At bloody last!!!!

[epistaxsis]

Finally got my extended FP111 up and running yesterday (at last!!!!) - and it is magical

However there is a awful lot of hiss coming through the speakers...

I have bunged in a couple of 2mu caps accross the 147K resistor in the shunt regulator which has helped a bit.

Power amps are 845PP types.

Any ideas?

 

[Doc B]

http://www.bottlehead.com/smf/index.php/topic,39.0.html

 

[epistaxsis]

interesting - many thanks.

 

[Grainger49]

Doc is encouraging you to determine if the gain of system is so high that you need to pad the input of your amp. 

Paul Joppa goes through preamp gain, amp gain, speaker sensitivity etc. to explain why some guys hear a dead silent preamp and others are listening to tube rush and the noise floor.

It is a good idea to read it all, not in one sitting but maybe in installments.  But you can jump down to " adjusting the amplifier/speaker sensitivity" which is probably the crux of your problem.  Just guessing.

A search of the forum will show that you are not alone, and the problem has always been fixed.  Hang in there.

 

[epistaxsis]

Doc is encouraging you to determine if the gain of system is so high that you need to pad the input of your amp. 

Interestingly I am using my old pair of proper ladder stepped attenuators from my FP2 (which are a *much* higher resistance) as varying the input inpedance depending on volume is something I prefer not to do...

Paul Joppa goes through preamp gain, amp gain, speaker sensitivity etc. to explain why some guys hear a dead silent preamp and others are listening to tube rush and the noise floor.

It is a good idea to read it all, not in one sitting but maybe in installments.  But you can jump down to " adjusting the amplifier/speaker sensitivity" which is probably the crux of your problem.  Just guessing.

The speakers are 88Db/W and the power amps are 90W PP845s so there may be some milage in this...

A search of the forum will show that you are not alone, and the problem has always been fixed.  Hang in there.

Please be aware that the noise floor is very very much below where my heavily upgraded Foreplay2 was!

Right now the sound is very "sat on" <-- this I suspect is because the output coupling capactors need to be burnt in...

 

[Paul Joppa]

...
Right now the sound is very "sat on" <-- this I suspect is because the output coupling capacitors need to be burnt in...

Haha! I like that, good description.

I doubt anyone else is old enough - or weird enough - to remember a kids radio show that occasionally featured "Mr. Bear Squash-You-All-Flat" who would sit on people who offended him...  :^)

 

[epistaxsis]

...
Right now the sound is very "sat on" <-- this I suspect is because the output coupling capacitors need to be burnt in...

Haha! I like that, good description.

I doubt anyone else is old enough - or weird enough - to remember a kids radio show that occasionally featured "Mr. Bear Squash-You-All-Flat" who would sit on people who offended him...  :^)

erm that one didn't quite make it to the UK

 

[Grainger49]

Paul is only a few years older than me, less than ten, and I didn't get that one.

 

[epistaxsis]

Interesting times - after stuffing in a pair of Rothwell attenuators at the inputs of the power amps the hiss has gone!

So it would seem that the power amps were too sensitive.

Still awaiting the output coupling capacitors to come alive though :-(