Simple Attenuators - Design And Testing

[colchar]

This thread is amazing. Even for someone like me who is functionally illiterate when it comes to electronics, it is amazing to read through all of this and to see the collaborative efforts and the community spirit (becoming much more rare these days!).

I am going to have a chat with someone here about one of these units, but wanted to ask a couple of quick questions here before speaking to him in person (it will help make me sound less of an idiot and he won't have to give me the 'For Dummies' explanations if I can tell him exactly what I want).

I only play at home, and never record so I only need an attenuator with no other functionality.

1) Is it possible to get a unit that works with more than one impedance? I am currently using a Hughes & Kettner 2x12 with V30s, which is a 16ohm cab. But I might want another cab at some point so was wondering if I could have that factored into a build now, or if it would necessitate another attenuator later?

2) I am currently using an Orange AD30 (I also have one vintage and one modern Traynor combos) and am very happy with the amp. It has master volumes, but I want to be able to push the power tubes to open the amp up. I cannot ever see myself diming the thing, it would likely only be played at 50%-75% of its volume. But I will be buying another head at some point so wanted to factor that into the attenuator build. I am currently thinking of grabbing an SC20 or SV20, but am open to other Marshall heads - if a 50 watt JMP, Vintage Modern, or JCM800 was to come along I'd snap them up. Then again, with a good attenuator maybe a Class 5 would be enough since I'd be able to turn it up nice and loud while controlling it with the attenuator.

But basically what I want to ask here is whether a 50 watt version of the attenuator will be enough for the amps I have mentioned? Even if I pick up one of the Marshall 50 watters mentioned above I cannot see myself diming it, and would only play it at 50%-75% of its volume.

3) Since I know bugger all about electronics, is there anything else I should be thinking about or is everything pretty much covered?

Thanks in advance.

 

[PelliX]

1) Is it possible to get a unit that works with more than one impedance? I am currently using a Hughes & Kettner 2x12 with V30s, which is a 16ohm cab. But I might want another cab at some point so was wondering if I could have that factored into a build now, or if it would necessitate another attenuator later?

Multiple options. You could have one with multiple impedence circuits, but you could also abstract the cab's impedence entirely and not let the amp ever notice a difference. Perhaps have an 8 and a 16 Ohm input - maybe just one of the two for simplicity. Then you could in reason attach any impedence cab. If you don't go absolutely insane with it you might just simply end up with a bit less volume than expected. (Simple version).

2) I am currently using an Orange AD30 (I also have one vintage and one modern Traynor combos) and am very happy with the amp. It has master volumes, but I want to be able to push the power tubes to open the amp up. I cannot ever see myself diming the thing, it would likely only be played at 50%-75% of its volume. But I will be buying another head at some point so wanted to factor that into the attenuator build. I am currently thinking of grabbing an SC20 or SV20, but am open to other Marshall heads - if a 50 watt JMP, Vintage Modern, or JCM800 was to come along I'd snap them up. Then again, with a good attenuator maybe a Class 5 would be enough since I'd be able to turn it up nice and loud while controlling it with the attenuator.

But basically what I want to ask here is whether a 50 watt version of the attenuator will be enough for the amps I have mentioned? Even if I pick up one of the Marshall 50 watters mentioned above I cannot see myself diming it, and would only play it at 50%-75% of its volume.

Hmmm, I'd go over spec. What if a 100-watter comes your way and you need to tickle its sweet spots? 100W rating for anything up to 50W and 200W rating for the 100W high gain amps... also depends on how much attenuation you want to apply of course. The more 'drop' you introduce, the more power is 'soaked up' and must thus be dissipated. Technically that would imply that a 10W attenuator would suffice for 10% attenuation on a 100W amp, but that's not how it works. The safety margin of a factor of 2 is really not as overkill as it might appear.

3) Since I know bugger all about electronics, is there anything else I should be thinking about or is everything pretty much covered?

A bypass switch seems a welcome option in most scenarios, perhaps?

 

[Gene Ballzz]

This thread is amazing. Even for someone like me who is functionally illiterate when it comes to electronics, it is amazing to read through all of this and to see the collaborative efforts and the community spirit (becoming much more rare these days!).

I am going to have a chat with someone here about one of these units, but wanted to ask a couple of quick questions here before speaking to him in person (it will help make me sound less of an idiot and he won't have to give me the 'For Dummies' explanations if I can tell him exactly what I want).

I only play at home, and never record so I only need an attenuator with no other functionality.

1) Is it possible to get a unit that works with more than one impedance? I am currently using a Hughes & Kettner 2x12 with V30s, which is a 16ohm cab. But I might want another cab at some point so was wondering if I could have that factored into a build now, or if it would necessitate another attenuator later?

2) I am currently using an Orange AD30 (I also have one vintage and one modern Traynor combos) and am very happy with the amp. It has master volumes, but I want to be able to push the power tubes to open the amp up. I cannot ever see myself diming the thing, it would likely only be played at 50%-75% of its volume. But I will be buying another head at some point so wanted to factor that into the attenuator build. I am currently thinking of grabbing an SC20 or SV20, but am open to other Marshall heads - if a 50 watt JMP, Vintage Modern, or JCM800 was to come along I'd snap them up. Then again, with a good attenuator maybe a Class 5 would be enough since I'd be able to turn it up nice and loud while controlling it with the attenuator.

But basically what I want to ask here is whether a 50 watt version of the attenuator will be enough for the amps I have mentioned? Even if I pick up one of the Marshall 50 watters mentioned above I cannot see myself diming it, and would only play it at 50%-75% of its volume.

3) Since I know bugger all about electronics, is there anything else I should be thinking about or is everything pretty much covered?

Thanks in advance.

FIRST> Concerning attenuator input/amplifier output impedance. It is totally doable to have multiple options here, but it gets kinda complicated, not so much in the building, but in usage. Current designs start with a base impedance (16Ω, 8Ω or 4Ω) and then use resistors and an added coil for modifying that input impedance. The down side is that deviation from the "base" impedance increases attenuation, by a couple/few db. It also opens the door for operator error in showing your amp's output the wrong impedance. My recommendation is choosing and sticking with one specific input impedance! In your case, I'd likely suggest a 16Ω based unit.
NEXT> As far as output impedance, the amp will only "see" generally the impedance of the attenuator and using different impedance speakers will only affect the input in minuscule amounts. Totally safe for the amp. The tone will be slightly affected, however, when deviating from the "base" impedance. Both the 16Ω and 8Ω designs incorporate extra, gently compensated outputs, to preserve the tone.
FINALLY> Of important note, whenever using a speaker load that is different than the input impedance, a bypass switch should never be activated! Also important to remember that a bypass switch should never be toggled without first turning the amp off or into standby mode!

Hope This Helps?
Gene

 

[donwagar]

I am going to have a chat with someone here about one of these units, but wanted to ask a couple of quick questions here before speaking to him in person (it will help make me sound less of an idiot and he won't have to give me the 'For Dummies' explanations if I can tell him exactly what I want).

When I built mine, I had to ask John a lot of dumb questions. He was excellent in explaining stuff that I didn't understand. Don't ever feel bad about asking.

As I understand it, someone will correct me if I'm wrong, lol, match the ohms of the attenuator to the head. Protect the OT. Don't worry about the speaker impedance. If all your heads have a 16 ohm out, I'd go for that as Gene suggested above.

50 watt is probably good. If you do someday buy a JTM 50 or 100 Watt, well, they are a different deal IMO, double spec a new attenuator for them (by that I mean if it's a 50W JTM buy a 100W attenuator).

When you say a vintage Traynor, you aren't talking about a YBA-1 are you? Even though they are rated, I think, about 40W, I'm sure dimed they push way more than that. If so, you might want to order a 100W right off the bat.

BTW I played through a YBA-1 one night, dead stock, attenuated and dimed. It was glorious.

 

[Gene Ballzz]

There are no "dumb questions" when researching an investment of time, $$$, and/or labor for a device to allow cranked use of an amp (without vaporizing small pets and children, at 10 paces) and properly protecting your amp while doing it! These attenuators are the coolest thing since sliced bread, for those of us who love that "cranked amp" sound, without compromises!
Simple Attenuatin'
Gene

 

[JohnH]

hi @colchar , all good advice posted above!
If you can identify an amp output impedance that will work across the amps that you have or might like, then you can build an M2 for that, and the attenuator can let you run either 8 or 16 Ohm cabs safely, and with good tone. If you like heads, I think most of them will drive 16 or 8. My Vintage Modern is a combo, which only does 8 or 4, so I build 8 for myself since it works for both my amps.

Good luck and keep calling in here!

 

[Gene Ballzz]

Hi @JohnH ,
I searched, page by page for your "dual" design and somehow couldn't find it! Do you recall page or post number?
Thanks,
Gene

 

[JohnH]

Hi Gene, no prob, I'll post the double-barrel one again when I get on a computer.

 

[JohnH]

Hj @Gene Ballzz Here's the double version, described in post #1731 on page 87



There's a couple of ways to do this, depending whether each half is an 8 or a 16 ohm circuit.(8 ohm halves shown here) It's also possible to do 4, 8 and 16 out of two 8 ohm circuits, but switches with the right poles and rating are rare/expensive.

 

[colchar]

When I built mine, I had to ask John a lot of dumb questions. He was excellent in explaining stuff that I didn't understand. Don't ever feel bad about asking.

As I understand it, someone will correct me if I'm wrong, lol, match the ohms of the attenuator to the head. Protect the OT. Don't worry about the speaker impedance. If all your heads have a 16 ohm out, I'd go for that as Gene suggested above.

50 watt is probably good. If you do someday buy a JTM 50 or 100 Watt, well, they are a different deal IMO, double spec a new attenuator for them (by that I mean if it's a 50W JTM buy a 100W attenuator).

When you say a vintage Traynor, you aren't talking about a YBA-1 are you? Even though they are rated, I think, about 40W, I'm sure dimed they push way more than that. If so, you might want to order a 100W right off the bat.

BTW I played through a YBA-1 one night, dead stock, attenuated and dimed. It was glorious.

No, I don't have a YBA-1. I have a YGL 3, which was their version of a Twin. Actually, it was known as the Twin Reverb killer.

And yeah, the wattage on vintage Traynors was at best a guess most of the time as models like the YBA-1 were waaaaaaaay louder than their listed wattage would indicate.

 

[colchar]

hi @colchar , all good advice posted above!
If you can identify an amp output impedance that will work across the amps that you have or might like, then you can build an M2 for that, and the attenuator can let you run either 8 or 16 Ohm cabs safely, and with good tone. If you like heads, I think most of them will drive 16 or 8. My Vintage Modern is a combo, which only does 8 or 4, so I build 8 for myself since it works for both my amps.

Good luck and keep calling in here!

I looked into it today and all of the amps I mentioned in my previous post are 16ohm, and they can also be run at 8ohm (not sure about the Class 5 on that one but I would likely go for one of the other amps anyway). So a 16ohm verison of the attenuator would work fine for me.

I probably should have checked that before my previous post.

I was also wondering if this attenuator is resistive or reactive? Not that it really matters as I don't know enough about this stuff to have an opinion either way and will trust the expertise of everyone else in this thread, I am just trying to learn a wee bit more about attenuators as I go along here.

 

[Gene Ballzz]

I looked into it today and all of the amps I mentioned in my previous post are 16ohm, and they can also be run at 8ohm (not sure about the Class 5 on that one but I would likely go for one of the other amps anyway). So a 16ohm verison of the attenuator would work fine for me.

I probably should have checked that before my previous post.

I was also wondering if this attenuator is resistive or reactive? Not that it really matters as I don't know enough about this stuff to have an opinion either way and will trust the expertise of everyone else in this thread, I am just trying to learn a wee bit more about attenuators as I go along here.

These units are both resistive and reactive. The reactive part surrounds the choke coil in the always on first stage of -7db, as well as how the speaker "reacts" to the unit!

A 16Ω based unit is excellent for your situation! Should you at some time find that the "always on" -7db stage is too much volume reduction, you can simply set/use the amp for 8Ω operation and use the attenuator (all stages active) in parallel with the 16Ω speaker load, for a -3.5db cut, while retaining the reactive nature of the attenuator circuit. FWIW, I've rarely found -3.5db to be preferable to -7db, except for testing and experimentation. Although, when using this attenuator with my Class5 or 13 watt 5E3, it CAN be a toss up! The designed -3.5db steps are really quite small and although audible, they are not drastic, from "one to the other!" (A little Twilight Zone reference/quote there, for those so inclined.)
Simply Buildin'
Gene

 

[PelliX]

Hj @Gene Ballzz Here's the double version, described in post #1731 on page 87

View attachment 112001

There's a couple of ways to do this, depending whether each half is an 8 or a 16 ohm circuit.(8 ohm halves shown here) It's also possible to do 4, 8 and 16 out of two 8 ohm circuits, but switches with the right poles and rating are rare/expensive.

... is it just me, or should this be called the Hewittzer?

 

[Gene Ballzz]

... is it just me, or should this be called the Hewittzer?

That may well be an appropriate model name for a +100 watt, "double barrel" with all the bells and whistles,, multiple imedance in/out, line out, headphone out, fans, etc, ad nauseam…….
Thanks For Playin' Along Here!
Gene

 

[JohnH]

... is it just me, or should this be called the Hewittzer

LOL, yeah maybe but...really just NO!

 

[Gene Ballzz]

LOL, yeah maybe but...really just NO!

Yeah, upon further consideration, maybe naming an attenuator as something that explodes and/or blows things up is less than ideal!

Still Kickin'
Gene

 

[colchar]

One more question (yeah, I know I could search through 14762 pages and find the info, but I've got a rye & coke in my hand, it ain't my first tonight, and I just don't feel like doing that search!!!) - do these attenuators come down in steps or do they have dials like a volume pot so that they can be dialed in?

 

[PelliX]

One more question (yeah, I know I could search through 14762 pages and find the info, but I've got a rye & coke in my hand, it ain't my first tonight, and I just don't feel like doing that search!!!) - do these attenuators come down in steps or do they have dials like a volume pot so that they can be dialed in?

Take your pick, but generally a knob is included in the design. Although the knob works in a similar fashion to a regular pot, it's called a rheostat or L-pad. Same concept, beefier.

 

[Gene Ballzz]

Take your pick, but generally a knob is included in the design. Although the knob works in a similar fashion to a regular pot, it's called a rheostat or L-pad. Same concept, beefier.

Sorry Sir,
But those are the crappy attenuators that don't pay attention to the critical balance of series and parallel resistance in the attenuator and have very little in common with the @JohnH design and generally sound like DOO-DOO and destroy the natural feel and response of the amp! And while yes, the JohnH principal could certainly be developed into a unit with a "continuous knob" control, the technical logistics would be very complicated and cost prohibitive. I swear to all that is holy in rock/guitar/music, the small steps of this attenuator design present no realistic issue! The standard M2 design provides ten small steps between full amp volume and babby sleeping in the next room volume! If retaining all tone, sound, dynamics, feel and response, with truly continuously variable volume control, one needs to step up to a rea-amping unit, like a Fryette, UA Ox, etc, along with the price and operating nuances! I'll take the JohnH all day, every day!

And @colchar , you really should give me a call! Real, human to human conversations can cover a lot more ground than typed messages on a discussin board and in a shorter time frame!

Also Just Sippin'
Gene

 

[PelliX]

With all due respect, a rheostat is simply a variable resistor. I see your concern with regards to the notion of just having a 'zero to full' attenuation range on the rheostat, but I've encorporated them for the 'fine control' in designs without issues. Will there be a tonal response difference across the dial? Sure, to a degree, depending on the rest of the circuit.

Or am I missing something here?