Two simple plug-in attenuators

[zhyla]

Personally, I'm over the moon w/ my PS1 attenuator.

I got one of those when they were $50 recently and it’s not bad, but the reactive attenuator I just built you can’t tell it’s there at all. Likely giving my PS1 away soon.

 

[johnDH]

The idea on this thread is good, and Ive worked with it too. Above is my version, to create an 8 Ohm load. The values are worked out by Spice simulation to give as close a match to a real 12" Celestion as I could get. The 22Ohm resistor helps with that and also adds stability at very high frequencies on some amps, My one is ok for about a 40-50W amp, where its the only load taking full power. Use it with a 8 Ohm speaker in parallel, as described in this thread, and its a -3dB drop and it takes 1/2 the power.

This circuit can give a good match to a real cab at low mid freqencies up. What it doesnt address is the low-end resonance that most cabs have. But to deal with that needs another much larger coil and a large non-polar cap, which are heavy and expensive. And it doesn't make much real difference since the resonance only affects the tone if you play on a small number of very low notes, eg around open low A in a closed back cab, or for and open cab such as most Fenders, around low E.

(BTW, my main work on this topic is based on the M2 Attenuator on the Marshall forum. The circuit posted above was developed as an add-on stage to help convert between input impedances.)

 

[Antoon]

I don't understand what your impulses are and whats is the difference between air and ferrite cores?

Now when your "power soak" is parallel with loudspeaker then when power output frequency is within loudspeaker resonance peak range the power soak will use most of the power. Loudspeaker still use the power what is available from actual output voltage. I think thats about what you wrote earlier?

When only speaker is used and when it resonate its impedance increase and this might increase tube amp output voltage and this slightly compensate the power drop.

I do not think i have to cope with the resonance frequency. All notes i play are above that. I believe the reason people use air core inductors is that they pass impulses unaffected because there is no core to magnetize. Whereas an actual speaker voice coil has a big iron "core", which would be the magnet pole.

 

[Antoon]

View attachment 1084367

The idea on this thread is good, and Ive worked with it too. Above is my version, to create an 8 Ohm load. The values are worked out by Spice simulation to give as close a match to a real 12" Celestion as I could get. The 22Ohm resistor helps with that and also adds stability at very high frequencies on some amps, My one is ok for about a 40-50W amp, where its the only load taking full power. Use it with a 8 Ohm speaker in parallel, as described in this thread, and its a -3dB drop and it takes 1/2 the power.

This circuit can give a good match to a real cab at low mid freqencies up. What it doesnt address is the low-end resonance that most cabs have. But to deal with that needs another much larger coil and a large non-polar cap, which are heavy and expensive. And it doesn't make much real difference since the resonance only affects the tone if you play on a small number of very low notes, eg around open low A in a closed back cab, or for and open cab such as most Fenders, around low E.

(BTW, my main work on this topic is based on the M2 Attenuator on the Marshall forum. The circuit posted above was developed as an add-on stage to help convert between input impedances.)

I was under the impression that everybody on this section of the TDPRI also read your epic thread about attenuators on the Marshall forum. Do you think an iron or ferrite core inductor would be better as a parallel load? An iron core inductor may resemble an actual speaker better. Also curious about the 20 ohm resistor. May give that a try. Does it have to be a high power resistor?

 

[johnDH]

I use the aircore inductors for this coil, representing the rise in impedance with frequency, based on advice by Randall Aiken, who wrote about reactive load boxes. The reason is that an aircored Inductor can't saturate, and always maintains its value when driven. Plus they are fairly simple and easy to buy. The 22ohm resistor can also heat up, but not as much as the main resistor. I think the max it could take is about 1/4 of total power, then put a factor of 2 or 3 on that.

 

[Len058]

my main work on this topic is based on the M2 Attenuator on the Marshall forum.

Thank you very much for the design. I've built the M-lite and I really like it!

 

[Antoon]

I use the aircore inductors for this coil, representing the rise in impedance with frequency, based on advice by Randall Aiken, who wrote about reactive load boxes. The reason is that an aircored Inductor can't saturate, and always maintains its value when driven. Plus they are fairly simple and easy to buy. The 22ohm resistor can also heat up, but not as much as the main resistor. I think the max it could take is about 1/4 of total power, then put a factor of 2 or 3 on that.

Perhaps I will experiment by sticking a piece of iron inside the coil while playing, and listen for any difference. Obviously the inductance would multiply when I do but also the pulse behavior of the parallel speaker will change. I expect the iron piece will vibrate with the low frequencies once stuck inside the coil and the firmer I will hold the piece in its place, the punchier the speaker will sound, I expect. We will see ;-)

 

[Supertwang]

Very smart but Personally & IMHO,...I'll stick with turning down the guitar output volume when playing amps 25 watts or less like Deluxe Reverbs. For the amps 35 watts and above I reccy a PPIMV,...Post Phase Inverter Master Volume. The problem with attenuators is the output transformer is getting worked too hard esp on vintage amps. Attenuators can really heat up the OPT. Most of the "tube tone" comes from the preamp tubes although I know there is a sound from output tubes really cooking that we all love,...that's why I prefer @ a 10 watt amp

 

[JFrankParnell]

I use the aircore inductors for this coil, representing the rise in impedance with frequency, based on advice by Randall Aiken, who wrote about reactive load boxes. The reason is that an aircored Inductor can't saturate, and always maintains its value when driven. Plus they are fairly simple and easy to buy. The 22ohm resistor can also heat up, but not as much as the main resistor. I think the max it could take is about 1/4 of total power, then put a factor of 2 or 3 on that.

I was just thinking, the guys on Gnutz would like this stuff

 

[Arfage]

View attachment 1083563

I build two reactive attenuators for black panel amps, as several sound guys complained that my Deluxe Reverb just a bit too loud. So I was aiming to knock off just a bit of volume with 25% or 50% less amp power.

They are based on my observation that BP amps sound just as good with an extra external speaker and a 100% impedance mismatch. So I wanted to plug either 16 or 8 ohms resistance as a parallel dummy load in the ext speaker jack socket.

Problem was that that would create a treble bypass loop for the amp as the impedance of the power resistor remains 8 ohm at higher frequencies, while the parallel speaker's impedance goes up to 30 - 40 ohms with increased frequencies.

So I placed an air core inductor coil in series, that has the same impedance as a speaker voice coil (0.9 or 1.55 mH in this case). Similar to a Julius load box. The inductor coil is supposed to emulate the increasing impedance with frequency of a real speaker.

Not a very refined design as there are no other components but we will see how it performs.

They are built around the Switchcraft 227 jacks that feature a nice metal base plate to attach other stuff and the attenuator fits into the back panel of the amp. $20 part costs per unit.

I will report back on how they perform!

View attachment 1083566

WOW that's refreshing after the big Webers I've owned. Great units, I recommend them highly and will probably end up buying another. But still another big piece of stuff to plug in more cords to deal with and stack on your amp. Nice job!

 

[Arfage]

Very smart but Personally & IMHO,...I'll stick with turning down the guitar output volume when playing amps 25 watts or less like Deluxe Reverbs. For the amps 35 watts and above I reccy a PPIMV,...Post Phase Inverter Master Volume. The problem with attenuators is the output transformer is getting worked too hard esp on vintage amps. Attenuators can really heat up the OPT. Most of the "tube tone" comes from the preamp tubes although I know there is a sound from output tubes really cooking that we all love,...that's why I prefer @ a 10 watt amp

I too have a PPI master circuit I like. An attenuator should not actually strain your trans if it is properly engineered. I've also found that using a master and attenuator together is good for your tone. You don't have to lean too heavily on either one and can keep both turned up a bit further. Whittling down the signal less in different places.

 

[Arfage]

I just got a Weber Mass 200 and I am extremely happy with it. I don't even need to use the treble compensation knob, the tone is exactly the same at any volume. Maybe they improved the design or something? Just wanted to throw that out there. (I play clean surf through blonde amps.)

Had one - should never have sold it. Don't let go of that one! It's one of the best.

 

[GPoint]

View attachment 1083563

I build two reactive attenuators for black panel amps, as several sound guys complained that my Deluxe Reverb just a bit too loud. So I was aiming to knock off just a bit of volume with 25% or 50% less amp power.

They are based on my observation that BP amps sound just as good with an extra external speaker and a 100% impedance mismatch. So I wanted to plug either 16 or 8 ohms resistance as a parallel dummy load in the ext speaker jack socket.

Problem was that that would create a treble bypass loop for the amp as the impedance of the power resistor remains 8 ohm at higher frequencies, while the parallel speaker's impedance goes up to 30 - 40 ohms with increased frequencies.

So I placed an air core inductor coil in series, that has the same impedance as a speaker voice coil (0.9 or 1.55 mH in this case). Similar to a Julius load box. The inductor coil is supposed to emulate the increasing impedance with frequency of a real speaker.

Not a very refined design as there are no other components but we will see how it performs.

They are built around the Switchcraft 227 jacks that feature a nice metal base plate to attach other stuff and the attenuator fits into the back panel of the amp. $20 part costs per unit.

I will report back on how they perform!

View attachment 1083566

Wooden base and PLASTIC ties, what will happen if oscillation happens? Do you have fire insurance?
How this jack plug fits into the output jack (I see 2 big screw heads)?

 

[emann]

Hi there,

I have also built the M2 attenuator...This is from my experience and after 2 attenuators finishing up on eeeeebay.

I went ahead and hands on myself with the JohnH attenuator and my Fender 65 DRRI....with the instrumental help of Gene himself! Granted I did not spend any 1000 euros to try the fryette or the UA models but the tone of the amp changes a lot..at least with the ones I tried.

I cannot say this is the case with the JohnH...the DRRI comes alive every day now in my cave man room at the roof of my house when I can crank it to 7+ on the volume coupled with the kingtone duellist or fuzz pedals...blues tone forever! I cannot say that someone in the next room will not hear the amp but definitely it is much quieter and most importantly it lets the amp shine its actual tone.

I will not hesitate at all to recommend you to try the JohnH...it comes just to over €100 of parts and some of your time in constructing it...believe me you will not be disappointed! Up to now the unit just got a tad warm when playing for about 2 hours with it sitting on the top of my amp....hence no worries for an fire accident whatsoever.

Have a look at the below!

 

[johnDH]

hi @emann , that's a really nice build and I'm very happy that it's working well!

 

[emann]

hi @emann , that's a really nice build and I'm very happy that it's working well!

@johnDH

wow - really glad to get a response from the designer of this unit!!!

I shall find some time to create sound samples and post them up with photos of the works in progress on the main mf in the complete built threads to help any one else to make up their mind that this attenuator is really fantastic and well worth it!

 

[Lynxtrap]

The problem with attenuators is the output transformer is getting worked too hard esp on vintage amps. Attenuators can really heat up the OPT. Most of the "tube tone" comes from the preamp tubes although I know there is a sound from output tubes really cooking that we all love,...that's why I prefer @ a 10 watt amp

AFAIK attenuators don't cause any problems with amps. What might cause problems is the user running the amp turned up to 10 all the time.

 

[Antoon]

Wooden base and PLASTIC ties, what will happen if oscillation happens? Do you have fire insurance?
How this jack plug fits into the output jack (I see 2 big screw heads)?

Those are pop rivets. Friday is the big day and I will let you know if it caught fire. And the attenuator exactly fits the back side of BP Fender amps and all the way in the ext. speaker jack.

 

[bblumentritt]

Deluxe Reverb was too loud? What kind of music?

 

[Antoon]

Deluxe Reverb was too loud? What kind of music?

Most gigs are with a CCR tribute band with either a Tele or a HB guitar. Lots of times I overdrive the amp with a treble booster. That's when it gets (too) loud, in almost all indoor venues I play nowadays (audience typically between 100 - 500). Typical amp setting is VTB 5/5/5 (all at 12:00h) on the vibro channel with the normal channel preamp tube pulled.