has anyone ever made an attenuator before?

George · Post by **George** » Thu Feb 20, 2014 2:28 pm

also, my amp has an external speaker out (the stock speaker cable is hardwired to the chassis but may be removed from the speaker), but the ohmage isn't listed. does it stand to reason that this would be 8 ohms to match the output transformer?

Benmurray85 · Post by **Benmurray85** » Fri Feb 21, 2014 7:38 pm

George wrote:does this schematic look good to go with the 3 way switch? i added the red.

this should cover 3 levels of brightness. can i swap the neutral and 4.7uf cap so it goes in order of brightness from bottom to top?

So just to clarify. Is this schematic "good" as it is drawn in this image? If it is I'm deffo doing the 3way switch now. Nice to have to options.

George · Post by **George** » Fri Feb 21, 2014 7:41 pm

the guy in this thread seems to get it to work okay. it looks like it's wired in the exact same way, except actually he joined the capacitors to lug 1 instead of lug 3 on the l-pad. i don't know what difference this makes if at all?

http://www.madbeanpedals.com/forum/inde ... pic=7777.0

George · Post by **George** » Sat Feb 22, 2014 5:08 pm

well, i've built the thing and it attenuates very well! unfortunately the bright switch doesn't work for some reason but there is no need for it because it's plenty bright at all settings. will open it up tomorrow to try and fix it.

also, my amp basically has no break up whatsoever on the clean channel. even at full volume with p90s it just manages a keith richard rhythm tone. not bad but i was hoping to get a really nice pure breakup sound without any extra stuff going on. the drive channel however, is very nice with full volume and middling gain. before it was totally unusable but this is maybe where it's strengths lie.

Benmurray85 · Post by **Benmurray85** » Sat Feb 22, 2014 6:53 pm

Oh well. I really liked the idea of that bright switch and your layout was in a suitable idiot proof way of me understanding how to knock it together. I guess I'll just copy the basic one that I have here.

Thanks for reporting back though!

George · Post by **George** » Sat Feb 22, 2014 7:17 pm

i'm sure it works, i think i've just joined it to the wrong lug on the l-pad or something. momentary hiccup cos i probably didn't follow it right

George · Post by **George** » Sun Feb 23, 2014 10:36 am

think i've fixed it. the guy had numbered the lugs on the l-pad differently to mine. i should have followed the position and not the numbers. anyway, swapped connections to lugs 1 and 3 round and now the bright switches work fine, however, the taper is backwards so to lower the volume you have to turn up the attenuator, as if you're adding attenuation. bit bizarre. will have a look at swapping that round at some point

ben, does the one you're borrowing lower volume when you turn the l-pad clockwise?

Benmurray85 · Post by **Benmurray85** » Sun Feb 23, 2014 1:26 pm

Yeah George it does. I was just trying to figure it out then by acting it out in my head but yeah clockwise ADDS attenuation, lowering the sound.

Aaaah ok so as the lugs in the diagram are numbered 321 those are the right connections to make but wire em kinda like a mirror image?

George · Post by **George** » Mon Feb 24, 2014 6:17 pm

LOL, sorry i was being a numpty. the schematic is absolutely correct, i just had my L-Pad turned 180 degrees the other way and got confused. anyway, it's wired up correctly and i'm very much enjoying it.

it's been a while since i've really been able to use full on boost pedals designed for tube amps. my saltbooster and klon clone sound really good. the saltbooster is better at lower volumes to add some slight breakup, whereas the klon sounds completely in a league of its own when ragging an amp with full output.

also, it doesn't run hot at all. i'd heard people saying that these overheat and can break but that isn't the case at all

Post by **Mike** » Mon Feb 24, 2014 6:19 pm

Nice work! I've always been intrigued by these - that video sounded insanely good.

I guess the results depend on what type of amp you have but it must be great fun experimenting with the attenuator and pedals up front

George · Post by **George** » Mon Feb 24, 2014 7:03 pm

yeah, it's really good fun, especially as i've not been able to push this amp before. seems to get a nice keith richard tone, probably on account of it being a fender style amp with 5881s. i think i may rebias it a little hotter too as the clean sound is a little more sterile than i remember and the tubes look a little a dim.

i've been playing too much on the mustang recently and forgotten how nice tubes can be.

Benmurray85 · Post by **Benmurray85** » Mon Feb 24, 2014 7:46 pm

So now I'm confused. Which way round should the lpad be. I didn't notice initially that it's numbered "backwards"

I would've had the lugs facing me (ie backwards) and numbered them 1 2 3. So are the numbers right or the physical/visual order of the connections?

George · Post by **George** » Mon Feb 24, 2014 7:56 pm

has your l-pad arrived yet? if so check your lug numbers against the ones in the schematic (the ones on your lpad should be numbered). completely forget what i did, otherwise this will get confusing

Benmurray85 · Post by **Benmurray85** » Mon Feb 24, 2014 8:01 pm

George wrote:has your l-pad arrived yet? if so check your lug numbers against the ones in the schematic. completely forget what i did, otherwise this will get confusing

Aaah I'm grabbing from my friendly post office tomoro. I'll post a pic

Dave · Post by **Dave** » Tue Feb 25, 2014 10:15 am

This is a fantastic thread and an awesome result George. Absolutely going to do the same when Â£Â£ allows.

George · Post by **George** » Tue Feb 25, 2014 11:10 am

cheers, yeah i highly recommend this particularly if you don't have master volume. i'm going to rebias my amp later today and will see if that improves breakup. definitely a great way to get nice tube sounds at low volume. however, i'm considering changing the cap values on the bright switch. the 10uf is way too bright.

also now want to look at el34 and other low volume breakup models...

Benmurray85 · Post by **Benmurray85** » Wed Feb 26, 2014 9:45 pm

So, it's been an eventful evening! I knocked up the version shown in the thread but I had issues getting the caps so I just (in my own logic) took that out of the schem and did the rest. It didn't work. It effected the volume but didn't make the amp drive. Whilst I was fiddling I got an enormous electric shock!

So I dismantled and just copied the basic one I have. It now works but most of the attenuation is in the (less than) last quarter of the dial but it does the job.

I'm temped to do a proper demo with it so if I do I'll stick it on here for reference as well. Thanks for everyone's help above, it's been fun!

George · Post by **George** » Thu Feb 27, 2014 8:30 am

Sorry to hear about the shock!

That's interesting about it not driving the amp. I wonder what's happening there. The drive is generated by the output tubes before the attenuator in the chain. The attenuator just lowers the volume, so it shouldn't affect the level of break up. Have you asked the guy you borrowed the original one from for a schematic?

Also what l-pad wattage did you get and what's the wattage of the amp? A very higher wattage might explain why the taper is all in the last quarter maybe?

Post by **Mike** » Thu Feb 27, 2014 9:19 am

George wrote:Sorry to hear about the shock!

That's interesting about it not driving the amp. I wonder what's happening there. The drive is generated by the output tubes before the attenuator in the chain. The attenuator just lowers the volume, so it shouldn't affect the level of break up. Have you asked the guy you borrowed the original one from for a schematic?

Also what l-pad wattage did you get and what's the wattage of the amp? A very higher wattage might explain why the taper is all in the last quarter maybe?

Nope, it's just the taper of the pot.

Did you get Linear or Audio/Log?

I would imagine you want Audio.

The wattage is just the amount of power it can safely dissapate, nothing to do with the taper.

Benmurray85 · Post by **Benmurray85** » Thu Feb 27, 2014 9:53 am

Pretty sure I got the one that you linked to George! Tbh it'll be something I must've done coz now it's working fine. I just haven't got the bright switch but I can live without that anyways. At home it's a bit muddy but live I'll only be taking the edge off the volume. I'm gonna be test driving it at a practice session tonight. So apologies to anyone in the easy lancs area if the leccy goes for a bit tonight!