Simple Attenuators - Design And Testing

[stickyfinger]

So what do I need to take Madisound 1.0 mH 19 AWG Air Core Inductor down to .9mH? I have a Fluke and thats about it.

 

[JohnH]

Ok I can help. I have a 1mH 18 gage that I unwound to 0.9mH. I assume your Fluke doesn't measure inductance? (my meter does but it's not common).

We can make a good estimate of how much to unwind, in terms of wire length to remove. Then compare it to how much I removed.

Can you please measure, as accurate as you can (like best estimate to the nearest 0.5mm)
Outer diameter of windings?
inner diameter of windings (ie inner diameter of the bobbin?
height of windings (ie inner face to face of bobbin)?

Given its fine tuning and it'd still work OK even at 1mH, we can be a bit conservative and take a bit less off.

 

[stickyfinger]

Ok I can help. I have a 1mH 18 gage that I unwound to 0.9mH. I assume your Fluke doesn't measure inductance? (my meter does but it's not common).

We can make a good estimate of how much to unwind, in terms of wire length to remove. Then compare it to how much I removed.

Can you please measure, as accurate as you can (like best estimate to the nearest 0.5mm)
Outer diameter of windings?
inner diameter of windings (ie inner diameter of the bobbin?
height of windings (ie inner face to face of bobbin)?

Given its fine tuning and it'd still work OK even at 1mH, we can be a bit conservative and take a bit less off.

Hi John, Parts just arrived today for two M2s but I haven't ordered the coils yet. I'm in the USA and I like their product as the coil is wound on plastic for easy mounting. This M2 will be used only with a 65 Supro Model 24 and the other for a Marshall 18 watt Model 1974. Ill have to get back to you on the measurements of the coil. Thanks!

 

[JohnH]

ok great, I'm sure we can work it out when you have them to hand

 

[jesone]

I assume that a 50w 20ohm is okay where I can’t find an Arcol 25w 20ohm version?

 

[JohnH]

I assume that a 50w 20ohm is okay where I can’t find an Arcol 25w 20ohm version?

Sure no prob!

 

[JohnH]

Looks awesome my only negative I can think of would be a Marshall is 8.25" wide. My rockcrusher is slightly bigger than my Marshalls and the feet barley sit on the head. Cosmetically and structurally if it were around 8 x 12 I say it be perfect.

Its a good point, and I see that even a JVM head is just 8.5" deep. I think combos may be deeper, eg my VM combo is 10" deep. The case I used in the diagram is about 10 x 10 x 4.

But I was looking for the most spacious case I could find and that Hammond is the biggest I could see listed by Hammond in their diecast range. It would indeed look better at about 8 x 12, but it'd need a different case to be identified. If it had to be 10 x10, the feet can be moved inwards so at least it'd sit safely on an 8" amp..

 

[maico996]

I have a hypothetical question for the attenuator gurus. Would it be possible to drive 4 16 ohm cabs with one amp, provided the amp had two speaker outputs and impedance could be set at 4 ohms? Here's my theory...you'd need two 8 ohm attenuators - one attenuator plugged into one of the speaker outputs, the other attenuator plugged into the other speaker output. Each attenuator would drive two 16 ohm cabs for a total impedance of 8 ohms at each attenuator. Since the amp is "seeing" two 8 ohm loads you'd set the amp impedance to 4 ohms. Does this sound logical? Does it make sense?
Note - I have not tried this, I've only thought about it.

 

[JohnH]

Hi @maico996

Yes that does sound logical, everything is in balance at the right load. Amp outputs at 4 ohms, matched by two 8 ohm attenuators. Each attenuator outputs at its native 8 Ohms, provided by two 16 Ohm cabs.

Doesn't mean it makes sense though! (ie, it sounds bat-shit crazy, but in a good way!)

 

[maico996]

Hi @maico996

Yes that does sound logical, everything is in balance at the right load. Amp outputs at 4 ohms, matched by two 8 ohm attenuators. Each attenuator outputs at its native 8 Ohms, provided by two 16 Ohm cabs.

Doesn't mean it makes sense though! (ie, it sounds bat-shit crazy, but in a good way!)

Thanks John! If one 4x12 sounds good, four 4x12s should sound five times better!

 

[AtomicRob]

I have a hypothetical question for the attenuator gurus. Would it be possible to drive 4 16 ohm cabs with one amp, provided the amp had two speaker outputs and impedance could be set at 4 ohms? Here's my theory...you'd need two 8 ohm attenuators - one attenuator plugged into one of the speaker outputs, the other attenuator plugged into the other speaker output. Each attenuator would drive two 16 ohm cabs for a total impedance of 8 ohms at each attenuator. Since the amp is "seeing" two 8 ohm loads you'd set the amp impedance to 4 ohms. Does this sound logical? Does it make sense?
Note - I have not tried this, I've only thought about it.

Or you could use one 16 ohm attenuator with four jacks wired in series/parallel to get 16 ohms total from the four cabs.

But... and I'm just guessing here, there doesn't seem like there would be much overlap between "people who rock four cabs at the same time" and "people who use an attenuator." LOL

 

[Gene Ballzz]

So what do I need to take Madisound 1.0 mH 19 AWG Air Core Inductor down to .9mH? I have a Fluke and thats about it.

Madisound will "de-wind" a 1.0mH to .9mH for a $3 fee.
Just Sayin'
Gene

 

[bobman34]

So I was planning on doing the full M4 (100W) and my plans changed, I found a killer deal on a deLisle amp switching unit so it will do all the DI stuff for me. It has an external attenuator loop option, so I'm going to pivot to the M2 version (8 and 16 Ohm outputs). I like what @BlueX did and I'm going to use the same enclosure and build. I've got most of the parts, just need to source a temp probe and display to fit. Hoping to have it up a running before Xmas.

 

[BlueX]

So I was planning on doing the full M4 (100W) and my plans changed, I found a killer deal on a deLisle amp switching unit so it will do all the DI stuff for me. It has an external attenuator loop option, so I'm going to pivot to the M2 version (8 and 16 Ohm outputs). I like what @BlueX did and I'm going to use the same enclosure and build. I've got most of the parts, just need to source a temp probe and display to fit. Hoping to have it up a running before Xmas.

Please share pic's, I'm interested!

I also looked at this Hammond 1453B enclosure, with pre-made vent slots, but it's quite expensive (I think).



Here are the parts for temp measurements that I used. The mini-switches only of you want to be able to switch between C/F and Internal/External sensor (one for each). Those functions can be hardwired instead.

https://www.digikey.se/sv/products/detail/lascar-electronics/EMT-1900/10259109

https://www.digikey.se/sv/products/detail/vishay-beyschlag-draloric-bc-components/NTCLE100E3103JB0/769411

https://www.digikey.se/sv/products/detail/adam-tech/SW-T3-1A-A-A3-S1/15284460

 

[stickyfinger]

Madisound will "de-wind" a 1.0mH to .9mH for a $3 fee.
Just Sayin'
Gene

Thanks, I had checked for any services on their website but could not that. I'll have to look again.

 

[bobman34]

Please share pic's, I'm interested!

I also looked at this Hammond 1453B enclosure, with pre-made vent slots, but it's quite expensive (I think).

View attachment 141025

Here are the parts for temp measurements that I used. The mini-switches only of you want to be able to switch between C/F and Internal/External sensor (one for each). Those functions can be hardwired instead.

Thanks for the parts info, I’ll just hardwire for F.

 

[drdreyer]

Hi @JohnH ,
I'm preparing for my second M2 build and am hoping you won't mind reviewing a proposed layout based on my enclosure and components I have collected.

To help me keep track of the wiring, I color coded the wires in the layout as shown in the attached wiring diagram.

It would be a tremendous help if you could review the wiring shown in my layout and confirm I have it shown correctly. It would give me more confidence to have someone confirm I'm on the right path.

Thanks,
Dan

 

[Maunster]

Ok so I built a 50watt unit. Still putting together that 2.7ohm one for my Vibroking..
I’ll post some pictures of the second box to the other thread once I finish.
..but I had to just stop in and say, goodness man. John H, this is quite the box. As an attenuator, it sounds invisible… As far as I care to notice.
But the thing that totally shocked me.. the line out!?! One of the best recorded guitar tones I’ve heard in a long time and I’ve recorded professionally, full time for over 15 years. The line out into a good pre and a good cab emulator plug-in is seriously blowing my mind a bit. The other guys I work with were kind of speechless. Well done, thank you JohnH!

 

[JohnH]

Hi @Maunster . that's great news and thanks for posting!

I'm interested in how your line-out is working too. The line-outs that I show are very simple things, just passive and unbalanced with no tone shaping, fed with a pot acting as a voltage divider off the amp input. But Im never quite sure how 'hot' to make them. The one on the M4 diagram is a bit cooler than the one for M2.

So on yours, which version did you build? what amp, Ohms and power? and what sort of input into the preamp do you use? is it a line-in. or a mic input? How high do t set the line-out to get it right for your use? is it a good range overall, or would it be better a bit hotter or less hot in terms of output signal range? Thanks!

 

[stickyfinger]

Should we be unwinding the coil to attach to the resistors or attaching leads to the coil? Maybe it doesnt matter?