Is it possible to run 2 stereo (integrated in poweramp mode) amps as monoblocks

[Huey2001]

Hi, I own a Marantz PM7004 and see many used ones for sale. I use mine in poweramp mode, with Minidsp Flex as preamp, but wonder if I can add a second one and use only one channel (poweramp in and loudspeaker outs) to hopefully use its full power on the separate channels.

Is this possible or will it damage its circuits?

 

[Huey2001]

According to deepseek it should be fine…

 

[NTK]

You'll first need to verify that the -ve speaker terminals of the L & R channels are common. Use a multimeter to measure the resistance between the two -ve terminals, if they are shorted together, you can use the amp as bridged monoblocks. From the picture below, it looks likely.
Note that the minimum speaker (load) impedance will be increased from 4 Ω to 8 Ω.

Second step obtain a device to generate a reversed polarity copy of the source signal, and supply it as the input for the second channel.
If you use the left channel for the normal signal, and the right channel for the reversed polarity signal, then connect the left channel +ve speaker output to the +ve speaker input terminal, and the right channel +ve speaker output to the -ve speaker input terminal. Leave the -ve speaker outputs unconnected or short them together using a short piece of jumper wire.

The trickiest part is to generate the reversed polarity signal. Easiest is to use your miniDSP Flex to generate them, but you will be using up two additional output channels. May be OK if you have a Flex 8. Otherwise you'll have to find or DIY something (e.g. something start from an opamp evaluation board).

 

[DVDdoug]

hopefully use its full power on the separate channels.

Without bridging you'll get the same watts-per-channel so having two unused channels won't gain anything.

Bridging MIGHT be possible but it's a "hack" if the amplifier doesn't have it built-in. I'd ONLY do it if the amp has a "bridge" switch on the back.

If the amp isn't current limited, bridging will give you 4 times the power (and a stereo amp becomes mono). But as NKT noted an amp rated for 4-Ohms will be rated 8-Ohms (minimum) when bridged.

If you want more power I'd advise a higher power amp. Watts are cheap these days.

 

[EJ3]

You'll first need to verify that the -ve speaker terminals of the L & R channels are common. Use a multimeter to measure the resistance between the two -ve terminals, if they are shorted together, you can use the amp as bridged monoblocks. From the picture below, it looks likely.
Note that the minimum speaker (load) impedance will be increased from 4 Ω to 8 Ω.

Second step obtain a device to generate a reversed polarity copy of the source signal, and supply it as the input for the second channel.
If you use the left channel for the normal signal, and the right channel for the reversed polarity signal, then connect the left channel +ve speaker output to the +ve speaker input terminal, and the right channel +ve speaker output to the -ve speaker input terminal. Leave the -ve speaker outputs unconnected or short them together using a short piece of jumper wire.

The trickiest part is to generate the reversed polarity signal. Easiest is to use your miniDSP Flex to generate them, but you will be using up two additional output channels. May be OK if you have a Flex 8. Otherwise you'll have to find or DIY something (e.g. something start from an opamp evaluation board).

The name of the item that you are looking for is a BRIDGE.
G.A.S. made a box they called simply the 'Bridge' to which two stereo amps (namely the 80wpch Son of Ampzilla X2 [capable of 2 OHM speackers]) are hooked up resulting in 320wpch at it's output. But no longer capable of 2 OHM speakers, only 4 OHM and higher.
But the impedance of speakers that you can hook up doubles (example: if you could hook up 4 Ohm speakers, now you can only hook up 8 Ohm speakers when using the bridge.
So be sure to check things like that.

 

[Huey2001]

Great, thank you all for explaining!

 

[EJ3]

Great, thank you all for explaining!

The why it is important to NOT do this (in GENERAL)
6 of my 8 amplifiers have bridging switches on them that are locked out by being screwed down. (There is a damned good reason for that)!
These amps are also capable of <2 ohm operation in stereo.
All that needs to be done even when the amps are designed to be run bridged:
In order to run bridged (which I do for each of my 2 subwoofers), I have to loosen the screw & move the switch, (and then run no lower than 4 Ohm speakers, reconfigure which output terminals I am using, tie my dual 4 Ohm voice coils that each sub has, together [and re-configure them so that their load is 4 Ohms]) and then I go from having 500 watts a channel stereo at 4 Ohms to having 1800 watts per amp MONO at 4 Ohms (1 for each subwoofer).
If you know what you are doing...

On the other hand, if you don't have the right gear, it is
MUCH BETTER AND SAFER to do as @DVDdoug says and buy another appropriate for your use amp, as it is a less complex (and SAFER) solution for those that are NOT versed in the intricassies of bridging amps.

WARNING: If done INCORRECTLY: YOU MAY END UP WITH TWO USELESS AMPS
(OR WORSE: DAMAGE TO YOUR HOME AND/OR YOURSELF [UP TO AND INCLUDING DEATH]).

 

[Huey2001]

Ok, so do not mess with the speakers and wires, or beware for your amps or your own life.
And without proper bridging there is no power gain.

But what about amp headroom? I understand that the available power is shared over the two channels, but with complex sounds and volume, the available power cuts short and "smearing" or "compression" can be experienced (right?).
One would say that if the amp can dedicate its available power to the resistance of one speaker instead of two, that would be improved?
(So now I have changed my quest from more power to same but more sufficient.)

PS: I agree more power can easily be bought, although easily still seams to imply a fair bit amount of money, at least in my opinion. I do contemplate an experiment with cheap class D amps (I applaud the innovation the Chinese techies bring). BUT I must admit I like the robustness of the Marantz amps, and think they deserve a second life. It is also good as reuse and minimise waste, not? (Maybe not so much energy use..)

 

[Roland68]

Ok, so do not mess with the speakers and wires, or beware for your amps or your own life.
And without proper bridging there is no power gain.

But what about amp headroom? I understand that the available power is shared over the two channels, but with complex sounds and volume, the available power cuts short and "smearing" or "compression" can be experienced (right?).
One would say that if the amp can dedicate its available power to the resistance of one speaker instead of two, that would be improved?
(So now I have changed my quest from more power to same but more sufficient.)

PS: I agree more power can easily be bought, although easily still seams to imply a fair bit amount of money, at least in my opinion. I do contemplate an experiment with cheap class D amps (I applaud the innovation the Chinese techies bring). BUT I must admit I like the robustness of the Marantz amps, and think they deserve a second life. It is also good as reuse and minimise waste, not? (Maybe not so much energy use..)

For €150-200 each, you can get an SMSL A300 amplifier, which, as a mono amp in BTL mode, delivers over 400 watts at 4 ohms and 220 watts at 8 ohms—both figures measured in Amir's test.
I have two of them connected to subwoofers and also tested them in my system beforehand. I think the price-performance ratio is outstanding.

 

[JeremyFife]

The urge to change our systems can be powerful (and irrational, and annoying). It's an urge that I am trying to deal with myself

What problem are you facing? Not enough volume, audible clipping/distortion on the peaks for very dynamic music? You might need more power or headroom for those issues ...

Otherwise, this may just be change for the sake of change. It's your system, and it's meant to be an enjoyable hobby so if you want to change something that's fine. I'd agree with the members above though, cobbling together a 'sort-of-monoblock' system doesn't sound like the best approach.

I don't know your speakers, but if you haven't already done this you could add a high-pass filter so that your amp doesn't have to deal with the low frequencies that your speakers can't reproduce anyway. Takes some load off the amp and gives you back some free headroom

 

[DanielT]

Hi, I own a Marantz PM7004 and see many used ones for sale. I use mine in poweramp mode, with Minidsp Flex as preamp, but wonder if I can add a second one and use only one channel (poweramp in and loudspeaker outs) to hopefully use its full power on the separate channels.

Is this possible or will it damage its circuits?

Don't make it hard for yourself. If you want more power than your Marantz PM7004 (Power Output (8/4 Ohm RMS) 70/100W):

...then sell it and buy a more powerful amp.

 

[DanielT]

The urge to change our systems can be powerful (and irrational, and annoying). It's an urge that I am trying to deal with myself

What problem are you facing? Not enough volume, audible clipping/distortion on the peaks for very dynamic music? You might need more power or headroom for those issues ...

Otherwise, this may just be change for the sake of change. It's your system, and it's meant to be an enjoyable hobby so if you want to change something that's fine. I'd agree with the members above though, cobbling together a 'sort-of-monoblock' system doesn't sound like the best approach.

I don't know your speakers, but if you haven't already done this you could add a high-pass filter so that your amp doesn't have to deal with the low frequencies that your speakers can't reproduce anyway. Takes some load off the amp and gives you back some free headroom

TS amp: Marantz PM7004 (Power Output (8/4 Ohm RMS) 70/100W).
So, it depends on the usual, as you know (speaker sensitivity, listening volume, music dynamics) but a decent amount of power (it's relative) has a Marantz PM7004.

 

[EJ3]

Ok, so do not mess with the speakers and wires, or beware for your amps or your own life.
And without proper bridging there is no power gain.

But what about amp headroom? I understand that the available power is shared over the two channels, but with complex sounds and volume, the available power cuts short and "smearing" or "compression" can be experienced (right?).
One would say that if the amp can dedicate its available power to the resistance of one speaker instead of two, that would be improved?
(So now I have changed my quest from more power to same but more sufficient.)

PS: I agree more power can easily be bought, although easily still seams to imply a fair bit amount of money, at least in my opinion. I do contemplate an experiment with cheap class D amps (I applaud the innovation the Chinese techies bring). BUT I must admit I like the robustness of the Marantz amps, and think they deserve a second life. It is also good as reuse and minimise waste, not? (Maybe not so much energy use..)

If this is the unit that I think that it is (Model PM7004), it is not set up to be bridgable BUT it does have PRE-OUT (the 4th [fourth] connection down in the connections section) that can be used to control any more powerful amp (while cutting it's own internal amp out of the loop [thus avoiding the BRIDGING issues]):

Specifications	Power Output (8/4 Ohm RMS) 70/100W Frequency Response 5Hz-100kHz (+-3dB) Total Harmonic Distortion 0,0002% Damping Factor 100 Input Sensitivity: MM 2.2mV / 47kohm Signal to Noise Ratio: MM 85dB Input Sensitivity: High level 200mV / 20kohm Signal to Noise Ratio: High level 88dB Input sensitivity: Power Amp Direct In 1.6V/16kohm Signal to Noise ratio: Power Amp Direct In 106dB
Connections	Audio Inputs 6 Phono Input: MM Audio Outputs 2 Pre-out Power Amp Direct In Gold Plated RCA sockets on CD Speaker A/B Number of speaker terminals 4 Marantz remote bus Headphone Output iPod input
Features	Channels 2 Current Feedback Topology HDAM version SA3 El Power transformer High Grade Audio Components Customised Components Symmetric PCB layout Aluminium extrusion heat sink Tri Tone Control (Bass/Mid/Treble) Balance/Bass/Treble controls
Circuit details	Linear Drive Power Supply CCNE Shottky diodes Input buffer amp on all inputs Source direct Power Amp Direct Standby mode
IR remote control included?
Dimensions W x D x H	440 x 365 x 127mm
Weight	10.5kg

 

[EJ3]

Don't make it hard for yourself. If you want more power than your Marantz PM7004 (Power Output (8/4 Ohm RMS) 70/100W):
View attachment 491603
...then sell it and buy a more powerful amp.

This sheet indicates to NOT bridge this UNIT. But it does not mention the PRE-OUT that I have seen mentioned in the specs that I found???

 

[Vincent Kars]

use its full power on the separate channels.

Have a look at bi-amping audiophile style.
Horizontal: one amp drives the woofers, the other the tweeters.
Vertical: one amp drives the L, the other the R
You need speakers with dual binding post to do so.
Whether you really need that power is another question....

The Well-Tempered Computer

 

[Huey2001]

Have a look at bi-amping audiophile style.
Horizontal: one amp drives the woofers, the other the tweeters.
Vertical: one amp drives the L, the other the R
You need speakers with dual binding post to do so.
Whether you really need that power is another question....

The Well-Tempered Computer

Well basically I am talking/thinking about vertical bi-amping, but without splitting the high and the low. My pre-amp has only one out per left and right (do not all pre-amps??) so then I would need to use a splitter. But does this not weaken the signal?
My speakers have biwire posts, but I can hardly believe they are filtered for high and low? (I have them all four in use but when I leave out 2, the sound will not change to high or low frequencies…I feel dual posts are just bs h…)

So my idea was just all on left posts per amp and respective speaker and keep right posts unused… and hopefully gaining headroom…

 

[MAB]

Well basically I am talking/thinking about vertical bi-amping, but without splitting the high and the low. My pre-amp has only one out per left and right (do not all pre-amps??) so then I would need to use a splitter. But does this not weaken the signal?
My speakers have biwire posts, but I can hardly believe they are filtered for high and low? (I have them all four in use but when I leave out 2, the sound will not change to high or low frequencies…I feel dual posts are just bs h…)

So my idea was just all on left posts per amp and respective speaker and keep right posts unused… and hopefully gaining headroom…

OK. I understand now.

All you need is an RCA splitter to feed the left signal to both channels one amp and the right signal to the second amp. Wire the tweeter to one channel of each amplifier (left for instance), and the woofer to the other channel (right in this example).

The crossover in your speakers has a separate high and low section.

You wont gain any headroom at all. Please read here:

Bi-amping 101

This article provides a quick look at how bi-amplification works. The conventional scheme is to split the signal into two frequency bands before the power amplifiers that drive the speakers. The bass (LF) amp sees only LF signals and drives only the LF driver (woofer). The treble (HF) amp sees...

www.audiosciencereview.com

People claim dramatic benefits in all of these sighted anecdotes, yet no change is observed. It's nice to help sell more cables and amps.

You also won't lower distortion. I posted the results trying to modulate the tweeter with a large woofer signal. Popular speculation is that the back-emf from a woofer can modulate the tweeter. It's never been demonstrated to my knowledge. I continued that tradition by showing there is no measurable change to a tweeter's signal when bi-amplification is used.

The only benefit is you will get a sort of tone control using the balance knobs of the left and right amps. An inconvenient tone control which might be slightly interesting if your speakers have an intrinsic mismatch in treble and mids. Otherwise not useful.

I feel dual posts are just bs h…)

This is true.

 

[kemmler3D]

Not sure if anyone has answered this directly, but the amp won't send its full power to one channel if the other isn't used.

The only way using one channel instead of both channels would give you more power, is if the amp's power supply is very deficient and can only supply full power to one channel at a time. In that case you might get more headroom in one channel by not using the other. But that would be an amp that is almost defective.

Bridging can get you 2x the power for one channel from a 2-channel amp, but this amp doesn't support it.

 

[Vincent Kars]

My speakers have biwire posts, but I can hardly believe they are filtered for high and low?

They are. Might it be you forgot to remove the jumpers?

 

[EJ3]

Well basically I am talking/thinking about vertical bi-amping, but without splitting the high and the low. My pre-amp has only one out per left and right (do not all pre-amps??) so then I would need to use a splitter. But does this not weaken the signal?
My speakers have biwire posts, but I can hardly believe they are filtered for high and low? (I have them all four in use but when I leave out 2, the sound will not change to high or low frequencies…I feel dual posts are just bs h…)

So my idea was just all on left posts per amp and respective speaker and keep right posts unused… and hopefully gaining headroom…

My pre amp has 2 pre amp outs (MAIN OUT 1 and MAIN OUT 2):