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Differences between OPA's

post #1 of 4
Thread Starter 
Hi All,

Well yesterday I got my OPA2132P's for my lilac Cmoy/Hansen amp (see 'Cmoy/Hansen Rawks' thread below) and I popped 'em in.

Now, I remember seeing a thread on Headwize about 2228's versus 2132's but I can't refer to it now (hopefully tomorrow!) so here are my observations:

With the OPA2228's running off one battery (9V) I get a little bit of motor-boat ocillation on the non-crossfeed setting but not on the two crossfeed positions. When I plug in the regulated 12V wall wart I get no ocillation in any position, no noise/hiss/distractions, etc... Bliss. Also, I can turn the volume up to the point of pain (wide open with the phones off my head) and hear no distortion. Really good demonstration for the geeks in the office.

With the OPA2132's running on 9V I get more ocillation on position 1 than with the OPA2228's. Positions 2 & 3 (crossfeed) are quiet. When I plug in 12V I get the same; flub-flub-flub in pos. 1, all quiet elsewhere. And the kicker - I can only turn the volume to 1/4 before it ocillates in any position.

Obviously the 2228's are going back in tonight!

Has anyone else any experiences like these?

ok,
erix
post #2 of 4
the 2228 in a gain less than 5 can be prone to oscillation. when using it in unity gain to buffer the output of crossfeed, i have heard some oscillation in some layouts. but the 2132 is incredibly stable, and i've never had a problem with that.
post #3 of 4
Motorboating is comon with tube amps using inadiquate power supplys but it is rare with solid state units unless the HF oscilation is so great it is loading down your power supply. The Motor boat sound is carictoristic of low frequency oscilation. Measure the current drain of the amp with no signal or load and see if it is within spec thats the Current drain of the opamp + any Led's and Virtual ground drivers also operating off the supply. Also check your supply caps maby two small or Bad.
post #4 of 4
Thread Starter 
ppl,

thanx for the reply.

maybe motor-boating wasn't a proper term to use. It is a lower register wub-wub-wub type noise.

I should have mentioned that the gain is 5 on this build. What effect does rasing the gain have, soundwise - not volume wise?

Could you explain how to make the current measurment? newbie here!

thanx,
erix

p.s. How was the Fair this year? I sure do miss Wild Berry Punch, Rev. Chumleigh, Energy Park, and the food (oh...the food......sigh)
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