matching is the key to good performance in a sound system. It seems like you may be having grounding issues causing noise. Also, the higher impedances in tube equipment, relative to solid state, may be coming into play here. High impedance devices tend to be more susceptable to noise pickup.

First, with the power off check your interconnects to ensure that they are plugged in properly. If they are, try different interconnects. Power up. If there is no improvement, power the equipment down then unplug all of the inputs from the preamp and leave the preamp hooked up to the power amp and the power amp hooked to the speakers. If the noise improves the CD player and/or another source is contributing to the noise problem. If the noise doesn't change then, plug all of your electronics into a power strip so that they are all on the same ground.  Then use one of those little three-light AC circuit testers to ensure that the house wiring is correct, at the wall socket. Power up and then, if the noise is the same, try touching a known good ground to the chassis of the preamp, then to the power amp and see if the noise changes. Be careful here, because if there is a wiring problem or other fault in the pre or power amp, high voltage AC may be present, and a spark will result.

If the noise does not change, power down and reconnect the CD player and power up. Try increasing the preamp gains and volume control to see if the noise lessens. If the power amps have input attenuators, try adjusting them, and readjusting the preamp controls and see if there is any improvement.

If none of this helps there may be an issue within the pre or power amp, or a compatibility issue between the different brands of equipment.

As for the sound changing when using different impedance taps, the speakers you are using have a widely varying impedance curve. from 8 ohms or so minimum, to around 30 ohms or so maximum. This may cause a variation in the frequency response of the loudspeaker. Some tube amps are bad about that.

Hope this helps, let us know how the experiments work out.

 

Excellent, excellent post Don. I wish we had sticky's on the Forum because with only minor changes this could be a stock instruction manual for tracking down hum.

Well done. 

I think, for several reasons using the 4 Ohm tap would be better: It essentially provides better control, by the amp, over the speaker. Could be the reason highs sound rolled of is that the highs are not really more rolled off, just less distorted.

 Leo

Has anyone ever looked at what a tub amp does?

2 words, Odd Harmonics

....fight..

Trey Cannon:

Has anyone ever looked at what a tub amp does?

2 words, Odd Harmonics

This is true, as far as it goes, but let's go a bit further. The presence of odd harmonics is more the result of the class AB push-pull circuitry used in the output stages of tube amplifiers, which supresses the even harmonic distortion, thus leaving the odd harmonics. This is the probably the reason for the popularity of the SET class A triode amps, which usually have even order harmonics in the 3%-8% range. They are rather low powered, however, requiring efficient loudspeakers for decent performance, such as  the Klipsch Heritage models.

No fight here, I am SS all the way. To me the greater headroom allowed by the newer SS gear, coupled with generally lower noise and better reliability, makes SS the way to go.

Don Richard:

No fight here, I am SS all the way.

I don't know. SS was pretty much discredited in the waning days of WW II. Indeed, most of it's adherents who survived were forced, rightly I might add, to flee for their lives. Given that even it's youngest members would be a minimum of 80 years of age, I think those who  favor tubes have little to fear from the trembling hands of an outmoded idea.

Thebes: Feisty bunch too, what's left of them.... No apologists in that gang!! There is an interesting resurgence in historical interest in the "Waffen SS" though. Thoroughly king hell bad as*es by most accounts.