Simple Attenuators - Design And Testing

[jaimebcn]

Thank you very much @JohnH !

171 pages is a lot of pages (and diagrams, versions, etc) and it gets a bit confusing at first, sorry.

 

[firel7]

Thank you so much for sharing this.

If I wanted to build a 50W@16 Ohm version (for use with a JTM45, 18W, etc) can I just use a 50W resistors instead 100W and 25W resistor instead 50W?

Cheers,

@jaimebcn I am glad you like the model of my build plans. I see @JohnH has already replied and I would certainly say follow his recomendations! He is the creator of this and knows his stuff! I merely followed his design and am building to my needs. The goal of my post was to ask a few questions and get feedback on my plans. I am certainly willing to contribute to this incredible thread and their efforts. I have created from the model drill templates that work amazingly well for my build. If anyone wants to follow that exact layout I have found that it worked quite well. In short I am thankful for the sharing of knowledge here and would give back in any way I can. I am waiting on a few resistors to be in stock to complete my build, and I will post photos of the build when they are in.

 

[Mcentee2]

Hi all and @JohnH -

Excuse the long context!

My M2 has been great for a while now, but the other day I decided to try my JTM50 as a clean platform so reduced the amp volume and also flipped my M2 on/off toggle to off.

I played for a bit then thought, if the M2 is off then I can just plug the speaker straight in and use the M2 elsewhere.

When I did this I seemed to get an audibly changed signal from the amp/speaker, it wasn't so much frequency loss, but maybe the high end Reduced enough to deafen the guitar/amp feedback and harmonics loop.

So I tested back and forth to make sure, also with my older built M2 so I was using the same speaker cables . The new M2 definitely was somehow less "reactive" with the amp, less lively, remember it was toggled off so the signal is straight through going nowhere near the coil or resistors.

There was definitely something going on with either my wiring, soldering, or the Cliff jacks.

I remembered I had put a line out on the output, this was a pair of resistors in a voltage divider arrangement, one between the speaker jack positive and the line out positive, and a smaller one between the line out positive and ground. I didn't make use of the Cliff switched contacts for this so they were always connected up.

So the Line Out is always connected between Positive and Ground so it will always be bleeding some signal to ground, even if no lead is connected to whatever the line out goes to.

Could this be bleeding off some of the signal leaving my M2 slightly hampered?

It's probably not very much but is "audible" in terms of the guitar reacting with amp and volume and playing the feedback

I removed it, but haven't tested yet.....

 

[JohnH]

hi @Mcentee2 , great to hear from you again!

Those are odd symptoms. The line out should be based around resistors and pot of several k, so bleeding a negligible signal from the system. If you have meter, it'd be good to measure, with bypass engaged, ground to hot at the input, and again at the output, and ground to ground, and hot to hot, input to output.

 

[Mcentee2]

hi @Mcentee2 , great to hear from you again!

Those are odd symptoms. The line out should be based around resistors and pot of several k, so bleeding a negligible signal from the system. If you have meter, it'd be good to measure, with bypass engaged, ground to hot at the input, and again at the output, and ground to ground, and hot to hot, input to output.

Thanks, indeed some continuity and resistance measurements are on my list this morning - playing will be later today!

I have already clipped out the Line out connections, so hopefully I will get expected continuity and open results across all those remaining in/out path points!

At some point I will probably have to dig my old laptop out needing many MS updates and get a signal into Audacity somehow but that's for the long term I think

 

[Mcentee2]

Bingo ( I hope!)

I was getting a reading of 20r to 27r between Positive and Ground when the toggle was off, which shouldn't be there, depending on which attenuator sections were on/off....of course something is wrong!

Tracing my wiring it looks like I had miswired my toggle somehow, it worked fine when ON but somehow I had done it so that when OFF the send to the attenuator section was fine, but the return from the attenuator section that should have gone back to the toggle had instead gone to the output jack positive directly, so there was always some resistance there to ground....oops.

I've rewired it properly now, so will test later, I am pretty sure it will be fine now.

Many thanks for the sanity check John!!


Edit: just played and yes, it's now fixed....phew!!

 

[uberlance]

First, thanks so much for all your efforts to create such an awesome useful tool and even more so for so generously sharing. I recently completed my M2 build and so far it seems to work great w all three different amps I've tried it with, providing near-bedroom level sound through a 2x12 cab. I will post some pics of the build on the other thread soon.

I got a redbox "clone" specifically to use with the M2 so that I can run my guitar directly into a mixer for recording/sampling while reducing amp volume. I had some questions about the proper connections and was hoping @JohnH or @Gene Ballzz may be able to provide some clarification.

If I understand correctly, the first option is to run the speaker output of the amp to the redbox, the redbox XLR output to the mixer, the redbox thru to the M2, and the M2 output 1 to the speaker cab. This would seem to allow recording of the un-attenuated sound from the amp directly into the mixer while lowering the output to the speaker only.

I'm a bit more confused by the correct connections where the speaker output of the amp is connected to the M2 and the line out on the M2 is then connected to the redbox input. Obviously the XLR output on the redbox goes to the mixer, but do I connect the speaker cab to the M2 (Out 1) or the redbox thru output? This approach seems to allow for the recording of attenuated sound from the amp directly into the mixer while also lowering the output to the speaker.

Also, I'm wondering whether either of these are preferable to the other, or it is is just whatever sounds best coming through the mixer.

Thanks!!

 

[Gene Ballzz]

First, thanks so much for all your efforts to create such an awesome useful tool and even more so for so generously sharing. I recently completed my M2 build and so far it seems to work great w all three different amps I've tried it with, providing near-bedroom level sound through a 2x12 cab. I will post some pics of the build on the other thread soon.

I got a redbox "clone" specifically to use with the M2 so that I can run my guitar directly into a mixer for recording/sampling while reducing amp volume. I had some questions about the proper connections and was hoping @JohnH or @Gene Ballzz may be able to provide some clarification.

If I understand correctly, the first option is to run the speaker output of the amp to the redbox, the redbox XLR output to the mixer, the redbox thru to the M2, and the M2 output 1 to the speaker cab. This would seem to allow recording of the un-attenuated sound from the amp directly into the mixer while lowering the output to the speaker only.

I'm a bit more confused by the correct connections where the speaker output of the amp is connected to the M2 and the line out on the M2 is then connected to the redbox input. Obviously the XLR output on the redbox goes to the mixer, but do I connect the speaker cab to the M2 (Out 1) or the redbox thru output? This approach seems to allow for the recording of attenuated sound from the amp directly into the mixer while also lowering the output to the speaker.

Also, I'm wondering whether either of these are preferable to the other, or it is is just whatever sounds best coming through the mixer.

Thanks!

@uberlance

I see several different ways you could use that Red Box with the M2 and choose which sounds best for you! I'm not certain how elaborate of a "line out" you built into the M2, but I'm betting it will be your least favorite!

A> Take a speaker cable out of the impedance output of your amp that matches the "base" impedance of your M2. Plug that speaker cable into the "In" of the Red Box and another speaker cable from the "Thru" output jack of the Red Box into the input of the M2. One more speaker cable from the output of your M2 into your speaker cabinet. Then use the XLR out of the Red Box to your mixer. This will leave the XLR output of the Red Box unaffected by any changes in your attenuator setting.

A1> Alternatively, if your amp has more than one speaker output jack, you could simply hook up your M2 as normal and plug the other output jack of the amp to the "In" of the Red Box, nothing from the "Thru" jack of the Red Box and again, XLR output of the Red Box to your mixer. This will also leave the XLR out of the Red Box unaffected by any changes in your attenuator setting.

B> Plug an instrument cable from the "line out" of your M2 into the "In" jack of the Red Box, nothing from the "Thru" jack of the Red Box and again, XLR of the Red Box to your mixer. Depending on what part of the attenuator your line out is connected to, it may or may not change the output level of the XLR of the Red Box.

C> Take a speaker cable out of the impedance output of your amp that matches the "base" impedance of your M2. Plug that speaker cable into the input of the M2. Take a speaker cable from the output of the M2 and plug it into the "In" jack of the Red Box and another speaker cable from the "Thru" jack of the Red Box to your speaker cabinet, and again, XLR of the Red Box to your mixer. This scenario will make the XLR output of the Red Box change with any attenuator level changes.

I don't personally use line out connections for guitar (I prefer a mic on a speaker, even attenuated), but I'm guessing that scenario A> or A1> will provide the most pleasing performance!

Please Let Us Know?
Gene

 

[JohnH]

Hi @uberlance and @Gene Ballzz

I agree with all that. Red Box and similar units have their own built-in pad to take the signal down from speaker level, down to a level that its internal circuitry can deal with. It looks like there may also be a 0dB or -26dB pad so it can deal with speaker-level inputs or line level inputs. Reb Box also offers a balanced output, with ground-lift option if needed.

You may not need the M2 line-out. The intention of this was just to get an adjustable signal level out that can go directly into a mixer, interface or similar, which doesn't have its own pad, and then do cab-sim or IR processing further down-stream. But you can try it as in case B above.

Things to listen out for:

1. Make sure that your final signal is not to low as to need massive mixer gain, nor too high as to clip somewhere.

2. M2 shows the amp a rise of impedance with frequency, like a cab, but not the bass resonance, which instead is created by the real speaker interacting with the M2. So scenarios A, A1 and B may miss a bit of low bass resonance, if you play notes at around open low A or lower. A signal derived from the M2 output, case C, assuming a cab is connected, would have this bass lift though.

But If you find you want more lows, I find a small lift in the lowest EQ channel on the mixer, plus a cut below 100hZ (usually a button on a mixer) does a nice job for this. Or, it might all be fine anyway!

For case C, Red Box fed from M2 output, if you are attenuating a lot, might work better without the -26dB pad. I find I can get a level direct from the M2 output in parallel with the speaker, at a level that is easily dealt with by a mixer line-in.

With care to make sure that the amp is connected to the M2 and so sees a correct load, all is safe to try. Start all at low level and build up.

As with Gene, Id also very much be interested in your feedback on this and happy to discuss more.

 

[Mcentee2]

FWIW, I have removed my line out (posts just above this set!) and am using a red box too

At the moment it is running straight from the amp to the M2, then M2 speaker out to the red box, thru to speaker and line out to my mixer for stereo reverb/delay....I think I am using -26db pad too.

 

[JohnH]

Hi @Mcentee2

Thanks! Just to complete this because it's an important use, could I ask if you would please post;

1. What amp and what power you're using?
2. 8 or 16 Ohm build?
3. What attenuation setting you use?
4. Confirm if the -26dB pad on the Redbox is active?
5. To the mixer, is it a mic input or a line input ?
6. What gain on the mixer input?

Sorry to ask all that but I'm smelling the opportunity yo get useful data for our ongoing project!

Any others reading, similar setting info on use of DI or line-out would be much appreciated!

many thanks
John

 

[uberlance]

Hi @uberlance and @Gene Ballzz

I agree with all that. Red Box and similar units have their own built-in pad to take the signal down from speaker level, down to a level that its internal circuitry can deal with. It looks like there may also be a 0dB or -26dB pad so it can deal with speaker-level inputs or line level inputs. Reb Box also offers a balanced output, with ground-lift option if needed.

You may not need the M2 line-out. The intention of this was just to get an adjustable signal level out that can go directly into a mixer, interface or similar, which doesn't have its own pad, and then do cab-sim or IR processing further down-stream. But you can try it as in case B above.

Things to listen out for:

1. Make sure that your final signal is not to low as to need massive mixer gain, nor too high as to clip somewhere.

2. M2 shows the amp a rise of impedance with frequency, like a cab, but not the bass resonance, which instead is created by the real speaker interacting with the M2. So scenarios A, A1 and B may miss a bit of low bass resonance, if you play notes at around open low A or lower. A signal derived from the M2 output, case C, assuming a cab is connected, would have this bass lift though.

But If you find you want more lows, I find a small lift in the lowest EQ channel on the mixer, plus a cut below 100hZ (usually a button on a mixer) does a nice job for this. Or, it might all be fine anyway!

For case C, Red Box fed from M2 output, if you are attenuating a lot, might work better without the -26dB pad. I find I can get a level direct from the M2 output in parallel with the speaker, at a level that is easily dealt with by a mixer line-in.

With care to make sure that the amp is connected to the M2 and so sees a correct load, all is safe to try. Start all at low level and build up.

As with Gene, Id also very much be interested in your feedback on this and happy to discuss more.

Thank you both for the quick replies!! My initial hunch seems to be correct-- that it is OK to connect in the various ways *so long as* either the M2 or redbox has a speaker load attached. I hope to experiment a bit this weekend and will report back as soon as I have the chance to try a few configurations.

 

[Mcentee2]

Hi @Mcentee2

Thanks! Just to complete this because it's an important use, could I ask if you would please post;

1. What amp and what power you're using?
2. 8 or 16 Ohm build?
3. What attenuation setting you use?
4. Confirm if the -26dB pad on the Redbox is active?
5. To the mixer, is it a mic input or a line input ?
6. What gain on the mixer input?

Sorry to ask all that but I'm smelling the opportunity yo get useful data for our ongoing project!

Any others reading, similar setting info on use of DI or line-out would be much appreciated!

many thanks
John

1. What amp and what power you're using? JTM50, el34, Normal High at about 7/8 with a start, fairly clean but with an edge if digging in, speaker is a Celestion Alnico Cream. But....I do the often use heavy fuzz face on top!!!

2. 8 or 16 Ohm build? 8 ohm

3. What attenuation setting you use? Default -7db or with a second stage -7db depending on if the neighbours are around

4. Confirm if the -26dB pad on the Redbox is active? Yes

5. To the mixer, is it a mic input or a line input ? I go from red box to a Lehle PSplit to isolate the signal, then to a dd500 and then stereo into a Behringer Xenyx 802 channel 1 and 2 Mic inputs

6. What gain on the mixer input? Mic gain is about 7, channel and master to taste, one panned left, the other right.

Using the Red Box EQ options I set the mixer at no cut or boost EQ on hi/mid/low. These are reverbs and delays though, not a dry signal, so I am not being particular about parity with the speaker EQ sound.


To be honest, the above is a bit flexible, I can sometimes use the 0db red box Out if I am playing really clean, and turn the mixer mic channel(s) gain down. Luckily the dd500 as a great headroom on input, but I have tried other pedals and they clip.

Conversely if I try to take a -26db signal into an overdrive/boost pedal I need a hell of a boost to get into the other Xenyx mixer Line Input channels.

So for me it has to be the Mic inputs.

I have a 2x6v6 5e3 type amp, a lot lower output and, although I haven't focus tested recently, I am pretty sure this can do the 0db red box output into Mic channel ok without serious clipping (lowish gain of course!).

Hope this helps, ask more if you need and I will see what I can answer.

 

[Gene Ballzz]

Thank you both for the quick replies!! My initial hunch seems to be correct-- that it is OK to connect in the various ways *so long as* either the M2 or redbox has a speaker load attached. I hope to experiment a bit this weekend and will report back as soon as I have the chance to try a few configurations.

@uberlance
You've got the main gist of this! Additionally, along the way though you may have missed that the M2 can also be used as a stand-alone load box on the speaker out of the amp, with no speaker attached, as long as it is set to maximum attenuation. This would allow for "silent" recording through the Red Box to your mixer, hooked up in the manner of your choice, from the choices/options I mentioned above, in post #3,428, just leaving the speaker out of the picture!
Hope This Helps?
Gene

 

[Mcentee2]

@uberlance


I don't personally use line out connections for guitar (I prefer a mic on a speaker, even attenuated)..

Thanks for the reminder this is an option!

I might go back and try this - it did sound very good for low volume stuff, but I remember with my home room set up I couldn't easily stop the delay from feeding back to the mic from my stereo monitors, on the one hand it was a great effect for 60s Floyd psychedelia, on the other hand it was a right pain for normal lead type stuff.

I'll dig out my Sennheiser e609 and see if I can tweak positioning a bit more!

 

[Echelon]

Hi all and @JohnH ,

After a long hiatus, I finally have time again to pick up my M2 build project. I've got all the parts and I'm trying to figure out a clean layout for my chassis. This is what I have now:



I tried multiple different layouts and ways of wiring based on the schematics. My latest plan is based on the suggested layout/wiring plan for the Hammond 1550G case:



This seems to be right, based on that. However, I can't check it based on the electrical schematic as there are some differences. For example, the R2A and R2B go to the com pole of the switch in the schematics, but in the suggested wiring layout it goes to one of the other poles. Is my wiring plan correct?

I hope someone can help, thanks!

 

[lojo16]

First time posting here. I gotta say, I'm just blown away by the works going on here ! @JohnH, the world is such a better place with you in it. Thank you so much for all the education you've given me. I knew very little about this stuff 2 weeks ago. Big Thanks go out to @Gene Ballzz also, you always come up with very interesting post's, and nice builds.( Love my 5e3 Deluxe too.) I LOVE THIS STUFF !
I've been gathering parts for my first build, after studying this thread for a couple weeks now. I can't wait to complete one ! I haven't read every page, but I do believe I've read the important ones. I got a good deal on Hammond 1590R boxes, and bought 5 of them. I'll probably end up building one for each amp, ( like Gene.B). These boxes have the ribbed walls in them, which did concern me for a bit, but I'm ready to heat sink the outside of them if need be, or the hole drilling. @JohnH & @Gene Ballzz, or whomever reads and has an opinion, maybe it's been posted before and I didn't see it yet, but Thermoelectric Modules interest the hell out of me. I mean they generate power from heat, possibly to run a fan off the temperatures in the box, or even warning LED's. They take heat on one side and put out cold on the other they claim. Just wondering if there might be a place for them here, anywhere, since we always have an over abundance of heat.
Love being here in this community ! Thanks again to all who contributed.
John

 

[JohnH]

hi @lojo16
Thanks for your interest, and looking forward to hearing more about your build.
I dont know anything about those thermoelectric modules. Id expect that what they could be useful for would depend on how much voltage and current they can drive with the temperatures that we have. We like to stay pretty cool though!

 

[JohnH]

Hi all and @JohnH ,

After a long hiatus, I finally have time again to pick up my M2 build project. I've got all the parts and I'm trying to figure out a clean layout for my chassis. This is what I have now:

View attachment 130736

I tried multiple different layouts and ways of wiring based on the schematics. My latest plan is based on the suggested layout/wiring plan for the Hammond 1550G case:

View attachment 130737

This seems to be right, based on that. However, I can't check it based on the electrical schematic as there are some differences. For example, the R2A and R2B go to the com pole of the switch in the schematics, but in the suggested wiring layout it goes to one of the other poles. Is my wiring plan correct?

I hope someone can help, thanks!

Thanks for your diagrams. I havnt traced your layout fully, but definitely the switching should be such that the joining wire between R2A and R2B goes to the common lug on the first switch. This is how its shown in the schematics and also the two wiring layouts linked from the first post.

Good luck!

(EDIT: I think, of you swap Lugs A with the common lugs on all switches, then its ok. But please check!)

 

[Gene Ballzz]

First time posting here. I gotta say, I'm just blown away by the works going on here ! @JohnH, the world is such a better place with you in it. Thank you so much for all the education you've given me. I knew very little about this stuff 2 weeks ago. Big Thanks go out to @Gene Ballzz also, you always come up with very interesting post's, and nice builds.( Love my 5e3 Deluxe too.) I LOVE THIS STUFF !
I've been gathering parts for my first build, after studying this thread for a couple weeks now. I can't wait to complete one ! I haven't read every page, but I do believe I've read the important ones. I got a good deal on Hammond 1590R boxes, and bought 5 of them. I'll probably end up building one for each amp, ( like Gene.B). These boxes have the ribbed walls in them, which did concern me for a bit, but I'm ready to heat sink the outside of them if need be, or the hole drilling. @JohnH & @Gene Ballzz, or whomever reads and has an opinion, maybe it's been posted before and I didn't see it yet, but Thermoelectric Modules interest the hell out of me. I mean they generate power from heat, possibly to run a fan off the temperatures in the box, or even warning LED's. They take heat on one side and put out cold on the other they claim. Just wondering if there might be a place for them here, anywhere, since we always have an over abundance of heat.
Love being here in this community ! Thanks again to all who contributed.
John

@lojo16

The thought of using the generated heat to produce electricity to operate the fan(s) is quite an intriguing concept! It would certainly electrically isolate the fan circuitry from the attenuator circuitry AND make the fan's operation/activation/deactivation somewhat automatic! I guess the key question is how much electrical energy can be harnessed from the amount of heat we are dealing with here. If it can work, it would be a brilliant addition to this design! Please keep us posted on any related research!

And oh yeah, to the forum!

Thanks For Sharin'
Gene