I tried a bright cap across the LPad once but strangely it made no difference at all. Can't remember if I tried it across any of the resistors though. Will give that a go .
I just read this interesting article by Mr Fischer.
It explains why the airbrake doesn't actually match the impedance and is I believe what vibratoking and Leo are talking about. Probably also explains why the Airbrake sounds fizzy to some. I guess it isn't going to be perfect for every speaker as obviously all speakers are different. I'm also wary of the airbrake as I recall Fischer had to replace the OT on a TW that was used with an Airbrake all it's life.
Also sorry vibratoking I misread the part where you said true impedance matching isn't worth it. I can't say I've ever found an attenuator that EVERYONE likes. For instance some people swear by the Weber Mass and others hate it.
Just to put it on everyone's rader I found this earlier.
I'm really struggling to find a suitable enclosure for this unit. I ideally want it to be able to sit on top of the amp like my current attenuator. I did find one enclosure but to make all 4 resistors fit I'd have to stack them in 2s. Not ideal.
Any ideas? The unit can't be any longer than 20cm or roughly 8inches.
The other option is to scrap the solo boost (2nd LPAD) but its a very useful feature.
Awesome, thanks for that. That unit is quite expensive but it does look good. Very smart looking build too btw.
I'm still unsure about the design as I know it will kill the tone. Basically I need to attenuate more than 12dB to get the TW Express down to the right level for practice and gigs with a soundman. Maybe multiple bright caps will help? One for each LPad?
I'm not nearly as proficient in theory as most of u and may be way off base but I think an overlooked problem with attenuators is. loss of bass and some mids as well. Try a larger cap to get some of this back as well. Say typical cathode bypass caps on a cathode biased amp.25-50 uf seems to work but don't be 5afraid to go higher. up to say 200uf. 50-100volt cap should work.
If Hendrix had lived would he have been as good as EDDIE? (Shaver that is)
Littlewyan wrote:Ok what about the chassis mount resistors? 995cm2 seems like a very large heatsink.
This is why heat sinks have fins. You get to stack that acreage in slices.
The data sheet for that resistor has a dimensioned drawing of the 995cm2 heat sink. With fins, it isn't that big. 65.2cm X 47.5cm X 24.1cm high. Mount it to the outside of your enclosure, of course, or you'll just build an oven!
Davidg - The problem with getting bass back with JUST a capacitor is you'll be bypassing the entire freq range to get to the lower freqencies, rendering the LPad useless as you're bypassing it. I think other attenuators use an RC network or something to achieve this.
dkochan - I think when they say heatsink they mean something that size in addition to the heatsink already on the resistor.
I'm currently looking at the Airbrake design at the moment and am trying to collect info on it in another thread.
.