Does anyone know of a easy attenuator circuit?

[daz]

I really would like to build something i can make with parts i can get locally and relatively inexpensively and is fairly simple. But if i have to go online for parts i would. I don't need something that will allow me to turn the amp to 10. I just want to get the output of my 2XEL34 marshall like design to the point i am getting maybe 20% or so of my OD from the PA and use my cascaded pre to add whatever amount of gain i need after that, and do it at home levels. The purpose is to get a little more clean dynamics when i turn the guitar down then i get now with only preamp OD.

[Chuck H]

I'm sure I've posted this before... The design is ohm load specific. If you want to represent a 4 ohm load cut the resistances in half. Double them for a 16 ohm load.

Mount the resistors with thermal paste to the inside TOP of an aluminum box and don't crowd them.

[John_H]

Check this out L pad calculator - attenuation dB damping impedance decibel loudspeaker speaker voltage divider - sengpielaudio Sengpiel Berlin

[John_H]

An easy one is for 8ohm@ 6db attenuation. All you need is an 8ohm, and a 4ohm resistors.

[tedmich]

something like this with a bright switch could work
DIY Attenuator - My Guitar Projects

I assume any given variable L pad can handle about 1/2 its "rated wattage" and needs good cooling anywhere near there

[Chuck H]

something like this with a bright switch could work
DIY Attenuator - My Guitar Projects

I assume any given variable L pad can handle about 1/2 its "rated wattage" and needs good cooling anywhere near there

It should probably be noted that there seem to be multiple definitions for "L-pad". One is just a rheostat with a log taper and doesn't offer anything over a standard rheostat beyond seemingly more intuitive settings. The OTHER L-pad is an atrocious thing with an onboard active load simulation circuit. They sound awful. Much worse than a strictly resistive load. And they are commonly rated at wattages much higher than they could ever handle from a tube amp with potentially dangerous consequences. Avoid them.

My point is that, with the exception of taper, rheostat = L-pad. So you can substitute one for the other for any of these circuits if it pleases you. If you can live with the less intuitive taper a common rheostat will cost a lot less too.

FWIW the above L-pad circuit is probably the simplest but has two drawbacks I eliminated in my design. One is that the load impedance on the amp (with the above example) varies from 5.5 ohms to 16 ohms when plugged into an 8 ohm speaker and varies from 8 ohms to 16 ohms plugged into a 16 ohm speaker. Probably "safe enough" but I wanted better. My circuit, when matched to the rated load (let's use the 8 ohm circuit) varies from about 6 ohms to 9.5 ohms. The other problem with the standard L-pad circuit is that half the load is always being carried by the attenuator and, being a purely resistive load, attenuated greater than half the amps power even when set full up. So stage volume versatility is very limited. My circuit has less than 2dB cut when full up so there is the possibility for more subtle attenuation levels. IMHO my circuit isn't complicated enough to warrant using the normal and clumsy standard L-pad type circuit with it's inherent drawbacks instead.

[Tom Phillips]

It should probably be noted that there seem to be multiple definitions for "L-pad". One is just a rheostat with a log taper and doesn't offer anything over a standard rheostat beyond seemingly more intuitive settings. The OTHER L-pad is an atrocious thing with an onboard active load simulation circuit...

Well, there is a at least one more definition of an L-Pad which, I believe, is the traditional variable speaker L-Pad that uses a parallel and series variable resistances in an "L" configuration. Two rheostats are mounted on one control shaft. As one increases in resistance, the other decreases, thus maintaining a constant load on the amplifier while passing variable power to the speaker. They were commonly used as volume controls for Hi-Fi extension speakers installed in rooms of a house remote from the main amplifier and speakers. Unfortunately, they do alter the attenuated sound because the impedance of a real speaker does vary with frequency.

[Chuck H]

Yup. I never see those outside of "salvage" electronics places anymore. You CAN buy dual ganged rheostats but they're aren't marketed as L-pads. You can, of course, use them as you describe for guitar amps and they work just dandy. Though they still have the disadvantage of over half the load going to the attenuator instead of the speaker even set full up. hat's why I didn't go that route with my attenuator. In the case of home speaker systems and the like I've seen mostly the dynamic impedance type L-pad, for which they work very well. WRT guitar amps they do more tonal harm than good even compared to a purely resistive load.

[nickb]

Hey Chuck - maybe I'm missing something -could you post a schematic of your attenuator?

No matter which way I arrange things I don't seem to come out with anything that matches your impedances. In fact, it looks like the wiper can put the 1 ohm right across the amp.

Thanks.

[daz]

I've tried a 8 ohm 100w L-pad and resistive attenuators via that L-pad calculator. They both ruined the tone in a big way. Chuck, yours looks like a combo of the 2. Why would it work any better?

[Chuck H]

Maybe I've arranged the diagram incorrectly compared to the schematic (and actual circuit). I'll look it over for mistakes again and repost.

EDIT: Good catch! I just had the jacks labeled wrong. I corrected the diagram in post 2. Here's a schematic.

[Chuck H]

All I can attest to is the listening. I've used a reactive L-pad type attenuator and I've used a simple shunt/series type circuit. My own attenuator actually has a dynamic load as the resistance (a combination of inductors, capacitors and resistors conceived by R. Aiken to simulate the impedance dynamics of a typical 4x12 Marshall cab). But I do have a customer with the simple resistive circuit version built in to his amp and it sounds great. WRT attenuators there is always going to be some compromise at the lowest volume settings. The same can be said of any volume reduction circuit. Chalk it up to Fletcher/Munson curve or whatever. Facts of life.

[daz]

Maybe i'll get the L-pad out again and play with it more and add some brightening to it. Although i tied that before with no success. Never did spend a lot of time with it tho so maybe i should. I'm just a little worried about using the amp cranked high enough to get output breakup with a L-pad.

[Chuck H]

Maybe i'll get the L-pad out again and play with it more and add some brightening to it. Although i tied that before with no success.

Finding what DOESN'T work and doing it again and again has never worked for me. But for some reason I keep doing it

Never did spend a lot of time with it tho so maybe i should. I'm just a little worried about using the amp cranked high enough to get output breakup with a L-pad.

Two things. First, you DID ask for a simple circuit with the most accessible parts. That doesn't offer much room for more ambitious circuits that may sound better. I mentioned that my own attenuator uses a dynamic impedance circuit instead of a simple resistor. I really can't complain. It sounds as good as I could hope.

Second, what is the nature of your L-pad. Three different models were discussed. Perhaps we can comment on the safety of your circumstances if we know all the information.

[daz]

Well now i know why i was afraid to turn it up....it's a 50w pad. It's 8 ohm which is good, but i remember now thats why i never used it turned up much. 50w ain't gonna get me safely to a point where the output is starting to crunch.

As to simple and easily available, i should clarify that. I should have said a GOOD attenuator with preferably locally available parts and simple as possible. Put it this way....it like some of them it has a bunch of hard to find parts and they are fairly expensive even when i do find them, i may as well just buy a attenuator. It's gotta work better than simple resistive ones like that calculator because that thing is just worthless. Totally ruins tone.