Reactive fixed attenuator design

lamesaint · Post by **lamesaint** » 07 Aug 2011, 23:13

Hi all guys,
this is one of the first time I write here on the forum, though i read it from months, so forgive my errors and be easy on me. Plus I'm not english

So here's the question:
I was hangin 'round on the net looking for a reactive attenuator design; I did'nt found anything, just the reactive loadbox design from randall Aiken page http://www.aikenamps.com/spkrload.html
And the idea was to take an L-pad network and to replace the resistor in parallel with the speaker with the Aiken load scaled for the right impedance (something like 2 ohms, 7 for the resistance in series, when the speaker is 8 ohms, kinda 14 db's of attenuation). Do you guys think it will do the trick mantaining a decent impedance response for the amp? A little schemo i did in 5 minutes: Hope it helps.

Thank you very much

DrNomis · Post by **DrNomis** » 07 Aug 2011, 23:43

lamesaint wrote:Hi all guys,
this is one of the first time I write here on the forum, though i read it from months, so forgive my errors and be easy on me. Plus I'm not english
So here's the question:
I was hangin 'round on the net looking for a reactive attenuator design; I did'nt found anything, just the reactive loadbox design from randall Aiken page http://www.aikenamps.com/spkrload.html
And the idea was to take an L-pad network and to replace the resistor in parallel with the speaker with the Aiken load scaled for the right impedance (something like 2 ohms, 7 for the resistance in series, when the speaker is 8 ohms, kinda 14 db's of attenuation). Do you guys think it will do the trick mantaining a decent impedance response for the amp? A little schemo i did in 5 minutes: Hope it helps.

Thank you very much

Looks like that should do the trick, if you can get them try using a 100V Bi-Polar cap for the 12.5uF cap, they're commonly used in crossover circuits in Hi-Fi speaker systems...

By the way, welcome to freestompboxes.org.....

lamesaint · Post by **lamesaint** » 08 Aug 2011, 00:03

Thanks man

I don't think I'm gonna find that caps, I'll put 10 uF and 2.2 uF in parallel.
Do you think the 7 ohm resistor's gonna kill all the reactive sistem?
By the way updated schematic, there was an error in the speaker wiring:

DrNomis · Post by **DrNomis** » 08 Aug 2011, 00:21

lamesaint wrote:Thanks man
I don't think I'm gonna find that caps, I'll put 10 uF and 2.2 uF in parallel.
Do you think the 7 ohm resistor's gonna kill all the reactive sistem?
By the way updated schematic, there was an error in the speaker wiring:

Putting a 10uF and a 2.2uF in parallel should give you about 12.2uF, which is close enough, capacitors usually have a tolerance of anything from +/- 10 to 20% of the marked value, tolerance is how close the actual value is to the marked value expressed as a percentage, this is because electronic components like resistors and capacitors are difficult to make in exact values, in reality most electronic circuits don't require exact values anyway, unless in special cases...

Providing that the 7 ohm resistor has an adequate power rating, I can't see any reason why it would have any adverse effect on the system reactances, it may cause some minor resonances (peaks) in the system's frequency response due to the resistor being a wire wound type and therefore exibiting some inductive reactance at some frequency, but apart from that it should be fine....

lamesaint · Post by **lamesaint** » 08 Aug 2011, 00:37

No more trouble with that cap, it was a wrong value, now i must find 800uF

BTW I will try and let you know... Any suggestion for improvements?

DrNomis · Post by **DrNomis** » 08 Aug 2011, 00:53

lamesaint wrote:No more trouble with that cap, it was a wrong value, now i must find 800uF
BTW I will try and let you know... Any suggestion for improvements?

None that I can think of at the moment, but if I do think of anything I'll post it in this thread.....

Hope it works well when you build the circuit, if you have any problems feel free to let me know.....