View Full Version : Bridging a Onkyo M-504


MacKee
08-11-2009, 03:12 PM
A question for those familiar with mono block Onkyo M-5xx amps. I am currently running a Yamaha M-40 bridged (using a bridging adapter) pushing a subwoofer. I have just acquired another Onkyo M-504. I would like to run it bridged. Doable?

Toasted Almond
08-11-2009, 03:15 PM
Nope. I don't recall any of the M-5xx series being bridge capable. Not too sure Onk ever made a dedicated mono amp either. I've had 504, 506, and still have 5090. None bridge capable.

kneeOhFight
08-11-2009, 03:38 PM
nooo...simply a waste of your time..I think you should just take that awful M 504 and give it to me, and get it out of your hair...:D
I'm crazy about this M-5160 I have...I can't imagine how sweet that thing must be...sucha beautiful piece to look at, to hear it must be sublime:yes:

whoaru99
08-11-2009, 03:44 PM
A question for those familiar with mono block Onkyo M-5xx amps. I am currently running a Yamaha M-40 bridged (using a bridging adapter) pushing a subwoofer. I have just acquired another Onkyo M-504. I would like to run it bridged. Doable?

It needs to be a common ground amplifer.

If you can find a schematic to confirm this, the same bridging adapter should work.

Alternately, measure resistance between two black (-) speaker terminals of a given speaker terminal pair. If it measures low resistance, like the same reading you get when touching the ohmmeter leads together, that would be a good indication of a common ground amp as well.

Jon_Logan
08-11-2009, 03:50 PM
Alternately, measure resistance between two black (-) speaker terminals of a given speaker terminal pair. If it measures low resistance, like the same reading you get when touching the ohmmeter leads together, that would be a good indication of a common ground amp as well.

The only time this doesn't work is the rare occasion where the speaker relay in "disconnect" or "off" mode grounds the speaker leads to ground. If they wire like this, the (+) and (-) terminals will all measure continuity to ground.

The good news is this isn't a very typical speaker relay wiring practice.

MacKee
08-11-2009, 04:01 PM
It needs to be a common ground amplifer.

If you can find a schematic to confirm this, the same bridging adapter should work.

Alternately, measure resistance between two black (-) speaker terminals of a given speaker terminal pair. If it measures low resistance, like the same reading you get when touching the ohmmeter leads together, that would be a good indication of a common ground amp as well.

I believe it is a common ground amplifer, but I am not sure.

MacKee
08-11-2009, 04:09 PM
nooo...simply a waste of your time..I think you should just take that awful M 504 and give it to me, and get it out of your hair...:D
I'm crazy about this M-5160 I have...I can't imagine how sweet that thing must be...sucha beautiful piece to look at, to hear it must be sublime:yes:

I will say the meters are sweet:D

Damage
08-11-2009, 04:25 PM
I think you might run into a problem with the "Servo" aspect of the design.

Jon_Logan
08-11-2009, 05:04 PM
The servo aspect of the amp should not present any additional problems to the amp. The amp's will run independently. The amps have know idea what is on the other side of the load. Each amp channel, in a bridge configuration, will just tug on it's side of the load. Each amp channel, in a bridge is just driving it's half of the load down to virtual ground.

If the amp is common grounded and can drive half the impedance of the connected load, it should be fine.

Damage
08-11-2009, 06:56 PM
I am under the impression that the "Servo" circuit is in the power amp and works in the NFL removing DC components and other such things. I believe though, that it responds to electromotive forces of the speaker system, which is why I would be concerned about bridging the amp.

I don't know if it's like the DD circuit in Kenwoods or not. As a matter of fact, there isn't a whole bunch on it at all. I'm not even sure if the 504 has Servo circuitry.

MacKee
08-11-2009, 07:10 PM
The M-504 does have servo circuitry, I do know that much about the amps. Geez, Yamaha amps are simple...

Damage
08-11-2009, 07:31 PM
I found one post where a guy was running his bridged on a subwoofer.

cbrworm
08-11-2009, 07:31 PM
I would be leery of trying to bridge it. They are great amps, but don't really seem to like low impedances for long - if you bridge it I would not run anything lower than an 8 ohm speaker which will be the same load as 2 4 ohm speakers non bridged. I am talking out of my butt here, but since the pk-pk voltage could be twice as high bridged - you may go out of the SOA of the output transistors.

whoaru99
08-11-2009, 10:40 PM
It's not my stuff, but, personally, I doubt there is any more risk of damage to the Onkyo than to the Yamaha.

MacKee
08-12-2009, 06:57 PM
Schematic at hifiengine.com shows a common ground.

Looks like it does have a comman ground.

Damage
08-12-2009, 08:02 PM
It's not the common ground I'm worried about, it the NFL system that's my concern. But again, one post from a guy on a random forum says he is bridged his.

MacKee
08-12-2009, 08:43 PM
It's not the common ground I'm worried about, it the NFL system that's my concern. But again, one post from a guy on a random forum says he is bridged his.

Aye, what post is this you speak of?

Damage
08-13-2009, 01:07 AM
Aye, what post is this you speak of?

A random one. So random in fact, that I will never find it again. He just said he was running his subwoofer with a bridged m504. No idea where.

MacKee
08-13-2009, 08:39 AM
I googled m504 bridged...nothing:boring:

I did see a post by a user named Sir Terrence on the audioreview site who has a M-508 running a sub. Now that's brutal:rockon:

Damage
08-13-2009, 11:14 AM
I wasn't audioreview I found the post. It was some HT site.

stereocuuple
08-13-2009, 11:29 AM
dont do this!!!! dont dont do not!

whoaru99
08-13-2009, 12:07 PM
dont do this!!!! dont dont do not!

That's not very helpful.

Why not?

And, what's your basis for why not?

dspear99ca
08-13-2009, 01:07 PM
I would be leery of trying to bridge it. They are great amps, but don't really seem to like low impedances for long - if you bridge it I would not run anything lower than an 8 ohm speaker which will be the same load as 2 4 ohm speakers non bridged. I am talking out of my butt here, but since the pk-pk voltage could be twice as high bridged - you may go out of the SOA of the output transistors.

You are right. Running bridged, each amp channel only sees half the load impedance. So if your amp is rated for 4 ohms, it'll only be rated for 8 ohms in bridged mode. Theoretically you should get 4x the power into the same load in bridged mode, but you'll burn up your outputs unless they can handle double the power dissipation. Also, unless the DC offsets of both amps are equal (in sign and magnitude) the amps will fight each other and waste power.

If you are looking to get more power out of two identical amps by running them bridged, you may well be better off paralleling them instead of bridging... there are a few rules to follow: you don't have to worry about load impedance as each amplifier connected to an 8-ohm load in parallel will see a 16-ohm load, but you need to add low-value resistors to the outputs, and you have to make sure your DC offset is as small as possible (ideally ZERO), and you have to make sure that the gain of the amps is as nearly identical as you can get it to avoid having the amps try to drive each other (which generates heat and is a waste of power).

MacKee
08-13-2009, 10:43 PM
If you are looking to get more power out of two identical amps by running them bridged, you may well be better off paralleling them instead of bridging...


I'm only interested in bridging one m-504...to run my sub.

Jon_Logan
08-14-2009, 08:41 AM
Tell us a little more about the load (the sub). Is it a dual voice coiled driver?
What is the spec'd impedance of the driver?

I think I disagree about bridging causing the twice as high P-P voltage causing an SOA problem. The transistors won't "see" the 2x voltage, only the load will. To the amplifier, each amp channel runs independently, albeit into the load/2. So, if an 8 ohm speaker is hanging in a bridge configuration each amp channel "sees" half the load. The center of the load is zero volts or virtual ground. That's why the impedance is halved for each channel.

If the amplifier signals were the same and not complementary, the impedance that the amp channels would see would be infinite since there is no voltage across the load.

The same goes for DC. If the offsets are common mode, there is no wasted power across the load. If the offsets are opposite polarity, then it is wasted current, but no different than wasted DC offset current of a single amp channel driving a load to ground.

I think paralleling through fractional ohm resistors is much more tricky. With paralleling, your amps feedback paths are now seperated by ~0.2 ohms and not a "squishy" 8 ohm load. ....just think of what happens if the volumes don't track. I'd much rather seperate my amp's feedback by a virtual 4 ohms than a real 0.2 ohms.

whoaru99
08-14-2009, 09:37 AM
I might make a simple recommendation that if you, MacKee, want a powerful amp to run a sub, pick up a Behringer EP2500. They are not very expensive new, and can be had for even less if you buy used. They have all the necessary functions built in to run normal or bridged operation, and are rated for 8, 4, or 2 ohms stereo, and 8 or 4 ohms bridged.

Load testing shows them to be about 2,000W bridged into 4 ohms. And, they have gain controls so if you don't need that much you can always cut back.

They are a favorite amongst many, many DIY sub people.

dspear99ca
08-14-2009, 10:37 AM
I think I disagree about bridging causing the twice as high P-P voltage causing an SOA problem. The transistors won't "see" the 2x voltage, only the load will.

The voltage swing will be double, and yes, each amp channel only sees half the total p-p. BUT, and here's where it gets tricky, power is a function of voltage SQUARED. That's why your 2x voltage swing causes a 4x increase in power into the same load. Your 100W per channel stereo amp (theoretically) puts out 400W bridged. So, there's the heat generated by twice as much power PER AMP CHANNEL to dissipate... it's gotta go somewhere. By halving the impedance seen by each amp channel, you are thereby (again theoretically, if amp can handle it) doubling the current drawn through the output devices (and hence the additional heat, killer of all things electronic).

I'd much rather seperate my amp's feedback by a virtual 4 ohms than a real 0.2 ohms.

Hence my comment about getting the gains as close to identical as possible, if it were me I'd measure it with an oscilloscope. It's a viable option when you've got an 8-ohm speaker and (two) amps that cannot drive a 4-ohm load.

stereocuuple
08-14-2009, 10:47 AM
The onkyo m 504 is not designed to chimney away the heat that will be created during this type of operation. It would require at least the addition of a cooling fan, a significant upgrade to the underrated power cord, and still I believe the enclosure would capture too much heat.

This alone should be enough reason for any cautious individual to say no to this type of operation. Let alone the fact that bridging this amp is not recommended by the manufacturer nor did the manufacturer see fit to incorporate this capability into its original design. The M504 is designed (SPECIFICALLY) to be operated as a two channel stereo amplifier. As for further comment, see my origional post.

p.s. if you would like to be able to fry bacon and french toast on top of your amp, go ahead. you will be risking multiple component failures.

if you would like a more powerful amp, i suggest you sell the onkyo and use the money to buy one.

eric:smoke:

Jon_Logan
08-14-2009, 10:50 AM
The voltage swing will be double, and yes, each amp channel only sees half the total p-p. BUT, and here's where it gets tricky, power is a function of voltage SQUARED. That's why your 2x voltage swing causes a 4x increase in power into the same load. Your 100W per channel stereo amp (theoretically) puts out 400W bridged. So, there's the heat generated by twice as much power PER AMP CHANNEL to dissipate... it's gotta go somewhere. By halving the impedance seen by each amp channel, you are thereby (again theoretically, if amp can handle it) doubling the current drawn through the output devices (and hence the additional heat, killer of all things electronic).




There's nothing tricky about it. A bridged amp driving an 8 ohm load, each amp channel sees 4 ohms as if it were a 4 ohm load single ended period. I say that many amps can drive 4 ohms. In a bridged configuration, both amps are running complementary signals, so each amp channel is working just as hard driving it's half of the load ....z/2 Bridging isn't a deathnell for an amp. It's just half the load. If it's an 8 ohm load, the amp must be capable of driving 4 ohms. .......just as if each amp channel was in-phase and driving individual 4 ohm loads. Not that much of a biggie.

Paralleling the amps won't buy much except reduced power dissipation of the output stages. ....no more voltage across the load, so I don't see the gain unless the amp is delicate.

dspear99ca
08-14-2009, 11:03 AM
You're right, if the amp is rated to drive a 4-ohm load, it should have no issues with driving an 8-ohm load in bridged mode.... as far as the output devices are concerned, there is no difference whatsoever.

whoaru99
08-14-2009, 12:18 PM
The onkyo m 504 is not designed to chimney away the heat that will be created during this type of operation. It would require at least the addition of a cooling fan, a significant upgrade to the underrated power cord, and still I believe the enclosure would capture too much heat.

As others have said, as long as the bridged amp is used on a 8 ohm load, it's not working any harder than at 4 ohms in stereo operation.

Surely a separate amp as nice as the M-504 is rated for operation at 4 ohms?

stereocuuple
08-14-2009, 12:41 PM
I'm not going to waste any more time explaining to you guys why this is wrong. I gave you very simple mechanical reasons why this is an ill-advised idea. I suggest the OP contact the manufacturer tech support to inquire as to the endless myriad of reasons why this is not a good idea. If onkyo had designed this amp to run in bridged mode, they would have provided purposeful and safe facilities for doing so.

Eric

stereocuuple
08-14-2009, 01:07 PM
We just called onkyo tech support, they said ABSOLUTELY DO NOT bridge this amplifier. IF you dont believe me, believe them. "Amplifier is not stable in bridged operation." Here is the phone number for onkyo tech support, good luck waiting on hold...

201-785-2600

Thanks,
Erin

dspear99ca
08-14-2009, 01:08 PM
I'm not going to waste any more time explaining to you guys why this is wrong. I gave you very simple mechanical reasons why this is an ill-advised idea. Eric

You sound frustrated, but you really didn't back up what you so vociferously stated, i.e. that the amp "The onkyo m 504 is not designed to chimney away the heat that will be created during this type of operation."

All you had to say was that the M-504 is not rated to drive a 4-ohm load, which is in fact the case... it's rated at 165wpc at 8 ohms and no 4-ohm rating is given in either the user manual or service manual.

Jon_Logan
08-14-2009, 01:13 PM
I'm not going to waste any more time explaining to you guys why this is wrong. I gave you very simple mechanical reasons why this is an ill-advised idea. Eric

I didn't see any data/concepts of why bridging is so much more dangerous than single-ended. The chimney effect and mechanical layout for convection cooling etc. that you're talking about applies to the amplifier with any output configuration. So, bridging an amp with a 8 ohm load is just as ill advised as connecting 2 4 ohm speakers, one per channel.

There is a benefit to bridging vs. driving the two channels in-phase. Bob Carver did this in his 400 cubes. ........the pull on the power supply is out of phase meaning each channel is drawing from complementary filters. less sag.

whoaru99
08-14-2009, 02:03 PM
If onkyo had designed this amp to run in bridged mode, they would have provided purposeful and safe facilities for doing so.

Eric

I'm not going to argue about what Onkyo said, or didn't, or if their information is good or not.

However as a general statement, there are many, many, many amps that do not have built-in bridging but can be bridged safely with an external bridging adapter.

The Yamaha M-40 that the OP has been using is a perfect example. It has no built-in bridging capability, yet it works fine with a bridging adapter.

Damage
08-14-2009, 02:35 PM
I'm not going to waste any more time explaining to you guys why this is wrong. I gave you very simple mechanical reasons why this is an ill-advised idea. I suggest the OP contact the manufacturer tech support to inquire as to the endless myriad of reasons why this is not a good idea. If onkyo had designed this amp to run in bridged mode, they would have provided purposeful and safe facilities for doing so.

Eric

That's not true in any way, shape, or form. Multiple companies sold a way to bridge amps externally called a bridging adapter, a la Nikko.

Damage
08-14-2009, 02:41 PM
Actually, the previous statement by stereocuuple jogged my memory. I had bought a bridging adapter from another AK member a few years ago. Back when I was trying to find some amps to power my Carvers, I tried a bridged Onkyo M-504 versus my Rotel RB-980BX using a Nikko bridging adapter. I found the Onkyo to be pretty lackluster to begin with (in stereo mode) since it had very little headroom. It never would push the meters past the 0db mark. And I always thought the bass response was relatively weak. I blame it on the use of only 4 transistors per side. Well, not sure if 4 is right, but it's not very many. Maybe only 2 per side.

Anyways, I did bridge the M-504 for a while on the very 8 ohm stable Carver Amazings Silvers and it did fine. Here are the ebay pictures I made when I sold it.
http://fastmustangs.com/images/ebay/onkyo/onkyo.jpg

dspear99ca
08-14-2009, 02:55 PM
Interesting that on an amp with no 4-ohm rating, they'd have multiple speaker outputs. And I can see that you can engage either both at the same time. Unless they expected you to have two sets of 16-ohm speakers, it's a fair theory that it'll drive 4 ohms (i.e. two pair of 8-ohm).

MacKee
08-14-2009, 07:55 PM
Alright everyone....wow! :yes::D:smoke: I should mention that the M-504 would be driving an 8 ohm load, which is a 15 inch Klipsch subwoofer. I asked the same question about the Yamaha M-40 and bridging it, with a Sonance Bridging Adapter, which I have learned from Sonance, eventaully, that it does exactly what most of us thought it would - it inverts one side, but it also has a gain control, which kinda through us for a loop (I guess I should of posted I heard from Sonance again...sorry, didn't mean to leave you'all hanging...:nono:)

The yamaha has been running bridged with no problems, as most said on my other thread that it should. But I also know the Yamaha has 4 ohm listed specs.

This is a great site, I really appreciate the input from everyone :thmbsp:

chris914NY
10-18-2009, 07:53 PM
Hello everyone .. I havent been here is a few years ,, But i just got a 504 .. The funny thing is ,, one of the guys i work with found it in a dumpster at work. And they know i love audio stuff . so i got a call that they found some speakers in the dumpster . when i got there was some car speakers and this big thing sitting on the end of a pickup truck tail gate .. I said to myself i looks like a amp // .. it was very dirty and some paint on it . So i took it home a lunch cleaned it up/ then i pluged it in and it powered up .. so when i got home after work i took off the covers to make sure ther were no bugs in it and cleaned it up some more .. Then put a pair of speaker to it and put it to the pre amp .. And crossed my fingers ,, it works just fine . the only thing wrong is a light in the right meter its out . is there a way i can get a new one. i see how to replace it where can i get one so i can i fix it my self ? chris NJ

rselby
09-22-2013, 08:22 AM
wow back from the dead...LOL ...I have (2) M 504 running at 4 ohms per CH...and they don't run hot or anything...work just fine for over 3 yrs now! may end up bridging another one I have to power my center speakers in a HT.