Input Oddity On The Aerosmith Amps..

[laatsch55]

This PCB seems to be on every amp from the Handley Sound purchase. Got any idea what they are for??

 

[NavLinear]

This PCB seems to be on every amp from the Handley Sound purchase. Got any idea what they are for??

Those would be the differential pair op amp circuit. You mentioned this a while ago and included the IC part number so we could look it up. This circuit allows long cable lengths to be driven between the mixer board and the amplifiers - using what is called balanced inputs in the audio world. One of the nice features of the balanced pair is that unwanted noise that is picked up in the long cable runs is canceled out by the differential pair.

 

[laatsch55]

Thanks Dennis....so this creates a balanced input plus some gain??

 

[NavLinear]

Thanks Dennis....so this creates a balanced input plus some gain??

The source is differentially driven so the amp requires a circuit that can process this signal converting it to a single ended input to drive the amp. If necessary the gain could be adjusted.

 

[laatsch55]

Ah...

 

[Northwinds]

You still got an amp packed and ready to go here Lee

 

[NavLinear]

Here's some info that may shed a bit more light on this:

http://en.wikipedia.org/wiki/Balanced_audio

 

[laatsch55]

You still got an amp packed and ready to go here Lee

Give me the dimensions and weight again Ron and I'll get another tag sent..

 

[laatsch55]

Here's some info that may shed a bit more light on this:

http://en.wikipedia.org/wiki/Balanced_audio

Thanks Dennis..

 

[Gepetto]

This PCB seems to be on every amp from the Handley Sound purchase. Got any idea what they are for??

Yes Lee, I told you when I did the surveillance scan before pickup. This is a kludge to put a balanced input into the amp for purposes of stage wiring. Total junk.

 

[laatsch55]

Ok Joe, I must have not made the connection....

 

[Gepetto]

Ok Joe, I must have not made the connection....

This was in the picture portfolio Lee...just one of many reasons that the chassis were all junked up.

 

[laatsch55]

Yep, the chassis were certainly trashed....Looks like they had problems with the Zoebel network. Ed tells me the Claire Bros 700 had 20 watt chassis mount resistors on the Zoebel. Too many 4 ohm loads driven to clipping for the stock ones to survive....

 

[Gepetto]

Yep, the chassis were certainly trashed....Looks like they had problems with the Zoebel network. Ed tells me the Claire Bros 700 had 20 watt chassis mount resistors on the Zoebel. Too many 4 ohm loads driven to clipping for the stock ones to survive....

Me thinks that was undetected high frequency oscillation causing that Lee...

 

[laatsch55]

I won't argue that...

 

[Gepetto]

I won't argue that...

There is a reason I say that Lee, the turnover on the Zoebel is 318KHz, not much audio going on at that frequency

 

[laatsch55]

And every Zoebel I've seen blow had an amp that oscillated...

 

[nakdoc]

When the old transistors were replaced with new substitutes, the 400 and 700 both tended to oscillate all by themselves, leading to eventual flames.