Simple Attenuators - Design And Testing

[abzic]

hi @abzic thanks for posting. A stripped down unit with just a couple of settings can be a very useful thing, and a neat simple build. And suppressing residual hiss and hum is another good purpose for an attenuator, for when you need to be at very low volume.

This has probably been covered before, but just in case, I want to comment that this attenuator complemented with a DI box (like the wirldwind director) and a software cabinet emulator with impulse responses (like two notes wall of sound) makes a killer solution for quietly recording a tube amp. I am using it this way and I can't be happier, consistent fantastic results everytime with no fuss. I have tried other setups for recording, including miking my cabs, and lots of different software/hardware amp modellers. With modellers, at least in my opinion, either the tone is not there or requires endless tweaking to get it, not to talk about the playing feel. Miking the cab has also proved difficult for me, among other reasons because of my room is far from adequate and my limited skills.

 

[dbishopbliss]

I built a third attenuator for a friend that does not want it (he has an Ox Box). I was thinking of listing it on Reverb with a link back to this thread for reference. Are there any rules against doing that?

 

[Dogs of Doom]

I built a third attenuator for a friend that does not want it (he has an Ox Box). I was thinking of listing it on Reverb with a link back to this thread for reference. Are there any rules against doing that?

no...

you can also list it in the classifieds here...

 

[Gene Ballzz]

I built a third attenuator for a friend that does not want it (he has an Ox Box). I was thinking of listing it on Reverb with a link back to this thread for reference. Are there any rules against doing that?

Which version did you build? Pics would be nice? Price?
Just Curious?
Gene

 

[JohnH]

I built a third attenuator for a friend that does not want it (he has an Ox Box). I was thinking of listing it on Reverb with a link back to this thread for reference. Are there any rules against doing that?

Ive no problem with that.

But, just putting this out there in case it is possible in due course: Id be very interested to hear any simple sound recording that you could make with A/B changes either between your M3 build with the resonance circuit, and with that bypassed so its an M2. And/or, any such comparison involving your friends Ox!

 

[dbishopbliss]

Ive no problem with that.

But, just putting this out there in case it is possible in due course: Id be very interested to hear any simple sound recording that you could make with A/B changes either between your M3 build with the resonance circuit, and with that bypassed so its an M2. And/or, any such comparison involving your friends Ox!

I will try to get some recordings soon. I also have a CaptorX and a Jet City attenuator (somewhere). The CaptorX works great for recording but the 20dB attenuator is too much for band practice. I generally use 10 or 14dB on the M2. I got the Jet City as a Christmas present years ago. I didn't care for the sound back then. Will be interesting to compare to the M2.

 

[ThePanda]

Prototyping M2 before I spend money on a chassis. Going with the Hammond 1590D in black.

** sorry for the size... I didn't know Imgur would do this... **

 

[dbishopbliss]

Prototyping M2 before I spend money on a chassis. Going with the Hammond 1590D in black.

One thing I found making my second attenuator is that you can minimize the number of separate wires required with some creative positioning of the resistors. For example you can connect groups of resistors like this:

EDIT: Text layout removed because the spaces were not maintained. Refer to the screen shot below for the proper layout.

Search back a page or two and you will see a photo of my M3 layout that does this. I used parallel resistors for R5 and R8 to get closer to the values in the design because the ebay vendor did not carry the exact values, buy you should get the idea.

 

[JohnH]

One thing I found making my second attenuator is that you can minimize the number of separate wires required with some creative positioning of the resistors. For example you can connect groups of resistors like this:

+--R8--+
|
+--R4--+--R6--+
|
+-----R2B-----+
|
+-----R2A-----+



+--R5--+--R7--+
|
+--R3--+

Search back a page or two and you will see a photo of my M3 layout that does this. I used parallel resistors for R5 and R8 to get closer to the values in the design because the ebay vendor did not carry the exact values, buy you should get the idea.

For others - It's definitely worth planning out positions and wiring runs to minimise wire-tangle, for a simpler and cleaner build. The schematics show what is connected to what but they needent be followed for specific wire runs. eg, take R4 and R6, connected to each other, and also to two switches. i would do a link switch to switch, one R4 to R6 then a single link from those switch lugs to the resistors. Also consider that it is usually easier if only one or two wires need to meet at a given lug.

dishopbliss - I can see when i quote your message above, that your text diagram is right as you intended, but when see it in my browser (Edge) within the post it's coming out wrongly, wires shifted etc. Could I please ask that it be replaced with a screen shot or something fixed? Its just that it could be a cause of confusion

 

[JohnH]

I think it should look like this:

 

[JohnH]

Hi @ThePanda , i just noticed on your parts photo. It looks like you are going for the 8 Ohm M2 with 3 output jacks. If so, Output 3 for use with a 16 ohm cab is intended to be a stereo jack with 3 lugs. When you plug in a normal mono plug, the ring gets shunted to ground, which brings in a resistor to adjust tone and impedance. its only an issue if you use a 16 cab with it so no biggie. Good luck with the build.

 

[Gene Ballzz]

Fairly early on in this thread, @JohnH mentioned preferring to use STEREO/TRS Cliff UK jacks throughout, even when only MONO/TS is needed, due to more solidly gripping /supporting the plug when inserted. Upon judicious consideration I agree completely! I'll even add the observations that it conveniently leaves the builder some switching options (should they be experimental modders, etc) and the fact that the cost difference is negligible. Heck, I've even seen sales that sell the STEREO/TRS for less. CLIFF UK is the important part, as the knockoffs are really terrible. I hear the REAN isn't bad, bur have little experience with them, here in the U.S.

And again, as has been previously advised, keep the attenuator circuitry isolated from the chassis, by NOT using stadard SWITCHCRAFT units!

Just Kibitzin'
Gene

 

[dbishopbliss]

I think it should look like this:

View attachment 92064

That is what I typed but it seems that the extra spaces are being collapsed in the HTML. I guess that is why you don't try to draw with text.

 

[ThePanda]

Hi @ThePanda , i just noticed on your parts photo. It looks like you are going for the 8 Ohm M2 with 3 output jacks. If so, Output 3 for use with a 16 ohm cab is intended to be a stereo jack with 3 lugs. When you plug in a normal mono plug, the ring gets shunted to ground, which brings in a resistor to adjust tone and impedance. its only an issue if you use a 16 cab with it so no biggie. Good luck with the build.

Thanks! I went ahead and ordered some stereo jacks (and chassis feet) that are coming today!

I was doing some research on the 16 Ohm Stereo Cab and don't really understand how it is used.

How is that used exactly?

 

[JohnH]

stereo cabs can either be in mono at 16ohms, or as two separate 8ohm pairs, depending on how you use the switch and jacks. I haven't really figured it out, but I font see them as much use. Best to just had it wired simply

Not related to the attenuator though. The 'stereo' jacks are used for other reasons.

 

[ThePanda]

This is what I came up with following you guys advice. I may play with some more before I start drilling.

The bottom plate to be the is supposed to be the bottom and the switches/jacks come out the side.

 

[JohnH]

Hi @ThePanda

it looks like you are using the same box that I used, which is a good solid one, great for spreading out heat.

My own build is on post 1, and its the earlier design M with two coils, but really works the same. My thinking is the 'lid' of the box becomes the base. I fixed the coils to that and everything else, switches jacks and resistors go into the body of the case, so the resistors end up on top. Plenty of large holes in base and top too for ventilation

Theres lots of ways to lay it all out though

 

[Blaoskaak]

I am looking for a attenuator for my sv20h. Now i use a harley benton cheap one and i hate the sound of my sv20h. When i played it without attenuator and blew my ears up, the amp sounds amazing! So i've been looking on google and everytime i'll end up on this topic. So it must be good. The problem is that i can't read diagrams, but i can solder.

Is there a summary somewhere of what parts you need and a roadmap? If this is there then I will probably figure it out and not have to spend 100s of euros for an attenuator.

Thanks!

 

[neikeel]

Currently planning 300w version on thermal pcb directly mounted to large heat sink, will be stealing basic layout from you John. Hopefully pics to follow.

 

[JohnH]

Currently planning 300w version on thermal pcb directly mounted to large heat sink, will be stealing basic layout from you John. Hopefully pics to follow.

Well that's cool! or maybe blisteringly hot! Will you use a fan?

I'm very pleased that such a respected member as yourself is trying this design and I'll be most interested in what you put together and your impressions of it.