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Vintage Ampeg SVT Question

jbass80

jbass80

Sep 3, 2009
88
0
Orange Park, Florida
#1
I have a question that I feel like a noob asking but here it goes anyway. I have just gotten a 70s svt and I'm curious to see the best way you guys recommend sending the sound to the house mix. I'm used to using the newer model ampegs that clearly label which send to use for the house as I directly run it out of the amp through a mic line. Which output would I use and what do I need for the send? There is a 1/4" output on the back of the svt that says speaker and one that says Ext. speaker. Would I just run a 1/4" speaker cable out of the Ext. speaker output into a direct box or other input?

Your help is greatly appreciated.

I did search for this both here and google, but I guess it's so obvious that no one has ever asked it before or I am just bad at searching. Someone please help me remedy my blond issue and tell me what I should do...
 
#4
There should be an "Ext. Amp" jack on the back which can be used to feed a mixing console if you want to send a 1/4" out. Note that this is the "Ext. AMP" not the "Ext. SPEAKER" jack. That will essentially give you an unbalanced pre-amp out.

A better solution would be to get yourself a good DI that can handle speaker level signal. There are a few, but I use a country man type 85. Very solid little box, will serve you well, and can be used before or after the amp depending on how you have it set. Or ask for/bring your own mic.
 
#6
I would be careful plugging anything other than a second four-ohm load into the SVT's external speaker jack, since when that jack is occupied the two-ohm secondary winding of the output transformer is enabled. (I'm 99% sure that's the case, but Jim or one of the other Ampeg gurus will come and and correct me if I'm wrong.)
 
#8
craig.p said:
I would be careful plugging anything other than a second four-ohm load into the SVT's external speaker jack, since when that jack is occupied the two-ohm secondary winding of the output transformer is enabled. (I'm 99% sure that's the case, but Jim or one of the other Ampeg gurus will come and and correct me if I'm wrong.)
Click to expand...

Yes, on the vintage amps without an impedance switch plugging into the second speaker jack taps the 2 ohm winding, as far as I understand.
 
#14
Don't plug anything into the speaker jacks except for speakers. (one 4-ohm load per jack)

Depending upon the vintage, it may have "Preamp Out" & "Power Amp In" jacks. (My Magnavox-era V9 does).

If you plug a guitar cable into the "Preamp Out" it interrupts the circuit between the preamp to the power amp. No sound. You will think something is broken. (But it's actually working the way it's supposed to.)

But if you use a MMF Y-cable, you complete the circuit to the power amp, and you get an unbalanced line out. Plug that unbalanced line out into a DI box and you're good.

(And for heavens sake, mic the cab TOO!)

The line out trick above will *not* work when the amp is on standby (for recording like the B15s), but it will work when the amp is on.
 

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#15
sounds good to me doing both speaker di and micing, but i prefer micing it. the frequency response is more to my liking. the speaker di can get too bright in the hands of a bad soundman. happened once too many times for my liking so i went back to a mic.
 
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#17
bassboysam said:
coreyfyfe said:
Yes, on the vintage amps without an impedance switch plugging into the second speaker jack taps the 2 ohm winding, as far as I understand.
Click to expand...

That is exactly what I have been doing with a Radial JDI. I have not had any problems but hopefully one of the Ampeg experts can chime in and confirm.
Click to expand...

I am not an expert. I'm just a long time (13 year) user. But based on what my amp techs have told me over the years, that sounds like a bad idea.

If you use both speaker outs, it expects a 4-ohm load on each speaker output and switches to 2 ohms. If you're using a 4-ohm load on one speaker out, and just the JDI on the other speaker out, I expect this will put some stress on your output transformer, and possibly damage it long term.

-Are you using the JDI *in-line* with another speaker cab (running two 8x10s) or are you running just one 8x10 and the JDI?

-How long have you been doing this? (How many years)?

-How long do you do it at a time? (A 45-minute set? or a 4-hour recording session?)

I know SVTs are pretty resilient when it comes to mismatched loads... but what you're describing sounds like it might damage your output tranny. Anyone know the real scoop?
 
#19
bassboysam said:
How difficult would it be to add parallel jacks to the cab?
Click to expand...

That won't work... if you were to run two cabs (or the JDI) in parallel, then you'd potentially have a 2-ohm load on the 4-ohm tap. That equals bad. That equals thermal runaway. (I have no idea what resistance (if any) the JDI provides)

There's no parallel jack on the 8x10 for just that reason.

IF you were to use the JDI in-ine with the 8x10 (which I don't know whether or not it's capable of) you'd go

SVT Head "Speaker Out" --> JDI "Input"

JDI "Thru" --> 8x10

But you must use speaker cable (not instrument cable) for the amp to be happy, and I don't know if that will work with the JDI.

I know the Countryman 85 DI has a toggle switch for speaker (vs. instrument), but I don't know if the JDI can accept a speaker load.

No doubt it's worth an email to Radial to ask them if it's OK.

Is there any "External Amp" or "Preamp Out" on the back of your SVT?

Again... the only thing I'd plug into the speaker outs are speakers. I'd personally stay away from the speaker outs with the JDI.

I don't know enough about speaker DIs. They scare me. Someone who has used speaker DIs with SVTs for years should chime in and school us both. (Jimmy?)
 

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#20
There should be an extension amp and that would be the best place to put your JDI. Plugging into the ext. speaker jack is going to do damage to your amp. Running a 4 ohm load when it's using the 2 ohm tap you run the risk of flashover in the tubes short term and damage to the output transformer long term.

I'm not an expert, but I've seen people modify amps (I think it was an old Sunn) so that the taps are switchable instead of wired to the jacks, but I don't know if that's possible on a vintage SVT or if it was even the same type of wiring for the transformer taps.

I've used the country man, that's the way to go if you want to DI off of the speaker out. It's rated to handle the equivalent of 2800 watts into 4 ohms according to the manual. It works by presenting a high impedance to the signal so it doesn't really appear in line with signal and the amp only "sees" the cab but it's able to pinch of a little signal to be sent out through the DI.
 

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