Metropoulos Forum

I only use the ammo box into speaker output 2. It adds a great sound even with a regular attenuator in speaker 1. The problem with any load is heat.

My new idea is to simply wire 4 arcol's like a 4/12 cab, then parallel each of those resistors with a Webber speaker load.

In case anyone is interested here is a great read on parallel loads: http://aikenamps.com/ParallelLoads.html" onclick="window.open(this.href);return false;

julkke wrote:In case anyone is interested here is a great read on parallel loads: http://aikenamps.com/ParallelLoads.html" onclick="window.open(this.href);return false;

Interesting how that reduces the highs and lows but increases the mids releatively. It also reduce the impedance rise at higher frequencies that you get with a regular speaker load.

vanhalen5150 wrote:

julkke wrote:In case anyone is interested here is a great read on parallel loads: http://aikenamps.com/ParallelLoads.html" onclick="window.open(this.href);return false;

Interesting how that reduces the highs and lows but increases the mids releatively. It also reduce the impedance rise at higher frequencies that you get with a regular speaker load.

That's the trick with these things. Keeping the load (resistive, reactive or combo) matching what you get from the speaker. I noticed the same thing when plugging a load into one speaker jack, the volume went down but the dynamics were crushed.

What type of load though?

I think things are getting a little confusing here. What I was trying to show in this thread was a multipurpose RESISTIVE load with:
1)The Rockstah Line out
2)The Ralle Line out/Speaker out (at least as I under stood it!)
3)An extension to add a transformer coupled output to approximate what we Mark Cameron and Robin L. described here as being used for slaving in in Ed's early live rigs. Coupled with the Plexi converted to a power amp shown here:
http://forum.metroamp.com/viewtopic.php ... 8&start=21
you can have a hell of a lot of fun! Especially, if you put some sort of reverb after the lineout and before the Power amp.

http://forum.metroamp.com/viewtopic.php ... 4&start=29



I don't think back then Ed gave a rats ass about the limitations of it being a purely resistive load... hell he would probably just stick a GE-10 in the chain!

As far as the Aiken stuff goes: He is describing how to build both kinds of load primarily as a bench tool.
For some tests you NEED a resistive load.
For some tests a reactive load is better.

Can you use his reactive load designs as a start to build a home brew attenuator? I would think so.
Might you use a reactive load in place of the resistive load shown in the load boxes above? Sure!

Yes, the Aiken stuff is talking mainly from a load bench tool aspect. I guess my questions with the coupled tranny would be is your amp still seeing both resistive and reactive? A line out from a resistive still allows your amp to see somewhat of a reactive load...or does it? It goes directly into another amp and not a speaker. Does the primary on the coupled tranny act as a inductor? I'm thinking it does.

The transformer definitely has one purpose, which is decoupling, which can undo ground loops, and eliminate weird oscillations. Another likely purpose is to step down the voltage. The Jensen I am using is a 4 to 1 reduction in voltage, but you could go 10 to 1 etc. All transformers are not equal... the Jensens are expensive(and used in high end audio equipment) because they do not alter the frequency response of the original signal. I don't think their inductive qualities really come in to play here.

Just to be clear on why a reactive load might be useful as a bench tool:
I resistive load is going to be the same impedance across ALL frequencies. A real speaker (even though rated at 16ohms for instance) reflects a different impedance back to the amps output stage at different frequncies. This is why, as Aiken points out, it can be useful to observe oscillations that might not be reproduced with a resistive load.

An attenuator probably needs to take in account this frequency dependent reflection, along with the peculiarities of human hearing in its design in attempt to sound to the listener like there is no tone change as the volume is lowered.

vh junkie wrote: An attenuator probably needs to take in account this frequency dependent reflection, along with the peculiarities of human hearing in its design in attempt to sound to the listener like there is no tone change as the volume is lowered.

I think THAT is the biggest challenge for an attenuator and a few have figured out how to do it.

Just one tiny thing... That line out of "mine" isn't quite how I have it... Here's a schem of how it's done...
Maybe I'm missing something, but the main load is suppose to be in serie with that line-load... The reason for the resistor being that small is two reasons;
1. it doesn't need to be an effect resistor since the main load of 4, 8 or 16 ohms take the whole heat.
2. the small resistor is in parallel over the speaker, wich bring the value for that package ( small reistor/speaker ) down to less that 0.5 ohms.
these 0.5 ( or 0.45 ohm ca ) ohms ends up in serie with the main load, wich is well enough within the margins.

The big main 8 ohm load in my pic here, symbolizes your big main load...

Please correct me if I'm not seing the whole picture here...

Can someone help me understand how the 20 ohm load works out with that switch. I can't seem to get the math right on that.

If you look at the schematic at the bottom of the first page, you can see that from bottom to top the load stack increases from 4 to 8 to 16 to 20 ohms. The switch shorts out the top part of the stack, so the amp only sees 16 ohm instead of 20.

Why yes it sure would, wouldn't it? The two 8 ohms in parallel (4 ohms) get bypassed. Stoop.

OK. I've ordered all the stuff to build this thing but where do I get the aluminum plate used to suspend the resistor within the enclosure? Anyone?

And how did we come up with the Jensen JT-6110 transformer info?