Simple Attenuators - Design And Testing

[JohnH]

hi @Echelon ,
If you were trying to get a lower resonance, you'd need a larger cap and larger inductor value. The resonant frequency is
F = 1/ (2pi.sqrt (L.C))

If you do use an open back, the tone you get has the resonance of that real cab in any case, M2 or M3. Its just the response in terms of over-driven bass harmonics will be as for the closed back. It'd be a very subtle change, given that even bypassing the bass circuit makes hardly any difference.

I think if you build it as drawn, but with a switch to bypass the resonant circuit, then you'll have plenty to explore. Or, just do M2 at least to start with.

An open cab might have a resonance at about 80hz. So its not even relevant until you are on the last few lowest notes on your low E string. And they will come through in any case, but the real character of the tone, for which a reactive circuit helps, is in the high mids and highs, covered by the small coil and the way its set up in the circuit.

 

[Gene Ballzz]

@JohnH ,
There is so much great info contained in this thread, you could write, publish and sell a book! Lots of those nit-picky little details that we anal retentive nut bags tend to really thrive on!

I do a lot of advertising of your design across the innernest. While I let them know that all the necessary info for a build is in the first post, I strongly encourage all to take the time to read the whole thread, for the amazing knowledge and understanding that can be gleaned from it! Your unending and relentless mission of making tiny improvements, along with helping others turn this design into a "Swiss Army Knife" of simple, yet effective attenuation is utterly amazing and greatly appreciated! As always THANK YOU SIR!
U B Da Man!
Gene

 

[JohnH]

@JohnH ,
There is so much great info contained in this thread, you could write, publish and sell a book! Lots of those nit-picky little details that we anal retentive nut bags tend to really thrive on!

I do a lot of advertising of your design across the innernest. While I let them know that all the necessary info for a build is in the first post, I strongly encourage all to take the time to read the whole thread, for the amazing knowledge and understanding that can be gleaned from it! Your unending and relentless mission of making tiny improvements, along with helping others turn this design into a "Swiss Army Knife" of simple, yet effective attenuation is utterly amazing and greatly appreciated! As always THANK YOU SIR!
U B Da Man!
Gene

Thanks Gene, I would never have carried on if you hadn't been the first to notice that it worked, and so I dug into how it worked!

I could indeed write it all up, and I'm thinking....
The first post, as with any post, is limited in max length. (10000 characters, and its at 999x). And we are at 108 pages, this is post 2143. There's a heap of stuff, but a lot of repeats, and some fluff too.

So I was thinking of writing it all up, soup to nuts for everything pertinent, with charts and diagrams etc, then make it available as a pdf online in some way, for a few $. Even though the whole thread can stay public, I reckon there'd be appeal in having an updated concise version.

Does anyone have a view on that?

 

[Echelon]

Hi @JohnH, I'll probably start out with the M2 as that seems like the more versatile version. Thanks again for the advice.

A pdf with all the information neatly in one place sounds like a great idea. I've worked my way through all the pages, but I'd definitely find that handy and would more than gladly pay for it. It would only be fair to get some $ back for all the time and effort you've put into this.

 

[Gene Ballzz]

Hi @JohnH, I'll probably start out with the M2 as that seems like the more versatile version. Thanks again for the advice.

A pdf with all the information neatly in one place sounds like a great idea. I've worked my way through all the pages, but I'd definitely find that handy and would more than gladly pay for it. It would only be fair to get some $ back for all the time and effort you've put into this.

My good friend @JohnH ^^^^^^^ What He Said! ^^^^^^^

I think a good format might be to have a "Foreword" detailing some of the finer points of your initial inspirations and testing. Then make a separate "chapter" for each differnt model/design, including the different impedance choices, along with the testing results. And then a final "chapter" detailing the various modifications and additions and how to best implement them! Then maybe even a section with pics of others' builds, along with the builder's descriptions and comments?

I'll Buy The First One Off The Press!
Gene

 

[Stephen H]

Mr H, I must thank you from the heart for your many hours of effort designing and testing and sharing so that we can spend only a little time and effort to produce an amazingly versatile, useful and great sounding and feeling unit. I finished mine last night and was able to give it a really good workout pretty much most of the day today. It's a real pleasure to hear the whole amp working as it should and not be limited to pre-amp distortion. my ppimv is redundant.

Many thanks! (probably some from my housemates too!)

 

[diego_cl]

I've just built an Aion FX Refractor (klon clone) and the instructions manual (PDF) was very good. If you're willing to prepare a PDF for sale, maybe you would like to take some ideas from there. General Guitar Gadgets have also very good documentation for people like me that doesn't understand about electronics.

It took me a long time to understand this thread before I was able to buy the parts needed for my first M2. It would have been a lot easier having a PDF with just the right information, bill of materials, wiring diagrams and some pictures.

Besides the PDF for sale, I think this project deserves something like a Paypal donate button.


I've found some good and inexpensive sellers on Aliexpress for the inductors, 1590D enclosure and for the 25W, 50W and 100W resistors that I like to share with you guys. Some of them are at sale right now.

Thank you John for this awesome circuit!
Best regards.

 

[CO_Hoya]

Hi @Echelon, sorry I didn’t see this sooner.

I don’t perceive a difference through the speaker with the bass resonance on/off. I’d like to spend the time to actually test that though as well as through the line out, but I will need some more time to figure out REW.

Sounds like you are going with the M2 design, which seems most sensible.

Hi @CO_Hoya, thanks for chiming in. I'm not planning on using a line-out (for now), so perhaps the M2-version might be the way to go.
Did you hear a difference when switching the bass reflex on/off when playing through speakers? If there was no perceived difference, then the M2 would make more sense for me.

 

[Gene Ballzz]

All of the ones I've built so far have been the M-lite, as when I purchased my coils, was fairly ealy in the life of this thread and I ordered enough of all components for three builds. The next one will be an M-2. It's gonna be a bit of a challenge, as it needs to fit in a fairly small amp head cabinet. My eventual goal is to have one mounted in each amp I own! I think the most practical will be to mount it to or make it as part of the removeable rear panel of the cabinet. I've found a piece of 2 or 3 mm thick, perforated aluminum plate that I could mount it all on and then simply leave it open on the inside of the cabinet?
Just Plannin'
Gene

 

[Tatzmann]

If your doing a pdf me thinks it would be
nice to have a pictured step-by-step
build instruction of the basic design,
lot of beginners need pictures additional
to the schematic to get them going.

 

[diego_cl]

Has anyone tried amphenol jacks?

According to digikey, contacts are made of tinned brass and it's rated to support up to 10A.

Product:
https://tubedepot.com/products/amphenol-acjs-ihs-stereo-1-4-jack

Specs:
https://www.digikey.com/en/products/detail/amphenol-sine-systems-corp/ACJS-IHS/10443421

 

[JohnH]

Hi @JohnH, I'll probably start out with the M2 as that seems like the more versatile version. Thanks again for the advice.

A pdf with all the information neatly in one place sounds like a great idea. I've worked my way through all the pages, but I'd definitely find that handy and would more than gladly pay for it. It would only be fair to get some $ back for all the time and effort you've put into this.

My good friend @JohnH ^^^^^^^ What He Said! ^^^^^^^

I think a good format might be to have a "Foreword" detailing some of the finer points of your initial inspirations and testing. Then make a separate "chapter" for each differnt model/design, including the different impedance choices, along with the testing results. And then a final "chapter" detailing the various modifications and additions and how to best implement them! Then maybe even a section with pics of others' builds, along with the builder's descriptions and comments?

I'll Buy The First One Off The Press!
Gene

If your doing a pdf me thinks it would be
nice to have a pictured step-by-step
build instruction of the basic design,
lot of beginners need pictures additional
to the schematic to get them going.

Thanks guys, I think Ill do it! and thanks for the suggestions.

Things that I'm trying to figure out are mainly based on how to actually make it available. I don't think it'll be high volume, so cant afford to spend much on hosting it somewhere if I want to keep a few $. It would need to be such that it can be paid for and sent to anywhere, so I may have to use Paypal or similar. Also need to consider how to discourage a pdf being freely posted elsewhere. Ebay does not allow such virtual goods as a pdf or ebook, but some do use it to sell things like pdf scans on old knitting patterns and car manuals.

I have some web space and i can write simple web pages. So maybe another way is to write it all there and find a way to control access to the inner pages.

On content, yes I probably would add a build layout for a specific simple version of an M2. Id probably build a new one in order to do it and present it. But Ive been cautious about this before because reading the schematic and interpreting it into a wiring diagram has been the entrance exam for building the design. Only those who have passed this test have built it, and so each one has been a success.

 

[JohnH]

Hi @Echelon, sorry I didn’t see this sooner.

I don’t perceive a difference through the speaker with the bass resonance on/off. I’d like to spend the time to actually test that though as well as through the line out, but I will need some more time to figure out REW.

Sounds like you are going with the M2 design, which seems most sensible.

Thanks, Ill be very interested in any insights you can gain from your testing. Differences if any, will be most apparent when driving low notes hard, like around low A 110hz and a few semitones each side.

 

[JohnH]

I've just built an Aion FX Refractor (klon clone) and the instructions manual (PDF) was very good. If you're willing to prepare a PDF for sale, maybe you would like to take some ideas from there. General Guitar Gadgets have also very good documentation for people like me that doesn't understand about electronics.

It took me a long time to understand this thread before I was able to buy the parts needed for my first M2. It would have been a lot easier having a PDF with just the right information, bill of materials, wiring diagrams and some pictures.

Besides the PDF for sale, I think this project deserves something like a Paypal donate button.


I've found some good and inexpensive sellers on Aliexpress for the inductors, 1590D enclosure and for the 25W, 50W and 100W resistors that I like to share with you guys. Some of them are at sale right now.

Thank you John for this awesome circuit!
Best regards.

Thanks for those Aliexpress links. They look to be very comprehensive ranges. If you buy a bunch, does shipping cost come out reasonable?

 

[JohnH]

Has anyone tried amphenol jacks?

According to digikey, contacts are made of tinned brass and it's rated to support up to 10A.

Product:
https://tubedepot.com/products/amphenol-acjs-ihs-stereo-1-4-jack

Specs:
https://www.digikey.com/en/products/detail/amphenol-sine-systems-corp/ACJS-IHS/10443421

That's good info thanks. i have a few of their guitar cords and they are very high quality. 10A rating on jacks would deal very comfortably with even 100W amps and low ohms.

 

[Gene Ballzz]

@JohnH
Retaining at least some semblance of an "entrance exam" approach is likely a very good idea. Some of the resistor connections to the switches are not really quite as obvious as they might seem. Even though I'm at least "marginally" savvy, if you recall, I needed to contact you through emails to go over some stuff. You really helped me out on avoiding multiple long back and forth wire runs that were more easily accomplished elsewise. What can get tricky is that each switch has two lugs that need to connect to another switch, as well as one lug of a resistor. Where and how to physically make those junctions, in the most convenient way, with the least amount of wire can be a little confusing. I have an idea for a layout diagram format that might make it a bit more clear. It'll be a couple/few days for me to get it to you and I'll send it directly to your email (for your perusal), rather than muddying any waters by posting it here. Even properly laying out a "bypass" was a bit more daunting than it would seem. Some of the physical layout is a bit like playing three dimensional chess, as solving one routing issue needs to consider the not so obvious (and sometimes unintended & detrimental) interaction of components with each other.

The subject of how to distribute and minmize free sharing between folks and also collect the funds is much trickier indeed! I have no suggetions on that!

Thanks Again, As Always!
Gene

 

[VintageCharlie]

What should be the rating for the C1 cap for a 50w amp and what would it be for a 100w amp?

I am planning to build the M3 version.

I am also wondering, if an 8ohm version with the added output 3 for the 16 ohm output would sound the same, as i when i wopuld build a straight 16ohm version or is there a compromise?

Thanks!

 

[VintageCharlie]

Parts availability looks OK apart from the 18mH iron core inductor. I'm in EUrope and the only option i can find is a 64 EUR (about 70 USD) inductor, which is a bit insane - half the price of what people seem to pay for the whole project parts wise.
Do you guys have any hints towards more budget friendly options?

This isn't an issue for the 8R version - there's good options for the 9mH inductor. You can also buy a different higher value and unwind it a bit until you have the right value.

 

[JohnH]

hi @VintageCharlie , thanks for your messages. Looks like you're planning for an M3 build? What kind of uses and amps etc do you have in mind? For most uses, M2 works really well and doesn't use the bass resonant circuit.

 

[Gene Ballzz]

@VintageCharlie
The best sources for inductor/choke coils is places that sell parts/components for build speaker cabinets and crossovers! Usually much cheaper than from an electronics supply like Mouser! And I agree with @JohnH that the M2 should make you more than happy!
Gene