why distortion and what is the cure

Thanks Joe
I am using CD as the source. The sound with both amps is fine at low volume but turn it up and yuck!! Have spoken to Sugden who suggest that A)one or two of the power transistors may have gone or B)the speakers arent sensitive enough for the amp. Amp is 12 watts class A and speakers are as above.I love the sound of the amp and really dont want to change it if i can help it.The speakers can go out with the trash. So cmon guys - solutions and speaker suggestions (pref F/S with waf)

I'm guessing its not a vibration issue, but simply overdriving your poor 12 W amp. You don't exactly have efficient speakers, so if you are trying to listen at high volumes (1 o'clock on my pre is deafening), your Sugden is probably running out of gas, distorting and clipping.

I'd have to agree with Edesilva's last comment, it sounds as if you have hit the output limits of your system. Many systems are at or near peak output at the 1-2 o'clock positions. And tube sound typically goes downhill very fast once you hit peak output.

I also agree with the under powered amp and clipping scenario. How old are these speakers? I couldn't even find this model listed in the Agon Bluebook. If they use '70's or early '80's drivers with foam surrounds (the outer edge of the speaker cones), you might check this material to see if it has deteriorated. I have seen foam surrounds actually turn to dust!

Tjz, I disagree regarding your statement about tube amps! Tube amps will gradually start to distort when overdriven (this can actually be beneficial, as guitar players use this method to generate a myriad of sounds and tones), while solid state amps usually start clipping almost immediately when overdriven...this is bad news for speakers!

You're right Fatparrot, a guitarist can use the distortion from a tube amp to create various sound effects, but that is in a totally different environment and setup than a home system. In fact, some guitar amps will include this "sound" to be added to the playback, depends which head you buy.

But in a home system setup, this sound would be very undesirable for playback. Fuzzy, static, breaks up, distorted, whatever you would like to call it. When a tube amp hits maximum output, the sound becomes undesirable for CD or LP playback.

In what garyatware@blueyonder.co.uk indicates, "When i turn up the amp past about 1 o'clock the sound just breaks up/distorts", his description indicates that his system is hitting maximum output.

The simple math: 87 dB speakers, 12 watts of power, your not going to get a lot of overall output in dB, maybe 90-93 dB, and then it will break up. It probably sounds good between 9-12 o'clock volume settings. And (keeping in mind that most systems vary) most systems will peak somewhere between that 1-to-3 o'clock setting on the volume knob (again, as described).

Now, I guess some of the troubleshooting questions I might ask is:

How old are the tubes? How many hours of run time are on them? Also, is the amp auto-biasing or does this need to be perfomed manually (I am not familiar with the setup and operation of a sugden). I might suspect that an older amp that has not been biased in sometime would require this, as well as old tubes. And especially if both are true, this would effect the sound quality, especially at higher outputs.

I might look into the amp and tube setup to ensure peak performance. Then I would check to make sure each tube is in good, operational state.

Thanks again, Todd