Guitar Amp Question

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williamsongs
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Guitar Amp Question

Post by williamsongs » Wed Feb 03, 2010 10:36 am

Fender '65 Deluxe Reverb REISSUE.

I am going to move the amp chassis into a head-only cabinet and use it to drive this very nice Daedalus speaker cabinet. I like the fender clean tone at all volumes with an archtop guitar, and am not interested in having breakup at any volume.

Problem is, the amp is made to see a total 8ohm load. The speaker is a very efficient 4ohm creature. What will I need to change to make this work the way I want?

I know that the amp is looking for an 8ohm load and can handle pretty wide variations from that, but not this wide, and I can't afford new tubes every 20 minutes.

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Post by Marc Alan Goodman » Wed Feb 03, 2010 11:17 am

Either grab another 4 ohm speaker and wire it in series (not parallel!) or just get an 8 ohm speaker. Don't use the 4 ohm speaker with a 8 ohm tube amp. Going down is bad. BAD. And it's more the transformer that I'd worry about as opposed to the tubes. Tubes are cheap comparatively.

If you REALLY REALLY wanted just the sound of that speaker weber (tedweber.com) makes a box that's essentially an additional transformer to bridge between different ohm loads. I haven't heard how it sounds but weber stuff is known for quality.

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Post by williamsongs » Wed Feb 03, 2010 11:32 am

Right, right. I was under the impression that at the least, the transformer would need to be changed to deal with the change in speaker demand. Is this right? I would not be running this combo of amp/cabinet without addressing that mismatch first. I'm not looking to toast anything. For now I'll just use the amp stock as it is, with it's 8ohm speaker.

Just wondering what I need to do to the amp to make my amp/cabinet idea feasible.
Thanks for thinking about this....

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Post by ckeene » Wed Feb 03, 2010 12:13 pm

Running a deluxe into a 4 ohm load is never going to be anything other than a theoretical problem

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Post by ??????? » Wed Feb 03, 2010 12:53 pm

Marc Alan Goodman wrote:Either grab another 4 ohm speaker and wire it in series (not parallel!) or just get an 8 ohm speaker. Don't use the 4 ohm speaker with a 8 ohm tube amp. Going down is bad. BAD. And it's more the transformer that I'd worry about as opposed to the tubes. Tubes are cheap comparatively.

If you REALLY REALLY wanted just the sound of that speaker weber (tedweber.com) makes a box that's essentially an additional transformer to bridge between different ohm loads. I haven't heard how it sounds but weber stuff is known for quality.
I disagree, slightly.

Recall that the onboard extension speaker jack on the DR is designed so that you put an 8Ω speaker in parallel with the onboard 8Ω speaker, for a total load of 4Ω.

This is perfectly fine to do with a Fender amp, and the transformers were spec'd to handle it.

And people argue whether mismatching upward or downward is worse, but most amp manufacturers go to the trouble to put a shorting jack on the speaker output for a reason... a short circuit (zero ohms) is a lot more tolerable to an OT than an open (infinite ohms). My experience bears this out. It's a very different matter for solid state amps, of course, as I'm sure you know. But most people who claim that the downward mismatch is more dangerous learned that bit of conventional wisdom in the context of solid-state amps, where it is true. For tube amps, many people (self included) will tell you quite the opposite.

Both upward and downward mismatches can be bad in a tube amp if you go too far, but generally halving or doubling on these old Fender amps is not going to kill anything. However, it will not give you the best performance or the most efficiency. Impedance is an always-changing, dynamically responding moving target, anyhow, depending on frequency.

In the OP's case, I would consider replacing the stock OT with a better unit with multiple secondary taps. Heyboer makes a nice one, as does Mercury ($$$), and a few others. The stock OT on the RI is nothing to write home about, anyway, so it might be an improvement all around.

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Post by KennyLusk » Wed Feb 03, 2010 1:02 pm

??????? wrote: In the OP's case, I would consider replacing the stock OT with a better unit with multiple secondary taps. Heyboer makes a nice one, as does Mercury ($$$), and a few others. The stock OT on the RI is nothing to write home about, anyway, so it might be an improvement all around.
+1 :^:
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Post by williamsongs » Wed Feb 03, 2010 1:14 pm

Thanks guys, I was beginning to feel like a dolt. That solution is what I had expected, to replace the output transformer with one appropriate for the load it's now going to see. The amp will then only ever feed this 4ohm cabinet, no combining or swapping around again. I'll never use the "external" output. The head will only drive the one 4ohm cabinet from then on.

Also, I like the idea that a replacement OT will even provide a somewhat better freq. response, at least better than the stock did.

Thanks again, all.

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Post by ??????? » Wed Feb 03, 2010 1:32 pm

Something else to consider is that there's no real reason to not get a multi-tap OT. That way you can hook it up for 4 ohms and tape the other leads off. If someone in the future decides to go back to 8 or even to 16, then the capability will be lying there waiting.

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Post by ckeene » Wed Feb 03, 2010 1:52 pm

??????? wrote:Something else to consider is that there's no real reason to not get a multi-tap OT. That way you can hook it up for 4 ohms and tape the other leads off. If someone in the future decides to go back to 8 or even to 16, then the capability will be lying there waiting.

No reason except 100 bucks and a few hours of time swapping out an OT that doesn't need to be replaced and will make zero tone difference for someone who's not driving the amp hard enough to saturate it. Seems like a fool's errand to me, unless you want to muck with your amp for fun.

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Post by KennyLusk » Wed Feb 03, 2010 2:22 pm

ckeene wrote:... will make zero tone difference for someone who's not driving the amp hard enough to saturate it.
So a transformer, is a transformer, is a transformer...?

Never heard that one before. :shock:
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Post by ckeene » Wed Feb 03, 2010 2:31 pm

KennyLusk wrote:
ckeene wrote:... will make zero tone difference for someone who's not driving the amp hard enough to saturate it.
So a transformer, is a transformer, is a transformer...?

Never heard that one before. :shock:
In this instance, I think the results will be underwhelming, particularly for someone who in his first post indicated he doesn't have a lot of dough.

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Post by williamsongs » Wed Feb 03, 2010 2:46 pm

Hey guys, thanks for keeping this going. To clarify, the only tone change I am looking for is in the use of the new speaker cabinet. It is a world of better to me.

I don't want to alter the tone of the amplifier, that's not my concern here. I simply do not want to destroy it by using a new cabinet.

So whatever OT will work to allow me to use the new cabinet, without damaging the amplifier... that's what I am looking for.

Other benefits to tone, well that's nice too, but that isn't my priority. Just not toasting my amp. Or not having to buy another amp. I guess I don't want to do that either.

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Post by roscoenyc » Wed Feb 03, 2010 5:16 pm

ckeene wrote:Running a deluxe into a 4 ohm load is never going to be anything other than a theoretical problem
Plug in your 4ohm speaker.
You'll be just fine. Its a Fender. The tolerance is wide.

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Post by calaverasgrandes » Wed Feb 03, 2010 8:07 pm

I am no fender expert, quite the contrary, I'm on record as being a little bit anti fender.
About output trannies. Some amps never want to see less than 8 ohms. I have seen Traynor and other amps blow their output tranny when hooked up to a 4 ohm load. I have yet to see any amp blow from being on a 16 ohm or 32 ohm load. Infinite ohms is not the same as going up or down one notch in the real speaker world. Speakers come in 4, 8, 16 ohms. Some weirdos make 32 and 2 ohm cabs but mostly those 3 are the only ones you ever deal with. (okay and the jackass 6 speaker 6 ohm cabs some guys made). So to clarify, many tube amps get quite mad if they were only ever intended to drive a 16 ohm cab, or maybe a pair at 8ohms and then you ask them to drive 4 ohms (like 4 cabinets!).
I am not familiar with the amp in question but yeah, it is likely that it may have a tap for 4 ohms. Oh snap, google search!
http://buildthemusic.com/content/amps/F ... manual.pdf
yes it does 22 watts into an 8ohm load!
I dont see taps coming off the transformer for different loads so I personally would not run that amp into 4 ohms. YMMV.
After looking at the manual it doesnt make sense. There is a parallel jack which the manual specifically says will put a speaker in parallel with the "8 ohm" speaker in the combo. Elsewhere it admonishes you to run at 8 ohms to "avoid distortion or damage". I would contact Fender CS and get this clarified. If they dont want folks blowing this thing up they should put a switching jack that disables the internal speaker when using an external one. Or at least be clear about supported impedances!

edit: wooops! wrong link first time. Thanks to google for returning the twin reverb above the deluxe reverb link? WTF?
??????? wrote: "everything sounds best right before it blows up."

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Post by ??????? » Wed Feb 03, 2010 10:52 pm

calaverasgrandes wrote:Some weirdos make 32 and 2 ohm cabs but mostly those 3 are the only ones you ever deal with.
Yeah, like the tweed Bassman and the blackface/silverface Super Reverb. Aren't too many of those around [/sarcasm]

:)

Anyway, the reason I bounced the replacement OT idea around is because the OP said he wanted the most clean volume and headroom. He sounds like a jazz player from his question.

The amp will run totally fine into 4 ohms all day, every day, as much as you want to give it. Trust me. I've owned two, a '65 and a '67, and repaired several more. BUT you will lose some volume and efficiency, there is no way around it. It will be quieter than stock and break up sooner, and will be a little harder on your output tubes. The OT will be totally fucking fine, if not it should be a warranty issue-- the amp is DESIGNED to run into 4 ohms with the ext. speaker jack. It's less than a non-issue.

If he really wants lots of headroom, and is married to this extension cab and the speaker in it, I would personally advocate an OT of matching impedance.

Easier might be to get a very high-sensitivity speaker like the Eminence Swamp Thing or Cannabis Rex, or a JBL D120, etc. in 8 ohms and load it in the new cabinet. That would both increase headroom even more AND match impedance/obviate the desire for a new OT.

Easier still would be to find an amp that suits his needs better from the get go, rather than carrying two heavy things and maybe modifying one of them. There are lots of great amps out there. If you like the DR only louder, you might like a Vibrolux or a Twin or a Pro or....

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