Ampeg Heritage 50th Anniversary SVT in 8 Ohm SWR 4x10

[thedovewarlord]

Hi All -- I'm completely stoked, I purchased my first Ampeg SVT and it's currently being shipped.

Reading the manual for the SVT online, I saw there's a switch to select 4 ohms or 2 ohms.

I have two cabinets: an Aguilar DB412 - 4 ohms and an old SWR Goliath 4x10 - 8 ohms.

The SWR is my practice cab, and I was planning to use the new head with it.

The Aguilar is large and does not get that much use, I usually use Aggie when my band comes over (a few times a year, we're hoping to get more on track).

Now I'm hoping I can run the SVT on the SWR without damage to the amp or the cab. This was a bit of impulsive purchase. I'll feel elated if I know I can run the amp on the SWR and practice.

I actually brought the SWR back to life thanks to people with wisdom on Talkbass, hoping for some help here again.

 

[Wasnex]

The person (Bill Hughes) who designed the original SVT made posts on Talkbass that indicate the amp is safe at 8 ohms. AFAIK this applies to modern SVTs as well.

The impedance mismatch will reduce the amp's ability to make power, and it will also accelerate tube wear.

 

[thedovewarlord]

thanks @Wasnex . I read so many posts in the last 24 hours I'm starting to think I should pursue matching the amps impedance, either 2 or 4 ohms. my next question also gets mixed results, so asking if i can convert this swr 4x10 cab that is currently 8 ohms to either 2 or 4 ohms without replacing the drivers? @JimmyM what do you think?

 

[thedovewarlord]

more info from the web, is this legit?

• The Goliath II features four 8 ohm, 10" P.A.S. drivers wired in a series-parallel configuration and a Foster Horn. The Foster horn tweeter is intentionally wired out-of-phase. Custom designed and hand made in the USA for SWR by Professional Audio Systems

based on this, can wire the drivers in parallel and have a 2 ohm cabinet:

• That would be very easy: just connect them in parallel. Resulting impedance will be 1/(1/8+1/8+1/8+1/8)=2 ohm
  
  

 

[JimmyM]

thanks @Wasnex . I read so many posts in the last 24 hours I'm starting to think I should pursue matching the amps impedance, either 2 or 4 ohms. my next question also gets mixed results, so asking if i can convert this swr 4x10 cab that is currently 8 ohms to either 2 or 4 ohms without replacing the drivers? @JimmyM what do you think?

Leave it alone and get a 4 ohm cab if you feel strongly about not using an 8 ohm cab.

 

[thedovewarlord]

Wife is not open to another cab, already maxed-out $ getting the SVT

 

[thedovewarlord]

Leave it alone and get a 4 ohm cab if you feel strongly about not using an 8 ohm cab.

My new amp arrived yesterday. I said, *** and hooked it up to the SWR 8 ohms. I made sure the amp was set to 4 ohms and was super careful not to go too crazy with the volume. I dialed in great sounds, tried bridging the two channels. Super elated and pleased with the amp. Played for hours just tweaking the eq and marveling at the response and oooohmf. I went to plug in earlier again tonight and then got a vibe like, am I pushing things here?? I wound up going online and reading posts about ohms law and all this stuff, instead of playing.

I'm in a tough spot, I love the amp. Getting a new 4 ohm cabinet is not in the cards. So looks like my only choice to be sure I don't blow this thing up is convert the SWR to a 2 ohm, which I think I can do if someone is cool enough to walk me thru.

I took it apart last year and carefully rewired it as it was so I can concentrate, keep things organized. Is there someone with experience that can help me wire it from series parallel to parallel.

Help

 

[Wasnex]

My new amp arrived yesterday. I said, *** and hooked it up to the SWR 8 ohms. I made sure the amp was set to 4 ohms and was super careful not to go too crazy with the volume. I dialed in great sounds, tried bridging the two channels. Super elated and pleased with the amp. Played for hours just tweaking the eq and marveling at the response and oooohmf. I went to plug in earlier again tonight and then got a vibe like, am I pushing things here?? I wound up going online and reading posts about ohms law and all this stuff, instead of playing.

I'm in a tough spot, I love the amp. Getting a new 4 ohm cabinet is not in the cards. So looks like my only choice to be sure I don't blow this thing up is convert the SWR to a 2 ohm, which I think I can do if someone is cool enough to walk me thru.

I took it apart last year and carefully rewired it as it was so I can concentrate, keep things organized. Is there someone with experience that can help me wire it from series parallel to parallel.

Help

I suggest pulling out and storing the old woofer wiring harness. If you ever decide to sell or donate the cab, put it back to stock so someone does not accidently gank their amp running a forbidden impedance.

Leave the tweeter connection alone.

Parallel is very simple. Connect all the positive terminals together, and then connect all of the negative terminals together...something like this:

 

[thedovewarlord]

I suggest pulling out and storing the old woofer wiring harness.
View attachment 4472848

Thank you for the reply @Wasnex but I really don't understand that statement.

All the drivers are connected by individual black & white insulated wires.

When I disassembled to find why it wasnt working (due to a bad tweeter) I had a bad tweeter and this photo is what it looked like when I tested before I put it back in the cabinet.

 

[JimmyM]

My new amp arrived yesterday. I said, *** and hooked it up to the SWR 8 ohms. I made sure the amp was set to 4 ohms and was super careful not to go too crazy with the volume. I dialed in great sounds, tried bridging the two channels. Super elated and pleased with the amp. Played for hours just tweaking the eq and marveling at the response and oooohmf. I went to plug in earlier again tonight and then got a vibe like, am I pushing things here?? I wound up going online and reading posts about ohms law and all this stuff, instead of playing.

I'm in a tough spot, I love the amp. Getting a new 4 ohm cabinet is not in the cards. So looks like my only choice to be sure I don't blow this thing up is convert the SWR to a 2 ohm, which I think I can do if someone is cool enough to walk me thru.

I took it apart last year and carefully rewired it as it was so I can concentrate, keep things organized. Is there someone with experience that can help me wire it from series parallel to parallel.

Help

Just follow Wasnex' diagram and forget the storing part. He's quite knowledgeable, but you will have to make a new wiring harness with the connections pre-wired (much easier that way), so I'd store it in case you want to go back to 8 ohms at some point.

For some reason, I think of all 410's as having 32 ohm speakers from using Ampeg stuff for so long

 

[beans-on-toast]

I’d get rid of the horn. If it fits, replace the metal cabinet plate with a metal dish with two speakon connectors.

Neutrik NL4MP

Penn-Elcom D0604K

Gasket

Better yet, find a kit with the dish, speakons and metric speakon mounting machine screws and nuts.

 

[JimmyM]

My new amp arrived yesterday. I said, *** and hooked it up to the SWR 8 ohms. I made sure the amp was set to 4 ohms and was super careful not to go too crazy with the volume. I dialed in great sounds, tried bridging the two channels. Super elated and pleased with the amp. Played for hours just tweaking the eq and marveling at the response and oooohmf. I went to plug in earlier again tonight and then got a vibe like, am I pushing things here?? I wound up going online and reading posts about ohms law and all this stuff, instead of playing.

I'm in a tough spot, I love the amp. Getting a new 4 ohm cabinet is not in the cards. So looks like my only choice to be sure I don't blow this thing up is convert the SWR to a 2 ohm, which I think I can do if someone is cool enough to walk me thru.

I took it apart last year and carefully rewired it as it was so I can concentrate, keep things organized. Is there someone with experience that can help me wire it from series parallel to parallel.

Help

Honestly, you're not going to hurt the amp even if you give it a little juice. I'd be more worried about the 410

BUT...

It does sound better and less tightly compressed to me if you run it in spec.

 

[Wasnex]

Thank you for the reply @Wasnex but I really don't understand that statement.

All the drivers are connected by individual black & white insulated wires.

When I disassembled to find why it wasnt working (due to a bad tweeter) I had a bad tweeter and this photo is what it looked like when I tested before I put it back in the cabinet.


View attachment 4472851

Here in early version of the cab with series/parallel wiring. The red terminals on the drivers should be considered + and the black terminals -.

The wires coming out of the filter network are white, black, and red. The white wire is positive, the black wire is common(-), and the red wire is positive for the tweeter. However the tweeter is connected in reverse polarity for phase compensation.


You need to run the black wire to all of the black woofer terminals. Run the white wire to all of the red woofer terminals. Leave the tweeter connected as is.

This diagram:

is electrically the same as this diagram:

All of the positive terminals are connected together. All of the negative terminals are connected together. The connections to the crossover can be at any point as long as you stay + to + and - to -.

These are exactly the same, even though the connection to the crossover is at a different place:

 

[thedovewarlord]

Awesome @Wasnex . I am going to go to nearest hardware store an d buy a multimeter so after I rewire I'd like to check the cabinet is there any other safety check I can run before I run this amp on this cab?

 

[thedovewarlord]

Here in early version of the cab with series/parallel wiring. .....
View attachment 4472958

@Wasnex I did it thanks for all the help!!!

 

[thedovewarlord]

For anyone interested (in the future, zombie thread maybe) -- you can convert a 4x10 8 ohm cabinet to 2 ohm if all four drivers are 8 ohms each.

My cabinet has four 8 ohm, 10" P.A.S. drivers originally wired in a series-parallel configuration.

In order to achieve 2 ohms, I needed to rewire it to a parallel configuration. Scroll up you will find very helpful schematics from @Wasnex but the diagram below most closely represents my cabinet.

For starters, two drivers had a direct connection to the plate's positive (white) wires, the two other drivers had a direct connection to the plate's negative (black) wires, I left them connected. I took the two other cables out and then them to connect the the two open positive connections on two of the speakers directly connected. I then needed to add two more wires and connect the two open negative contacts. I left the horn "as is".

This was a bit time consuming because I decided to work from the back of the cabinet, fitting my hands and forearms thru the port and connection plate opening was a struggle, getting the wires connected to the push contacts took me a while, if I was to do this all over again, I'd probably consider taking the grill off and pulling the drivers out. Then again, that process also takes time and those speakers are heavy. At any rate, before I hooked up my amp to the cabinet, I went to my local hardware store and bought a multimeter and tested it.

Since I tested the banana connection, I decided to use my 1/4" to banana adapter and then switched the Ampeg's impedance switch right below the speaker outputs from 4 ohm to 2 ohm. Powered up and played it. Once I heard everything working, I played away, no longer concerned I was damaging the amp.

I want to say, I really appreciate everyone responding, but for every post that said "it's ok to run at 8 ohms, just a low volume" there were enough "don't ever do that, I killed my tubes, my OT..." I didn't want to have a sob story and I learned a bit more about wiring.

I love this AMP!!!!!!!

(diagram courtesy Wasnex)