Connecting 2 modern Ampeg SVT810 to a 1974 Vintage SVT Head ??? (and Traynor YBA-3)

nitram · #1 05-31-2011, 07:58 AM

Hi everybody...

I just got another SVT 810 cab the other day... it's a SVT 810E Classic series... 800W @ 4 Ohms... The classic fridge...

I already had an Ampeg SVT810AV cab to wich I swaped the speakers to 8 new Eminence B810... So another SVT cab wich I estimate to be at 1200 W @ 4 Ohms...

My question is, can I plug these two monsters to my 1974 SVT head without any risk with the impedence issue ? I'm really not a tech with all this, I'm still learning the tricks of the trade so perhaps somebody here (like JimmyM

) could help me out ???

Can I do that ???

Also, same question with a Traynor YBA-3... Could I do that ???

Thanks for any help !

Martin

bass bart · #2 05-31-2011, 08:10 AM

It should be no problem, just make sure your SVT head is set to 2 Ohm

And with the Traynor, I'm not sure, but I think it's minimum impedance is 4 Ohm?
If that is so, you can only use one 810...

JMac4strngr · #3 05-31-2011, 08:13 AM

The SVT was originally designed to run with two 810's. You'd be at a 2 Ohm load, which is safe with the SVT (and the YBA-3 as long as it is capable of 2 Ohms, which AFAIK it is). Should be nice, tubey, and loud...... Oh Yea, dont even let anyone tell You any garb about underpowering the cabs as it is a debunked myth....

blastjv · #4 05-31-2011, 08:16 AM

You'll need to check your head, but both those cabs in parallel will be 2ohms ~~and I don't think a '74 SVT will do 2ohms~~. (edited to avoid confusion)

-JV

PS - I also have an 810AV loaded with B810's and it is awesome!!! I would think that if I ever got another cab, I might swap speakers so there are 4 B810's in the top 4 slots of each of the 2 cabs...just a thought... I've toyed with the idea of a second cab, but it's really totally unecessary for me.....but still a fun idea...

beans-on-toast · #5 05-31-2011, 08:40 AM

Yes you can connect the two 810 cabs to your 74 SVT.

Connect the first one as usual, from the speaker out to the cab. Use another speaker cable and connect from the EXT SPEAKER jack on the back of the amp to the second speaker cabinet.

What this will do is tie your two 4 ohm cabs in parallel and connect them inside the amp to a 2 ohm transformer tap.

There are a few versions of the YBA-3 and the outputs are different. The YBA-3 (not the A version) has an 8 ohm speaker out jack and an external speaker jack. If this is what your amp has (check the writing on the back of the amp), you can connect your two 4 ohm 810 cabs, one to each jack. Internally, when both cabs are plugged in, the amp connects the cabs in series to the 8 ohm tap. If you have a YBA-3A with the 2/4 ohm switch on the back. Plug into the two cabs into the speaker and ext out as above and set the switch to 2 ohms.

nitram · #6 05-31-2011, 08:42 AM

Quote:

Originally Posted by bass bart

It should be no problem, just make sure your SVT head is set to 2 Ohm

And with the Traynor, I'm not sure, but I think it's minimum impedance is 4 Ohm?
If that is so, you can only use one 810...

Thanks for your reply Bass Bart !

The thing is not in front of me right now, but I don't remember seeing an impendence swith on this beast...

The YBA-3 is not in front of me either (it's my latest GAS I got these days...

), but I think there's a 2-4 Ohms impedence switch on the back of this thing...

lazyone2 · #7 05-31-2011, 09:38 AM

The SVT does have a 2 or 4 ohm switch on th back.

iCombs · #8 05-31-2011, 09:43 AM

do the impedance math...

(I[1]*I[2]/(I[1]*I[2])

In this case, it's an easy 2 ohms...but you can use that formula to check to see if you're with safe bounds if you happen to have cabinets with different impedance.

anonymous02282011 · #9 05-31-2011, 09:48 AM

Quote:

Originally Posted by lazyone2

The SVT does have a 2 or 4 ohm switch on th back.

no it does not.

However, you can daisy chain the two cabs together and run them from the SPEAKER output as others here have already stated.

HOWEVER ... i'd argue it's wiser to run one 810 from the SPEAKER output and second 810 from the EXT.SPEAKER output.

why?

because if you run them daisy-chained and for some unexpected reason the speaker gets disconnected from the head you will be running a tube amp without a speaker load, which will likely damage the amp. If you run each 810 from each speaker output and one of the cabs accidentally comes disconnected you still have the other 810 attached and won't risk damaging the amp.

bass bart · #10 05-31-2011, 09:49 AM

I remember something I read somewhere, that some older SVT versions didn't have an impedance switch, but just two speaker outputs, and it switches to 2 Ohm if you connect a speaker to each output..

nitram · #11 05-31-2011, 10:28 AM

Major thanks to all for your replies !

Quote:

Originally Posted by bass bart

I remember something I read somewhere, that some older SVT versions didn't have an impedance switch, but just two speaker outputs, and it switches to 2 Ohm if you connect a speaker to each output..

Can somebody confirm this ???

I wonder where is JimmyM today ???

Nitram

nitram · #12 05-31-2011, 10:29 AM

Quote:

Originally Posted by adbass

no it does not.

However, you can daisy chain the two cabs together and run them from the SPEAKER output as others here have already stated.

HOWEVER ... i'd argue it's wiser to run one 810 from the SPEAKER output and second 810 from the EXT.SPEAKER output.

why?

because if you run them daisy-chained and for some unexpected reason the amp gets disconnected from the head you will be running a tube amp without a speaker load, which will likely damage the amp. If you run each 810 from each speaker output and one of the cabs accidentally comes disconnected you still have the other 810 attached and won't risk damaging the amp.

Thanks for this important piece of information mate

Nitram

blastjv · #13 05-31-2011, 10:31 AM

Yes, that is what beans-on-toast is referring to above.

JimmyM seems to have been banned for some reason. Don't know anything about it, just noticed it in his 'user title' in other older posts...

-JV

nysbob · #14 05-31-2011, 10:40 AM

Quote:

Originally Posted by bass bart

I remember something I read somewhere, that some older SVT versions didn't have an impedance switch, but just two speaker outputs, and it switches to 2 Ohm if you connect a speaker to each output..

I have an older one, and that is correct. Two output jacks, 4 ohms each.

nitram · #15 05-31-2011, 10:51 AM

Quote:

Originally Posted by blastjv

Yes, that is what beans-on-toast is referring to above.

JimmyM seems to have been banned for some reason. Don't know anything about it, just noticed it in his 'user title' in other older posts...

-JV

BANNED ??? But why ???

Such an important ressource here for all Ampeg lovers...

Nitram

nitram · #16 05-31-2011, 10:52 AM

Quote:

Originally Posted by nysbob

I have an older one, and that is correct. Two output jacks, 4 ohms each.

Thanks brother !

What year is your SVT head mate ?

Nitram

anonymous02282011 · #17 05-31-2011, 10:56 AM

Quote:

Originally Posted by nitram

BANNED ??? But why ???

Such an important ressource here for all Ampeg lovers...

Nitram

he'll be back.

He gets a little .... passionate sometimes

beans-on-toast · #18 05-31-2011, 10:58 AM

The OP has a 74 SVT. This model just has the SPEAKER out and the EXT SPEAKER out. There is no impedance switch as adbass said. The newer models have the switch so this is causing some confusion.

One important point to note. If you plug in to the SPEAKER jack, the impedance is 4 ohms. If you are plugging a cab into each jack, each cab needs to be 4 ohms (the 810's are).

Now it gets even more confusing. If you daisy chain the two 810's, the overall impedance is 2 ohms. You can connect a single cable but it should be connected to the EXT SPEAKER jack. Also in order for this to work you would need to plug a dummy plug into the SPEAKER jack. A dummy plug is simply a plain 1/4" plug with nothing wired to it. The plug opens a switch on the SPEAKER output jack and breaks a short. Without this you would be shorting your speaker cabinet.

beans-on-toast · #19 05-31-2011, 11:48 AM

Here is a more detailed explanation.

Below is the vintage SVT output section. Note that there is a 2 ohm tap and a 4 ohm tap on the transformer. The SPEAKER output is connected to the 4 ohm tap. When you plug a second cab into the EXT SPEAKER jack, a switch connects both the SPEAKER jack and the EXT speaker jack, which are wired in parallel, to the 2 ohm tap. To use just the EXT SPEAKER jack by itself with a 2 ohm load, you must insert a dummy plug (a 1/4" plug, no wire connected to it) into the SPEAKER jack for this to work.

To summarize:
one 4 ohm cab, plug into SPEAKER
two 4 ohm cabs, plug one into SPEAKER, one into EXT SPEAKER
two 8 ohm daisy chained cabs, plug into SPEAKER

one 2 ohm cab, plug into EXT SPEAKER NOTE: you need a dummy plug (a 1/4" plug, no wire connected to it) inserted into the SPEAKER jack for this to work.
two 4 ohm daisy chained cabs, plug into EXT SPEAKER NOTE: you need a dummy plug (a 1/4" plug, no wire connected to it) inserted into the SPEAKER jack for this to work.

By daisy chained, I mean a parallel daisy chain connection. This is normally the output of one cab plugged into the input of another cab.

View image: vintage SVT output

nitram · #20 05-31-2011, 11:55 AM

Quote:

Originally Posted by beans-on-toast

The OP has a 74 SVT. This model just has the SPEAKER out and the EXT SPEAKER out. There is no impedance switch as adbass said. The newer models have the switch so this is causing some confusion.

One important point to note. If you daisy chain your speaker cabs, you need to plug into the EXT SPEAKER jack and not the SPEAKER jack on the back of the amp.

If you plug in to the SPEAKER jack, the impedance is 4 ohms. If you plug in to just the EXT SPEAKER jack the impedance is 2 ohms. If you are plugging a cab into each jack, each cab needs to be 4 ohms (the 810's are).

Now it gets even more confusing. If you daisy chain the two 810's, the overall impedance is 2 ohms. You can connect a single cable but it would have to be connected to the EXT SPEAKER jack. You leave the SPEAKER jack disconnected.

All right !!!

Thanks I understand better and better.

So say if I had one 2 Ohms cab only, that would need to be plugged in the EXT SPEAKER output jack of my 1974 SVT...

That said, I don't plan on daisy-chaining the 4 Ohms SVT810...

All I'm planing to do is use the two output jacks of my SVT... The EXT SPEAKER and the SPEAKER jacks... each outputing to a single 4 Ohms SVT810 cab...

But what makes that last scenario possible ? I mean, inside the head ? What makes it technically possible ? Is it the thing (forgot the name) that previous posters reffered to that switches the "ohmmage" to be ok with 2 SVT 810's of 4 Ohms each ?

I'm sorry, I'm a no brainer with this...

Thanks for every bit of info ! This place rules !

Nitram