Completed JohnH Attenuators?

[Gene Ballzz]

After much delay... my 100W 16ohm M2 build is done. This was built in a salvaged case from an old car audio amp, which has a massive heat sink on top and sides. The front panel is 1/4" black acrylic, laser cut and engraved on a Glowforge laser cutter. I "experimented" with filling in the etched lines on the front with paint, which sort of didn't work well but I decided I like it looking a bit distressed anyway. I couldn't do the back panel in acrylic because I didn't have jacks that work in a 1/4" thick panel, and thin acrylic is too flexible.

Schematic follows the M2 50W version with all the ratings doubled - except a couple resistors R6 and R7 which according to my ltspice sim only dissipate about 4W and 8W each even with a 170W input like a superlead. So those are just the usual 25W parts. R1 is two 100W parts in parallel. I used Carling mini-toggles for the stages as these never see more than about 2.5A current, so the 5A mini toggle is ok. Bypass and cab switch are full size 10A rated toggles. Inductor is a 15ga part from partsexpress. Internal wiring is all 18ga. The cab switch is mostly for convenience at home, where I usually have two different cabs in the music room - so I can keep them both hooked up. I originally was going to have a dual input switch but decided to use it for bypass instead. In hindsight it's so transparent I should have just not bothered with the bypass and done the input switch, oh well next time.

I don't have any gut shots but let's just say it's not my proudest soldering job. I felt like a real beginner getting good joints on those 100w Arcol resistors, and that's with a fairly high-end soldering station. Ended up using an absurdly large chisel tip and plenty of extra liquid flux.

Sound quality is amazing, many thanks to @JohnH for this great design!

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WOW! I'm quite happy to say that sure puts my builds to shame! Great to see folks taking this design and running with it, to the next levels! And yeah, they sure do work great, don't they? Please let us know about heat, when cranked for long periods of time? Is there a fan included?
Great Job!
Gene

 

[AtomicRob]

WOW! I'm quite happy to say that sure puts my builds to shame! Great to see folks taking this design and running with it, to the next levels! And yeah, they sure do work great, don't they? Please let us know about heat, when cranked for long periods of time? Is there a fan included?
Great Job!
Gene

Thanks Gene! There is currently no fan or vent holes... we’ll see how it goes. I haven‘t yet done a full torture test with the superlead, but will share more info when I do.

I did some calculations in ltspice but that involves some questionable assumptions, in particular the actual guitar amp output is not really a max power sine wave, as in ltspice, plus Arcol’s rating for heat rise on 100w parts for example is based on a 995 cm2 x 3mm thick heat sink. My case is smaller but much thicker, more like 7mm, and ribbed. It probably weighed 5 pounds empty, at least. So hopefully it’s enough.

 

[Wizardof_Oz]

Hey guys, I just finished my M2 8ohms with an additional 4 ohms jack.
Explicitly I want to thank John and Gene for their exceptional support and tips!

I already own an attenuator with a much simpler design (Cabulator by SPL/Tonehunter, specialized in studio equipment) as shown in pictures 7 and 8. Attenuation works ok, but I was never satisfied with the rather dull and flat sound. Compared to this, the M2 at the same volume level honestly is a different league! The M2 sound is fat and my DSL20 with the 2x12 cab (UK celestion vintage 30) is very responsive. The various volume levels work perfectly fine.

If anyone is interested: I created a 3D model of the 1590DE housing and Arcol resistors with Sketchup 2017 incl. the mounting and venting holes. It's not flawless, but good enough to plan what you're doing...

Cheers,
Frank

 

[JohnH]

hi @Wizardof_Oz , that looked great! Thanks for posting and thanks for trusting our design.

 

[Gene Ballzz]

@Wizardof_Oz ,

Nice Job! I like the utilitarian/steam punk vibe of leaving he box unpainted. I'm very pleased that it performs as intended and desired!

Who was the source for the inductor coil? Do you possibly have an "all in" cost estimate? What size screws did you use for resitor mounting?

As for the 3D model, many of the units I've been doing might require cramming an additional two, 25 watt resistors into that box.

Great, Very Nice, Neat Work!
Gene

 

[[email protected]]

I have build 2, both in the cabinet. For both I added a by-pass switch, but in practice they are standard 'on' in the lowest setting.

The first is in my Fender Blues Junior IV. The circuit really is SUPER for this amp, now I can finally get all tones out of it I want at 'room volume'. I often use the maximum setting if I crack up the amp. For this I added even an extra -14db circuit.

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Secondly I build a 'low power' version for my DSL5. Turning the DSL5 more open does not change the tone very much, but it makes it a lot less 'sensitive' at the volume pots at low volumes. So also a 'standard on'.



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Very happy with both of them!

Nice work!
I am thinking of building a M2 for my dsl1c, and your dsl5 is a very good start for my build. I intend to do a stand alone box, though.
Do you have the parts list of your build?
Did you print a PCB, or did you use one of those pre-printed universal PCBs (example)?
And do you have pictures of the underside of the board? Curious if you have any additional insulation there, or if it is just the screws and spacers, with the board “floating“ on the back panel.

 

[Wizardof_Oz]

@Gene Ballzz

@Wizardof_Oz ,

Nice Job! I like the utilitarian/steam punk vibe of leaving he box unpainted. I'm very pleased that it performs as intended and desired!

Who was the source for the inductor coil? Do you possibly have an "all in" cost estimate? What size screws did you use for resitor mounting?

As for the 3D model, many of the units I've been doing might require cramming an additional two, 25 watt resistors into that box.

Great, Very Nice, Neat Work!
Gene

Thxs, Gene! I sanded and polished the box a little, but now it's sensitive as hell (especially fingerprints)...If somebody has some experience with clear coating on aluminum, I'd be open for ideas. Simple spray coating doesn't seem to work :-(

The air coil (Visaton SP5013) can be sourced at various places (at least within Europe), I got mine from an electronics distributor in Germany (Reichelt). Visaton is a German accustics and HiFi specalist. Not sure if you can get it in the US, though. Maybe Ebay?
My BOM is roughly 75 EUR incl bits & pieces. Besides Reichelt I ordered at Tube Town and Distrelec. The mounting holes in the Arcol resistors are D3.2mm, so I took M3x10mm screws. Mounting them with this little space in the housing was a little fiddly, especially the M3 nuts were a PITA:-( However, a few additional 25W resistors should work ok in the 1590DE, maybe on the side walls.
Did you ever measure the heat dissipation over the various resistors? I guess the main heat dissipation will happen at stage1? So the large resistors should stay on the bottom or top. Would be interesting to know for placing the fan in a design for high powered amps.

Cheers
Frank

 

[JohnH]

Hi @Wizardof_Oz

My own builds, which are just 'Prototype' quality, just get a black enamel spray can onto the raw aluminum. Some of them have been knocking around for a few years now and still look fine. I do the drilling, then go over the box with a fine wet/dry paper used wet, then wire wool. Then it gets a good wash and left to air-dry in a clean place. For the painting, I prop up the parts from inside, and make very fine passes with the well-shaken can, each one not a full coverage, and from a distance of maybe 15 to 20 cm. These passes dry enough in a few minutes so that another can be applied, always moving, always from a different direction, until after several such sweeps, I have a complete coverage, and a slight satin finish even from a gloss paint. Then dry in a clean place for a few days.

Ive worked out power dissipations in every resistor at every switch setting. Then I multiply by 3 (based on 50W amp - to allow for overdriving and imperfect heat sink) and round up to the nearest of 100W, 50W or 25W

R1 actually takes about half the total amp power, R2A and R2B share about 30% depending on frequency and the others get less dependent on switch setting. (I have a table, but image uploading isn't working for me this morning!)

 

[Gene Ballzz]

@Wizardof_Oz

Actually, the time to paint(I powder coat my builds) was after drilling and prior to assembly. At that time it needed to be washed/wiped down with naphtha, alcohol, acetone or lacquer thinner, to remove any molding release contaminents on the surface. Think about it, the chemicals in the casting mold were there to keep the die cast material from "sticking" to the mold and if not removed, those same compounds keep paint and/or other finish from "sticking" or otherwise adhering to the die cast box!

I don't know what to suggest, short of unmounting everything (no need to un-wire), cleaning as mentioned, applying a finish and re-assembling! The alternative is to warmly embrace the "steam punk" look!

Just Sayin'
Gene

 

[andtheUgly]

Like many, I joined this forum after discovering this great thread on attenuators, which I had been interested in buying or making for a while. This is my recently built 50W, 16 ohm A2 with bypass, in a Hammond 26827PSLA. Works a treat. I don’t know if this layout has been done before, but it’s what I came up with. I wanted to have the lid of the box as the base with all the resistors on it, the jacks/switches on the long sides and coil bolted to the centre of the top (with a plastic nut/bolt and 2 acrylic spacers). This layout means some of the wires are a little longer than I would ideally like, to enable access/construction (which is slightly awkward). It also means there is little room for vent holes in the base, so there are plenty in the ends and top for adequate ventilation (the unit does not get hot). Total cost of all the parts was about 100GBP plus a load of postage. Many thanks to JohnH for the design (credited on the underneath), and JohnH and everyone else for all the advice. I now realise how noisy my amp is when it is turned up (it may need looking at!). Regards to all, Colin.

 

[stickyfinger]

Like many, I joined this forum after discovering this great thread on attenuators, which I had been interested in buying or making for a while. This is my recently built 50W, 16 ohm A2 with bypass, in a Hammond 26827PSLA. Works a treat. I don’t know if this layout has been done before, but it’s what I came up with. I wanted to have the lid of the box as the base with all the resistors on it, the jacks/switches on the long sides and coil bolted to the centre of the top (with a plastic nut/bolt and 2 acrylic spacers). This layout means some of the wires are a little longer than I would ideally like, to enable access/construction (which is slightly awkward). It also means there is little room for vent holes in the base, so there are plenty in the ends and top for adequate ventilation (the unit does not get hot). Total cost of all the parts was about 100GBP plus a load of postage. Many thanks to JohnH for the design (credited on the underneath), and JohnH and everyone else for all the advice. I now realise how noisy my amp is when it is turned up (it may need looking at!). Regards to all, Colin.

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Nice looks very professional! How did you get the vent holes drilled so perfectly?

 

[andtheUgly]

Thanks. Just carefully marked and centre-punched, and I have a small drill press in the garage - one of the best thing I ever got - for drilling nice neat holes!

 

[K Dub]

@andtheUgly I wouldn't be embarrassed to have that attenuator sitting on top of my Marshall amp. Very impressive. And I even think @Gene Ballzz would also be impressed by yours!

 

[Gene Ballzz]

Like many, I joined this forum after discovering this great thread on attenuators, which I had been interested in buying or making for a while. This is my recently built 50W, 16 ohm A2 with bypass, in a Hammond 26827PSLA. Works a treat. I don’t know if this layout has been done before, but it’s what I came up with. I wanted to have the lid of the box as the base with all the resistors on it, the jacks/switches on the long sides and coil bolted to the centre of the top (with a plastic nut/bolt and 2 acrylic spacers). This layout means some of the wires are a little longer than I would ideally like, to enable access/construction (which is slightly awkward). It also means there is little room for vent holes in the base, so there are plenty in the ends and top for adequate ventilation (the unit does not get hot). Total cost of all the parts was about 100GBP plus a load of postage. Many thanks to JohnH for the design (credited on the underneath), and JohnH and everyone else for all the advice. I now realise how noisy my amp is when it is turned up (it may need looking at!). Regards to all, Colin.

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NOICE, indeed! If heat becomes an issue, there is certainly room in the bottom for some holes. While they might not be able to be in as nice of a pattern as the top and ends, they'd be unseen on the bottom. I really like the warning reminders!
Great Execution!
Gene

 

[Sonny_R]

New JohnH build. It's an M2 8 ohm version with one 4 ohm and two 8 ohm outputs. Sounds really good! Thanks for sharing.

 

[JohnH]

hi @Sonny_R , that looks to be a really nice build! thanks for posting!

 

[Gene Ballzz]

New JohnH build. It's an M2 8 ohm version with one 4 ohm and two 8 ohm outputs. Sounds really good! Thanks for sharing.

Nice, neat and tidy execution! Thanks for sharing and to the forum! What amp are you using this with? Don't be a stranger.
Great Work,
Gene

 

[Sonny_R]

Thanks, guys! I'm using it with a homebrew blackface Deluxe Reverb variant at the moment. Here are some more pics of the completed unit. I may do faceplates eventually. My vent holes are all over the place, but the net effect looks okay, I guess. I also built a caddy so it sits on the amp nicely. Cheers

 

[AndyD]

Thanks, guys! I'm using it with a homebrew blackface Deluxe Reverb variant at the moment. Here are some more pics of the completed unit. I may do faceplates eventually. My vent holes are all over the place, but the net effect looks okay, I guess. I also built a caddy so it sits on the amp nicely. Cheers

That’s a really cool idea! ( the caddy!).

 

[LordoftheLivingRoom]

Built mine nearly 3 years ago now... One each for my Deluxe Reverb and JTM45 clones. Original post here. Still going strong! I'm thinking of building another one for my recently completed D-style amp.