Amp Tech Thread / Ask a tech Q

Hemisaurus · March 21, 2011, 03:36:30 PM

Dustcaps are only really important in PA cabs that move a lot of air. There they function to help keep the driver air-tight and to pull and push cool air into the driver core. I've know a lot of 2x15 cabs that didn't have dustcaps and ran just fine.

Rubber cement is generally used to hold them on, if you are worried you can buy stuff from http://simplyspeakers.com last time I ordered dustcaps from them they also included a tube of adhesive, so I assume they sell it.

LogicalFrank · March 21, 2011, 05:06:31 PM

I think I might have asked this on the old forum right before it exploded but... I plugged an amp which turned out to be all kinds of hosed into a speaker cab and it didn't make any sound but then smelled kinda funny immediately after (but no smoke at least). After that, none of the speakers made a sound when plugged into a known working amp and if you push on the voice coil it feels like they kind of grind against the sides. I re-speakered the cab since I didn't really like the sound of it anyway but I kept these speakers on the off chance they could be re-coned or otherwise fixed. So is there any chance these speakers could be re-coned or otherwise fixed?

Also, if anyone in Chicago wants four possibly completely ruined speakers from a 4x10 Travynor cab, they are all yours if you wanna pick 'em up.

Hemisaurus · March 21, 2011, 05:35:37 PM

Any speaker can be reconed, unless it's physically deformed, I'd suggest you take it to Van L. up on Western, Near Foster I think (it's been a good 14 years) and ask them what they think.

Looks like they are still there http://www.vanlspeakerworks.com/contact.htm

Van L Speakerworks
5704 North Western Avenue
Chicago, IL 60659

773-769-0773

Store Hours:

Tuesday 11 a.m. - 8 p.m.

Wednesday 11 a.m. - 6 p.m.

Thursday 11 a.m. - 8 p.m.

Friday 11 a.m. - 6 p.m.

Saturday 11 a.m. - 3 p.m.

Closed Sunday and Monday

(I'll usually answer the phone on those days too)

VOLVO))) · March 21, 2011, 07:38:06 PM

I use two part epoxy and the corner of a towel to put dust caps back on. Its strong enough to hold em tight. Just dont go crazy with it. A thin layer all the way around is enough. I am going to disagree with Herb, and advise strongly to put it back on. It's there for a reason, or else they wouldn't come with dust caps... my .02$...

hayseed · March 21, 2011, 08:17:50 PM

I got everything back together and i think i may have hooked it up wrong. It sounded fine without the dust cap but now it is crackling like there is a loose wire or something in that respect. I wander if i broke off a wire that leads to the wire hookups for the speaker. I took the speakers out of my Sunn cab and put them in my Fender Bassman 215 cab (Sunn Guitar Transducer and Jensen Special Design) just to have a second working cab and it sounds awful! Those speakers rattle so bad! The speakers are front loaded and i think i may need some insulation tape around them.

Tomorrow is another day....

Hemisaurus · March 21, 2011, 09:45:17 PM

could be you didn't seal that dustcap on right and it's buzzing off the cone, check for gaps on it.

hayseed · March 22, 2011, 03:21:35 AM

I never put it back on.

Hemisaurus · March 22, 2011, 07:28:37 AM

That rules that out then

A crackle, if your sure it's a crackle, and not a rattle or a buzz, does tend to be more likely to be electrically related, so yeah check all your wiring, make sure the jack socket is nice and snug and all that good stuff, before deciding to confine that speaker to the trash.

Wesogkan · March 22, 2011, 06:14:14 PM

Ok, the game plan has changed...I'm close to possession of a Sunn 2000s that needs rebuilding. I'm thinking of doing it up pretty original, but with the Green/Orange overdrive in it. Crazy? Would probably need too many knobs on the front panel...oi. I may need a separate pre-amp unit.

Hemisaurus · March 22, 2011, 11:18:42 PM

Maybe not, if you do the Mat pre, you could instead of doing a 4 position rotary drive, do two toggle switches instead for stage/studio and normal/brite put them in two of the 4 input jacks, and use the contour as the FAC, hmm still need a pot space for boost, suppose you could take out the bass boost switch, and convert that to you fifth pot? It could look pretty natural that way and all the labels would still make sense.

The trouble is your short a half tube in the preamp section.

VOLVO))) · March 23, 2011, 12:43:10 AM

Herbie, Why didn't you ever build that beta bass preamp? You ought to hook me up with one, in rack mount form. I have a 2000 watt power amp waiting to devastate nerds who like dubstep...

Hemisaurus · March 23, 2011, 07:42:53 AM

I never needed it, I found a ready-made solid state preamp that worked fine, that I already owned that was part of something else.

Then I saw this guy, who had made a tube preamp for his bass, just taking a regular tube amp schematic and skipping all the pesky power tube stuff, and I thought well that's simpler than a bunch of chips, though it takes up more space

so I started scribbling ideas down, looking for a cheap transformer etc.

Then I thought, well shit, if I'm going to all the trouble to wire up a preamp, and it's not going to fit in a 1U, why don't I make room for the power amp section too, so I sketched all that out, came up with a good way to make my own chassis, started looking at bigger transformers, trying to decide between KT-88's and the more esoteric, but cooler looking 807's.

Then I found a circuit I built into my bass, which meant less to carry, so I didn't need a preamp atall

and during all this time I was still fixing other peoples amps, doing my 9-5, playing in a couple of bands, refurb'ing my Alamo, becoming a dad, doing sound for people etc. etc.

hayseed · March 23, 2011, 09:34:06 AM

what size/ type of wire do i need to re wire a cab? I think the wiring in the Sunn Cab has be soldered and spliced too many times so i think i will just rewire the thing and hopefully it will stop my problems. any suggestions from the techs?

Hemisaurus · March 23, 2011, 10:00:02 AM

16 gauge would be fine, 14 gauge if you're nervous, 12 gauge or lower if your hardcore

Type of wire, any kind of flex, not solid core wire or shielded cable.

Strip an old extension cord or power cord and use that. Or buy some lamp flex or speaker wire, or use the stuff you can get at the auto store.

VOLVO))) · March 23, 2011, 10:14:57 AM

I use super high quality wire on everything I use.

What would it entail to have one built? I want the PB-20/10 but they're crazy hard to find for under 500 bucks.

VOLVO))) · March 23, 2011, 10:34:49 AM

I'm also wanting to throw it in front of my JCM800...

Hemisaurus · March 23, 2011, 10:37:54 AM

Take a Beta (you have a bunch), adjust to suit. Make a box for it, or hacksaw the frontpanel down to 19" width

Look at the service manual, there's the preamp board, and the power board, all the preamp board requires is +/- 15V. Either disconnect everything else on the power board or make your own +/- 15V supply, whatever you want.

Or buy that Sunn/Muff thing Baltar posted months back.

hayseed · March 23, 2011, 10:56:12 AM

Quote from: Hemisaurus on March 23, 2011, 10:00:02 AM
16 gauge would be fine, 14 gauge if you're nervous, 12 gauge or lower if your hardcore

Type of wire, any kind of flex, not solid core wire or shielded cable.

Strip an old extension cord or power cord and use that. Or buy some lamp flex or speaker wire, or use the stuff you can get at the auto store.

Thanks you sir. i was going to stop at the local Radio Shack and see what sort of stuff they carried.

VOLVO))) · March 23, 2011, 11:03:41 AM

I don't want to hurt one of my already-working betas

I just want to be able to super-power the fucker so I have sufficient low end wattage. Maybe if I find myself in a situation with 16 guitar cabs, I can use 2000 watts of power to level a small village or something.

Hemisaurus · March 23, 2011, 11:08:23 AM

Quote from: hayseed on March 23, 2011, 10:56:12 AM
Quote from: Hemisaurus on March 23, 2011, 10:00:02 AM
16 gauge would be fine, 14 gauge if you're nervous, 12 gauge or lower if your hardcore

Type of wire, any kind of flex, not solid core wire or shielded cable.

Strip an old extension cord or power cord and use that. Or buy some lamp flex or speaker wire, or use the stuff you can get at the auto store.
Thanks you sir. i was going to stop at the local Radio Shack and see what sort of stuff they carried.

Hardware stores carry lamp flex, and extension cords, dollar stores carry extension cords, auto stores carry hookup wire, if you can't make it to the shack. I'm working my way through a 50ft extension I bought at WalMart

Hemisaurus · March 23, 2011, 11:12:40 AM

Quote from: SunnO))) on March 23, 2011, 11:03:41 AM
I don't want to hurt one of my already-working betas

I just want to be able to super-power the fucker so I have sufficient low end wattage. Maybe if I find myself in a situation with 16 guitar cabs, I can use 2000 watts of power to level a small village or something.

So pick up a non-working one, one where the power section is blown, but the pre is OK preferably. Or just use the Accesdory out on one you already own, doesn't that work?

Or, distilled down to it's simplest, 3 hex inverters in a pedal.

Wesogkan · March 23, 2011, 11:48:48 AM

Quote from: Hemisaurus on March 22, 2011, 11:18:42 PM
Maybe not, if you do the Mat pre, you could instead of doing a 4 position rotary drive, do two toggle switches instead for stage/studio and normal/brite put them in two of the 4 input jacks, and use the contour as the FAC, hmm still need a pot space for boost, suppose you could take out the bass boost switch, and convert that to you fifth pot? It could look pretty natural that way and all the labels would still make sense.

The trouble is your short a half tube in the preamp section.

Oooohh..that might work. On the other hand one of my V4's is already wired up for an external pre-amp...so I could use a pre-amp with 2 different amps if I went the other route. Decisions, decisions...

Hemisaurus · March 23, 2011, 06:51:48 PM

That almost makes it sound like it would be worth building a separate power amp section, and have different pre sections you can plug in. I know Randall did something like this, but I'm thinking more like the original OR-200 Lead where it's an OR-200 Slave with a preamp built onto the front panel.

hayseed · March 24, 2011, 11:10:01 AM

Ok Hemi...help me before i jam my bass through my cabinets!

I completely rewired my Sunn Sorado cab and returned the original speakers to their home. Sounds better, has a little crackle but i think my head may need a good cleaning. Now here comes my problem...I rewired my Fender Bassman 215 and put the EV SRO's back in. When i plugged in , i got no sound at all BUT my Power Amp Limit light on my head was kind of pulsating(not staying on constant but enough to worry). I disconnected the cab and plugged into my head and the Overload light peak when i played hard, like normal.

What the hell did i do?

Thanks for answering my dumb questions...i am a novice at fixing/upgrading stuff

Hemisaurus · March 24, 2011, 03:53:51 PM

Sounds like a short, or maybe a duck, probably a short though