ADCOM Bridging?

[AMC]

I want to bridge my ADCOM GFA-7400 5 channel amp. How do I bridge this amp?
I could really use the power for my Martin Logans.

 

[markw]

Some amps, like NAD, make provisions for bridging and have a switch on the back to facillitate that and provide instructions onl how to do it in the owners manual.

Your owners manual makes no mention of bridging, nor are there any switces for tat purpose on it's back so my guess is it wasn't designed with that in mind.

Perhaps some other, more technically oriented person, might guide you through rewiring the guts, but that won't be me.

 

[Pyrrho]

You don't. Look at the manual for yourself:

http://www.adcom-usa.com/userguides/gfa-7400-ug.pdf

If you require more power, you need to just get a different amplifier. If you do that, remember that it takes a doubling of power to get just a 3dB increase in volume, so don't bother with something that is only slightly more powerful, as that would be a total waste of money.

What Martin Logans do you have, and what is the problem you are having with your Adcom?

 

[AMC]

I have the Odysseys.
It just seems like I get little bass from the drivers in the base of the unit. I have heard people who put 400W Emotiva amps on these seem to get great bass respond from the drivers. I get decent SPL from the pannels, but not the cone woofers. I was hoping to bridge and get more power to the ML's

Of course my GTP-750 died and now i need a pre amp, I am looking to purchase a used Onkyo TX-SR875 as a pre amp and use the receiver's amps for the souround channels. The guy wants me to pay $450 for it, thoughts??

I really need a pre-amp, as I am down to only a Victrola XX-IV for my music!!!!

 

[GranteedEV]

I have the Odysseys.
It just seems like I get little bass from the drivers in the base of the unit. I have heard people who put 400W Emotiva amps on these seem to get great bass respond from the drivers. I get decent SPL from the pannels, but not the cone woofers. I was hoping to bridge and get more power to the ML's

If I were you, my first suspected culprit would be the SPEAKER PLACEMENT and SEAT PLACEMENT in the ROOM, not the amplifier. Get yourself some measurement equipment.

 

[markw]

When all you ave is a hammer, everything looks like a nail.

If I were you, my first suspected culprit would be the SPEAKER PLACEMENT and SEAT PLACEMENT in the ROOM, not the amplifier. Get yourself some measurement equipment.

That's a 60 wpc amp and 60 watts only goes so far with an 8" driver with a passive radiator.

Those speakers could seriously benefit from a few hundred watts for the cone/bass section.

 

[GranteedEV]

That's a 60 wpc amp and 60 watts only goes so far with an 8" driver with a passive radiator.

Those speakers could seriously benefit from a few hundred watts for the cone/bass section.

First of all, from the spec sheet, I read

100 watts into 8 ohms.....<0.075%
150 watts into 4 ohms.....<0.075%

now ML claims two things:

35–22,000 Hz ±3dB
90 dB /2.83v/m

So into a 4 ohm load, it should be capable of about 24.5V

IOW, we should be able to get 108.7 db SPL at 1m, assuming the entire bass section isn't shelved down like 3db or something.

Now if you sit 10ft away, it should still be able to drive those 99db.

Now 99db is pretty loud, probably louder in-room.

Now if it dips to 2 ohms in the bass, then that might be closer to 95db or what half you.

that's still pretty friggin loud. Not reference level loud, but I don't think his amps are clipping. I think his placement is just a problem. But i can not say that conclusively without measurements.

 

[markw]

Dunno where I pulled that 60 watts from, but they could still do with a coupla hundred watts. I have maggies and even though some say only a few watts is needed, they take 250 - 300 to bring out the bottom end. Some speakers are just like that.

 

[GranteedEV]

Dunno where I pulled that 60 watts from, but they could still do with a coupla hundred watts. I have maggies and even though some say only a few watts is needed, they take 250 - 300 to bring out the bottom end. Some speakers are just like that.

Bear in mind that planar magnetic and electrostatic speakers can create really reactive phase angles and low impedances.

But the martin logans use a dynamic driver to handle everything below 250hz.

I'm pretty skeptical.

 

[markw]

Well, we'll just have to agree to disagree on this one. I know we both hope the OP works it out and, with two possible solutions, his chances are doubled.

 

[TLS Guy]

Well, we'll just have to agree to disagree on this one. I know we both hope the OP works it out and, with two possible solutions, his chances are doubled.

I agree with you Mark.

Electrostatic speakers are an amplifier torture test. The impedance of those speaker is 1 ohm at 20 kHz.

I have not heard that speaker, but audition Martin Logan hybrids over the years. Matching an electrostatic panel with cone woofers is a dead end.

Peter Walker the inventor of the electrostatic speaker said blending the two in a credible fashion was not possible and so he never produced a hybrid.

In all of those hybrids I'm constantly aware of the transition point. Also I have never found those ML bass sections to be stellar performers.

The electrostatic part sounds very nice. However all good speakers are the sum of the parts. Here MLs always fall short of the mark to me.

I Think he should invest in a Quad 909 amp, that is specifically designed to perform well with electrostatic loads.

 

[AMC]

I agree with you Mark.

Electrostatic speakers are an amplifier torture test. The impedance of those speaker is 1 ohm at 20 kHz.

I have not heard that speaker, but audition Martin Logan hybrids over the years. Matching an electrostatic panel with cone woofers is a dead end.

Peter Walker the inventor of the electrostatic speaker said blending the two in a credible fashion was not possible and so he never produced a hybrid.

In all of those hybrids I'm constantly aware of the transition point. Also I have never found those ML bass sections to be stellar performers.

The electrostatic part sounds very nice. However all good speakers are the sum of the parts. Here MLs always fall short of the mark to me.

I Think he should invest in a Quad 909 amp, that is specifically designed to perform well with electrostatic loads.

This sounds acurate, the panels sound great in my opinion, but the woofers seem to do absoultely NOTHING. I have a seperate powered B&W ASW1000subwoofer that provides all the bass, but I would like to pass the higher bass to the ML woofers above 80HZ and lower the crossover to the sub. Can I just bridge this amp and hope it does not die?

Can I just put another amp on the woofers?

 

[TLS Guy]

This sounds acurate, the panels sound great in my opinion, but the woofers seem to do absoultely NOTHING. I have a seperate powered B&W ASW1000subwoofer that provides all the bass, but I would like to pass the higher bass to the ML woofers above 80HZ and lower the crossover to the sub. Can I just bridge this amp and hope it does not die?

Can I just put another amp on the woofers?

Do not bridge the amp, you will blow it. You would need a speaker that does not dip below 8 ohm to bridge. It is very unwise to bridge an amp that is not designed for it. You would have to modify it.

You need a better amp, like the Quad 909 for those speakers. That is your ideal choice.

 

[Pyrrho]

...

Electrostatic speakers are an amplifier torture test. The impedance of those speaker is 1 ohm at 20 kHz.
...

That is very different from having such a dip lower down, say in the midrange or bass. There is very little musical content at such high frequencies, and so the amplifier is not going to be facing that dip very much at all, nor is it likely to be asked to deliver much power into it when there is content at that frequency. So it would be wrong to judge the difficulty of the load based solely on what the minimum impedance is, as the particular frequencies matter a great deal.

 

[markw]

Can I just bridge this amp and hope it does not die?

What amp are you talking about here?

 

[TLS Guy]

That is very different from having such a dip lower down, say in the midrange or bass. There is very little musical content at such high frequencies, and so the amplifier is not going to be facing that dip very much at all, nor is it likely to be asked to deliver much power into it when there is content at that frequency. So it would be wrong to judge the difficulty of the load based solely on what the minimum impedance is, as the particular frequencies matter a great deal.

That is true. However electrostatic speakers have tortuous phase angles, so much so that some amps are sent into oscillation. It takes a really good amp to get good sound from electrostatics.

 

[AMC]

What amp are you talking about here?

ADCOM 7400.

It sounds good right now, especially the pannels, there is no speaker I would rather have, it is just that the woofer section seems to do very little. I do not have the woofer selceted to -3db or anything dumb like that.

I like the sound I am getting from the pannels and the subwoofer I have (B&W ASW 1000) seems to really make up for the lack of low Hz on the MLs, but it just seems like I could really benefit from more power and actually get some mid bass out of those woofers.

Also my preamp died and I am looking at dropping $450 on a used Onkyo TX-SR875. Any thoughts????

I am soundless at the moment, other then the Victorla and need a pre amp.....

 

[markw]

Can I just bridge this amp and hope it does not die?

What amp are you talking about here?

ADCOM 7400.

This was already covered in the first part of the thread. Didn't you get the memo?

On second thought, if you could find someone who could re-engineer that amp for you, I guess it's possible, but simply buying a more powerfil amp might be cheaper.

 

[WaynePflughaupt]

Never tried it, but I’ve always heard you can bridge an amp by driving the inputs out of phase (i.e. one channel with reversed signal polarity). That said, I doubt bridging would work well with these speakers, if they are as difficult to drive as everyone says. Most amps become less tolerant of difficult loads when bridged.

Regards,
Wayne A. Pflughaupt

 

[GranteedEV]

Most amps become less tolerant of difficult loads when bridged.

Yep. If a speaker is a 4 ohm load with dips to 1 ohm, a bridged amplifier will "see" a 2 ohm load with dips to .5 ohm.