Attenuator Rant & Myths!

[JohnH]

hi @LargeBoxSmallBox , thanks for raising the Air Brake design. When I was researching, the Air brake helped me realize a key thing!

Its a simple resistive attenuator, but unlike most, it puts the series branch towards the speaker, showing the speaker a high impedance and not damping it, unlike those designs based on Lpads that damp the speaker with a very low impedance at low volume.

The issue with is it that it doesn't control load to the amp very well. But with a series of stages each optimised, instead of a single variable stage as in an Airbrake, we can keep control and so youll see a sequence of 'Air Brake - like' stages in our designs.

I think FM hearing effects get blamed for too many attenuator issues that are really caused by electrical design.

 

[tmingle]

hi @LargeBoxSmallBox , thanks for raising the Air Brake design. When I was researching, the Air brake helped me realize a key thing!

Its a simple resistive attenuator, but unlike most, it puts the series branch towards the speaker, showing the speaker a high impedance and not damping it, unlike those designs based on Lpads that damp the speaker with a very low impedance at low volume.

The issue with is it that it doesn't control load to the amp very well. But with a series of stages each optimised, instead of a single variable stage as in an Airbrake, we can keep control and so youll see a sequence of 'Air Brake - like' stages in our designs.

I think FM hearing effects get blamed for too many attenuator issues that are really caused by electrical design.

I wish I had the recording skills to better demonstrate my results. I did have a Weber Mass for a short period & it did not work nearly as well as yours. There is no perfect solution to any of this, but this is the most economical solution that I have found. IMO, an attenuator is not needed with the 40CR. The master volumes work quite well on that amp with both power settings.

I also have a Helix & let me tell you, the tone tweaking & knob turning discussed in these attenuator threads pails in comparison to what you will encounter in modeling forums.

 

[JohnH]

@tschrama

I dont disagree with any of your statements about how amps work and how they interact with speakers etc, clearly you know your stuff.

But you are misunderstanding or misreading or not reading how I have tried to explain how the design works, how it is analyzed and tested, and then making incorrect statements that misrepresent our design. If any of that is because my explanations are lacking in your opinion, then Im happy to discuss or clarify further. And since the whole design has been a great learning experience, Id be genuinely interested in any insights that you may have.

The only testing that finally counts is real-world testing in practice, supported by measured testing with recordings of real amps

On post 1 of the design thread, there are sound samples that cover the range from full unattenuated with no attenuator, down to -31.5 dB. They were made with an overdriven amp and my prototype design M rather than M2. You can hear them building up in volume, or nomalized, or see them plotted as frequency response curves. On one part of the plot, I subtracted curves from each other to see differences and I used the -7db curve for this because it gave a clearer graph. You can see the difference to full volume, and then lower volumes.

See also @tmingle 's samples above and also as linked on post 1 of the design thread, , recent samples by @rowandg. Those were particularly interesting to me because they were with very different amps to the two that I designed around but still show good consistency, audibly and in plots.

But to develop designs, the physical testing is too unwieldly and so analysis models are needed. I use SPICE models for trying a new idea, and then I code them into a spreadsheet so i can more quickly run all settings. Models are useful if they help make good design choices, but they cant capture everything. My models are all linear, based on classical theory of L, R and C components. Speakers are represented by models that capture measured speaker cab impedance. For the amp, I just represent it as a signal source and a resistive output impedance (based on advice). This value is chosen from tests, but clearly in reality it varies at different frequencies, according to how NFB, resonance and presence is configured, and between different amps. It also varies dynamically through the signal cycle when the amp is overdriving, and I cant capture that directly. So although I base my designs on a nominal value for amp output impedance, I then test again with widely different values. What we see is the response adapting quite well through the range where I have a reactive impedance in the attenuator. The analysis models that I use are good because they have lead to designs that have been proven to work. Modelling the amp overdrive explicitly in an analysis would be difficult - could be done in SPICE but I haven't gone there. So my calcs are based on clean tone, and representing the impedance seen by the amp as accurately as needed so that overdrive happens correctly, and then explored with physical tests (see below about whether this is need just for the treble rise or for the bass resonance too).

BTW, any time on our threads that you see a plot with smooth curves, its an analysis result. If it has bumps and spikes, its a recorded response.

Coils - Im well aware of the low bass resonance of a speaker cab and how to represent it with large L and C parts. This is included in designs M3 and M4. Its not in design M2, nor in the original design M. M and M2 have proven to work just fine without them, for attenuating a guitar speaker, since the real speaker makes its own resonance when interacting with the attenuator. Adding the LC circuit makes it a bit more accurate, and it can be better for taking a line-out, but it adds considerable bulk and expense, so its good to have the choice to have it or not. And ultimately, the bass resonance only affects a few of the lowest notes on the guitar, and not the lower mids and upwards where the character of the guitar tone resides. But initially I really expected that the LC circuit would show a clear benefit. but even without it, pushing hard on recorded tests with deep overdriven bass notes, I couldn't find this.

BTW Our designs do not in fact have the same fundamental shortcomings as a number of others, since they are better at controlling tone and they do not cost $1000.

I look forward to any of your further objective analysis that you feel like sharing, whenever you feel up to it.

 

[JohnH]

I wish I had the recording skills to better demonstrate my results. I did have a Weber Mass for a short period & it did not work nearly as well as yours. There is no perfect solution to any of this, but this is the most economical solution that I have found. IMO, an attenuator is not needed with the 40CR. The master volumes work quite well on that amp with both power settings.

I also have a Helix & let me tell you, the tone tweaking & knob turning discussed in these attenuator threads pails in comparison to what you will encounter in modeling forums.

The discussion of Weber and Airbrake fits well with my mental picture of how these units work! Despite its reactive speaker coil, Weber Mass units attenuate with an L-pad that gives low tone-damping impedance at low volume, wheras Airbrakes go the opposite way. and keep output impedance high.

 

[10kDA]

Thanks to all for your contributions. I've been thinking about building a JohnH attenuator but I was having a hard time going through the original thread. Now I'm inspired to take a shot at building a M2.

 

[WillyW]

So I have solved the attenuation problem for me.

I have been experimenting with bi and tri amps.

Two guitar amps for dirty and clean and sometimes adding a bass amp

Clean amp is easy to get sounding good at low volumes and various amps work well for that. (Master vol preferred ) delay, reverb, chorus added there.

Bass amp works fine with the few effects I use there,

My problem was I was unable to crank most any amp to its full potential.

I wanted to be able to have the amp clean with the guitar volume at 6-7 and dirty on 10-11

Sweetwater had the bugera ps-1 on sale for $49.

It allows me to crank my SV20C at a much lower volume than I was able to achieve even on the 5w setting.

20w attenuated sounds much better than the 5w.

Myths?

Tone loss? It sounds so much better than it did at low volume. I was completely unable to crank the amp at home so how can I compare?

Attenuator overheating? I have read on the interwebz that the bugera gets very hot.

I’m really have no clue what the complainers were trying to attenuate, but mine is barely warm. And that’s fully cranked on 20w.


I’m not trying to use some mythical stadium amp in my bedroom. I’m trying to use real life equipment that could be used at home or a small venue AND could be mic’s when the stadium tour starts. So that may be why I’m happy with my inexpensive passive attenuator.

I love working on and building guitars, and I could probably build my own pedals and an attenuator.

but my eyes glaze over when looking at electronics schematics and I don’t find it fun. So buying one is fine with me.

 

[tmingle]

So I have solved the attenuation problem for me.

I have been experimenting with bi and tri amps.

Two guitar amps for dirty and clean and sometimes adding a bass amp

Clean amp is easy to get sounding good at low volumes and various amps work well for that. (Master vol preferred ) delay, reverb, chorus added there.

Bass amp works fine with the few effects I use there,

My problem was I was unable to crank most any amp to its full potential.

I wanted to be able to have the amp clean with the guitar volume at 6-7 and dirty on 10-11

Sweetwater had the bugera ps-1 on sale for $49.

It allows me to crank my SV20C at a much lower volume than I was able to achieve even on the 5w setting.

20w attenuated sounds much better than the 5w.

Myths?

Tone loss? It sounds so much better than it did at low volume. I was completely unable to crank the amp at home so how can I compare?

Attenuator overheating? I have read on the interwebz that the bugera gets very hot.

I’m really have no clue what the complainers were trying to attenuate, but mine is barely warm. And that’s fully cranked on 20w.


I’m not trying to use some mythical stadium amp in my bedroom. I’m trying to use real life equipment that could be used at home or a small venue AND could be mic’s when the stadium tour starts. So that may be why I’m happy with my inexpensive passive attenuator.

I love working on and building guitars, and I could probably build my own pedals and an attenuator.

but my eyes glaze over when looking at electronics schematics and I don’t find it fun. So buying one is fine with me.

I would think the Bugera has the power handling capability to handle 20W & shouldn't get very hot. My concern with the Bugera would be build quality. If it were to fail, the cost to repair that amp would easily buy 5-6 of the Bugera's. I don't care for the potentiometer in any of these because they are a failure point. I have box full of wire wound Pots that would work for this, but I don't trust them. I used 15A switches for mine. I realize this is overkill, but mine should never fail.

 

[Salty Rose]

I was in the same spot, the quickest easiest solution was get a good deal on a power brake which I have found to sound great in my opinion.

+1

 

[rockgod212]

here is the ken fisher airbrake i built some years back, i use it with my 1987 50watt clone, never tried it with my 100watters though. it works and sounds great. i used another rheostat instead of the other big resistor, so better volume contol.

 

[WillyW]

I would think the Bugera has the power handling capability to handle 20W & shouldn't get very hot. My concern with the Bugera would be build quality. If it were to fail, the cost to repair that amp would easily buy 5-6 of the Bugera's. I don't care for the potentiometer in any of these because they are a failure point. I have box full of wire wound Pots that would work for this, but I don't trust them. I used 15A switches for mine. I realize this is overkill, but mine should never fail.

thanks for that information,

so the volume is controlled through the switch or a series of switches?

Im only using the attenuator for keeping home levels within reason. I do have the potentiometer on the bugera set where its goi to stay and make further adjustments on the amp.

for any studio or recording, I’m leaving that up to whatever Skunk tells me I’m playing, and playing through.

 

[LargeBoxSmallBox]

hi @LargeBoxSmallBox , thanks for raising the Air Brake design. When I was researching, the Air brake helped me realize a key thing!

Its a simple resistive attenuator, but unlike most, it puts the series branch towards the speaker, showing the speaker a high impedance and not damping it, unlike those designs based on Lpads that damp the speaker with a very low impedance at low volume.

The issue with is it that it doesn't control load to the amp very well. But with a series of stages each optimised, instead of a single variable stage as in an Airbrake, we can keep control and so youll see a sequence of 'Air Brake - like' stages in our designs.

I think FM hearing effects get blamed for too many attenuator issues that are really caused by electrical design.

Great post! Such a lot of good info in very few words, well said.

The Air Brake would get pretty hot, if I ran it for any somewhat lengthy time. I used it with a 50-watt Marshall and 2x12's, but I didn't make a habit of using it with 100-watt Marshalls, as I was worried I might fry it. I'm super curious about the your attenuator, but I wouldn't have time to build one at present. Maybe someday...

 

[Cal Nevari]

First, let me say that this is intended as a discussion about passive attenuators, especially in the affordable “sub - $500” price range. While the active, re-amping units, such as the Fryette Power Station, BadCat Unleash, WAZA TAE, etc, etc, are wonderful devices, with many great features, they simply don’t fall into the intended discussion category and are not really attenuators, even if they are marketed as such.

Also, please understand that I really have no dog in this fight, other than being a very old guitarist who has been chasing a rather elusive means of taming the volume of amps that are simply too loud, when cranked to their tonal “sweet spot” while still retaining full range tonal characteristics, dynamic response and feel. While I do actually build “one off” attenuators for some folks, the small fees I charge (less than $5 an hour for my time) do not really qualify as a business. I simply want to share the liberation obtained through the use of a really great and simple, passive attenuator that won’t break most guitarists’ bank accounts. I also strongly encourage the DIY approach and am willing to actively assist with tips, diagrams, etc, for those who have at least some experience with the use of a drill, simple hand tools and soldering equipment. The cost for materials for DIY is between $100 & $150, depending on the sourcing, and a little less than $300 for me to assemble a simple one for you. Trust me when I say that putting together a cosmetically acceptable unit, while fairly simple and easy, is VERY time consuming, especially for a one off, first time build! If even the simplest of these units were produced commercially, the price would need to end up at $500 or more!

Bottom line here is that when it comes to “affordable” passive attenuators, there is the @JohnH design and then all the others! While MOST commercially available attenuators have proven themselves to be safe for use, within their stated design and use limits, sonically the @JohnH design is far superior in nearly every way, and there are many features, bells and whistles that can be fairly easily added to the build, if desired. Some of these features, I won’t do, as I’ve not found standards for them that I’m comfortable with, or implementing them becomes too complicated and/or more time consumptive than I want to deal with.

Now on to the myth that “All Attenuators Suck Tone!” Yes, although most attenuators will knock volume down, while allowing an amp to be cranked to its “sweet spot” almost all of them do indeed suck tone, response and feel as the volume goes down. How much these losses are perceived has a lot to do with how much of your targeted tone and sound is achieved by the direct interaction of a guitar plugged generally direct into an amp, as opposed to being created through multiple stomp/pedal/foot/thingies! And unfortunately, once the volume goes below a certain point, the capabilities of harmonic feedback become reduced, with any volume reduction method. With that said, the @JohnH design retains more of what we all want than any other unit out there!

Here's a link to the thread detailing DIY building of the @JohnH 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

Contact me privately for any assistance!

Rant Over!
Gene

Very cool! Thanks Gene!

Recently tried out the Bugera PS1 with my SV20C and it worked pretty well. Cost about $130.

 

[tmingle]

thanks for that information,

so the volume is controlled through the switch or a series of switches?

Im only using the attenuator for keeping home levels within reason. I do have the potentiometer on the bugera set where its goi to stay and make further adjustments on the amp.

for any studio or recording, I’m leaving that up to whatever Skunk tells me I’m playing, and playing through.

Mine has 3 DPDT switches. The 1st switch selects bypass or -7db. The 2nd & 3rd switches each add more volume reduction. Please see the photo in my earlier post. I also use an MXR 10 band eq in the loop to adjust the tone accordingly. You can also use the 10 band as a preliminary volume reduction. I don't lower the volume much here though. This is a very versatile setup & I am sure it will work for you. A properly constructed JohnH unit will last a lifetime.

 

[crossroadsnyc]

Gene, what wattage amps are you guys using these on? Do they have to be built specific to an amp, or could you use one with a variety of amps? For example, could you use the same attenuator on both a C5H as well as a YJM100?

 

[JohnH]

Hi @crossroadsnyc - the attenuators have a base spec intended for 50W amps - overdriven - maybe with a fan, but there's no change to the circuit for any amp up to that so they are intended to be versatile. For a 100W amp, we would double power ratings. Can still try it though with a smaller unit. If the components don't get too hot to touch for a few sec, then its all fine.

 

[Dogs of Doom]

Gene, what wattage amps are you guys using these on? Do they have to be built specific to an amp, or could you use one with a variety of amps? For example, could you use the same attenuator on both a C5H as well as a YJM100?

if you build it for the 100 watter, it will work w/ both...

The normal build is 50 watts. Not sure of the limits, but, it's perfect for the 20 watt SV & similar amp's. For the C5, you could go lighter, which would save a few bucks, but, having a 50 watter would be pretty indestructible w/ the C5.

I'm not that technical, but, IMO, you want anything after the speaker out to be pretty much fail-safe, or you're asking for catastrophe...

Better to build more robust, than skimp, that way you'll have less worries in function.

They can spec the units to any wattage/impedance, so, whatever you want, it can be done, but the higher wattage ones will be more involved, as the more power, the more heat that needs to be absorbed. The more heat, the more robust you want the absorbent materials (resistors) to be.

 

[crossroadsnyc]

Thanks to the both of you for the explanation. I’ve always been pretty pleased with the EPA on the YJM100, but I’ve read accounts of people using other attenuators on the amp with better results, so it’s something that’s been on my mind for many years. The reviews on the JohnH have been pretty spectacular, so I’ve been thinking that if I were to give this a go, that’s the direction in which I’m leaning.

 

[Gene Ballzz]

@crossroadsnyc

The price increase for the higher wattage resitors for a 100 watt build is not very significant, but add in the bigger enclosure, more robust switches, added heat control, and higher wattage choke coil and it does go up a bit! I have a 100 watt build, in a box, on the back burner, but have not realistically priced out the components yet, as I kinda bought in bulk. My ballpark, spitballin' guesstimate of component cost increase, from 50 watt to 100 watt, would likely be in the $60 to $100 range, maybe just a tad more, depending on the sourcing.

As for the 50watt units, unless size/space is crucial, I don't see much cost and/or labor benefit from building it for lower wattage. It might save $10-$15 or so in parts, but no labor savings at all! And then with lower wattage specced resistors, heat and its dissipation becomes an even more critical issue!

What base/native input impedance would you be looking for? Maybe you could be the guinea pig for my first 100 watt build? I believe the parts I have are for a 100 watt, 16Ω build, with both 16Ω and tonally compensated 8Ω outputs! Any further discussion of details would need to be done privately, as I'm not a business, instead just a guy who is passionate about sharing the benefits and liberations of this fantastic design that @JohnH has so diligently developed!

Just Thinkin'
Gene

 

[Gene Ballzz]

Cool to learn about this @JohnH DIY and will check it out.

Otherwise, I have tried and used so many attenuators over the years and have two current go-to’s. The re-amping Fryette Power Station and the passive Harley Benton PA-250, the latter you need to know about. This model has been available for just over a year and still carries the amazingly reasonable price tag of $133+shipping. Have only found available thru Thomann online store out of Germany. But even shipped totaled under $175.

Works at 8 or 16 ohms, has all of the useful attenuation features, but most importantly, sounds and feels excellent…as far as passive attenuators go. Like all passives, there’s a drop in high-end as you decrease to bedroom volumes. But at stage level, almost indiscernible.

The biggest discrepancy I’ve had with any attenuator is how it affects a clean signal. Many attenuators I’ve tried have not been capable of translating that stellar clean sound of a Marshall Super Lead, Hiwatt or Fender without introducing a slight fizzy crunchy or crackly artifact across the top of the signal. The Tone King models and the Rock Crusher both have this issue (to my ears at least), among others. Cranked distortion masks it. But as soon as you try for a clean tone it’s irritably apparent. Both of these units don’t have that issue.

Also deLisle’s attentuator design that he incorporates into his multi/amp switchers are really clean.

But for bang for the buck, the Harley Benton is unbeatable, except for possibly the @JohnH design, I’m assuming, as you are all describing.

Here’s the link in Thomann store:
https://www.thomannmusic.com/harley_benton_pa_250_power_attenuator.htm

Are you located in the states? I'd love to have an experienced, gigging player do a side by side shootout comparison of the 50 watt JohnH and that Harley Benton PA-250! Maybe I could arrange to temporarily send you one for that purpose, if you have time and/or inclination. Given that , IIRC, you have two identical SV20H rigs, there couldn't be a better and more simple/convenient comparison! If you love the JohnH you could buy it, or simply send it back to me, all on my dime, of course.

Let Me Know?
Gene

 

[[email protected]]

@JohnH & @Gene Ballzz : you should be proud of what you have done. When the internet was first invented this is the sort of things that people (and me!) hoped for it.

I had a look at the other thread, but only a few pages of it, and admire johnh’s engineering work, and Gene’s hands on application.

I just bought a DSL1CR. It is already very nice at low volumes, but I will soon try a volume box in the effects loop (cheap build). If that fails, or regardless of that, this attenuator build sounds exciting, even if I am not great with a soldering iron.

I have a question, and maybe John already replied on the other post - which I will read through the next days / weeks. Why the -7 dB reactive and the rest resistive? And would there be other higher attenuation reactive first step possible build?

My interest is apartment playing, so practical volumes are 65-75 dB (I know, that is very low), and I’d like to crunch the clean channel of the dsl1.

Once again, brilliant work on this. So kind of you!