FE167E, Zobel and/or BSC

[Jeb-D.]

Can anyone recommend good Zobel and/or BSC circuits for this driver? It's in a BR box being driven by a low power Pentode amp that has a Zout of aprox 8ohms. So as you can imagine given the impedance curve of this driver. It starts to sound harsh in the upper-mid and the mid has a tendency to shout.

I've seen a few odds and ends of circuits for this driver, but for different circumstances.

Thanks!

[planet10]

Martin King has some tools for helping figuring out BSC.

Given the high output impedance of your amp, a zobel is probably more what you need. There are a number of calculators on the net if you can't find someone that has already figured the Zobel values (Bob Brines?)

dave

[GM]

Greets!

Hmm, if the output impedance is indeed ~8 ohms, it 'sounds' like you need a larger box and/or tuned lower.

GM

[Jeb-D.]

Hmm, if the output impedance is indeed ~8 ohms, it 'sounds' like you need a larger box and/or tuned lower.

Yeah, that would be cool, but I purchased these ones pre built. The Mid bass is earth quaking though. Just kidding, it sounds ok down low.... for bookshelf sized speakers.

The problem I have for figuring the Zobel is that the inductance is not specified on the drivers data sheet.

I saw somewhere a guy is using a 8-10ohm with a 6.8uF cap. Can anyone verify these are the right values?

[GM]

Well, you could tune it lower if it's vented or vent a sealed one. Anyway, just 'eyeballing' what 2*7.1 ohms (Re) is on the vague Fostex data sheet it calcs to ~8.9 ohms/5.6 uF cap, so now you have a range of caps to try. The resistor you can dial in by just measuring the coil's (Re) and multiplying it by 1.25.

GM

[Piek]

Hi,

I had success with 15Ohm 15uF 0,10mH paralell, it works in the 1,5k-4,5k region and reduces shout a lot.


(But i use chipamps, no experience with tube amps and impedance)


Regards, Micha

[Svein_B]

I do not think a zobel is going to do much to the "shouty" sound of the Fostex - with or without tube amplifier.

The Fostex tend to sound a bit shouty especially when new. A BSC filter and/or a notch filter will probably be required to balance the sound in a BR cabinet.

The impedance curve of the FE167E is fairly benign with a 16 ohm peak around 50Hz, and a gradual rize from 8 to 16 ohm for the higher frequencies.
Using a tube amp with 8 ohm internal resistance, the result will be 3-4 dB higher signal where the speaker impedance is 16 ohm compared to the 8 ohm in the midrange.
The small rize in level at the highest frequecies may in fact be desirable with a FR driver.

SveinB.

[Bob Brines]

I run the FE167E with a BSC of 1.5mH||6ohms. I do not use a zobel on either the FE167E or FE207E. If it is still too bright with you amp, try a zobel of 6.8uF=8ohms. If need be, use a bypass cap to bring the top back up.

Bob

[Jeb-D.]

Thanks for all the input. I'll have to experiment with the recomendations.


Bob, do you know the FE167E's Le?