Hi Grinder
No not the BK amps as I wasn't aware that they had plate amps at the time. Plate amplifiers appear to be made by quite a few manufacturers, Parts Express, Jaycar, and MCM for example. I chose MCM because they willingly emailed me the full schematic diagrams which were needed for in-depth circuit modifications.
My RSUB-15 has developed a loud hum and Tannoy will not (for whatever reason)supply the circuit diagrams. Okay I will be able to manage without for this type of fault. What I am saying is get the technical info first and then buy the amp, not the other way around. In the past BK have been very helpful and have supplied me with circuits but check first, as policies change and most suppliers will refuse.
The Critical Q subwoofer is described in detail on the following website:
http://members.ozemail.com.au/~joer/sub_index.htm (Must find out how to patch a live web address, sorry)
I used the info therein as a basis for my circuit changes but have varied component values to obtain the results I required.
The modifications on my amp are:
(1) Increased gain on input op amps (I needed the extra power output)
(2) Sub-sonic cut-off filter lowered in frequency to extend LF resonse.
(3) Input capacitors changed from electrolytic to audio grade.
(4) Added additional low pass filter circuit.
(5) Feedback loop capacitor changed from electrolytic to bi-polar.
(6) Crossover filter- frequency lowered.
(7) Switching for extended LF (music/movie mode) in process.
Results are dramatic even at 5Hz. the cone movement was energetic to say the least, so I changed some component values temporarily to obtain 10Hz. at -6dB. (to play it safe on LFE sources.) Using AB switching I tested my sub against the RSUB-15. I used the switch blind so I did not know which sub was selected to remove any pre-conceived ideas. Overall the differences were not as great as expected, as I thought the RSUB-15 would walk away with the prize. Okay the tests were purely listening at this stage but my sub sounded deeper, cleaner, better transient response, and importantly, more musical, more Hi-Fi. It soon became apparent which sub was operational. The bass could be felt even at moderate volume. This was on CD music sources. A DVD movie source with LFE is yet to be evaluated.
The Q value or magnification factor at the box resonance can have a range of say around 0.1 to 10. Where 10 is a highly peaked response and 0.1 falls off sharply. Where there is a resonance, if the Q is kept down to or below 0.5 it can be described as critically damped. I think the term originated from the Linkwitz-Riley 2nd. and 4th. order crossovers having a specified Q of 0.49, again this is mentioned in the above website. Hi-Fi buffs usually like a Q of 0.7 for a smooth bass but that is very different from from an equalised sub-bass. All the above is based on using the Peerless XLS 12" loudspeaker which costs around £150 so great care is needed. I tested my amplifier into a 8 Ohm resistive load, and only when satisfied did I connect the speaker.
sonic65
The above website will error if clicked....Perhaps easier to search on Google.
Type in "Critical Q"
sonic65