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Message started by Burgermeester on 05/20/22 at 09:34:50

Title: Bridging
Post by Burgermeester on 05/20/22 at 09:34:50

WARNING: ABSOLUTE CLUELESSNESS AHEAD

I have a pair of UFOs on order that I am planning to use monoblocked. To do this i need to "bridge" the output (speaker binding posts) on the amps.

Understanding this is proving difficult. There are plenty of videos on YT but they all suffer from the same problem, like that nightmare you used to have as a college student where you dream you're in a class but you're walking in a month late not knowing what's going on.

I see that Steve is offering the cables to bridge the INPUTS as well as the outputs on an amp. Can anyone explain why I would want to bridge inputs?

Title: Re: Bridging
Post by CAJames on 05/20/22 at 12:42:37

You need to split the incoming signal from your source so both the left and right channels of your UFO are amplifying the same thing.

Title: Re: Bridging
Post by Same Old DD on 05/20/22 at 13:39:22

I remember Steve used to offer an internal modification for this which eliminated using a seperate adapter cable as a split.
That was a semi permanent mod, however.

Without that mod, you will end up with basically two "Y" cables to input your two mono amps one for left amp, both inputs and one for right amp both inputs.

The bridging actually happens when you connect a speaker system to the "Hot" out on one channel and take the "Neg" out from the opposite channel on the same amp.

Title: Re: Bridging
Post by Lin on 05/20/22 at 18:23:43

From the owners manual:

The SE84UFO can be connected as a mono amplifier and a single amp
used to drive each loudspeaker. This is desirable when you want more
power or you want to use shorter speaker cables.

To wire the amplifier for mono two things have to happen.
1) A signal must be fed into both input jacks, usually accomplished
with a Y-Cable.
2) The speaker jacks must be connected in series with a single piece
of wire 10 to 12 inches long. It connects between the left positive
and the right negative speaker jack on the amplifier. The two
remaining speaker jacks, one on each side, are used to power the
loudspeaker.

Title: Re: Bridging
Post by Same Old DD on 05/20/22 at 18:59:44

Good one, Lin.
I was trying to be so precise answering his input question, I failed to complete the info regarding the output.
Glad you stepped in!

One more point to consider; running the outputs in series/mono, the amplifier will no longer be expecting an 8 Ohm load, but rather a 16 Ohm load.
But if you can safely run them at 4 Ohms in stereo, 8 Ohms in mono will be fine.

I can not say if that makes much difference with a UFO, but I know many other amps would not like running at half the rated impedance without some heat build up.

I have run my older SE84C amps at 2 Ohms in mono without a stutter or much difference in heat at normal levels. I also remember Steve saying that these OLDER amps would sutain a welding arc for a few seconds with no harm. Never tried that one.
I assume the UFO is even better.

Maybe someone can talk more about the UFO impedance requirements in mono mode.

Title: Re: Bridgin
Post by Lin on 05/20/22 at 20:20:58

Tube amps are not exactly like solid state in this regard.
The power tube likes to "see" a certain impedance and the speakers present their own (much lower) impedance, so an OPT tries to match the two. The newer OPTs with a 4/8 ohm switch can help. Tube amps are pretty tolerant of "mismatches" though and at extremes will decrease distortion and power (light loading) or just increase distortion without much power increase.

IMO/E the 3 dB in output will not make much difference in most cases. Moving your chair a couple feet closer has the same effect.

Title: Re: Bridging
Post by Same Old DD on 05/20/22 at 22:05:47

Thanks, Lin.

I was concerned about what changes the new OPT had made. I had only read about the impedance switch, but I have no first hand experience with the UFO.
That's the reason I raised the question.
Mine are the old ones.

Title: Re: Bridging
Post by Burgermeester on 05/20/22 at 23:48:11

Thanks everyone. Much clearer.

Lin's explanation does raise another point -- the impression I had from watching YT videos on this subject, i.e. that bridging stereo amps into mono is not necessarily the same thing, and not necessarily as good, as having an actual mono amp. Then again, this relates to solid state and as Lin notes, tubes are different. (I guess that explains why DW offers at least one speaker in both 8 and 16 ohm versions?)

My sole reason for getting two UFOs and further annihilating my bank account was to eliminate the lack of power issue that is consistently brought up -- for every person who says 2.8 watts is fine, another says "not in my room." It seems that 2.8 is kind of borderline, so I figured 6 watts would be a safer choice (I am committed to SET and not young enough to play around with one UFO before deciding I need another one -- by then the queue will be four years).

I don't suppose Steve would build me a pair of mono UFOs. That would be a whole other design and tube compliment, presumably.

Title: Re: Bridging
Post by Dana on 05/21/22 at 02:46:14

model SE84UFO3
Monoblock version of SE84UFO2

https://www.decware.com/newsite/SE84UFO3.html

Title: Re: Bridging
Post by Lin on 05/21/22 at 04:04:02

Burgermeester, what speakers?

The mono amps (UFO3) are just that, mono, no more power.

Title: Re: Bridging
Post by Burgermeester on 05/21/22 at 05:01:56

Yes. Apparently the only way to get this particular SET up off 2.8 watts is by bridging...

Tube Tots at the moment.

Title: Re: Bridging
Post by BicycleJoe on 05/21/22 at 06:43:28

As of yesterday in the DECWARE Silver Reference Cable section

this SE 84 bridging kit has been listed

https://www.decwareproducts.com/product-page/se84-bridging-kit

or this jumper set

https://www.decwareproducts.com/product-page/jumper-set

Title: Re: Bridging
Post by Burgermeester on 05/21/22 at 09:39:41

Yes, I'm waiting for Black Monday. I should have my dual UFOs about 18 months after that.

Title: Re: Bridging
Post by Analogue1 on 05/26/22 at 14:04:31

I've been using 2 SE84UFO2's as mono amps for a while now.
It's actually a simple setup once you've done it. After bridging 2 speaker outputs (L+R) with any single strand speaker wire, it's just a matter connecting the RCA Y adapters.

With the UFOs each having 2 inputs, you need 2 RCA Y adapters per amp if you plan to run 2 music sources.

The Y adapters you need are 2 male RCA plugs to 1 female RCA.
The kit Decware offers shows 2 male RCA plugs to 1 male RCA plug. Decware are longer cables that plug directly to your music source. Both types will work. One of my turntables has dedicated RCA cables so I use the 2 male to 1 female type.

The RCA Y adapters are available for a few $ each for cheap ones up to audiophile grade ones like Decware offers.

For example only, here is a mid grade one (no affiliation):
https://www.audioquest.com/custom-installation/splitters-connectors-adaptors/splitters/flx-x-rca-splitters-female-to-2-male

My UFO amps work great bridged to mono and they drive Klipsch Heresys to quite loud levels. No preamp needed or used.

Hopefully, I haven't added confusion with this post.

John

Title: Re: Bridging
Post by Analogue1 on 05/27/22 at 02:46:58

Steve D tells how best do it in 2017 -

Re: Using SE84ckcs as mono amps
Reply #1 - 07/06/17 at 22:28:32

It is easy to bridge the amps into mono. If you download the current owner's manual there are diagrams on how to do it.

In a nutshell it is just as simple as getting a Y-Cable (2 male, 1 female) for each amplifier's input jacks and a 12 inch piece of wire for each amp to connect the left positive speaker jack to the right negative speaker jack. The remaining unused positive and negative speaker jacks will be used to connect your speaker.

Title: Re: Bridging
Post by BicycleJoe Lo-Fi on 08/29/22 at 11:34:34

Bump