Class A from scrap

For the three and more legged things
Graeme
Needs to get out more
Posts: 1566
Joined: Tue Oct 28, 2008 9:25 pm

#46

Post by Graeme »

chris661 wrote:Wow... 100dB@1w/1m!???!

Given, say, 2 watts into such a speaker, that's 103dB@1m. Add 6dB for the other speaker and amplifier channel and it's really really really loud!! Like permanent hearing damage in less than the time for a CD to play through.


On an unrelated note...
Anyone else ever heard/felt their ears clipping before?

Depends what you mean on the ears.

Ive felt/heard what seemed like my ear drums running out of movement LOL.

At a rave a while back, the system was pushed hard for about 10 seconds before all the electrics went.

You could actualy feel the pressure of the air in your ears, like when your waiting for your ears to pop, but in time with the bass line.
Everyone in the club stopped, jaw on the floor in amazement.

It sort of blocked out all other noise, all you could hear/feel was the pressure waves of the bass line.

Very odd indeed, quite unpleasant.

Ive been to alot of loud gigs and aves and ive never experienced anything like it!
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#47

Post by Mike H »

There's little muscles that tighten up your little ear bones, that's your "automatic volume control". They were probably pulled right up :D


 
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
chris661
Shed dweller
Posts: 2556
Joined: Mon Feb 22, 2010 7:29 am
Location: Sheffield

#48

Post by chris661 »

Yeah, you're describing what I experienced.

This was with 3 guitar amps intended for stage use, and a drum kit, and a singer w/mic. In a very very small room (for that much equipment), maybe 6'by10', acoustically treated to stop sound escaping.

People kept turning it up, it got to a point where I could feel the bass drum and the lower notes of my guitar amp in my ears, but I couldn't hear anything.
We played for some time like that, and I suspect it's the cause of occasional ringing in my ears.

There was maybe 200w of kit in use, plus a practice drum kit.
brig001
Old Hand
Posts: 550
Joined: Sat Nov 13, 2010 9:56 pm
Location: Back home in Preston now

#49

Post by brig001 »

Back to the amplifier...

I was looking at the board over the weekend with a view to putting it in a box :shock: and realised that the output stage should be reasonably immune to power supply noise etc., but the input stage certainly isn't.

Do we think adding an RC filter to R2, R3 would be a good idea. I was thinking from the positive supply, 6K, then 47uF to ground, 6k to input and 12k to ground.

Brian.
brig001
Old Hand
Posts: 550
Joined: Sat Nov 13, 2010 9:56 pm
Location: Back home in Preston now

#50

Post by brig001 »

or I could just replace R3 with a constant current source.
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#51

Post by Mike H »

Yes I would use a RC filter feeding R3. Make it 6k as well and double R4 to 12k, otherwise input impedance will be even lower.

 
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
brig001
Old Hand
Posts: 550
Joined: Sat Nov 13, 2010 9:56 pm
Location: Back home in Preston now

#52

Post by brig001 »

Thanks Mike. I could change both input resistors while I am at it to 47k or something.

Still undecided between RC and CCS. Will have a go at simulating tonight with some PSU noise and see what the difference is.

Brian.
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#53

Post by Mike H »

I would like to raise the input impedance if it were me yes. :D

Re the CCS on the input, not sure I've ever seen anything like that so not sure about that idea
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
brig001
Old Hand
Posts: 550
Joined: Sat Nov 13, 2010 9:56 pm
Location: Back home in Preston now

#54

Post by brig001 »

Thanks Mike, I haven't seen it before, so got to be worth a go.

Simulates OK with R4 at 47k, so much better on the input impedance. Time to get the soldering iron out methinks. Will post a diagram later.
brig001
Old Hand
Posts: 550
Joined: Sat Nov 13, 2010 9:56 pm
Location: Back home in Preston now

#55

Post by brig001 »

OK, done one side, and it sounds slightly better, I think. Seems to be better definition between instruments, and that was before I had figured out which side I had done. Certainly no worse, and should reduce crosstalk via the common power supply, so going to get the other side done too. Funny how a simple, two transistor amplifier now has six...

Brian.
Edit: Corrected the component numbers.
Attachments
Getting complicated.
Getting complicated.
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#56

Post by Mike H »

Verrry interesting!

Thought ~ you could make the two BC212 into a current mirror, R9 then becomes 100k, with the same current (mirrored) R4 will have half the Volts of R9.
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
brig001
Old Hand
Posts: 550
Joined: Sat Nov 13, 2010 9:56 pm
Location: Back home in Preston now

#57

Post by brig001 »

Hi Mike, interesting idea, but doesn't seem to isolate from the power supply as well as a CCS. Done the other side now and sounding good. Just need the house to myself for a proper listen now...

Brian.
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#58

Post by Mike H »

Ah, R9 would have to be a CCS then. A la op-amp topology.
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
brig001
Old Hand
Posts: 550
Joined: Sat Nov 13, 2010 9:56 pm
Location: Back home in Preston now

#59

Post by brig001 »

Just to finish this off, I found a dead PC power supply and a dead hard disk, so used the PSU heatsinks and the aluminium disk drive chassis as heatsinks, and the PSU case as, well, a case. I know jack sockets aren't ideal, and will get some 4mm binding posts one day, though Speakon would be better. This will either be attached to the back of a speaker, or hidden in a corner somewhere, so looks aren't important for this project - thankfully

Thanks all for the help.
Brian.
Attachments
P2200167.JPG
Post Reply