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Simple Attenuators - Design And Testing
- Thread starter JohnH
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JohnH
Well-Known Member
hi @diego_cl
You'll see a few versions on the many different builds in this thread. I like to do it like this:
For M2, most of the power and heat is in R1 R2A and R2B, so I'd make sure they are reasonably central., if possible
Vents above and below, well distributed for good thermal-driven air flow.
I mount these hottest parts in the box part, with this then being on top with the flat case lid being the base, with feet to raise it (see mine in post 1)
But its not too critical as to exact specific locations. Main thing is a good thick case, thermal paste and bolts for the resistors, plus the vents
You'll see a few versions on the many different builds in this thread. I like to do it like this:
For M2, most of the power and heat is in R1 R2A and R2B, so I'd make sure they are reasonably central., if possible
Vents above and below, well distributed for good thermal-driven air flow.
I mount these hottest parts in the box part, with this then being on top with the flat case lid being the base, with feet to raise it (see mine in post 1)
But its not too critical as to exact specific locations. Main thing is a good thick case, thermal paste and bolts for the resistors, plus the vents
Yamariv
Well-Known Member
Thanks John! I was a worried about having to add another aircoil to my build to retrofit as I don't think I have room. I think my best option, is to build an M2 8Ohm version and I'd be covered for my 8ohm out amp. Thanks again for all your help! I'm loving my attenuators, a whole new world has opened up
Guitar-Rocker
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Nice job Gene !
Gene Ballzz
Well-Known Member
@JohnH
So, I find myself needing to build an 8 ohm unit for my soon to be new Mea Boogie Fillmore 25! I'm torn between the 8 ohm M2 and the 8 ohm M-lite. For the M2, my preferred vendor (Madisound) for chokes, only offers 0.85mH and 1.0mH, not the specified 0.9mH. All parts for the M-lite are available to spec. Is there any benefit of one over the other? And if I wanted to do the M2, which of the two available values I mentioned would be best? Or would I just be better off with the M-lite? Of course, they do offer the 0.90mH choke in 16 ga, if I want to go that way.
Thanks,
Gene
So, I find myself needing to build an 8 ohm unit for my soon to be new Mea Boogie Fillmore 25! I'm torn between the 8 ohm M2 and the 8 ohm M-lite. For the M2, my preferred vendor (Madisound) for chokes, only offers 0.85mH and 1.0mH, not the specified 0.9mH. All parts for the M-lite are available to spec. Is there any benefit of one over the other? And if I wanted to do the M2, which of the two available values I mentioned would be best? Or would I just be better off with the M-lite? Of course, they do offer the 0.90mH choke in 16 ga, if I want to go that way.
Thanks,
Gene
JohnH
Well-Known Member
Hi Gene, all of those options would be fine. If I was picking one for general advice to others, it would probably be the M2 with 0.85mH. Its a more compact design than M, and 0.85 is very close to 0.9. But I doubt you'd notice any difference with 1mH. Once the values are close, its not like there is a super critical point where all the planets align and the sky goes black.
But M-lite is fine too!, and at 8 ohms its effectively the same as the 2019 build that I play every day
But, for you, lets apply a bit more to the choice, for this very cool amp. What do you know, or can you predict, about this amp and its use in your rig? ie:
amp - tube type? does it use NFB in the power amp? does it have a presence control?
speakers - what will you use it with, or might in the future?
Apart from 8 ohms, might you use it with 4 or 16 ohm cab/speakers?
what level or range of attenuation would you expect to be the most important for you with this amp? (If thinking about this based on use of other amps, allow that x2 on power is a 3db change)
But M-lite is fine too!, and at 8 ohms its effectively the same as the 2019 build that I play every day
But, for you, lets apply a bit more to the choice, for this very cool amp. What do you know, or can you predict, about this amp and its use in your rig? ie:
amp - tube type? does it use NFB in the power amp? does it have a presence control?
speakers - what will you use it with, or might in the future?
Apart from 8 ohms, might you use it with 4 or 16 ohm cab/speakers?
what level or range of attenuation would you expect to be the most important for you with this amp? (If thinking about this based on use of other amps, allow that x2 on power is a 3db change)
Gene Ballzz
Well-Known Member
Well @JohnH ,
6V6 tubes at supposedly 18 watts "clean" and 23 watts "fully driven" what ever that really means. Same wattage range of 14 to 20 watts as I'm wont to use these days. Will likely use it most often with its Made For Mesa Boogie Celestion Custom 90 or a 65 watt Creamback. It does have a "Presence" control on each channel, but I'm not sure if Boogie uses negative feedback from the output transformer or as an NFB loop earlier in the circuit. I expect to usually be in the -3.5db (parallel mode) to -10db range. Although for personal bedroom level practice, I tend to prefer using what ever my current performance rig is, cranked to its sweet spot and then use the attenuator to keep the love of my life happy! This helps me get my effects levels and settings right (mostly echo/delay) and this kind of use is another place where these attenuators really shine. I can get all of the harmonic overtones and feedbacks that I could achieve un-attenuated at much lower volume levels, due to these fantastic attenuators!
Here's a link to the amp. You might want to check out the manual at the Mesa Boogie website. Very cool features and if it can actually do Marshall sounds (like most if other Boogies can't), it may be the Holy Grail!
https://www.sweetwater.com/store/de...-25-18-23-watt-1x12-inch-2-channel-tube-combo
Thank You Sir,
Gene
6V6 tubes at supposedly 18 watts "clean" and 23 watts "fully driven" what ever that really means. Same wattage range of 14 to 20 watts as I'm wont to use these days. Will likely use it most often with its Made For Mesa Boogie Celestion Custom 90 or a 65 watt Creamback. It does have a "Presence" control on each channel, but I'm not sure if Boogie uses negative feedback from the output transformer or as an NFB loop earlier in the circuit. I expect to usually be in the -3.5db (parallel mode) to -10db range. Although for personal bedroom level practice, I tend to prefer using what ever my current performance rig is, cranked to its sweet spot and then use the attenuator to keep the love of my life happy! This helps me get my effects levels and settings right (mostly echo/delay) and this kind of use is another place where these attenuators really shine. I can get all of the harmonic overtones and feedbacks that I could achieve un-attenuated at much lower volume levels, due to these fantastic attenuators!
Here's a link to the amp. You might want to check out the manual at the Mesa Boogie website. Very cool features and if it can actually do Marshall sounds (like most if other Boogies can't), it may be the Holy Grail!
https://www.sweetwater.com/store/de...-25-18-23-watt-1x12-inch-2-channel-tube-combo
Thank You Sir,
Gene
JohnH
Well-Known Member
Hi @Gene Ballzz , that looks to be a very well considered amp, it should be a killer!
Not everything is known, but inferring, it has a Celestion speaker, so let's assume its inductance isn't far off other Celestions. It's got Presence, and its described as in the Poweramp stage, so assumed basically normal, with NFB, and it should be a perfect place to tweak the attenuated tone.
Given the key use is not much attenuation a bit of the speaker reactance should still reach the amp, so if you go M2, (I hope you do!) then the 0.85mH is a great choice.
If you might like to try with a 16Ohm speaker, id highly recommend building in the 16 out. Its zero risk, you can use it or use the other outputs, but it just gets the tone back on track with the higher ohm speaker. You can also run 2x8 ohm = 4 ohm of course, just as the 16 attenuators work well with 8 ohm speakers.
cheers J
Not everything is known, but inferring, it has a Celestion speaker, so let's assume its inductance isn't far off other Celestions. It's got Presence, and its described as in the Poweramp stage, so assumed basically normal, with NFB, and it should be a perfect place to tweak the attenuated tone.
Given the key use is not much attenuation a bit of the speaker reactance should still reach the amp, so if you go M2, (I hope you do!) then the 0.85mH is a great choice.
If you might like to try with a 16Ohm speaker, id highly recommend building in the 16 out. Its zero risk, you can use it or use the other outputs, but it just gets the tone back on track with the higher ohm speaker. You can also run 2x8 ohm = 4 ohm of course, just as the 16 attenuators work well with 8 ohm speakers.
cheers J
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mike_lawyer
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Anyone have a good source for 25W resistors? I am having a hard time tracking down ones for 4.7 ohms on Ebay from China.
Second question - what heat paste is everyone using to mount the resistors?
Third question - is there a good source in the US for the screws to mount the resistors? I am wondering what size to use. Thanks.
Mike
Second question - what heat paste is everyone using to mount the resistors?
Third question - is there a good source in the US for the screws to mount the resistors? I am wondering what size to use. Thanks.
Mike
JohnH
Well-Known Member
hi @mike_lawyer , welcome to our project!
For the 4.7 resistor, you can use 5 instead and its available on a few chinese ebay stores such as this:
25/50/100W 0.01-5k Ohm Watt Shell Power Aluminum Housed Case Wirewound Resistor | eBay
For the thermal paste, not very critical what type but important to have it. Ive used either a white grease, or a grease with aluminum in it. A place that fixes pcs will have some.
The screws I use for resistors are 10mm M3, steel with nuts. They seem good with the chinese resistors. (but the coil should avoid normal steel bolts or it will throw off the inductance. Nylon or stainless bolts, or zip ties, or a dab of silicone and have it sit on the base is good.)
For the 4.7 resistor, you can use 5 instead and its available on a few chinese ebay stores such as this:
25/50/100W 0.01-5k Ohm Watt Shell Power Aluminum Housed Case Wirewound Resistor | eBay
For the thermal paste, not very critical what type but important to have it. Ive used either a white grease, or a grease with aluminum in it. A place that fixes pcs will have some.
The screws I use for resistors are 10mm M3, steel with nuts. They seem good with the chinese resistors. (but the coil should avoid normal steel bolts or it will throw off the inductance. Nylon or stainless bolts, or zip ties, or a dab of silicone and have it sit on the base is good.)
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Osman Qureshi
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JohnH
Well-Known Member
Schematics software
I've just been monkeying around with some software for drawing schematics. My diagrams to date have just been hand-carved out of MS Word, so I've been looking for something a bit more mission-specific. I've tried Tinycad, which is a free open-source download and works quite well, and also Scheme-it which is an online app based at Digi-key (you have to sign up to save diagrams).
So here's some versions of the Attenuator M2 diagram. No design changes here, just playing with graphics:
This is from Tinycad:
Here it is from Digi-key Scheme-it:
And here it is tricked-out with some colours and added info, using Word:
Tinycad was easy to use, and you can work offline, but I like the clarity of the Scheme-it linework and its also user friendly.
I've just been monkeying around with some software for drawing schematics. My diagrams to date have just been hand-carved out of MS Word, so I've been looking for something a bit more mission-specific. I've tried Tinycad, which is a free open-source download and works quite well, and also Scheme-it which is an online app based at Digi-key (you have to sign up to save diagrams).
So here's some versions of the Attenuator M2 diagram. No design changes here, just playing with graphics:
This is from Tinycad:
Here it is from Digi-key Scheme-it:
And here it is tricked-out with some colours and added info, using Word:
Tinycad was easy to use, and you can work offline, but I like the clarity of the Scheme-it linework and its also user friendly.
Last edited:
Gene Ballzz
Well-Known Member
I like the look/graphic of the switches better on the Scheme-it, but the overall look is cleaner and a bit more standard looking with the Tinycad. Which ever is easier for you and allows you to do what you want it to do would be the best! Though I must say that your diagrams have always looked pretty great to me!
Just Sayin'
Gene
Just Sayin'
Gene
mike_lawyer
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For the air core resistor, does anyone have a good source in the US? I just need to source that part. Thanks!
JohnH
Well-Known Member
hi @mike_lawyer , madisound seems good. What amp power are you building for? they do a range in 19 gage which should be good for a 50W amp.
mike_lawyer
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I am looking to make one for a 50 watt plexi (1987). Sounds like 19 gauge should work, I will check it out.
JohnH
Well-Known Member
ok, in 19 ga, i think they do a 0.85mH send a 1mH. 0.85mH is fine instead of 0.9. Or, if you are building to 16 ohms, see if they do a 1.8mH
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Hi all, especially @JohnH who is still totally astounding in his commitment to helping others! Coming back here after a month or two out, I feel very much like I'm entering a "Welcome Back My Friends to the Thread That Never Ends": Fantastic!!!
I've tried the search function within the thread and not had too much luck, so I'll put my idea/questions out there... My early build of M1 is still going great, and although I did try using it on smaller amps, I find that because of how good it is, it is simply more fun to use it on my 60W HotRod DeVille! Oh for what it's worth, I ended up buying a couple of those mini Vox MV50 amps and the attenuator works just fine on those as well, even though they are basically solid state (with a NuTube pre-amp tube).
Anyway, the only time I find that I don't like the attenuated tone is when I need truly bedroom level volume (+/- 70db), nothing to do with the attenuator and everything to do with the amount of air being pushed! So I've been thinking of modifying my unit to allow for a Line Out, with the idea of running that into an IR box, perhaps something as simple and relatively inexpensive as the Mooer Radar, in order to actually divert the sound through smaller studio speakers which probably will "sound" "better" than a large guitar speaker cab.
But this brings up the question of how to modify the unit so that it effectively becomes a Load-Box so I can disconnect the cab speaker totally. This is essentially what I've tried searching for but can't find the best (I'm sure they're there) earlier posts. Same for the possibility that the actual Line-Out add-on has been perfected somewhere within!
Finally, I note that JohnH has recently mentioned that he, too, is thinking about IRs, so I will probably wait to hear his thoughts before actually investing in a dedicated IR box. I'm basically trying to avoid using my computer for this application, by going direct from valve amp to attenuator to IR-something-or-other to powered monitor speakers for live use.
So sorry if this has been properly addressed above in which case perhaps someone can help direct me to its location
I've tried the search function within the thread and not had too much luck, so I'll put my idea/questions out there... My early build of M1 is still going great, and although I did try using it on smaller amps, I find that because of how good it is, it is simply more fun to use it on my 60W HotRod DeVille! Oh for what it's worth, I ended up buying a couple of those mini Vox MV50 amps and the attenuator works just fine on those as well, even though they are basically solid state (with a NuTube pre-amp tube).
Anyway, the only time I find that I don't like the attenuated tone is when I need truly bedroom level volume (+/- 70db), nothing to do with the attenuator and everything to do with the amount of air being pushed! So I've been thinking of modifying my unit to allow for a Line Out, with the idea of running that into an IR box, perhaps something as simple and relatively inexpensive as the Mooer Radar, in order to actually divert the sound through smaller studio speakers which probably will "sound" "better" than a large guitar speaker cab.
But this brings up the question of how to modify the unit so that it effectively becomes a Load-Box so I can disconnect the cab speaker totally. This is essentially what I've tried searching for but can't find the best (I'm sure they're there) earlier posts. Same for the possibility that the actual Line-Out add-on has been perfected somewhere within!
Finally, I note that JohnH has recently mentioned that he, too, is thinking about IRs, so I will probably wait to hear his thoughts before actually investing in a dedicated IR box. I'm basically trying to avoid using my computer for this application, by going direct from valve amp to attenuator to IR-something-or-other to powered monitor speakers for live use.
So sorry if this has been properly addressed above in which case perhaps someone can help direct me to its location
mike_lawyer
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Will using a 16 AWG at 0.9 for the coil work? I see Madisound has them. Would that be too large for most enclosures?
JohnH
Well-Known Member
hi @TonyK , nice to see you again
There has been a few line outs on this thread, and ive been mulling over how best to do them. One one hand, many different ways would work ok, but what is best? Many different uses, different signal levels in and out, different input impedances, balanced or unbalanced?
For a simple one, Im thinking a pot in series with a resistor, and use a log pot to give good sensitivity at low level. Heres one that I was discussing with bitslover on the TDPRI forum (snipped from his diagram):
Ive seen versions where the resistor is higher. use a full size pot and about 1/2 w resistor
It could go across the amp input if you are running with no speaker. Or put it at the speaker to pick up a bit more of the speaker influence.
If no speaker, set the attenuator to max attenuation and then it is a good load box for the amp.
But the one Im thinking of will have a balanced option, but i haven't tested yet.
Mooer radar looks to be a great little unit, Im also working up an analogue cab-sim, just to see what it will be like.
There has been a few line outs on this thread, and ive been mulling over how best to do them. One one hand, many different ways would work ok, but what is best? Many different uses, different signal levels in and out, different input impedances, balanced or unbalanced?
For a simple one, Im thinking a pot in series with a resistor, and use a log pot to give good sensitivity at low level. Heres one that I was discussing with bitslover on the TDPRI forum (snipped from his diagram):
Ive seen versions where the resistor is higher. use a full size pot and about 1/2 w resistor
It could go across the amp input if you are running with no speaker. Or put it at the speaker to pick up a bit more of the speaker influence.
If no speaker, set the attenuator to max attenuation and then it is a good load box for the amp.
But the one Im thinking of will have a balanced option, but i haven't tested yet.
Mooer radar looks to be a great little unit, Im also working up an analogue cab-sim, just to see what it will be like.
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