Amp bridged mode?

hydrostream

Would it be ok to run a Adcom 555II along with a 555 in
bridged mode?
thanks jerry

ben62670

For non SDA's, but the performance gain might not be worth it. There may be a noticeable sound difference, and balence issues. That's an awefull lot of power.
Ben

Systems

+1 with what Ben said.When operating amps in bridged mode they should be identical.Depending on the changes introduced in the series II version of that amp you could have some SQ and gain differences between channels.

F1nut

It's also very important to keep in mind that bridged amps do not like to see loads less than 8 ohms.

ben62670

F1nut wrote: »

It's also very important to keep in mind that bridged amps do not like to see loads less than 8 ohms.

The 555's are good to 4ohms bridged;) Good to see you around:)

F1nut

Seriously? That's highly unusual.

ben62670

F1nut wrote: »

Seriously? That's highly unusual.

Seriously. Most amps cannot handle it, but the 555's have 10 15amp trannies in NPN, and PNP each:) Keep it where it can breath, and you will have no problem;)
Ben

Systems

ben62670 wrote: »

Seriously. Most amps cannot handle it, but the 555's have 10 15amp trannies in NPN, and PNP each:) Keep it where it can breath, and you will have no problem;)
Ben

Yep , amps with beefy power supplies and multple pairs of outputs can drive 4 ohm loads bridged.

hydrostream

Thanks guys i think i will just stick to a single 555. I think i need
to take a break from this audio thing. Its almost as bad as being
hooked on drugs always wanting more.
jerry

ben62670

hydrostream wrote: »

Thanks guys i think i will just stick to a single 555. I think i need
to take a break from this audio thing. Its almost as bad as being
hooked on drugs always wanting more.
jerry

If you find an answer to how to drop audio addiction please share:o

heiney9

F1nut wrote: »

Seriously? That's highly unusual.

Yes, it can be done. Not sure if there will be a sonic benefit or not. Most well designed, beefy tranny, multiple pair output amps can drive a 4 ohm load when bridged. I'm not sure I would recommend it though, strictly from a sound issue probably nothing to be gained and I doubt you'd really gain much more headroom.

For most situations a bridged stereo amp is great for a sub or center channel but I'd steer clear of using it for anything else. I'm not just referring to the Adcom, but any bridgeable stereo amp. There are exceptions like a Monarchy SM70, but thats a different topology that actually benefits from running in bridged mode.

YMMV

H9

reeltrouble1

I ran my NAD's bridged with my SDA 1C's with outstanding results, although not the same amp, actually NAD is a bit better amplifier, I would try it and see if you like it.


RT1

Face

ben62670 wrote: »

The 555's are good to 4ohms bridged;) Good to see you around:)

Does that mean they're 2 ohm stable normally? I was under the impression that when you bridge a amp, it can then only handle half the impedance load as unbridged.

heiney9

Face wrote: »

Does that mean they're 2 ohm stable normally? I was under the impression that when you bridge a amp, it can then only handle half the impedance load as unbridged.

Yes, actually they are good down to 2 ohms in stereo mode. The gen II being a little better than gen I.

From the original Stereophile review
With a minor dealer modification, you can even drive 1 ohm loads like the Scintilla. I can't measure whether the Adcom delivers its rated 800 watts per channel into 2 ohms, or 20 amps peak, but I can tell you that it does a superb job of driving this superb speaker. Anything in its price range (or even close) generally changes timbre and degenerates when driving the Scintilla at 1 ohm.



It can drive 2 ohm loads w/o modification

H9

Face

That's pretty impressive.

heiney9

Face wrote: »

That's pretty impressive.

It is; considering the times in which the Adcom hit the market (1985) and it's initial cost compared to the heavy hitters of the day. They still remain an extremely nice sounding amp at a bargain price on the used market. There are a lot of contenders now that are comparable but I think $$ for $$ they are hard to beat.

Newer isn't always better.

YMMV

H9

Systems

Face wrote: »

I was under the impression that when you bridge a amp, it can then only handle half the impedance load as unbridged.

When bridged each channel will see only half the load impedance.

Systems

Ben what changes were introduced in the series II version?

heiney9

GV#27 wrote: »

Ben what changes were introduced in the series II version?

Darlington output configuration, larger heat sinking, slightly larger tranny and unfortunately coupling caps.

It's a bit more complex having the Darlington output configuration which I believe also added servo's for the DC offset control. Thermal overload indicator as well. Teflon input connectors.

H9

heiney9

GV#27 wrote: »

Ben what changes were introduced in the series II version?

Superficially, the new '555 appears identical to the old. A closer look, however, reveals a greater number of cooling vents in the case and a cooling fan lying just under the top plate. (This fan, a $100 option, is triggered by heatsink temperature and didn't turn on during my auditioning, where average output levels were generally below 8V RMS into the 6 ohm Avalons—just under 11W.) There is now a red LED on the front panel labeled "Thermal Overload," a greater number of fuses between the rear-mounted, curved-edge heatsinks, and the input sockets are now much higher quality and use Teflon insulation. The power transfomer has been increased in size, potted to improve heat transfer, and offers greater regulation. The output circuitry has also been changed (Darlington output config), and the LF signal path has been stripped of polarized (electrolytic) capacitors. A new DC-servo circuit minimizes output DC offset.

Both amplifiers are polarity-correct, but the Mk.II version has slightly higher gain—27.75dB vs 26.9dB at 1kHz when loaded by the Avalon speakers. The 0.85dB difference was compensated for during the auditioning.

Systems

Ah Ok thanks H9.:)Apparently the gain did change with rev II as we said might be a possabilty ,so hydro would have had a balance mismatch.The addition of the servo is nice as it eliminates the need for coupling caps.

tonyb

F1nut wrote: »

It's also very important to keep in mind that bridged amps do not like to see loads less than 8 ohms.

Great point,and one mostly overlooked. If your speakers are 4 ohm with some big impendance swings,you could be in for a world of hurt.Personally,if I thought I needed more juice,I'd get a bigger amp instead of bridgeing.More juice does not necessarily equate to louder volume,if that was your intent.