# 8 Ohm Attenuator



## Paul Running (Apr 12, 2020)

I have begun to build a simple attenuator for partial loading of amplifiers, eventually I want to build an active load that will accurately emulate a speaker load. Here's the project so far:


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## player99 (Sep 5, 2019)

The Weber Mass Attenuator (and others I presume) use a speaker motor.


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## Frenchy99 (Oct 15, 2016)

Nice.

Will you put it in a metal enclosure.

Have to dig mine up. Following this.


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## Alan Small (Dec 30, 2019)

cool stuff...i remember pouring epoxy into an old voice coil to keep the unit quiet and still be reactive( not sure where I would have learned this would work in the early 90s...maybe a gerald weber book?


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## Alan Small (Dec 30, 2019)

who sells those nice rheostats?


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## Lincoln (Jun 2, 2008)

Paul Running said:


> I have begun to build a simple attenuator for partial loading of amplifiers, eventually I want to build an active load that will accurately emulate a speaker load. Here's the project so far:
> View attachment 347196


Very simple design. Is that big honkin rheostat only 2 ohm? Looks like something you'd rob from 200 amp Lincoln welder 😋


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## Paul Running (Apr 12, 2020)

Lincoln said:


> Very simple design. Is that big honkin rheostat only 2 ohm? Looks like something you'd rob from 200 amp Lincoln welder 😋


I got a job lot box at a vintage radio auction and it was full of Dale power resistors and rheostats, that was 20 years ago and I'm still using them for projects. Back then few people would bid on the junk boxes however, I don't believe that it is like that now...this hobby has really taken off, probably a lot to do with communications on the internet.


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## Paul Running (Apr 12, 2020)

Frenchy99 said:


> Nice.
> 
> Will you put it in a metal enclosure.
> 
> Have to dig mine up. Following this.


Yeah, I will mount everything in some type of enclosure. I'm hesitate, looking at other designs has me thinking about trying to simulate the speaker load more accurately. Analyzing the Weber has me thinking more now. Odd how it works...your mind says go for it and the gut says, wait a minute buddy.


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## Paul Running (Apr 12, 2020)

Alan Small said:


> cool stuff...i remember pouring epoxy into an old voice coil to keep the unit quiet and still be reactive( not sure where I would have learned this would work in the early 90s...maybe a gerald weber book?


I had thought about that however, the restriction should simulate the cone load in order to produce the correct dampening effect, otherwise the transfer curve would be different.


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## lightman (Sep 4, 2013)

Paul Running said:


> I have begun to build a simple attenuator for partial loading of amplifiers, eventually I want to build an active load that will accurately emulate a speaker load. Here's the project so far:
> View attachment 347196


Have you seen this on the Marshall forum a DIY reactive load attenuator.





Simple Attenuators - Design And Testing


Background Passive attenuators are wired between the amp output and the speakers. Their function is to absorb most of the output power of the amp, feeding a smaller amount to the speaker itself. This allows the amp output stage to run at higher power, letting the glorious tone of a good valve...




www.marshallforum.com




People seem very happy with it and it does not seem to change the sound.


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## Alan Small (Dec 30, 2019)

Paul Running said:


> I had thought about that however, the restriction should simulate the cone load in order to produce the correct dampening effect, otherwise the transfer curve would be different.


✅


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## Paul Running (Apr 12, 2020)

lightman said:


> Have you seen this on the Marshall forum a DIY reactive load attenuator.
> 
> 
> 
> ...


Thanks, this will keep me occupied for a long time.


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## loudtubeamps (Feb 2, 2012)

Paul Running said:


> I had thought about that however, the restriction should simulate the cone load in order to produce the correct dampening effect, otherwise the transfer curve would be different.


If you can get your hands on some ferro-fluid ...this would be the preferred fix to keep the chatter to a minimum while allowing the coil to do its job.


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## Yamariv (Jan 15, 2018)

lightman said:


> Have you seen this on the Marshall forum a DIY reactive load attenuator.
> 
> 
> 
> ...


THIS!!^^  I just built two of the M2 16ohm versions and they are absolute killer! They are my first attenuators and I've been missing out all this time. Its a long thread on the Marshall forum but the most recent versions are on the first page. JohnH who is the Attenuator designer is awesome to help you if you have any questions. They cost me about $100 a piece, you just can't beat that but you'll need some soldering skills.

Pic of one of my attenuators to prove it happened!


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## traynor_garnet (Feb 22, 2006)

Yamariv said:


> THIS!!^^  I just built two of the M2 16ohm versions and they are absolute killer! They are my first attenuators and I've been missing out all this time. Its a long thread on the Marshall forum but the most recent versions are on the first page. JohnH who is the Attenuator designer is awesome to help you if you have any questions. They cost me about $100 a piece, you just can't beat that but you'll need some soldering skills.
> 
> Pic of one of my attenuators to prove it happened!
> 
> View attachment 347354


Is this design close to or related to any commercially available product?

TG


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## Yamariv (Jan 15, 2018)

traynor_garnet said:


> Is this design close to or related to any commercially available product?
> 
> TG


Not sure, as far as I know it's his full design and he did a lot of testing and modifications as the thread progressed. It's a lot to read but worth it if you're looking to build one


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## Yamariv (Jan 15, 2018)

Yamariv said:


> Not sure, as far as I know it's his full design and he did a lot of testing and modifications as the thread progressed. It's a lot to read but worth it if you're looking to build one


Seriously boys, if you have the skills to solder, build one of these for pennies on the dollar compared to the high value ones and these sound just as good. Something to think about, everyone on the thread who builds them is extremely happy..including me!!


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## Paul Running (Apr 12, 2020)

Yamariv said:


> Seriously boys, if you have the skills to solder, build one of these for pennies on the dollar compared to the high value ones and these sound just as good. Something to think about, everyone on the thread who builds them is extremely happy..including me!!


Oh by reading the thread it certainly looks like a great project...that was an interesting thread...watching it evolve.


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## traynor_garnet (Feb 22, 2006)

Any demos?

TG


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## Yamariv (Jan 15, 2018)

traynor_garnet said:


> Any demos?
> 
> TG


They have lots of recordings and graphs on the Marshall thread. No real point from my end as to me it sounds exactly like my cranked amp but turned down


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## traynor_garnet (Feb 22, 2006)

Yamariv said:


> They have lots of recordings and graphs on the Marshall thread. No real point from my end as to me it sounds exactly like my cranked amp but turned down


Thanks. I tried finding them but a 77 page thread, interspersed with personal reviews of 800 different other attenuators and the inevitable "get a MV or use a smaller amp" debate, makes it very hard to weed through.


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## Yamariv (Jan 15, 2018)

traynor_garnet said:


> Thanks. I tried finding them but a 77 page thread, interspersed with personal reviews of 800 different other attenuators and the inevitable "get a MV or use a smaller amp" debate, makes it very hard to weed through.


I'd suggest you post a reply on the Thread with your set up ie: amp, cab etc and ask the designer what he would recommend for you and your set up. He has several versions and is always there to help and quick to respond. His M2 8ohm or 16ohm version should cover everything you need up to a 50watt amp. If you want 100 watt setup you simply have to double the resistor wattages. For about $100-$125 in parts, just build one and see if you like it..I have yet to see one person on the whole thread who has built a version of his attenuator that didn't like it.


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