WAD 300B PSE Coupling Cap Size

[paul(555)]

I use my amps to drive a pair of Bastanis open baffles with a XTZ active sub-amp driving 15 inch base units. As the 300Bs don't need to produce low base I'm considering reducing the size of the coupling cap to reduce their output below 80Hz.

At this point my lack of knowledge hits home. Am I correct that the coupling cap is C2 (0.22uf) and the load resistor is R3 (100k)?

I'm assuming that I would use a value of 0.01uf for the coupling cap but can any of the wise people here advise how to check this by calculation?

As a final thought has anybody actually tried this?

Thanks,
Paul.

[Richard]

Hi Paul, R3 is the anode load of the 6AU6.
The coupling you'd need to adjust would be C2 into ECC82 gridleak R8.
As standard this is 0.22uF into 1M = 0.7Hz.
Using 0.01uF would give 16Hz. This is the nominal -3dB point so it would be rolling off from higher than that and is probably a good value to try.
Here's an easy calc to play around with values, http://www.muzique.com/schem/filter.htm
Bear in mind couplings and losses through the amp are cumulative so expect the real response to roll off higher than just by setting that coupling hence it is very low at the moment.

[paul(555)]

Many thanks Richard, that's very helpful as always.

[Ali Tait]

Which Bastanis do you have Paul?

Got these a while back-



Very happy after a bit of fettling.

[Greg.]

Cool set up, Ali. Which Redford is that?

[Ali Tait]

It's a 15 I think. Pic is from the last NEBO.

[Greg.]

Ah, ok, so not yours?

[Ali Tait]

It belongs to Mick, who posts as Mik Rik. Heard it a few times now, great sounding amp.

[paul(555)]

Originally Posted by Ali Tait

Which Bastanis do you have Paul?

Got these a while back-



Very happy after a bit of fettling.

Hi Ali, I bought a pair a few years ago which had been built by a guy from Bath. They had Gemini tweeters and Crystal widebands with a sealed twelve inch bass driver. Although very well built they looked challenging to say the least.

Having seen what Vic was doing with open baffle bass, i.e. your layout, I accquired a pair of fifteen inch Selenium Neo bass drivers from him and had a pair of bamboo baffles made from 40mm bamboo worktop. The final result not only sounds good but looks much better.

[Ali Tait]

Sounds interesting, any chance of some pics?

Vic has moved further now, interesting thread here if you've not seen it-
https://www.lencoheaven.net/forum/in...&topic=31371.0