Confession time
 

In article , Ian Molton
wrote:
On Thu, 20 Nov 2003 18:46:40 -0000 "Mike Gilmour"
wrote:

Any audio tales of stoopid actions .i.e. like plugging in when mains
selector set to 110V...come on, we'll laugh with you not at you -
promise.

Ok, heres mine...

Just rebuilt Quad405 (40 odd quid in parts,mostly big transistors), and
realised that I needed a preamp.

thought 'I know, I'll use this tinypower amp with the gain set low'.

of course, it had a capacitor coupled output, so the first thingit did
was runthe Quad405 flat out into its (thankfully connected and working)
output protection board.

Anyone got a spare set out output transistors?

Not clear what you are describing above. Are you saying that the *Quad 405*
blew its output devices due to your injecting an input spike when your
'preamp' sic was switched on? Or are you saying the preamp output
devoices blew?

Anyhow, this is the event that made me decide to mod the amp. the
current limiting on the 405 was too severe, which is what allowed the
o/p trannies to blow (before the fuses could save them).

Puzzled. The point of the current limiting is to ensure the output devices
*never* blow up. The severe limiting on early 405's gets in the way of the
music sometimes, but should avoid failures. Hence I am puzzled by your last
sentence above.

Im modding the amp (rebuilding the PCBs) such that:

the gain is halved (1Vp-t-p inputs, less noise) use better quality parts
in the input,particularly one resistor that sets the performance of the
whole amp double the input cap values use a more modern op-amp and
adjust the supply to it to avoid hiss dc couple some transistors now
that higher voltage parts exist - like the 606 design. eliminates a
couple of passive components. apply the 405-mkII current limiter (better
performance, less blown outputs.

I'll make full parts lists and layouts available once Im ready.

Have you checked the stability margin? Reducing the overall gain and
changing various devices to different types may affect this.

Jim... did you ever look at the schematic I sent you ?

I am afraid I haven't. :-/ Too many other things have been distracting me
over the summer - many of them unfortunate. Sorry about this, but I had
completely forgotten. Can you remind me of the details by email?

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Confession time
 

On Thu, 20 Nov 2003 18:46:40 -0000, "Mike Gilmour"
wrote:

Any audio tales of stoopid actions .i.e. like plugging in when mains
selector set to 110V...come on, we'll laugh with you not at you - promise.

Many years ago I acquired a HiFi News Test CD. I decided to use the
spot frequencies to see how high I could hear. I was pleasantly
surprised to be able to hear 18kHz (not too bad, being in my late 30s
at the time). But I couldn't hear 20kHz.
Thinks: "I wonder if I would hear it if it was louder?". So I slowly
raised the volume control until I did hear something: the distinctive
popping sound of both tweeters burning out.

Confession time
 

On Thu, 20 Nov 2003 18:46:40 -0000, "Mike Gilmour"
wrote:

Any audio tales of stoopid actions .i.e. like plugging in when mains
selector set to 110V...come on, we'll laugh with you not at you - promise.

Many years ago I acquired a HiFi News Test CD. I decided to use the
spot frequencies to see how high I could hear. I was pleasantly
surprised to be able to hear 18kHz (not too bad, being in my late 30s
at the time). But I couldn't hear 20kHz.
Thinks: "I wonder if I would hear it if it was louder?". So I slowly
raised the volume control until I did hear something: the distinctive
popping sound of both tweeters burning out.

Confession time
 

On Fri, 21 Nov 2003 08:55:19 +0000 (GMT)
Jim Lesurf wrote:

Not clear what you are describing above. Are you saying that the *Quad
405* blew its output devices due to your injecting an input spike when
your'preamp' sic was switched on? Or are you saying the preamp
output devoices blew?

the 405.

Anyhow, this is the event that made me decide to mod the amp. the
current limiting on the 405 was too severe, which is what allowed
the o/p trannies to blow (before the fuses could save them).

Puzzled. The point of the current limiting is to ensure the output
devices*never* blow up. The severe limiting on early 405's gets in the
way of the music sometimes, but should avoid failures. Hence I am
puzzled by your last sentence above.

It appears to limit current just enough to prevent the fuses blowing but
not quite enough to save the transistors.

Im modding the amp (rebuilding the PCBs) such that:

Have you checked the stability margin? Reducing the overall gain and
changing various devices to different types may affect this.

No, not yet. I havent really had time for the project lately...

Jim... did you ever look at the schematic I sent you ?

I am afraid I haven't. :-/ Too many other things have been
distracting me over the summer - many of them unfortunate. Sorry about
this, but I had completely forgotten. Can you remind me of the details
by email?

Sure.

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with
ketchup.

Confession time
 

On Fri, 21 Nov 2003 08:55:19 +0000 (GMT)
Jim Lesurf wrote:

Not clear what you are describing above. Are you saying that the *Quad
405* blew its output devices due to your injecting an input spike when
your'preamp' sic was switched on? Or are you saying the preamp
output devoices blew?

the 405.

Anyhow, this is the event that made me decide to mod the amp. the
current limiting on the 405 was too severe, which is what allowed
the o/p trannies to blow (before the fuses could save them).

Puzzled. The point of the current limiting is to ensure the output
devices*never* blow up. The severe limiting on early 405's gets in the
way of the music sometimes, but should avoid failures. Hence I am
puzzled by your last sentence above.

It appears to limit current just enough to prevent the fuses blowing but
not quite enough to save the transistors.

Im modding the amp (rebuilding the PCBs) such that:

Have you checked the stability margin? Reducing the overall gain and
changing various devices to different types may affect this.

No, not yet. I havent really had time for the project lately...

Jim... did you ever look at the schematic I sent you ?

I am afraid I haven't. :-/ Too many other things have been
distracting me over the summer - many of them unfortunate. Sorry about
this, but I had completely forgotten. Can you remind me of the details
by email?

Sure.

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with
ketchup.

Confession time
 

In article , Ian Molton
wrote:
On Fri, 21 Nov 2003 08:55:19 +0000 (GMT) Jim Lesurf
wrote:

Anyhow, this is the event that made me decide to mod the amp. the
current limiting on the 405 was too severe, which is what allowed
the o/p trannies to blow (before the fuses could save them).

Puzzled. The point of the current limiting is to ensure the output
devices*never* blow up. The severe limiting on early 405's gets in the
way of the music sometimes, but should avoid failures. Hence I am
puzzled by your last sentence above.

It appears to limit current just enough to prevent the fuses blowing but
not quite enough to save the transistors.

That is odd. The protection was - particularly in earlier models - too
severe. However it really *should* protect the output devices. Were some
small signal devices earlier in the amp also damaged? If so, it may be that
this lead to a failure that the protection system isn't designed to deal
with.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Confession time
 

In article , Ian Molton
wrote:
On Fri, 21 Nov 2003 08:55:19 +0000 (GMT) Jim Lesurf
wrote:

Anyhow, this is the event that made me decide to mod the amp. the
current limiting on the 405 was too severe, which is what allowed
the o/p trannies to blow (before the fuses could save them).

Puzzled. The point of the current limiting is to ensure the output
devices*never* blow up. The severe limiting on early 405's gets in the
way of the music sometimes, but should avoid failures. Hence I am
puzzled by your last sentence above.

It appears to limit current just enough to prevent the fuses blowing but
not quite enough to save the transistors.

That is odd. The protection was - particularly in earlier models - too
severe. However it really *should* protect the output devices. Were some
small signal devices earlier in the amp also damaged? If so, it may be that
this lead to a failure that the protection system isn't designed to deal
with.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Confession time
 

On Sat, 22 Nov 2003 09:39:53 +0000 (GMT)
Jim Lesurf wrote:

That is odd. The protection was - particularly in earlier models - too
severe. However it really *should* protect the output devices. Were some
small signal devices earlier in the amp also damaged? If so, it may be that
this lead to a failure that the protection system isn't designed to deal
with.

on one board yes - the class A 'pre' driver failed.

on the other, just the output transistors.

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with ketchup.

Confession time
 

On Sat, 22 Nov 2003 09:39:53 +0000 (GMT)
Jim Lesurf wrote:

That is odd. The protection was - particularly in earlier models - too
severe. However it really *should* protect the output devices. Were some
small signal devices earlier in the amp also damaged? If so, it may be that
this lead to a failure that the protection system isn't designed to deal
with.

on one board yes - the class A 'pre' driver failed.

on the other, just the output transistors.

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with ketchup.

Confession time
 

On Thu, 20 Nov 2003 23:39:51 GMT, "Wally" wrote:

Moving into my first flat many moons ago, I was only concerned with the
important stuff - floor cushions, coffee machine and hifi.

I lived in several accommodations where I slept on a mattress, propped
against a wall by day. Then I could fit my piano in.