The sunn Forum
Sunn Musical Equipment => Q & A => Topic started by: Bond...James Bond on February 18, 2006, 01:23:18 pm
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HELP! - I'm using an old tube 1200s head for my bass amp - Anyone know of an inexpensive & reliable way to get more power out of this beast? It starts to overdrive when I turn it to 7 or so &, at a gig, I want it loud & clean!
Thanx in advance
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It is fairly normal that a Sunn 1200s is going to enter harmonic distortion at 7 on up. To many, of course, this is a desirable trait.
About all I can tell you is to try a quad of Groove Tubes KT88s with a rating of 10. Groove Tubes test each power tubes point of distortion level as a part of their matching process. They are at a premium, however, and I don't know that they will satisfy the need.
You could email them at groovetubes.com and discuss with them.
Louder may actually require you to double what you have. Driving two separate bottoms with two separate heads fed buy one instrument may be the way to go. You could then approach ear splitting, clean sound.
Louder, retaining clean, via tube amps, is going to cost you more.
Regards,
Chuck
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HELP! - I'm using an old tube 1200s head for my bass amp - Anyone know of an inexpensive & reliable way to get more power out of this beast? It starts to overdrive when I turn it to 7 or so &, at a gig, I want it loud & clean!
Have the filter capacitors ever been replaced that you know of? What kind of speakers/enclosures are you running through?
It is fairly normal that a Sunn 1200s is going to enter harmonic distortion at 7 on up. To many, of course, this is a desirable trait.
I think both of these points are dead on. If your power supply is strong, you probably need to be using some efficient (ie: big, heavy and hard to move) speaker cabs.
Although I've not used a db meter for verification, it seems the loudest/cleanest, most HiFi any of my Sunns get is when loaded with Ei KT90's.
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THanks for your input.
I'm using an SWR 4x10 cab & a Ampeg single 15 cab. - reasonably efficient I would think. I had the amp serviced when I got it 2 years ago - not sure if they replaced the caps but I have the bag of parts he replaced & there's two tubes (one IEC Mullard Gf2 12au7a & one 12AX7A) as well as one Cornell Dublier pm4S22 .022 & one .047. That means little to me as I'm not a tech-y - but might mean something to you.
The amp is reasonably loud - esp with a guitar plugged in! But when we play outdoor gigs, we need to turn up & the distortion is not wanted. I don't think I'll run two heads -hauling that one is enough! If it came to that I would likely buy a more powerful head like an Ampeg SVT.
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It sounds as though the amp is working properly, though I could be wrong about that. If it is, there's very little that can be done. Even if you could get another 20-40 watts out of it, that's not much in dB, meaning you'd not likely hear the difference.
Suggestions: mike it, or use a line out/direct box.
Double up on your cabinets. Make sure the total impedance is still appropriate for the amp. This will do two things for you. It will increase your efficiency by 3 dB overall, as well as letting the drivers work in the center of their range, which is usually more efficient, and it will also narrow down your polar response, helping to project the sound better. OTOH, you'd have to buy and carry twice as many cabinets, and that's only if the impedance issues make it doable.
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Isaac - the back of the head has two outputs - one is for speaker 8 ohm & the other is for an ext speaker 4ohm. Both of my cabs are 8 ohms so should I use the two outputs from the head to driive the cabs? Or use the 8 ohm head output & then have the 2nd cab running from the output jack on the first cab? (daisychained) thanx
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When you plug one speaker cord into the 8 ohm jack, it connects to the 8 ohm tap on the transformer. When you plug into the 4 ohm jack, it connects to the 4 ohm tap. Here's the tricky part: when you plug into both, the 8 ohm jack is disconnected from the 8 ohm tap, and both jacks are connected to the 4 ohm tap.
What's it all mean? If you use one 8 ohm cabinet, plug into the 8 ohm jack. If you use one 4 ohm cabinet, plug into the 4 ohm jack. If you use two 8 ohm cabinets (a total load of 4 ohms), plug one into each jack.
I advise against plugging one 8 ohm cabinet into the 8 ohm jack, and a 4 ohm cabinet into the 4 ohm jack. That would result in a total 2.7 ohm load, and could damage the amp. I know, you weren't going to do that, but every once in a while, someone thinks it would be okay.
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I had them daisy chained but will switch so I have one plugged into each output jack. Thanks again!
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Daisy chaining is okay, too, if you use the 4 ohm jack. In general, I try to avoid it, because of the series resistance of the cabling.
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Having been the SWR rep back in the good old days, I CAN tell you that Sunn heads don't particularly like SWR cabinets; I tried a number of combinations including what I thought would KILL--a 2000S head with two 4x10 SWR cabinets. The sound bordered on Moosepoops. :^>) . Couple that with the fact that the 1200S head was maxxed out at 150 watts (marketing numbers were becoming a bit on the high side by that time) and you add to the problem. You might also want to make sure that both cabinets are in phase.
Bass-ically Yours,
Rich Briere
www.richbriere.com
The Sunn Shack
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Rich - Just making sure we're talking about the old Sunn 1200S tube head from late 60's.
How do you make sure cabinets are in phase?
Thanks!
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Yup.....that's the head.
You can check the phase by taking a nine volt battery and laying the speaker cable tip across the posts. Ground to shaft and tip to positive. Actually, a quick tap will tell you which way the speakers are moving. They should be moving in the same direction in both cabinets. They should also ALL be moving together in a multi-speaker cabinet. I've always been suprised by how many people will bring in cabinets that have been "worked on" or rewired and I discover that the "problem" is one of phasing.
Bass-ically Yours,
Rich
www.richbriere.com
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Gotcha - but do I need to do this test if the speakers have never been opened up/worked on?
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Well, let me put it this way. I've done the test on BRAND NEW cabinets and found that they had problems. I do it routinely. Takes 15 seconds and can change your life.
Bass-ically Yours,
RB
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ok - I'll be Ampeg & SWR's quality control & check it out - thanks for the tip.