Amplifier and speaker protection circuits

[Peter Daniel]

Originally posted by fcel


Currently, I always turn on my BOSOZ first before I turn on the power amp. If I do that in reverse, my speaker woofer would almost seem to depart from the enclosure.

I have a "DC protection and Turn on Muting" kit from Vellerman (model #4700) and I'm thinking of installing it on my BOSOZ. I would really hate to install this kit and introduce another signal path if there is another easier and simplier way of doing it.

Any help or suggestion would be very much appreciated.

If you are not really concerned about your electric bill (which in case of BOSOZ shouldn't be that big) you should leave or your line components permanently ON and forget about thumps in your system.

Thats what I'm doing. My transport, DAC and crossover is always ON and the only thing I'm switching are the amps because they are really current hungry.

[fcel]

In fact I do leave some of my other pre-amps on at all time. I just thought that if there is a simple turn-on mute circuit that I can install on the pre-amp, it would be great. It's good lesson for future pre-amps building too. So, please, people .... Thanks.

[annex666]

Originally posted by roddyama
I wonder why would we go through all the trouble of using special caps, resistors, HEXFRED's, silver coated OFC wire, etc, etc, and then stick a fuse or a relay contact on the DC rail or speaker output. There should be no fuses or relays after the rectifiers, it just doesn't make good audio sense.

Rodd Yamas***a

Although a non-linear resistance (as fuses are due to heating) in the output of an amp can (and will) affect the output waveform a fuse on the DC line will not have much affect espicially if the PSRR is high (as it is on most well designed class AB amps - class A is a different story of course much with higher quiscient current).

[Peter Daniel]

Here is a simple delay circuit I use in my DAC. 1 resistor, 1 cap and 2 transistors. The input on the left is 12V from a bridge rect. followed by a 1000u cap. All thanks go to David Broadhurst.

[2Bak]

fcel, bosoz delay:

I'm building the bosoz also and has the same concern, and I really prefer to be able to turn of my amps and I'm also looking for a delay-before-operation solution.
In Audio Electronics 6/97 you will find an article by Mike Rosenstein, A Simple Delay Timer. This circuit may be used in different setups. I can e-mail you a scan if you're interested...

[fcel]

Peter,
I can't read the 1000uf cap on the left but I'll try to look it up on the DAC thread somewhere on this forum for the David Broadhurst web site. Thanks.

2Bak,
Yes, please, email me the scan. Better yet, do you think you can place the scan on this thread so that everybody can see it. Thanks.

[fcel]

Since we're on the subject of amp and speaker protection and since I've not read anybody mentioned this before, I thought I'll brought it up here.

What does it REALLY mean when the Aleph amp service manual stated that "the Aleph Amp will NOT be damaged by driving a short circuit"?

I was wondering ..... if there is really a short circuited load, the line voltage fuse would protect the amp and in fact the one fuse IS the protection circuit? Nelson Pass is so confident that the fuse would blow before anything else goes? Or is it that the protection circuit is somehow "in" the circuit even though we (at least me) do not realized it?

Comments, anybody?

[Peter Daniel]

fcel,
I didn't show the rest of the circuit because it was irrelevant and complicates the delay circuit. It consists of a rect. bridge and 1000u smoothing cap, the voltage is about 12V.

As to Aleph there is indeed a protection. I'll just quote Tortello from the other thread:
"In the Aleph 5 design, R15, R16 and Q4 form a sort of clipper to protect the active side's hexfets: R15 and R16 fix the maximum value of the current in each hexfet.
I think that this choice is not critical: the current limiter should not operate in "normal" conditions, and the high current capability of the power Hexfet (15A) assures a wide range of values.
In my Aleph 5 -hence with 3 Hexfets per side- biased with 3A -1A per Hexfet- I found a good mix with 220 Ohm for R15 and 150 Ohm for R16. The source resistor is 0.47Ohm.
The clipper operates at about 3.14A per Hexfet, 9.5A for the whole stack."

[2Bak]

fcel, scan of articles and publishing on forums would be breaking the copyright, wouldn't it...? please help me out...

[fcel]

2Bak,

I have read a thread dealing exactly on that copyright topic but I could not recall what was the resolution .... I think the discussion was still going on and I did not follow up on it.

Audio Electronics .... is that the new name for Audio Amateur?