Simple Attenuators - Design And Testing

[Dwayne Eash]

Hi Dwayne,sound clips as you request are already done and posted in post 1. Its attenuator M which will be the same as M2. Not sure if you saw these before.

Here they are:

Attenuator M: Max attenuation to non-attenuated:

https://vocaroo.com/i/s1QgVDnl1XQi


Attenuator M: Normalised:

https://vocaroo.com/i/s1cnuucLz8yK

Its a looped riff placed in my delay pedal working as a looper, pushing the amp quite hard (harder than I usually do). The first recording is with me then stepping through each setting on the attenuator from max attenuation through to zero attenuation, recorded from the speaker through a dynamic mic with no other settings changed. Then the second one is the same recording, boosted in software so each setting is the same volume. The recording level at the mixer was set for the loudest setting, so it s pretty quiet recording to start with.

Obviously your amp and playing, set your way, will sound different, but just listen for the consistency. The riff is played twice at each attenuation setting.

There's actually nothing wrong with the bass in M or M2, which is why I have never built M3. You still get the resonant bass peak which is created at the speaker. If there is a difference, it would be in the added distortion of the bass tone when you hit the very lowest notes very hard. it would only be the fundamental note as affected by the power amp, not the harmonics coming from the guitar, nor from the preamp or any distortion pedals.

The only difference between M2 and M3, is another coil and large cap. But to do this right with the right parts is about another $100. But, if we base your design on M2, these parts could be easily added later if you leave space for them.

There should be no tone loss with good switches. Can add it all as you wish. The reasons for suggesting not to have a bypass is that it is one switch that you need to be very careful with. Don't ever flick it while playing or else the amp can see transients. But that's not different in any such commercial attenuator of any type. I have literally never used my bypass switch on my 40 and 50W amps, nor has Gene who gigs regularly using smaller amps. Maybe if you have it, you could put it at the back while all the others are at the front? Other switches you can flick on and off at any time.

I've listened to them before, I just listened to them again, and although it is pretty transparent, it seriously lacks bass. Your not really playing lower notes, but the recording is rather decidedly not warm and fat.

If this is the only before and after attenuation I have to go by, I can not tell. Not enough bass and warmth was displayed. Could you point me to another clip, or someone else who made another clip? I trust my ears, not someone's word it handles bass well.

Bass is by far the hardest frequencies to handle well, and I don't like hearing you say, it handles the bass well, while at the same time you don't give an audio example where the low end is included.

Here's hoping we get to hear a sampling that includes the lower end, check out the warmth and if the bass remains tight, and accurate tone.

 

[JohnH]

I've listened to them before, I just listened to them again, and although it is pretty transparent, it seriously lacks bass. Your not really playing lower notes, but the recording is rather decidedly not warm and fat.

If this is the only before and after attenuation I have to go by, I can not tell. Not enough bass and warmth was displayed. Could you point me to another clip, or someone else who made another clip? I trust my ears, not someone's word it handles bass well.

Bass is by far the hardest frequencies to handle well, and I don't like hearing you say, it handles the bass well, while at the same time you don't give an audio example where the low end is included.

Here's hoping we get to hear a sampling that includes the lower end, check out the warmth and if the bass remains tight, and accurate tone.

OK so I can try another clip, maybe something in drop D, some 'Cinnamon Girl' maybe.

But lets get something totally crystal clear right now. I am providing free help to you, and having suggested a simple solution to your attenuator search, you are adding more and more requests and looking to be provided with a new more complex custom design to suit your needs with a heap of advice to go with it. That's all cool, I enjoy working things out. But I need some respect please. If I say it handles bass well, that is my opinion based on about a year with testing these designs, backed up by analysis. If you don't like to hear what Im saying I will stop.

Ok? If so, its all fine and we can continue...

 

[JohnH]

Have a listen to these, which try to show bass response. It's my attempt to play the start of Cinnamon Girl. First, attenuator bypassed, then switched to -21db, both from the same loop.

Full volume (attenuator bypassed), then -21db:
https://voca.ro/jwLCSg3wC9x

Here it is with the attenuated second part normalized in software back up to the same volume:
https://voca.ro/ncne6xsR8JS

Its miced off the VM2266c, Master volume at about 6.

I picked this since the dropped lower D gets frequencies down to 73 hz for low D, and has some notes at E#, G and A above that, so it should be in the range of the bass peak for comparison.

I hope that helps.

ps. another small nugget of info, this test was done using the -7 and -14db stages to make -21db. Audacity, which I record with lets me check that, and the actual difference in levels as miced, is -20.7db, so numbers are good.

 

[Mcentee2]

Have a listen to these, which try to show bass response. It's my attempt to play the start of Cinnamon Girl. First, attenuator bypassed, then switched to -21db, both from the same loop.

Full volume (attenuator bypassed), then -21db:
https://voca.ro/jwLCSg3wC9x

Here it is with the attenuated second part normalized in software back up to the same volume:
https://voca.ro/ncne6xsR8JS

Its miced off the VM2266c, Master volume at about 6.

I picked this since the dropped lower D gets frequencies down to 73 hz for low D, and has some notes at E#, G and A above that, so it should be in the range of the bass peak for comparison.

I hope that helps.

ps. another small nugget of info, this test was done using the -7 and -14db stages to make -21db. Audacity, which I record with lets me check that, and the actual difference in levels as miced, is -20.7db, so numbers are good.

Now *that* is why this build is so good......

 

[Dwayne Eash]

I thought I already gave this project serious props, saying something like, guitarists have been seriously needing a great project like this for eons,, and,, this design could possibly compete well with Ted Weber's MASS attenuators, because they seem to perform similarly, but your price is DIY low, and that is very cool!

I'm pretty sure I gave you another glowing remark about this excellent project, but if I haven't already said it, I think it's brilliant. And big thanks to Aiken amps for providing the solid state speaker emulation circuit for free. Both efforts deserve a round of applause from us all.

You seem to be giving it away to those who want it for the least price possible, and so I find that spirit of helping others, quite admirable.

So your open source attitude, is also admirable, more of the future, and should be supported. Whereas the next guy with the same info, could have setup a closed minded and self centered perspective, created a cool product, and then manufacture it, and sell it for a profit, and possibly get rich.

Because this project has low overhead, and relatively small parts, so the factory footprint would be pretty small, probably could easily be started in someone's home/garage/basement/pole-barn. Maybe do both open source DIY and a retail version?

But instead of profit before people, you put people before profit, so you were kind and smiled on us guitarists, and offered it to us, without entry fee, as a DIY project. Just show some respect, and don't hassle with change upon change.

That is very cool!!! That is a generous and helpful spirit. And much appreciated!

I've been wanting a reactive type power attenuator for 6-8 years. Just can't afford one yet.

I'm sorry if I had not made all this more clear to you earlier, but at least one of those compliments was probably given away from our conversation. Nothing but respect, for one of the finest DIY guitar projects, I've ever seen.

~~~

As for the audio clip, I hope your sitting, because that's another matter. hehe Things are becoming more clear to me now. I did a search on youtube, and listened to your amp model and, wow, I'm not sure how to say this,, gently,,

,, that is ,, I don't,, it's possibly,,

Gosh,, I'm trying to phrase this properly, but I'm having a hard time finding the right words.

Sorry, and remember, this is my personal taste test opinion. But I really really really dislike the tone and the sonic nature of the distortion, from that amp.

I sure hope we can get another audio clip. Please forgive my personal taste. The DSL is much more along the lines of what I'm used to, and appreciate.

Please, at your convenience, do another clip, using the DSL, that would help me, concerning an audio sample. I am sorry for being so unique, thus demanding.

~~~

As for evidence I wish to reduce the load, not increase it, I already did take back the request for foot-switchable clean boosts, if too many switches provide too much detriment to sound purity.

And I also said I was also willing to give up the bypass switch, actually on more general purposes, if you feel strong enough it's somehow sonically better without it,, already showing I defer to your much more experience view, of your own technology and design.

I think it's brilliant, but,, so far,, not the audio sampling choice of amps. But maybe that's just me. Sorry, but maybe I just gotta say it. I never though a Marshall amp could sound that bad. That's some rough harsh distortion, and lacking tone. But that's just my personal opinion.

Best wishes always. I love great guitar sounds and great guitar projects. Thank you for showing us all such generosity, and what seems like a great project!

 

[Dwayne Eash]

Oops, update seems required. I just saw another video, and the amp has a lot of versatility I did not know about. My bad for judging too quickly. For my defense, this is the first one. I could not get through 3 minuets of it and I was offended too much. hehe No worries tho, seems this was just a bad example is all.

When this amp is dialed in, it can sound very sweet. So again, my bad for judging too quickly. I still would prefer a DSL clip of 70-80's oriented rock and roll gain area, but like you already did, to show off the low and warm half of the spectrum.

This video is what turned me off. But next up, what changed my mind! But it's a different sound with those KT66's. When they sound good they sound out of this worldly good, but,, when they,, anyway,, nuff said. Please also watch the next video, to hear the same amp, sound much better, arguably great.

 

[Dwayne Eash]

And, here's a great video of the same amp sounding much better. Enjoy!

Sorry about my previous length, so I put it in such a long post, as I do not wish to take up many posts on one page. I appreciate your time and space, and will keep things short and sweet. You've been a great help. Thanks again for the awesome project!

 

[JohnH]

Ok that's all good then.

My DSL is a DSL401, actually nothing like the tone of the more classic ones.
also my recording set up (and playing) is not great. its enough to show differences in the settings but doesn't necessarily do justice to a good amp. All the clips are for is to show to what extent what goes into the attenuator comes out at the other end.

To help the discussion, do you have a clip of the sounds that you like? either yourself or elsewhere online? (OK just saw what you posted above)

 

[Dwayne Eash]

Dig it man. After some reflection, I suppose a clean recording is the main thing. The distortion on the un-attenuated side, makes it harder to judge the attenuated tone, because there's not as much tone to listen to and compare. Maybe use the same amp, but without the heavy distortion settings. I like the warm clean side of that amp. Thanks for the grace and great design.

 

[Dwayne Eash]

And I'm not kidding, if you build this out, and refine the offering of foot switchable clean boost(s) for the ultimate in clean boost transparency, then I do not doubt you could go into business selling these and become financially successful, because of it being cheaper to build it than a Weber Mass, yet does a very similar job as the MASS, at a discount in price.

People with an amp they like the sound of it, will love having an amp provided clean boost. That is simply genius for those who prefer the sound of their amp. I love how my amp sounds, so this option seems like a must have.

I believe one guy on this forum already installed a nice looking line-out, a feature many will like for their unit. You might also consider implementing a full dummy load option, as well. I know I would opt for that option if it was available.

Forgive me if you have no desire to mass produce these. But this DIY project, could easily be a worthwhile business venture. Too bad Ted did not have more of an open source mentality, or I could have built my own power attenuator years ago from an old speaker motor, and I would have thrown Ted Weber some of my money as well. But so far, nope, I held out for a better deal. Glad I did.

We have too much self interest in profit over people these days. Thanks for demonstrating it's better to prioritize people over profit. But don't be afraid of making some money off these as well. If you can outsource the box, the rest is little more than soldering it together.

After parts are collected, probably doesn't take an hour to build the device in a manufacturing plant, start to finish setting. So that's only 10-15 bucks labor and handling per unit. Talk about nice overhead costs.

One of your finished units, with clean boost foot switching, and a line out, and dummy load, would easily fetch $200 as opposed to Weber's $275-$300 for his units of similar reactive power attenuation. If you could make them for around 150 per unit, including labor, you could make about 50 bucks a unit, and still afford to pay someone 12 bucks an hour to build them for you. You just sit back and handle orders and customer service if you want.

Something to think about. Peace!

 

[What?]

Have a listen to these, which try to show bass response. It's my attempt to play the start of Cinnamon Girl. First, attenuator bypassed, then switched to -21db, both from the same loop.

Full volume (attenuator bypassed), then -21db:
https://voca.ro/jwLCSg3wC9x

Here it is with the attenuated second part normalized in software back up to the same volume:
https://voca.ro/ncne6xsR8JS

Its miced off the VM2266c, Master volume at about 6.

I picked this since the dropped lower D gets frequencies down to 73 hz for low D, and has some notes at E#, G and A above that, so it should be in the range of the bass peak for comparison.

I hope that helps.

ps. another small nugget of info, this test was done using the -7 and -14db stages to make -21db. Audacity, which I record with lets me check that, and the actual difference in levels as miced, is -20.7db, so numbers are good.

Sounds pretty dang spot on here. I'm guessing that the noise in the normalized attenuated audio is due to the noise floor of the recording being raised along with the signal, i.e., that level of noise would not be there in person.

 

[Dwayne Eash]

Sounds pretty dang spot on here. I'm guessing that the noise in the normalized attenuated audio is due to the noise floor of the recording being raised along with the signal, i.e., that level of noise would not be there in person.

I have no problem with recording clarity. The slight distortion, or static from volume normalizing is perfectly acceptable to me. Just to clarify, and not that you are responding to my idea, but the distortion I was referring to, was not from the recording rig and mic, but the guitar amp settings with too much gain or boost buttons, so the signal is pushed into heavy distortion and overdrive.

Which would you rather have to listen to, to determine if the signal was sonically altered, a distorted signal, or a clear clean signal?

I say the choice is clear. Because of too much distortion in the amp, that makes judging the tonal transparency more difficult. I like to hear both distorted sounds, and clean sounds, to better gauge the effect on the sound quality. But at this point, I agree, the attenuator seems to do no noticeable harm to the sound quality, even using more warmer low end frequencies.

And that's encouraging news. I just can't clearly distinguish tonal variance, with a fairly highly distorted signal.

I look forward to a cleaner sample of warmth and low end, maybe including a bit of a bass roll, instead of more wide open sounding chords, because of overlapping, which can serve to cover up tones, instead of highlight them. But I like to hear some strumming too. It all helps.

I would like to start this project, ASAP. I have been wanting a good reactive power attenuator, like for most of a decade.

 

[What?]

Which would you rather have to listen to, to determine if the signal was sonically altered, a distorted signal, or a clear clean signal?

The sound of a given amp, at whatever volume it sounds best. That almost always means a cranked up amp and distorted tone. Some amps will be much more distorted than others when cranked up, so it's not a fixed type of tone (clean or distorted) across amps.

 

[JohnH]

Thanks for the comments guys.

The open source nature of this project is a key thing and actually we wouldn't have this design without it. The feedback is an enormous part of making it better. In fact, if @Gene Ballzz hadn't built one and noticed that it was doing a great job, I probably wouldn't have developed it beyond an early version. For example, for his first version, I tweaked the ratio of the inductors to better optimize the response based on the numbers. It brought it to life an he noticed it first while my then latest prototype had previous values that didn't bring out the proper benefit of the reactive circuit.

On recordings and noise floor, yes boosting in software is bringing up everything in the signal, and the sound signal is embarrassingly tiny at -21db. For interest, here's how the traces for the last clips look like, for the original and normalized versions:



Clearly it would have been better to get the attenuated trace by boosting the mic level instead of downstream within the software recording. But it's interesting to see what a -21db signal reduction looks like. At just over a 1/100th factor on power, the signal voltage is reduced by factor of just under 1/10th, which is as you can see in the upper trace. And if you look at equivalent sections of the lower trace, there is much similarity between full volume and normalized signals, but they are not quite identical. The real speaker is obviously being pushed harder at full volume and is adding its own non-linearities.

There's anther noise-floor benefit, not picked up here. Any biggish amp has its own bit of residual hum and hiss even at zero volume. If the alternative to an attenuator is just to turn down volume, then you still get this coming through from the full power amp. But an attenuator squashes this back down in proportion.

To test out a reactive attenuator, most is revealed in a signal where the power amp is saturating and that's what the clips so far have aimed at. This is where the varying impedance being fed back to the amp makes the amp react and compress. With clean signals its all a lot more linear and the comparisons can be less revealing of differences. But Ill put that on the 2do list.


As to making $, sure I like it too. But to set up and run such a business properly, with warranties, taxes, paperwork, suppliers, shipping etc, for $50 profit per unit doesn't fit into my life right now. btw, IRL, I'm a structural engineer (electronics is a hobby since high-school). I design large buildings, and I teach it at Sydney university. It uses all my time and $50 wouldn't replace much of it.

 

[Dwayne Eash]

Thanks for the comments guys.

The open source nature of this project is a key thing and actually we wouldn't have this design without it. The feedback is an enormous part of making it better. In fact, if @Gene Ballzz hadn't built one and noticed that it was doing a great job, I probably wouldn't have developed it beyond an early version. For example, for his first version, I tweaked the ratio of the inductors to better optimize the response based on the numbers. It brought it to life an he noticed it first while my then latest prototype had previous values that didn't bring out the proper benefit of the reactive circuit.

On recordings and noise floor, yes boosting in software is bringing up everything in the signal, and the sound signal is embarrassingly tiny at -21db. For interest, here's how the traces for the last clips look like, for the original and normalized versions:

View attachment 73676

Clearly it would have been better to get the attenuated trace by boosting the mic level instead of downstream within the software recording. But it's interesting to see what a -21db signal reduction looks like. At just over a 1/100th factor on power, the signal voltage is reduced by factor of just under 1/10th, which is as you can see in the upper trace. And if you look at equivalent sections of the lower trace, there is much similarity between full volume and normalized signals, but they are not quite identical. The real speaker is obviously being pushed harder at full volume and is adding its own non-linearities.

There's anther noise-floor benefit, not picked up here. Any biggish amp has its own bit of residual hum and hiss even at zero volume. If the alternative to an attenuator is just to turn down volume, then you still get this coming through from the full power amp. But an attenuator squashes this back down in proportion.

To test out a reactive attenuator, most is revealed in a signal where the power amp is saturating and that's what the clips so far have aimed at. This is where the varying impedance being fed back to the amp makes the amp react and compress. With clean signals its all a lot more linear and the comparisons can be less revealing of differences. But Ill put that on the 2do list.


As to making $, sure I like it too. But to set up and run such a business properly, with warranties, taxes, paperwork, suppliers, shipping etc, for $50 profit per unit doesn't fit into my life right now. btw, IRL, I'm a structural engineer (electronics is a hobby since high-school). I design large buildings, and I teach it at Sydney university. It uses all my time and $50 wouldn't replace much of it.

That was with you paying someone to do the work, you'd mostly just need to do watch over orders and customer service to keep the employee count down.

If you make more money as a building engineer, then that's perfectly understandable why you are not interested in smaller earnings. I'm glad you seem to be doing so well. I'm so poor, I can't pay attention. hehe But I have great ideas I feel the world needs. It's too much of an upside down world. Too much corruption.

I suggest you save up, and prepare to work for yourself. Because the future is not guaranteed. The economy could collapse because of this plandemic. After that, all plans for careers can be canceled if it's not essential enough. AI, and manufacturing automation, is gradually pushing out the worker, so there are less jobs, and more people without jobs.

Sooner or later, something has to give. I'm saying, be prepared for hard times. Lets hope it does not get that bad, but it could become another great depression.

 

[JohnH]

Sure, good points.

So what should your design be at this point?

A few extra things to know:

A line out is easy to add, which youd then need to feed through a cab-sim or IR processor to make a sound for recording or PA use.

Any if these designs can be a load box with no mods. You just set to max attenuation, and then the amp sees negligible difference whether or not a speaker is there (at -31db, less than 1/1000th of the power would reach the speaker anyway)

Can have the relay footswitching if you want it, which would cut the level further when engaged, then bring back up to level if off. An alternative to adding two more full switched stages with extea resistors, would be to have relays that could override the standard 7 and 3.5 switched stages when the footswitch is plugged in, saving the extra resistors.

Have the full bypass if you wish.

 

[Dwayne Eash]

Sure, good points.

So what should your design be at this point?

A few extra things to know:

A line out is easy to add, which youd then need to feed through a cab-sim or IR processor to make a sound for recording or PA use.

Any if these designs can be a load box with no mods. You just set to max attenuation, and then the amp sees negligible difference whether or not a speaker is there (at -31db, less than 1/1000th of the power would reach the speaker anyway)

Can have the relay footswitching if you want it, which would cut the level further when engaged, then bring back up to level if off. An alternative to adding two more full switched stages with extea resistors, would be to have relays that could override the standard 7 and 3.5 switched stages when the footswitch is plugged in, saving the extra resistors.

Have the full bypass if you wish.

Good points, thanks for clarifying. I don't need a line out, so I figure, no line out.

As for saving gain stages from the footswitch,, so far,, I think not,, but your right to bring it up as there's still too much attenuation, because of my foot-switches. I love the idea of two transparent clean boosts. And I like those transparent boosts, to act isolated from the attenuation volume functionality.

I think you once said that the attenuator options should probably be 3.5, 7 and 14, and I agree! But those settings are functionally "just" for volume level. Kinda like, set them, and forget them. Like controls on the amplifier!

The clean boost settings, are JUST for clean boost levels within a song, and so the two different functions are not really combinable in the same stage, since they each do different things. I don't want to sometimes render one of the clean boosts, unavailable. So the two functional sections, the set it and forget it part, and the foot switchable part, functionally speaking, should work independently from each other.

I would much rather pay for the extra relay switching system, and for two extra gain stages, in order to keep the foot switchable clean boosts functionally independent from the power attenuation options.

Here's my first semi-final rough draft.

Speaker Emulation Stage (always on)
7 dB *
Attenuator Stages (set and forget per show/session)
14, 7, 3.5
foot switchable clean boost stages (frequent changes, even per song/musical number)
7, 3.5 either (A/B) and (on/off)

*Question, what's the lowest value that still works well for this spot? And what is the best value for this spot?

 

[Dwayne Eash]

I just realized, on the foot-switch relay stomp box, for the two foot-switches, I want one on/off relay switch, and one A/B selection relay switch. Here's how it works. Stomp on first stomp switch, to light up an LED showing activation of the stomp box.

This also actives one of the two stages. The other stomp box switch, designates which stage is being called upon, the 3.5 or the 7. That way, with one stomp, I can double the boost, or half the boost. Just one stomp. And with just one more stomp, I can shut the “boost” off, or turn it “on”.

If I had a separate on/off switch for each stage, then, just to go from one stage to the next, I would have to hit “two” foot switches, instead of “one”, and that's twice as time consuming, and clumsy.

~~~

I'm giving up a combined third stage in the clean boosts, and I'm very much ok with that. Question, can I add a (good quality?) line out to the unit later? Or is it best to add it when building it?

If it does not cost much time or money to add a quality line out, then cool, I'll add it, but I don't really have much plans for recording or re'amping.

I mostly just need a transparent power attenuator. So I'd prefer saving the money now, if I can add a line out later, just plan for it ahead of time, and leave enough space. Getting closer to design finalization!!!

 

[JohnH]

-7db is best as stage 1. Can probably squeeze it another db to -6 but needs checking out.

With the added foot switched stages, we don't really have a boost, just more cuts. Just need to be sure that its loud enough. I think it would be with a 50W amp going in.

So let's say the first stage can be -6db. That defines the loudest lead sound. A 50W amp is now like a 12W amp, still pretty loud, or 10W if Stage 1 remains at -7. Then, if your rythym volume is another 7 or 6db less, it is at 2 or 2,5W. Fine for home use, jamming, recording etc, but if you were giggiing, it might start to be limiting?. What do you think? There's always PAs though...

 

[JohnH]

As for line out, actually it's just a jack a pot and a resistor. Parts <$10. It's just easier to drill a case all before anything goes into it.

I don't use a line out, despite my tones, I Mic the cab since I don't need a silent solution and don't have the cab-sim or IR needed.