Resistive Attenuators

[Littlewyan]

I was thinking earlier on about certain resistive attenuators sounding better than others. I know some people complain about the Airbrake sounding buzzy, I found the attenuator built into my JTM1 sounds buzzy, however my LPad attenautor isn't buzzy at all and I think I know why!

My LPad attenuator works differently to the Airbrake and JTM1 Attenuator. My LPad puts a resistor in parallel with the speaker and then puts a resistor in series between that and the amplifier. The Airbrake and JTM1 Attenuator do the opposite, they put a resistor in parallel with the amplifier and then a resistor in series between that and the speaker.

What do you guys think?

[caps8419]

Id go Reactive instead. Much more accurate representation of how a speaker reacts than just using a resistive load. Pete Thorn did a great comparison vid of a handful of popular resistive and reactive loads. Pretty clear differences even via youtube... Hope it helps!

https://www.youtube.com/watch?v=i770M9pM0_k

[Leo_Gnardo]

FWIW just did a little mod to a Z-amp Brake Lite in a Crate V15. Owner's complaint was loss of presence as lower settings were selected. Put in a 4.7 uF 400V film cap to pass hi frequencies to the output, he's delighted.

In a too-fizzy or bright situation, a similar cap could be used to shunt hi frequencies to ground as in a tone control. Worth a try.

[Littlewyan]

The trouble with reactive loads is they can be very bad for your amp. A resistive load is much safer.

http://www.aikenamps.com/index.php/technical-q-a

Just over halfway down is a question: Why are resistive attenuators harder on an amp than an inductive attenuator or speaker load?

Aiken then goes on to explain why that isn't true.

I might try that Leo. I had the 0.1uF on my rheostat in my Custom Airbrake, however it was extremely fizzy with that and all I got out of the speaker was a load of hash. However my Airbrake only mismatches the load up to 9Ohms whereas the original mismatches it to 22Ohms. So I'll need a slightly larger cap to have the same effect.

That aside my LPad attenuator doesn't lose much high end at all at low settings and replicates the tone very well. The Airbrake gets even more buzzy the more you turn it down (Post cap removal).

[caps8419]

Mr. Aiken is speaking in terms of bench testing an amp to confirm power outbut, frequency response etc. In that instance yes Resistive is best for the reasons he mentioned. Yes you are still cranking the hell out of your amp but you are doing that regardless, things are going to wear. When actually playing your amp, reactive is the way to go for best feel and sonic qualities IMO.

Check out Aiken's Gold Brick and his recommendation of using a Reactive Load for silent recording or Reactive attenuator for "live" use.

http://www.aikenamps.com/index.php/prod ... gold-brick

-M

[Littlewyan]

Dam, wrong article.

Here it is

http://www.thegearpage.net/board/index. ... te.327189/

3rd Post down by Reaiken.

Also I watched the youtube video you posted. It shows the differences quite clearly. It also shows the attenuator's tones are in line with what people say, the hotplate loses high end and the Airbrake is bright. The graph was also very interesting showing the impedance curve differences, I've always wanted to know that.

[jazbo8]

The graph was also very interesting showing the impedance curve differences, I've always wanted to know that.

The image from tgp isn't showing up for me, could please you repost it here?

[Littlewyan]

Sorry I was actually talking about the graph in the youtube video. However I managed to find the graph you're talking about somewhere else (think it was here actually). Here you go

Anyway the original point of this post was that moving the positions of the parallel and series resistor in an attenuator seems to change the tone. I wonder how you record those impedance curves that were shown at the end of that video. I wouldn't mind doing some tests on my attenuators.