Bridging 2 amps, 1 with new caps; sound different?

dan98svt

If I bridge 2 Carver M-500t amps for my Polks, will the sound be different in each speaker if one amp was re-capped? Let me rephrase that... will I hear a difference? Using CDs, no vinyl (yet).
Dan

ZLTFUL

Any modifications or repairs, especially when replacing capacitors has a chance to change the sound profile of the amp. Usually for the better depending on the quality of replacements used.

Will it sound significantly different? The only real way of finding out is A/B comparing them.

tonyb

If one is recapped...yeah, it's going to sound different.

But....why in bridged mode ? You do realize most amps in bridged mode do not like impedance swings much below 8 ohms....and usually sound worse.

F1nut

You do realize most amps in bridged mode do not like impedance swings much below 8 ohms....and always sound worse.

Fixed it for ya.

tonyb

Can always count on you Jess.

I just don't get the fixation some have with bridging amps. They must still be equating more watts to better sound. Right tool for the right job and all that.

dan98svt

Hmmm, I didn't think the amps would sound worse when bridging them. Haven't seen any mention of that in other posts. I have a 145 wpc amp on some SDA1Cs and it just doesn't push them. Even with the bass turned up all the way, I need to use the powered subwoofer to get any lows (and yes, I have them positioned properly). I'm getting some SDA SRS 1.2Tls and I know my amp won't push them and figured 200 wpc from the M-500t wouldn't do much better. I'm not planning on running them with the full 700 wpc bridged, but thought the extra umph would provide better sound, especially at lower volumes.
I'm now looking at an M1.5t with 375 wpc @ 8 ohms. The speakers are 6 ohms and I figured about 410 wpc from the amp like that. Would that be enough for the 8 mid-woofers and 4 tweeters in each 1.2, or am I diistributing all those wpc down to about 35 watts per speaker?
Dan

F1nut

Hmmm, I didn't think the amps would sound worse when bridging them.

When stereo amps are bridged the noise floor increases, which is never a good thing.

I have a 145 wpc amp on some SDA1Cs and it just doesn't push them. Even with the bass turned up all the way, I need to use the powered subwoofer to get any lows (and yes, I have them positioned properly).

Something isn't right somewhere, you should have plenty of bass from those speakers. Power amp or receiver? If it's an amp, which one? Have you checked the speakers for air leaks by doing the push test?

This just my personal opinion, I've never heard a Carver SS amp that I liked. For all that high wpc ratings they lack guts. More voltage than current.

dan98svt

I'm using an Onkyo 7.1 receiver at 145 Watts x7. I'm not sure if it's this new digital stuff that just doesn't sound powerful, but my older Kenwood 5.1 with 100 watts x5 sounded a lot better than this thing, and my even older Denon 2 channel would smoke this thing.
The speakers seem all orignal and they are connected properly. I haven't opened them up to see if someone tinkered with them and screwed up some wiring, but the screws don't look like they were ever touched. I have done the push test (while I bought them) and everything works nicely. I listen to Floyd and watch the drivers move and push the radiator, they just don't move much until I'm starting to piss off the neighbors, even with the bass turned all the way up. I'm not looking for excursion like a 15" subwoofer in a Honda, but I would like some bass out of them.

dan98svt

I was also looking at these: "Dan, I have 2 Phase Linear 400 amps from the 70's. They have been completely rebuilt as Adcom GFA555 series 2 amps with stronger output transistors. The meters are in fine working order. 120V original transformers and new capacitors. Running about 325 wpc @ 4 ohms"
Like this one:

Does this sound right? Can they be upgraded like that? I supposed I could use one for the SDA SRS and one for the SDA1C if they would be powerful enough.

Dan

F1nut

An AVR is not a good choice for 2 channel music, IMO. However, you should check the settings anyway. Have you tried Pure Direct?

Again, something is amiss as those speakers are capable of producing more than enough bass. I've heard 1C's driven with both a 40 wpc tube integrated and a 75 wpc tube amp, plenty of good, deep bass.

How far from the back wall are they? Are they sitting on carpet?

dan98svt

The AVR *Onkyo TX-SR805* only has 2 spkrs hooked up to it (just moved, been to lazy to dig out any surround spkrs...). Pure direct sounds worse than stereo. The Polks are about 8" from the back wall (there is a 1500 watt transformer behind one, cables too short to put it anywhere else, therefore can't back the speaker up any further) and about 3' from the nearest side wall. Sitting on real hardwood in front of real stone walls (Germany). Big flat rug about 3 feet in front of spkrs. Spkrs have rubber feet to keep them from moving with the rhythm.

F1nut

The AVR *Onkyo TX-SR805* only has 2 spkrs hooked up to it (just moved,

You will still need to check the settings, so run the set up program.

Pure direct sounds worse than stereo

Actually, that doesn't surprise me.

The Polks are about 8" from the back wall (there is a 1500 watt transformer behind one, cables too short to put it anywhere else, therefore can't back the speaker up any further)

One half inch can make or break the bass response. Generally, 5 to 6 inches away is ideal. 8 inches is definitely too far away, so figure out a way to move that transformer.

Spkrs have rubber feet to keep them from moving with the rhythm.

Rubber feet are no good. Install spikes with the metal disc floors protectors.

tonyb

I'll add to the previous poster's comments....

Have these speakers been owned by you for any length of time ? They are pretty old and if no work has been done to them it may be time. Also the Carvers are pretty old too with some work also most likely being needed.

The AVR you have should be sufficient for decent bass out of them, so I'm thinking settings in the receiver may be part of your problem. Make sure they are set to LARGE and subwoofer set to no or none. Then put the avr in in 2 channel mode, stereo or pure direct. There is more of a setup process in newer receivers than the work horses of yesterday.

Which brings us to what are you using to play music.....computer,cdp ? Also cables matter too, what have you got for speaker and IC'S ?

allstock

F1nut wrote: »

You do realize most amps in bridged mode do not like impedance swings much below 8 ohms....and always sound worse.

Fixed it for ya.

Easy on the absolutes there F1, my Cambridge Audio 851w's sound spectacular bridged, IMO better than running in stereo, and are perfectly happy driving my 1.2tl's. As for other amp's bridged I can't say, I haven't tried anything else bridged in my rig. You should know better than to use words like "always" in this hobby lol. As for op's issue I moved from a Carver amp 250 per and I always found the bass lacking with that amp.

tonyb

Good point Skipper, well put. Have a feeling Jess's answer wouldn't have been.....um, as polite ? lol

I do however agree on one point ALLSTOCK made, those Carvers were never big bass kickers to begin with. It's about current, not watts as we so constantly promote.

allstock

DSkip wrote: »

allstock wrote: »

F1nut wrote: »

You do realize most amps in bridged mode do not like impedance swings much below 8 ohms....and always sound worse.

Fixed it for ya.

Easy on the absolutes there F1, my Cambridge Audio 851w's sound spectacular bridged, IMO better than running in stereo, and are perfectly happy driving my 1.2tl's. As for other amp's bridged I can't say, I haven't tried anything else bridged in my rig. You should know better than to use words like "always" in this hobby lol. As for op's issue I moved from a Carver amp 250 per and I always found the bass lacking with that amp.

Actually, it is pretty much an absolute. The noise floor does increase as you bridge an amp - that's a given. Your system (don't take this wrong) may have enough noise in the chain that the increase is indistinguishable though.

Well in any event my rig sounds better in every respect with my current amps, as for noise floor I can't hear any difference with my ear 2" from the drivers so afaic it's a moot point.

ZLTFUL

OP, avoid the Phase Linear amps. There is a reason that the 400 was also affectionately called the "Flame Linear 400". They are also a bit heavy handed on the higher end.

The negative aspects of bridging amps are well documented. Yes, you get higher wattage but along with that, you also get higher noise floor, higher distortion levels, lower dynamic ability (bridging amps tends minimize the amp's ability to handle impedance swings). There is a reason that it is recommended to run speakers double the impedance in bridged mode over the impedance you would run in stereo mode...less chance of those swings causing overheating and ultimately destruction of the amp.

There is also the long term damage that bridging amps can bring. It places more stress on the circuit...virtually everywhere in the circuit...shortening the lifespan of an amp.

allstock wrote: »

Well in any event my rig sounds better in every respect with my current amps, as for noise floor I can't hear any difference with my ear 2" from the drivers so afaic it's a moot point.

I am sure it is louder...but is it really better? In less than technical terms, it is a *fact* that noise floor and distortion increase in bridged amps. It is also a *fact* that the dynamics of the amp are reduced.

tonyb

...and the louder the distortion.

Good sound is certainly subjective, but until you've heard the absence of the noise/distortion.....that's the key right there. Most think it's actually part of the music and don't identify it as noise, hence they don't have a problem. Get rid of the noise and you'd be surprised how clear and precise your music can sound.

BlueFox

allstock wrote: »

Easy on the absolutes there F1, my Cambridge Audio 851w's sound spectacular bridged, IMO better than running in stereo, and are perfectly happy driving my 1.2tl's.

I have two Cambridge-Audio 840W amps in bridged mono driving my Aerial Acoustic 7T speakers, and they sound fantastic. When I added the second amp, going from a single amp in stereo mode to dual mono amps, it was a straight up obvious improvement. It is obvious these amps were designed as mono blocks with stereo added to help sales.

In bridged mono mode they are rated at 800W/ch at 4 ohm. The only reason I upgraded to the Pass X600.5 was I needed a bit more volume at high SPLs. At normal listening levels the Cambridge amps easily give Pass a run for the money. Anybody who says the CA amps are better in stereo than mono has no idea what they are talking about.

allstock

Actually the biggest difference I find is at lower listening levels, not at high volume, although it sounds very happy and relaxed at 95+ db too. Perhaps because these amps run Class A at lower volume it mitigates the issues common to bridged amps. Cambridge Audio's website provides lots of info on how they achieve this, Class XD amplification

Our proprietary amplification system switches dynamically between Class A and AB systems. Class A amplification delivers the purest possible sound, using only one transistor to conduct, but can be energy inefficient. Class AB involves both transistors conducting simultaneously, but makes it impossible to maintain a balance of low crossover distortion and power efficiency.

Our Class XD system operates in both Class A and Class AB mode, dynamically moving the crossover point depending on the audio output volume. This combines the near zero crossover distortion of pure Class A with improved efficiency of Class AB at higher volumes, without any compromises in performance for the best of both worlds.
As I said above, I don't have other experience with bridged amps, but these provide 500w into 8 ohms and 800w into 4 ohms and the big SDA's seem to love them.

tonyb

All the info I see says 500 watts bridged mono into 8 0hms, no mention of 4 0hm capabilities in bridged mode. Normally, a 4 ohm spec is reserved for monoblocks in that regard.

The Cambridge may have some advantages bridged due to amp design, I dunno, but we are talking Carvers....not Cambridge....and most amp designs of the Class A/B nature. I'm sure there may be some exceptions to the rule out there, but none that I'm aware of to date.

The Cambridge looks by all the info to be designed as a monoblock first, then added a switch to split it up.

allstock

350W per channel into 4 Ohms

Power output – bridged mono
500W 8 Ohms
800W 4 Ohms

THD (unweighted)
< 0.001% 1 kHz
< 0.005% 20 Hz - 20 kHz

Frequency response
5Hz – 80kHz

S/N ratio (ref 1W / 8 Ohn)
>90dB (unweighted)

Sensitivity – stereo or mono
1.5V rms unbalanced
1.5 + 1.5V rms balanced

Sensitivity – bridged mono
0.775V rms unbalanced
0.775V + 0.775V rms balanced

Input impedances
Balanced input 38 kOhm
Unbalanced input 68 kOhm

Power amp damping factor
> 110 at 1 kHz

Max. power consumption
2400W

Standby power consumption
Standby <0.5W

Colour
Black or silver

Dimensions (HxWxD)
148 x 430 x 365mm (5.8 x 16.9 x 14.4”)

Weight
19.1kg (42.2lbs)
At any rate I didn't want to start a peeing contest about bridged amps, just my opinion to the OP. I know better than to try to contradict the old boys club here at the Polk forums lol ; )

BlueFox

allstock, this is all good information for lurkers. From what I have found, the 851W is basically the 840W with a prettier face. The biggest negative reviewers had for the 840W was that it was plain looking. Since there might be some with limited funds, like all of us, who are looking for a new amp, knowing about the Cambridge amps can help them. At $5k list for a pair of CA amps, versus $22k list for a pair of Pass, the decision is easily made between the two. There is a reason why The Absolute Sound listed the 840W amp as a high-end bargin.

tonyb

Pass amps Fox, are in another league than Cambridge. You should know this as your gear has certainly entered the higher end realm.

I will stand by my comments that the Cambridge was designed as a monoblock first and foremost, thus doesn't apply to our assertions about bridged amps. An apples to apples thing if you know what I mean.

voltz

need a yellow highlighter to highlight some key parts of this thread !

One thing I've learned is you don't know how much noise is in your rig until its gone. ****


Good sound is certainly subjective, but until you've heard the absence of the noise/distortion.....that's the key right there. Most think it's actually part of the music and don't identify it as noise, hence they don't have a problem.

good info like what DK & Blue have have talk about in some of their threads...

but this is the hardest part for some of us to do and understand. I think I'm learning a little though.