Beta Bass "pop"

[DP]

I have a Beta Bass 115 combo that I have been using since the early '80's, and it has always been a solid and dependable amp.  One thing I have always wondered about, though, is that it makes a significant "pop" through the speaker about 1/2 second or so AFTER the power is turned off.  It doesn't seem to hurt anything (it's been doing it as long as I have had it), but I've never had an amp do that before.  Can anybody confirm that that is normal for a Beta Bass, or give me a clue as to what may be causing it?  Also, does anybody have any experience with putting a JBL K140 in a Beta?  Any changes recommended for the porting, etc?
Thanks!

[Geoff]

Hi DP,

I can't speak to the pop problem but I may have a little info on replacing the speaker.

First, you can find the K140 T/S parameters here:

http://www.jblproservice.com/pdf/Small%20Thiele%20Parameters/Thiele.pdf

They don't appear very consistent about their units.  Vas appears to be given in liters....others appear to be mixed metric/English.  Interesting.

Anyway, here is an online unit converter if you're interested:

http://www.graniterock.com/calculators/calcconv.htm

With a Vas of about 10.5 ft^3, the K140 would probably like to see a bigger box than the one the BB115 has to offer.  There are probably several computer programs available currently (free and $$) to help you map the theoretical response of the driver in the BB enclosure, change the porting, etc.  I've used one called "Perfect Box" before...also the Parts Express PE box program is good if it contains the driver data you're looking for.  You can also work out the details yourself with good ol' pen and paper.

In the interest of best performance, you might have to adjust the port tuning or possibly scrap the idea of using the K140 because I think the K140 is sufficiently different from the stock driver (with much lower Fs and higher Vas, for instance).  However, I'm not saying it can't be done.  I ain't an expert...just making a guess.

Best of luck!

[Don T.]

Hello:
 Actually both the 20-0135 and 20-0166 powerboards pop when turning off in any gear they were installed in. Its just that the power supply does not discharge equally on the + and - sides at equal rates. Never seemed to hurt anything.