Amp Tech Thread / Ask a tech Q

[Instant Dan]

Ok, some good news and bad news.

Got the amp back today and still had some hum left

Notice when I changed inputs from Lo to Hi, the hum disappeared on the Lo input but still remains ,but is manageable, on the hi input.

The only thing I can figure out is maybe it is the cables I am using (they're almost ten years old) or it is just the room I playing in. The thing is, I don't remember with my electric amp 4x12 with mesa head being that noisy. I doubt it is the cab as I ran my epiphone valve through it and it sounded fine, no noise.

Maybe it's just the head

Still sounds good though!

EDIT: The more I listen to youtube stuff online. It sounds like that is the nature of the beast if you have it in the hi-input. Not mega quiet.

[Hemisaurus]

If the hum is really bugging you, borrow a power conditioner, see if that makes a difference. If it does, great.

[Instant Dan]

Nah, I think it has to do with the room as I noticed when I turned off the lights in the room, the buzz/hum went to zero on both channels.

That being said,

[Hemisaurus]

Fluorescents?

[Instant Dan]

Fluorescents?

Yep

[VOLVO)))]

I bought a power conditioner today, mother fuck of GOD! I have NEVER heard my beta leads without a shitload of noise. I LOVE IT. Everything also sounds a tad louder, and clearer. Time to EQ again...

[Hemisaurus]

I mentioned one of my "mods" a month or two back and finally got around to opening it up and taking some pics. Well I had this weird feedback loop going on, but didn't know what exactly was happening. I figures it out this weekend and it's a new mod that I have not found on the net. I rigged it up in a switch, so I can use the muff as normal, or put it into super self oscillate mode, as I've come to call it. I have a voltage drain on my muff, and no tone stack. That might have something to do with how mine works. Turn the voltage and sustain up to about 3 o'clock, and the thing starts to self oscillate and sounds like a synth. Can be made to sound theremin-like by varying the sustain level. You have to do it manually, but it makes for a nice "vibrato" effect that also changes pitch. When playing notes, it sounds like an octave fuzz out of control, but you don;t even have to play any notes and the thing takes off on it's own. Even if the voltage and sustain is low enough to avoid self-osc, it still has a much more fuzzy character than in normal mode. The other weird thing about it is that even when the pedal is off, but in super osc mode it still affects any pedals that are before the muff in the chain. I had my fuzz rite clone before it yesterday and it made the fuzz rite even more fizzy and sputtery. Pretty cool. Thought I'd share




So, it's a wire to the first diode from the input jack. That's it.

[VOLVO)))]

I think it's time to put a three-prong on my Sonaro. It shocked the everliving fuck out of me tonight.

Instruction is required, possible consequences for switched wires, will it mess up the value, whatever?

[Hemisaurus]

First find me a schematic

I'm looking at the schematic for the 2000s as it's meant to be similar?



I'm not sure about those weird symbols, like a cap in a circle? and whats the other one an extra outlet that's switched?

Anyhoo, if the Sonaro has a polarity switch on it, it's similar enough to say this, get rid of the polarity switch  

Basically you have a cap there that's connecting the AC line to ground, ostensibly for getting rid of noise, but it's a bad, bad, idea when the cap shorts, owch time.

What to do, the 3 wire should just connect to the primary of the transformer, looking at that diagram one pole to the power switch and one pole to the fuse, disconnect the polarity switch and any other capacitors that are on the primary side, you can leave the outlet there if you wire it up right. Hook the earth wire to a convenient chassis point, you can either solder it in place, or crimp a circular connector onto it, and hook it to one of the transformer bolts.

If you are worried about RF noise and the like, you might want to fit an IEC jack instead (kettle power cord socket) you can buy them with built in noise suppression.



if you have chassis clearance to fit one.

[Hemisaurus]

I'm a dumbass, cap in a circle is a neon light, not sure what it's doing wired like that though. Looks like it would be permanently lit, or I'm having a brainfart.

[VOLVO)))]

The schem should be the same as the 200s, it's the same three knob 60 watt output amp.

I'm worried about taking out the polarity switch, will there be issues if I leave it/add the three prong anyways?

[Hemisaurus]

Yes. The polarity switch allows you to connect one side of the line to ground via a cap. If you are getting shocked it could be that cap is already bad.

Wire it up with a 3 wire, without the polarity cap, safety firzt

Use the polarity switch as a secret booster or something

I'd use it as a disconnect for the negative feedback loop, that would be fun

[VOLVO)))]

I'm going to shoot gutshots, and you can circle the cap for me... haha, I'm worried about toasting this one, It's fragile... at least I feel like it is. I don't want to install that kettle power socket, it'd require some holes being drilled that I don't want to. I may eventually sell it, but I want to bring it into the 21st century first... haha.

[VOLVO)))]

Also, will regular 60/40 solder do, or do those lines get too hot?

[Hemisaurus]

Shouldn't get that hot, certainly not the power lines, even if they run fairly close to the transformer.

It's usually pretty easy, you'll be ending up with less wiring than you started with

[bloodofkings]

Got a question for you guys. Buddy of mine snagged an Ampeg 8x10 for free. Downside is it only has 4 functional speakers. He was thinking of making a 4x10 and 1x15 cab out of it being he's got a bunch of lumber and a bunch 15" speakers laying around and always dug the sound of that cab. My question is, what would the impedance of the 15" speaker need to be to acheive 4 ohms? Or are there any alternative wirings you guys would know? Thanks in advance.

[Hemisaurus]

Dang, it depends on the age of the cab. The original SVT drivers were 32 ohms each and they were all in parallel for a 4 ohm load. The newer ones use 8 ohm drivers in series / parallel (like a 4x12) for 2 8 ohm loads or a single 4 ohm load.

Either way, my addled mine just realized, it would be best to get an 8 ohm driver

So you'd have 8 ohm top, 8 ohm bottom, or 4 ohm total.

[bloodofkings]

Yeah it's an older cab. Only one input on the back 4ohm load. So, 8ohms on the 15"?

Yeah, I had to edit the brainfart. I meant 8 dammit, not 4.

[Hemisaurus]

No 8 ohms.

The total cab impedance is 4 ohms, some cabs have it split in two for two 8 ohm loads as well, so you'll have 8 ohms on the top with your 4 10"s and 8 ohms on the bottom with your one 15". Total impedance of those two sections will be 4 ohms.

[VOLVO)))]

8.

32-32-32-32 in series is 8 ohms. Id tap a second jack for the 15 so you can run either/or.

[bloodofkings]

Yeah, I caught that brainfart after I hit send, then edited. Not too swift today. Haha.

[Hemisaurus]

Yeah, or / and, remember that the 15" either has to be 4 times the power of one of the 10" or half the power of the biggest amplifier you are going to drive the entire cab with. It will be handling half the total power applied to the cab.

[VOLVO)))]

You make speaker cables out of rad extension cables, where do you get your quarter inch males? I wanna buy in bulk.

[Hemisaurus]

I was cannibalising. I know I saw switchcrafts recently for like $1.25 or $1.75 can't remember where.

[Hemisaurus]

Anyone feel up to critiquing a dumb Sunday night half asleep thought.

If I have a 120V to 12V transformer, that is a 10:1 turns ratio.

If I connect the primary of a second identical transformer to the secondary of the first, I should get 1.2V which represents 100:1 turns ratio.

If I do it again, with a third transformer, thats 120mV, 1000:1 turns ratio.

So if i hook an 8 ohm speaker to the secondary of the third, I should see 8000 ohms on the primary of the first, so I've just cobbled an output transformer out of three old wall warts, don't imagine it has much of a power rating though. Wonder if I could drive a 6V6 with it  

Now I'll use another 120 to 12 and a 120 to 9 (reversed) for the power