Carlsbro BassBeaver combo

resistor,

Replaced with 8.2 ohm, 2.5W vitreous with extended down the traces soldering in the end, as ST don't seem to think its necessary for a mains bourne surge dv/dt snubber ,or whatever its function

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

The R-C combination is a Zobel network, and can be quite important to the correct operation of the amp. It's purpose is to neutralise the inductance of the speaker voice coil, with the intention of flattening its impedance curve at the HF end. However, without this network in place and doing its job, I have known output stages to burst into spontaneous ultrasonic or even RF oscillation. The values of R and C are calculated according to some esoteric formula that I'm sure real audio buffs could quote at you chapter and verse, but the general rule of thumb is that you start with a resistor of equivalent value to the voice coil's nominal impedance, and then calculate C from there. Assuming that Carlsbro ( who are actually quite helpful if you phone them ) know this, then there's a good chance that if the speaker is 8 ohms, the resistor will also be in this region.

Arfa

metal

even

2 different Carlsbro this one Beaver and the other one, Hornet, with 2 x 3055 I'd not heard of Zobel. Does it relate to a specific type of speaker as there is no mention on the ST sheet relating to the TDA7293 and this R-C

no, RC or RL on the output are standard protection against oscillation.

NT

Ah, OK.

I didn't look at the postings quite closely enough to spot that thay referred to different amps. I just saw the Carlsbro bit and assumed both the same job. Zobel networks are absolutely standard on the ends of amps. As far as I am aware, they are nothing to do with any particular type of speaker, so long as we are talking one with a normal voice coil, which obviously possesses inherent inductance. I guess that " Zobel " is actually some guy's name. It must be germanic, as it is normally spelt with an umlaut-ed "o". Anyway, one job or two, what I said about such networks is valid anyway. Try a Google on " Zobel Network ". I just did, and there is cartloads of info. I had a quick scan of one article picked at random, and it said basically the same as I did.

Arfa

Rod Elliot has info on Zobel networks here