Simple Attenuator Thoughts

[dbishopbliss]

I recently build a VOX AC15 as well as refurbished a Silvertone 1482. I'm happy with both amps but they are much louder than I require. At band practice I can barely get the volume above 1 and people are complaining that I am too loud. If I turn the volume down then the tone gets really thin and there is no overdrive harmonics just breaking up character (whatever you want to call it) that I like.


I have a cheap commercial attenuator (Jet City) that decreases the volume but it seems to impact the tone and feel of the amp. I believe it is resistive only. A friend suggested I needed a "reactive" attenuator. After reading about a number of commercial offerings I can across a DIY design found on another forum with 80+ pages of information and positive responses. I build the "M2" design that does not have the bass resonance circuit.


If you buy parts off of that big auction site, then it can be built for around $50. Unfortunately, the shipping from China these days estimates delivery to be mid-August so I paid the extra money and bought the resistors from Mouser. I was able to get a US made enclosure and the jacks, switches and inductor from Parts Express. Total ended up being about $80 for everything.


While most of the builds in the thread have enclosures with lots of holes, etc. I just installed the resistors in the enclosure to see what would happen. Ends up that my lower power amps don't need the extra ventilation. I was able to use the attenuator at band practice for 3 hours without it getting warm at all. I was able to play along side the drummer, bass and guitar without any issues. I adjusted the amp's controls for the tone I wanted and then engaged the attenuator. All I needed was about 10dB reduction for people to stop complaining. :-D


I'm wondering if anyone else has built this attenuator or something similar (I think it was really just an evolution of the Aiken attenuator). What are your thoughts? I'm pretty happy for a simple cheap solution to my volume issues.

[shooter]

fwiw
I like my version of the 1482 also, I did 2 builds in one really, used 6K6 and a 12AU7 to get the volume down.  You do have to re bias but 2 R's and it's done.
when I want louder, barn volume, slap in an AX, 6V6's, couple R's, and it's annoy the neighbors time 

[dwinstonwood]

That looks like a really cool project dbishopbliss. Great job. I also found that the AC15 I built was too loud to play in the evenings where I live. I thought about trying to build an attenuator from plans online, but caved and bought a Weber Mini Mass for about twice what you spent.

[Pick-n-Strum]

I'm wondering if anyone else has built this attenuator or something similar (I think it was really just an evolution of the Aiken attenuator). What are your thoughts? I'm pretty happy for a simple cheap solution to my volume issues.

No - but I've been wanting an attenuator for a while!  I think I may make this my next build...Yours looks great - I'm going to have to read through the other thread to try and understand better but thanks for making a thread on this!

[pullshocks]

I'm wondering if anyone else has built this attenuator or something similar (I think it was really just an evolution of the Aiken attenuator). What are your thoughts? I'm pretty happy for a simple cheap solution to my volume issues.

Just tried out my newly built M2 attenuator for the first time today.  Never tried an attenuator before, did not know what to expect. 


It works.  With my amp on 4, the attenuator takes the SPL from 85-90 down into the 60s and below.  It is a different sonic experience, but after I got used to it, it's like listening to a record at lower volume...tone is "there" though  the listening experience is different.


You are right, not much heat produced.  I added ventilation holes, but they are not really needed.


Thanks to John H for posting the circuit, and thanks to Dummyload's ultracool STAC web site for inspiration on building the enclosure.  No CNC in my shop, so the metalwork is much cruder his.

[dbishopbliss]

Looks like we are on the same forums. I'm not aware of the STAC website. Please provide a link.

[pullshocks]

Well, it looks like they have the site down for revision (hopefully to add more cool stuff), but here is the adddress:


South Texas Amp Co. (sotxampco.com)

[tubeswell]

I'm wondering if anyone else has built this attenuator or something similar (I think it was really just an evolution of the Aiken attenuator). What are your thoughts?

The modern Fender Eric Clapton series amps (EC Tremolux/Twinolux) use simple arrangements of wire wound 25W cement resistors in series parallel with the speaker, that are switched with the 1/4-power switch etc

[jjasilli]

I had the same vol problem as you, with amps in that power range.  One solution is to tilt the amp back, or put it up on a chair or something so that it blows directly at your ears.  Otherwise it can be way too loud for others, while you can barely hear it.


For an attenuator I built this,  It's simple & works great for me.

[mcamelo]

I'm wondering if anyone else has built this attenuator or something similar (I think it was really just an evolution of the Aiken attenuator). What are your thoughts? I'm pretty happy for a simple cheap solution to my volume issues.

I've built an M2 6 months ago which I use with a 18W Marshally amp. Works like a charm and I can't notice any significant degradation in tone from the amp as long as the speakers are being pushed around hard enough. I wish I had picked a better enclosure as I hate the extra footprint of the bottom cover. I did at a general kill switch, which I do recommend for the convenience. Agree that no vent holes are necessary when used with an 18W amp.

I like it so much, in fact, that I will build one right into my next amp's circuit.

[Joel]

I built a pair of the M2's last year (My build report and pics are buried somewhere on the Marshall forum thread - around pages 50's or 60's).

The attached pics show some gut shots of my build (pics 1 & 2).  Pic 3 is the closed box.  The final pic show the pair installed in the music room of my house, one for the Hoffman single channel Deluxe Reverb, and one for the JTM45 clone.  My enclosure is steel, hence the vertical mounting of the coil.

These are great attenuators.  I have a much better low volume playing experience when using these and I highly recommend them.  I cranked my JTM45 clone for about an hour and the attenuator did get noticeably warm.  But since I prefer the sound of the amp on the clean side it's very rarely turned up - so no worries about stressing the amp or attenuator. 

[dbishopbliss]

Those are nice looking enclosures. I've been looking for something with a little more space so I can try/compare the M3 circuit. The enclosure I used is nice and compact, but there is no way I can get another inductor and capacitor in there.

[FranciscoPerez]

Wow thanks for starting this thread. I've been tempted to build an attenuator for some time now, and will probably try this!

I'm reading through the other thread you posted, but could I just halve all values and make a 4ohm version? I will be using this mostly in 4ohm cabs.

[jjasilli]

IMHO all that power soaking isn't needed for amps 50W and under.  A simple L-pad will do.  N.B.: figure that an amp in power tube overdrive will "put out" 2X its nominal, rated wattage.  So, spec L-pads or fixed R's accordingly: a 50W L-pad for amps 25W and under; 100W L-pad for amps up to 50W. For amps above that I'd use power soaking R's. 

[dbishopbliss]

IMHO all that power soaking isn't needed for amps 50W and under.  A simple L-pad will do.  N.B.: figure that an amp in power tube overdrive will "put out" 2X its nominal, rated wattage.  So, spec L-pads or fixed R's accordingly: a 50W L-pad for amps 25W and under; 100W L-pad for amps up to 50W. For amps above that I'd use power soaking R's.

I need to dig out my Jet City and compare it side by side. If I recall, it is essentially an L-pad.

[Joel]

IMHO all that power soaking isn't needed for amps 50W and under.

You're correct.  However, it's not just about power soaking.  The premise behind this design is to tailor the reflected impedance of the attenuator to approximate that of a speaker as simply as possible.  There is some good info on the thread linked in the original post.  The first post of that thread used to be updated with links to specific pages with design updates and analyses.

[jjasilli]

However, it's not just about power soaking.  The premise behind this design is to tailor the reflected impedance of the attenuator to approximate that of a speaker as simply as possible
That's exactly the function of an L-pad.  I'm a ware of the fixed R method; nothing wrong with it.

[dbishopbliss]

I bought these push button switches for my next attenuator. The chassis has a thick front plate so regular switches don't have enough thread. They require a 3V to light up the LED. It seems they are always on when voltage is applied. I was hoping they lit up only when latched.


Is there a way that I could use the speaker output voltage to light up the LED?


https://www.parts-express.com/SPDT-Latching-16mm-Stainless-Steel-Tamper-Waterproof-Raised-Push-Button-Switch-with-Blue-Rin-060-958

[sluckey]

The LED operation is totally separate and independent  from the switch operation.

https://www.parts-express.com/pedocs/tech-diagrams/060-958-spst-no-momentary-16mm-stainless-steel-switch-technical-drawing.pdf

[acheld]

Looks pretty cool.   You could add a dropping resistor from the heater circuit if needed, but it looks like there is a resistor in the circuit already. 

I normally use big, fat Carling switches, but would consider something like this.   

[dbishopbliss]

The LED operation is totally separate and independent  from the switch operation.

https://www.parts-express.com/pedocs/tech-diagrams/060-958-spst-no-momentary-16mm-stainless-steel-switch-technical-drawing.pdf

Yeah, I see that now. When using my meter to check continuity the LED would light up. I was wondering if I could connect one leg of the LED to the center of the switch and the other to the "pushed in" side of the switch so that it would only light up when it was on. But I'm pretty sure the voltage would be too high for the 3V LED.


Am I right?

[dbishopbliss]

Looks pretty cool.   You could add a dropping resistor from the heater circuit if needed, but it looks like there is a resistor in the circuit already. 

I normally use big, fat Carling switches, but would consider something like this.

I was going to use the Carling switches (I have them), but the thread is too short for the front panel of the enclosure I'm using. The push button switches have plenty of space... plus they will look cool.

[acheld]

I think a 30K 1W resistor to common might do the trick.

You should double check my calculations, however.

[PRR]

> use the speaker output voltage to light up the LED?

The speaker is not always speaking.

Do you want to switch the speaker? Or the lamp?

If you gotta switch both, now you are into a relay. And a power supply.

Which is a lot to manage if your real problem is a thick front panel.

[dbishopbliss]

Which is a lot to manage if your real problem is a thick front panel.

Nevermind... I will just add a battery pack and a switch on the back to light up the LEDs and have them always on. Make them easy to see in the dark.