Subject: RE: Question about speaker protection circuitry
Date: Oct 11, 2010 11:27 PM
Hello Kurt,
Thanks for taking the time to email us on this topic.
The pre-Klipsch amps were identical to the Klipsch-era amps with regard to protection mechanisms. With any protection scheme, it's important to associate the failure modes that could lead to speaker damage to the failures that are to be protected against:
Output Device Overheating:
One of the failure mechanisms is pure overheating of the amplifier card leading to device failures (which could lead ultimately to speaker damage). To protect against overheating, all the Aragon and Acurus amps used a similar thermal sensor mounted on the heat sink which immediately cuts the signal applied to the amp in the event the temperature exceeds a preset protection threshold. Once the amp cools down again, the circuit is automatically reset.
Internal Component Failure:
All the Aragon and Acurus amps prevent internal component failures from resulting in speaker damage by opening the supply rails at the particular channel with fast-acting fuses. In the case of a component failure, a blown fuse is not a nuisance but an indicator that service work needs to be done to determine the cause and repair the amp before continued use. This is a reason why the rail fuses were located internally where generally only service personnel would work.
Output DC:
Significant DC at the amp output is one of the most likely causes of speaker failure. All amps were adjusted for DC offset at the factory and nearly all the designs except the early 4004 were of the DC servo variety. The pre-Klipsch Aragon amps (not the Acurus amps) and the Klipsch-era Aragon Palladium and 8008 and all their variations had output relays with DC offset detection.
Other mechanisms:
There are other protection mechanisms in all the Aragon and Acurus amps to deal with excessive transformer temperatures, external ground faults, excess current draw from the mains, inductive loudspeaker loads, etc... These mechanisms ultimately help protect the speakers by protecting the amp. The Aragon and Acurus amps generally did not employ output device current limiting or input signal limiting (in an effort to prevent failure in the output devices) as the most reliable and transparent of these circuits are typically quite expensive and many engineers deem them to be of limited value unless used for pro sound reinforcement applications.
Going forward:
We at Indy Audio Labs intend to provide at least as much protection as the predecessor designs we're starting from. Of course we'll be applying grueling tests to our amps prior to release to ensure they're safe and "do no harm". We'll also be adding the benefits of microprocessor monitoring of internal conditions to some of our new designs. However, as you point out, there is no history that we can see, of Aragon or Acurus amps having any reputation for damaging loudspeakers due to design inadequacies. To the contrary, these amps have been some of the most reliable on the market since the late 1980's. Having spent a few years in audio service early in my career, it was ironic to observe how many amp "failures" were attributable to failures of very elaborate protection circuits rather than the amps themselves.
Best Regards,
Rick
Indy Audio Labs, LLC
http://www.indyaudiolabs.com
main: +1 (866) 559-5113
mailto:support@indyaudiolabs.com
