Silly NOOB theory question

I think I already know the answer but I have to ask the experts....

Why not build combo amps with the chassis on the bottom of the cabinet, the speaker(s) in the middle and a control panel in the upper front. This would put the bulk of the weight in the bottom and make the amp very difficult to accidently tip over, it would put the controls right where you can see and easily use them, it would orient the tubes so they wouldn't fall out and the heat would go up and away... the only thing I can guess is that (besides the minimal expense of a bit more wire) you may be introducing a source of noise by running the control wires from the amp to the control panel.

Is that the reason or is it just a tradition thing?

There were some amps built that way "back in the day".

That's not really a question about theory. I think the reason they do this is that splitting the controls and chassis would probably be expensive to do, and make maintenance an issue. The bulk of the weight is the speaker and cab, anyway, not the chassis.

My main amp has the chassis and controls on the right side - Sears Silvertone 1482 - looks like an old television. It doesn't seem "right heavy."

It's a little more than a small expense of wire. You have an extra chassis for the controls as well as the time to assemble the extra control panel to the amp. It doesn't sound like much but when you can save $5 an amp on parts and labour when you are making 10000 amps a year it adds up.

Now, I'm not disagreeing with you, it does make sense, but the almighty dollar rules in high volume manufacturing.

That's not really a question about theory. I think the reason they do this is that splitting the controls and chassis would probably be expensive to do, and make maintenance an issue. The bulk of the weight is the speaker and cab, anyway, not the chassis.

My main amp has the chassis and controls on the right side - Sears Silvertone 1482 - looks like an old television. It doesn't seem "right heavy."

Certainly the speaker is heavy, but also the transformer is pretty heavy too. But I agree the probable reason is the expense. If you are building your own you ought to try it.

That and the fact that people are always gonna throw cables ,covers and all kinds of junk in the back of their amps to make it easier to carry. All that stuff dropping in on the tubes and knocking tubes loose either when thrown in or pulled out adds up to service problems.

I think I might try this! I just found a conversion schematic for the Hammond L-112 AO-43 I recently aquired that yeilds the following controls... Volume, Bass, Treble, Reverb Tone, Reverb Depth. Originally I was thinking I would bend up a new chassis because of the looks of the original but if I "bury" it in the bottom of the cabinet and put a separate control panel up front on top with the reverb tank right behind the controls, nobody will see the chassis anyway. Maybe I'll pop a piece of expanded metal over the chassis so I can still throw junk in there without bothering the tubes.

The extra wire and extra panel certainly would add up in a production evironment (I know this stuff as my day job is as a Cost Accountant in a manufacturing company) but for home built, it might be a nice way to add some uniqueness to the build.

The gretsch amps put the power amp on the bottom and the pre-amp stuff on top, or at least a couple did. I built a bassman once based on the early 1x15 with everything on the bottom and the controls, light, jacks etc. on top. Used an octal socket on each and wired up all the sends and returns with an old organ octal to octal cable. Hummed like a bastard. You have to be careful how you run your ac to the light, as well as fuse etc. Check out the 5b6 layout. Those hammonds make fantastic Princeton Reverbs, just depopulate the thing, and assemble the Fender layout on the turret boards. Have fun and good luck.

Rollinbender, have you seen pics of the new Fender Excelsior? It's built exactly the way you described in your first post. Picture attached.

The photo shows an early prototype Excelsior. Production versions use a metal conduit between the top and bottom chassis; wires carrying high voltages are inside the conduit to prevent accidents.

-Gnobuddy

After botching a lead dress job on my first build, I know how sensitive some of those wires from chassis to pots/switches/lamp can be! (Idiot! tried to make my own custom layout on first build!) Everything was wired perfectly, just too long or crossing wrong wires, etc. So I'll bet this Excelsior, and any other amp with separate controls, inputs, lamp and such will need a shielded conduit, not just for safety, but for noise issues.

I'll bet this Excelsior, and any other amp with separate controls, inputs, lamp and such will need a shielded conduit, not just for safety, but for noise issues.
Could be, but remember, all the sensitive electronics (small-signal stages in the preamp) are in one grounded metal box, and all the high-voltage stuff is in the second box (down at the bottom of the box).

This is an excellent way to provide shielding - the high voltage stuff is kept far away physically from the low voltage stuff, and in addition each part is shielded inside a grounded metal box.

That prototype seems to have been used at the last NAMM show - so it would seem there weren't any stability issues. But here on TDPRI a few people seemed bent on criticising everything about the Excelsior, and one of the criticisms was that those wires inside the case could be carrying dangerously high voltage, and therefore the amp was unsafe - if you did something stupid like poke around inside the amp with a sharp metal object while it was powered on.

Well, the claim is ridiculous as far as I'm concerned - the same could be said of every electric extension cord in your house. And IMHO if you're dumb enough to poke around inside ANY electrical appliance with sharp metal tools while it's powered on, you deserve what's coming to you. But I bet someone at Fender read those posts, and decided to make 100% sure to eliminate that particular safety concern, hence the conduit.

I suppose the metal conduit could also be required by contemporary electrical safety certification standards, as it is for household wiring in the USA. I'll leave that to an appropriately informed person to confirm or deny.

-Gnobuddy

Could be, but remember, all the sensitive electronics (small-signal stages in the preamp) are in one grounded metal box, and all the high-voltage stuff is in the second box (down at the bottom of the box).

True, but aren't there quite a few signal-carrying wires succeptible to external interference up to those things?


Well, the claim is ridiculous as far as I'm concerned - the same could be said of every electric extension cord in your house. And IMHO if you're dumb enough to poke around inside ANY electrical appliance with sharp metal tools while it's powered on, you deserve what's coming to you.

Hehe! I think I'll play my electric guitar in the bath or poke around inside the amp with an ice pick...

I built one similar about three years ago for my son. It had a preamp in a small box on the top like an amp head and the power amp was on the bottom of the speaker cabinet. used the octal plug and jack combination to wire it. Worked fine but I came to the conclusion that there was no reason to do it that way.

Use shielded cable & it's all possible.

Use shielded cable & it's all possible.

My point exactly. It CAN be done, but not by just haphazardly running an extra foot or so of wire for every connection to the 'satellite' controls.

If it IS possible, I'd love to have all the controls about 40" off the floor... no more stooping while holding the guitar! Yay!:razz:

True, but aren't there quite a few signal-carrying wires succeptible to external interference up to those things?

There's lots of amplification in the top chassis, so I think the signal from there to the power amp (which is in the lower chassis) is going to be quite large - several volts rather than the hundred millivolts or so you get from the guitar. I think this signal is big enough to be pretty robust and fairly immune to interference.

Think of it this way, that cable from top to bottom chassis in the Excelsior is a bit like running a cable from your clean-boost pedal to your guitar amp's FX-loop input jack...the signal is strong and has been buffered, so it's not going to suffer much during the journey.

Hehe! I think I'll play my electric guitar in the bath or poke around inside the amp with an ice pick...
Exactly, or try cutting a hedge with a lawn-mower, as two infamous nitwits supposedly once did. (Yes, there was blood and body parts lost, and a lawsuit followed.) :shock:

-Gnobuddy

If it IS possible, I'd love to have all the controls about 40" off the floor... no more stooping while holding the guitar! Yay!:razz:
That would be very nice! Great idea, you should do it!

Remote-controlled guitar amp, anyone? :mrgreen:

-Gnobuddy

That would be very nice! Great idea, you should do it!

Remote-controlled guitar amp, anyone? :mrgreen:

-Gnobuddy

That'll work! Wait a sec... Neil Young's Deluxe has a "Whizzer!" That'd be nice, too. :wink:

Then again, a HUD (heads up display) with thought control would be even better. Whoa! Too much S-F...

Maybe just stacking the 5E3 on a matching extension cab will do the trick. :eek:

But getting back to the OP's question...

Like someone said, economics is probably a big factor. Most amps are purposely made pretty short and squat, so knocking them over is probably not a big issue. Until you stack them, then trannie and chassis location is not as much a factor as the stability of what's underneath.

Actually, I did design a combo that was 40" high, with controls at the top. Since it was only a 5W, I left the chassis on top as usual. The 10" speaker was about mid-height, to get it off the floor. The bottom was an empty area for a few foot pedals. I was going to add ballast in the bottom, like a sandbag or water bladder.

The reasoning was that space is tight in Japan, and like I said earlier, I hate bending down to fiddle with controls. Hmmm... I might still make that thing! :wink:

I did it!

http://www.tdpri.com/forum/shock-brothers-diy-amps/329462-junk-mine-continues.html

I have it put together right now but will be taking it back apart soon so I can put some finish to the wood and I still need to make the control panel and wire that end.

While you are at it incorporate a remote standby so if your amp is buried back stage somewhere in the dark, you can put it in and out of standby from your pedal board. Maybe using a relay in the amp. Just me jumping in on this...

Rollinbender, have you seen pics of the new Fender Excelsior? It's built exactly the way you described in your first post. Picture attached.

The photo shows an early prototype Excelsior. Production versions use a metal conduit between the top and bottom chassis; wires carrying high voltages are inside the conduit to prevent accidents.

-Gnobuddy

I actually got to play through one of those amps a couple days ago. My first impression was that it sounds really good and the tremolo was pretty cool but because it only has 2 knobs (tremolo speed and main volume), it is pretty much a one-trick pony... if you don't like what you hear, it's time to move on.

The layout with the amp split is rather cool though... I liked that part.

That'll work! Wait a sec... Neil Young's Deluxe has a "Whizzer!" That'd be nice, too.


I think about this A LOT being a massive Neil Young fan. I am so surprised that in all my messing around on DIY forums that I haven't seen anyone attempt to make one of these! I know it would be a big undertaking, but people do some crazy stuff all the time on these forums. It would be just killer for a 5e3 with it's super interactive controls. I want to see a schematic and layout on here PRONTO!

Actually, I did design a combo that was 40" high, with controls at the top. Since it was only a 5W, I left the chassis on top as usual. The 10" speaker was about mid-height, to get it off the floor. The bottom was an empty area for a few foot pedals. I was going to add ballast in the bottom, like a sandbag or water bladder.

The reasoning was that space is tight in Japan, and like I said earlier, I hate bending down to fiddle with controls.
Those seem like good reasons to me. :)

And here's one more: the wider a sound source, the narrower the sound dispersion. All else being the same, two 10" speakers one above the other will disperse sound to the sides better than two 10" speakers that are side-by-side.

(Think about those line array PA systems being sold by Bose, Fishman, etc - they use a tall narrow column of speakers because that's a good way to disperse sound to the sides.)

So there is actually a good acoustic reason for tall and narrow (relatively speaking) guitar cabs, rather than short wide ones!

Will guitarists accept that? Heck, no! Most will still want an amp that looks like the one their childhood guitar hero used.

-Gnobuddy

I like Neil Young too but not anal enoough to need a whizzer for sound presets. But if you are thinking of building then look at this old POST

http://www.thegearpage.net/board/showthread.php?t=565212

As you can see the POSTER made his own whizzer using R/C servos, etc. Big project, but could be something you want to do.

I personally like a A/B footswitch plugged in to two of the 5e3 channels which are preset to different sounds. I also like to add a pedal or two sometimes on one of the lines.