Help me wire my Ampeg SVT210 AV for Biamp!

ianangus

ianangus

Oct 7, 2009
48
38
4,571
Kitchener, Ontario
#1
I have a project in mind and would love help and opinions from all the experienced folks on TB!

Here's the situation:

I have an amp and a cab that I love but they don't fit very well together. The amp is a vintage Garnet PA40 with two amps putting out 40w RMS at 4ohms. The cab is an Ampeg SVT 210AV (200w RMS at 8ohms) So the problem is that with an 8 ohm load I am only using one channel of this fantastic amp, and I'm only getting about 20w out of it!

But the Ampeg cab has 2 x 4 ohm speakers, so it should be a candidate for biamping allowing me to run each side of the amp at 4ohms getting 4 TIMES THE POWER!!!!!

BUT sometimes I want to be able to run the cab the way it was designed, two speakers in parallel making 8 ohms so I can use the other side to power a second cab.

Here's the solution I've come up with. I would like to wire a speakon connector into the cab with two pins going to each speaker, make a custom speaker cord speakon to 2 1/4" mono, and wire a defeat switch into the parallel circuit between the two drivers so I can separate the two drivers when running in biamp mode. It should work as long as the switch is always in the right position while in operation, lest I go into parallel mono mode, lose all my power, and potentially fry my amp.

I will be making up a wiring diagram and thinking about this some more. All you experts, amp builders, DIYers and fiddlers out there: do you see any potential problems with this setup?? Am I missing anything important? Is there an easier way to do this?

Thanks y'all!!

27194530844_70f49b3eda_k.jpg
For TalkBass by Ian Angus McLennan, on Flickr
 
#2
A few points to ponder:

1. Bi-amping means to split highs and lows via a crossover. I think you simply want to run two channels of the amp, essentially dual-mono.

2. Are you sure the cab has two 4-ohm drivers in series? It could instead have two 16-ohm drivers in parallel. In the latter case, you can stop right now, because 16-ohm drivers won't improve your amp's performance.

3. Twice the power from a single channel only amounts to about 3dB in loudness, which is not really going to make an audible difference. Having four times the power gets you only 6dB; it takes 10dB to hear a doubling in loudness.

4. Your mention of the possibility of frying the amp with the switch wrong should be reason to cancel the plan. One little mistake could ruin a performance. This is especially risky if anyone touches your equipment, even during a break.

5. You would have to verify that both channels run in phase to avoid a virtually total cancellation of sound. You could solve this by having the speaker switch flip polarity on one driver, but now we've got a rather complicated switch/wiring arrangement. It can be done, but it'd take some careful thought.


My suggestion is to borrow another cabinet (best would be the same model) and just try running the two cabinets. If it doesn't float your boat, then you haven't spent time hacking your cabinet. (Realize, of course, that going from two to four drivers gives you a 6dB loudness bump right there.)
 
#3
Rick Auricchio said:
A few points to ponder:

1. Bi-amping means to split highs and lows via a crossover. I think you simply want to run two channels of the amp, essentially dual-mono.

2. Are you sure the cab has two 4-ohm drivers in series? It could instead have two 16-ohm drivers in parallel. In the latter case, you can stop right now, because 16-ohm drivers won't improve your amp's performance.

3. Twice the power from a single channel only amounts to about 3dB in loudness, which is not really going to make an audible difference. Having four times the power gets you only 6dB; it takes 10dB to hear a doubling in loudness.

4. Your mention of the possibility of frying the amp with the switch wrong should be reason to cancel the plan. One little mistake could ruin a performance. This is especially risky if anyone touches your equipment, even during a break.

My suggestion is to borrow another cabinet (best would be the same model) and just try running the two cabinets. If it doesn't float your boat, then you haven't spent time hacking your cabinet. (Realize, of course, that going from two to four drivers gives you a 6dB loudness bump right there.)
Click to expand...



Thanks for your replies! Lots to consider.

Thanks for the correction on terminology. I have tried the amp with two cabs and was hoping to get the same level boost without carrying the extra cab. The cab does indeed have two 4ohm speakers in series, so I should be able to get my 6db by running each speaker off of one side of the amp. I'm wondering if there's a creative and clever way to make a switch safe, such as mounting a recessed switch under the grillcloth. Just spitballing. Would be smart to wire it up with each speaker connected to one jack before I start cutting holes, to see if the sound and additional volume is worth the trouble. It would be easy enough to reverse.

Thanks again for your expertise!
 
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#6
I don't know if you've looked at the wiring in the 210av, but if I remember mine right, the jacks are mounted to a pcb board, and there is a small box sealing the jacks and plate from the rest of the cab. And I think there was some sort of black goo sealing the hole the wires went through. Long story short, it looks like a bit of a pain to re-wire. I opened it to swap the 1/4 inch for a neutrik. Not really that difficult, but for some reason it made me think twice about modding it (I didn't).
 
#7
mono to stereo is not wildly hard to do, lots of marshall cabs come with patch panels allowing for that along with series or parallel operation.

(thinking further) you could just wire each speaker to one of those jacks (for stereo), then make up a special series Y-cable that plugged into both jacks then added the two in series at the other end for normal 8Ω mono.
 
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#8
Update on this!

On the good recommendation of Rick Auricchio, I've wired up the cab in "dual-mono" without making any major or irreversible modifications to the cab. I drilled a hole through the back of the box under the back plate, put two pairs of 14ga zipcord through it, soldered terminals to each pair, and a new input jack to each pair. I chose to use new jacks and terminal so I can keep the original wiring intact and inside the cab in case I want to put it back to original. If necessary it should be a 10 minute job.

I don't know if I got my 6db but it is DEFINITELY louder and sounds more controlled, though I won't have a great idea until I take it out for a gig.

One of the perks of this setup that I've discovered is that with a stereo amp I can use stereo effects with a single cab!

27741903832_ceff83cb36_k.jpg
20160621_224205 by Ian Angus McLennan, on Flickr

27565527580_5b55c57a51_k.jpg
20160622_154956 by Ian Angus McLennan, on Flickr

27767416991_f344cb6297_k.jpg
20160622_154520 by Ian Angus McLennan, on Flickr
 
#10
punkrocko said:
I could be wrong, but I don't think that's a stereo amp. It looks like two output jacks on a mono amp. In which case you would be running a 2 ohm load in your current configuration.
Click to expand...

I was concerned about this at first two, but it does in fact have two amps in it, which is strange cause it only has mono inputs and has no panning or other stereo abilities. I've never seen another PA head like it.
 
#11
Hello ianangus :

I too have the made by Garnet /Gibson labelled PA40 ! You are 100% positive there are two amplifiers inside ? It is a very light and basic unit , but I will indeed be pleasantly surprised if your report is true ! I am so skeptical , I am considering disassembling mine to see ......
 
#12
solodb said:
Hello ianangus :

I too have the made by Garnet /Gibson labelled PA40 ! You are 100% positive there are two amplifiers inside ? It is a very light and basic unit , but I will indeed be pleasantly surprised if your report is true ! I am so skeptical , I am considering disassembling mine to see ......
Click to expand...

I am also in doubt. Usually the graphics would separate the two jacks if they are fed from separate power amps, not place them inside one block. If it is running at 2 ohms it will be louder, for how long will be the question and are output devices still available for replacement if they burn out. If it does have two power amps then each amp would be 20 watts (PA 40 not PA 80).
 
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#15
This sure looks like a mono-amp to me and a very bad match with your cab.

Vintage Microphone Mixer & Amplifier PA40
  • Manufactured by Garnet Amplifier, Ltd.
  • Made in Winnipeg, Manitoba, Canada
  • 120 Volts - 60 Hz - 80 Watts
  • Serial No. 45 SPA
  • 4 Mic Inputs
  • 2 Speaker Outputs
  • 40 Watt Amp
  • 7 Controls
  • Size: 17-3/4" long x 8" wide x 4-1/2" high
  • Heavy Duty Handle at end
 
#18
ianangus said:
it's really hard to believe anyone marketing a PA head with one 40w amp, but I guess it was a different time.
Click to expand...
Wrong tool for that job. It is not for a stadium concert, for that you would use a separate power amp.
It is a Public Address amp for speech and light playback music, 40 Watts is pretty big for the time.
I still run for speech only in my building two of these Bogen 35 watters one on each floor, for addressing the public they are loud.


IMG_1648_zpseihou8w0.jpg
 
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#19
S-Bigbottom said:
Wrong tool for that job. It is not for a stadium concert, for that you would use a separate power amp.
It is a Public Address amp for speech and light playback music, 40 Watts is pretty big for the time.
I still run for speech only in my building two of these Bogen 35 watters one on each floor, for addressing the public they are loud.


IMG_1648_zpseihou8w0.jpg
Click to expand...

I guess I'll leave it at home for my next stadium show and save the sweet tones for playing at home and the odd recording. ;)
 
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#20
S-Bigbottom said:
Wrong tool for that job. It is not for a stadium concert, for that you would use a separate power amp.
It is a Public Address amp for speech and light playback music, 40 Watts is pretty big for the time.
I still run for speech only in my building two of these Bogen 35 watters one on each floor, for addressing the public they are loud.


IMG_1648_zpseihou8w0.jpg
Click to expand...

Very handy for when you have to say, "Elvis has left the building. Repeat, Elvis has left the building."
 
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