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Making my amp happy

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Posted on February 14, 2017 at 20:40:32
timm
Audiophile

Posts: 143
Location: Ann Arbor Mi
Joined: January 15, 2008
Hi all.

I have a sunfire signature 5ch amp. I currently use 4 channels to bi-amp Martin Logan odysseys. Amp is rated at 425 @8 ohm and 850 @ 4ohm. Given the wicked impedance curve of the logans 1-2ohm at the upper frequencies - do you think the amp would be happier with a 20.7 -as an example (obviously no bi-amp). ? Thanks tim

 

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RE: Making my amp happy, posted on February 14, 2017 at 21:25:42
Satie
Audiophile

Posts: 4222
Joined: July 6, 2002
Not unless you modify the 20.7 crossover to allow biamping. Otherwise the amp is going to be strained since the 20.7 are inefficient. If you need to raise the impedance of the top end section of the Odyssey then consider an autoformer to match up impedances.

 

RE: Making my amp happy, posted on February 15, 2017 at 08:44:24
timm
Audiophile

Posts: 143
Location: Ann Arbor Mi
Joined: January 15, 2008
The amp does not have trouble driving the logans Just wondering if the Maggie's would give an easier load to the amp the odysseys are not that efficient either I would have to check the spec

 

RE: Making my amp happy, posted on February 15, 2017 at 09:49:54
Satie
Audiophile

Posts: 4222
Joined: July 6, 2002
The 20.7 do give the amp an easier and less reactive load. If you want to avoid the warranty issue and save some funds, go for a used 20.1 and biamp it with an external crossover, then you can use 4 channels on the amp and have it see a mostly resistive load.

If the speaker is older and eventually suffers delamination the repair for both speakers + original cost should add up to to about half the cost of a 20..7.

 

RE: Making my amp happy, posted on February 15, 2017 at 10:29:10
neolith
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Posts: 3762
Location: Virginia
Joined: February 21, 2002
Contributor
  Since:
December 2, 2004
I think the only way to know is to lug your amp to a dealer where you can audition the 20.7. The impedance load may make your amp happier -- it seems to be up to the task now -- but a change in speakers may not make you happy. FWIW, I think 850 wpc at 4 ohms is sufficient for the 20.7s.



I married the perfect woman. The downside is everything that goes wrong is my fault.



 

Bass Ackwards?, posted on February 15, 2017 at 11:05:47
M3 lover
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Posts: 4982
Location: So. California
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  Since:
July 4, 2007
The most reasonable approach for me has been to select speakers first, then match other components to them.

So in this case I'd decide between the MLs and Maggies first, then find the best amplification I could afford to match them.

"The piano ain't got no wrong notes." Thelonious Monk

 

RE: Making my amp happy, posted on February 15, 2017 at 11:30:22
timm
Audiophile

Posts: 143
Location: Ann Arbor Mi
Joined: January 15, 2008
I does like dem 20.7s.... I have given them quite them about a 3 hr listen..... I would never blindly switch over with speakers..... I have done it with other components based on reviews from real humans - that have gear that maybe I have heard - and they are replacing... that sort of thing. Quite frankly - I like my Odysseys a lot as well... I just think the 20.7s are magical....

As you may have noted on my other thread in the Amp/pre asylum - I had my pre go down - and only then realized I may have a synergy issue when I went direct with my DAC..... So, then I started thinking about this speaker move.... and wondering about synergy there as well etc....

 

RE: Bass Ackwards?, posted on February 15, 2017 at 11:32:54
timm
Audiophile

Posts: 143
Location: Ann Arbor Mi
Joined: January 15, 2008
I agree completely with what you are saying... Unfortunately.... I did go Bass Ackwards.... I admit it... :) .... If I had oodles of funds I wouldn't care.... I have enough for what I consider a monster purchase in the 20.7.... but I have been talking about this for years... jeez.... although..... I think it might happen this time!! hahaha....

 

wattage, more than low impedance.. Tweeters use a few watts max., posted on February 15, 2017 at 12:34:49
3+4=5
Audiophile

Posts: 419
Location: Midwest
Joined: December 24, 2016
The 'wicked' impedance of treble does NOT MATTER if all your amp is pushing is a few watts at most to the treble.
An amplifier which can manage at all doing low impedance does way better if the load is small. Tweeters are a really small load.
So biamping, and the bass has a reasonable 4 ohms.. no problem.

IMO you are really over thinking this.
The notion of swapping speakers just to ease the no-problem imaginary load issue on your amp is really crazy overthinking.

 

RE: wattage, more than low impedance.. Tweeters use a few watts max., posted on February 15, 2017 at 12:48:57
timm
Audiophile

Posts: 143
Location: Ann Arbor Mi
Joined: January 15, 2008
I think you misunderstand. The speaker swap has nothing to do with it. I have wanted to do this for a long time. I am questioning whether the move would actually improve the performance of the amp based on the diff load and sensitivity

 

RE: Tweeters use a few watts max ..., posted on February 15, 2017 at 14:35:55
andyr
Manufacturer

Posts: 11419
Location: Melbourne
Joined: September 2, 2000
True - and up until last weekend, I would've agreed with you.

But I found something out about feeding HFs into a 2 ohms load that has changed my mind.

I run triamped Maggies - so I have an 70w (into 8ohms) ss amp driving my ribbons directly. The amp is stable into 2 ohms - ie. it hasn't blown up! :-)) - and my treble sound is great (or so I've always thought!!).

But I recently did some sweeps using REW and a calibrated mic ... and noticed that the FR graph showed a steep drop-off after 16Khz. (Given the mic is calibrated, the FR should be flat to 20Khz.)

So I did some crude measurements, driving my tweeter amp directly (bypassing the miniDSP XO) with a signal generator and measuring the voltage at the ribbon terminals.

To my surprise, the voltage I read at 16Khz was much lower than the voltage at 6Khz ... and at 30Khz, it was down a lot more! This says to me that my tweeter amp - even though it is "stable" into 2 ohms - cannot perform at HFs into a 2 ohm load! :-(( I have been told by an amp designer (not the designer of my amp!) that this is typical of the 'power envelope' of Mosfet power amps.

So I am going to borrow a transistor-based power amp which is renowned for being able to drive 2ohm loads and see if the REW sweep becomes flat to 20Khz!

So my point is - just because an amp:
* has bags of power for a 2ohm driver
* and is "stable" into this load

... doesn't necessarily mean it will perform well into that 2ohm load.

Andy


Andy

 

RE: Making my amp happy, posted on February 15, 2017 at 14:53:33
neolith
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Posts: 3762
Location: Virginia
Joined: February 21, 2002
Contributor
  Since:
December 2, 2004
I heard the 20.7 in demo as well and sat around moping for several days. Unfortunately going up the ladder from the 3.7i was not a viable option, monetarily and, more importantly, WAF =0. I have not heard the ML so I cannot comment on whether the 20.7 is better and even if I did voice an opinion; the only opinion that ever counts is your own.
I did respond to your amp impedance question and I think you need to find a more compatible pre. I would do this before making the speaker swap.



I married the perfect woman. The downside is everything that goes wrong is my fault.



 

RE: Tweeters use a few watts max ..., posted on February 15, 2017 at 15:06:22
neolith
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Posts: 3762
Location: Virginia
Joined: February 21, 2002
Contributor
  Since:
December 2, 2004
Very interesting, I would not have expected that. Did you try measuring the current through the tweeter as well? I wonder if you added a 1 ohm resistor in series would you see the same voltage drop? By doing so you could also measure the voltage across the resistor and calculate the current.
OTOH you are probably stone deaf above 16 kHz :).



I married the perfect woman. The downside is everything that goes wrong is my fault.



 

RE: "OTOH you are probably stone deaf above 16 kHz" ..., posted on February 15, 2017 at 15:42:04
andyr
Manufacturer

Posts: 11419
Location: Melbourne
Joined: September 2, 2000
That may well be true, neo, but let me relate a story which indicates to me, anyway, that we can respond to much higher frequency sounds than 20Khz.

The first version of my single-ended, jfet-based 'Muse' phono stage that I built about 5 years ago was regarded by the people who listened to it (comparing it to other phono stages) as being slightly rolled off in the treble. This first version was a circuit that came out of Silicon Chip in the late 80s.

A mate modelled the circuit in LTspice and told me that the simulation showed a LP roll-off at 120Khz. This was caused by a cap which had been put there for stability reasons ... but probably wasn't necessary.

So I removed this cap - and the phono stage no longer sounded dull in the treble! So we could hear the effect of a LP filter at 120khz! who woulds think it!! ;-))

Re. current through the ribbon - surely "V = IR" where:
* R = 2, and
* V = 2.3v at 6khz

... means I = 1.15a?

And W = I^2R means the amp was delivering 2.6 watts at 6Khz.

Whereas with V = 0.9v at 30Khz, I = 0.45a and W = 0.4 watts.

Andy

 

RE: "OTOH you are probably stone deaf above 16 kHz" ..., posted on February 15, 2017 at 16:35:28
Satie
Audiophile

Posts: 4222
Joined: July 6, 2002
I had that sort of issue but didn't measure the voltages with the Bryston 4B NRB which I tried on the tweeters. It is rated to 4 ohms and has oodles of power, but only "stable" to 2 ohms. Though it did drive them, it ran hot and sounded thin. When I had the option I swapped with a MOSFET Fosgate amp that weighs the same but has 1/4 the power rating. Also rated to 4 ohms and manufacturer suggests cooling fans when running into a 2 ohm load. It was run with and without a 1 ohm resistor in series. Without a resistor the amp got hot and images became tiny. When it got hot to the touch I would turn it off and put the resistor back, which is how I ran it most of the time. But for that one time when I forgot and ended up burning the amp. I have another which I use on occasion, and always with the extra resistor, which I also use with my tube amp. The only amp that drove the tweeter with no problem at all was the Classe DR9. Which is rated to 2 ohms. Ran a bit warm just as it did on the 6 ohm mids. The PSE Studio IV didn't stress on the tweeters but ran hot.

I did hook up the Crown just to see what would happen. Which was nothing in particular, it sounded like the Bryston on top, which is as expected. But there was no heat, the fans never turned on and the load light was never lit. But then it is rated to 2 ohms and stable to 1 ohm.

So I see that a low impedance load can be a problem for an amp not designed for it regardless of power rating. Experimenting with different resistors on the Fosgate amps it was rather obvious that it did best when the load was over 4 ohms. Even though it was losing nearly half its output to the resistor it was never stressed and never ran hot playing single ended (40W) and definitely no problem in bridged differential mode (80W), which did not sound as good as it did in single ended mode.

BTW if you are wondering why I didn't use the resistor all the time it was because it was the OEM Maggie ceramic resistor and it sounded like $^#$T. It took me time to admit to the fact and order a nice mills wirewound piece. Once I had that at hand I did not run the tweeter amps without the resistor, except for the DR9 which didn't need them.

For the OP
Thinking further then it seems if the high freq impedance drop is a concern for your amp''s high freq performance then you should find the 20.7 a substantial improvement. But then, I don't know that it actually is an issue for it. I second Neo's suggestion to take the amp with you to the dealer's to try it out on the 20.7. While there ask him about any "sanctioned" conversion of the XO to biamp.

Though there are many other factors involved, I think that if your amp sounds brighter on the maggies than it sounds on the MLs then it is likely that its upper end FR is drooping into the low impedance load of the MLs.

 

RE: Tweeters use a few watts max ..., posted on February 15, 2017 at 16:41:47
timm
Audiophile

Posts: 143
Location: Ann Arbor Mi
Joined: January 15, 2008
You know... I just stumbled across this because my pre went down then I started to question the synergy of everything. The psaudio directstream going straight to the amp sounds pretty good. My power supply has been shut down for weeks on my Cary. I see something where the AC connects which indicates a fuse behind some plastic piece which I have to figure how to pry open. In any case, if it is a fuse - I'll figure it out and report back.

 

RE: Making my amp happy, posted on February 15, 2017 at 20:32:54
hahax@verizon.net
Audiophile

Posts: 3034
Location: New Jersey
Joined: March 22, 2006
The Sunfire circuit is quite robust and probably handles lousy loads better than most amps in its price range. It's interesting that the sliding power supply voltage also makes the output more linear than with a conventional power supply. This was hidden in the long white paper written by Carver but not really mentioned in the sales story.

 

"sanctioned" conversion of the XO to biamp., posted on February 16, 2017 at 05:55:26
neolith
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Posts: 3762
Location: Virginia
Joined: February 21, 2002
Contributor
  Since:
December 2, 2004
I discussed this in detail with Wendell when I got my 3.7i. Basically he said "why take a step backward when we already optimized the crossover". In other words, NO.



I married the perfect woman. The downside is everything that goes wrong is my fault.



 

RE: "sanctioned" conversion of the XO to biamp., posted on February 16, 2017 at 10:06:11
Satie
Audiophile

Posts: 4222
Joined: July 6, 2002
We are talking about copying the XO electrical performance into a parallel line level XO, not substituting a new design. Which is hopefully what others who biamp are doing.

 

RE: "sanctioned" conversion of the XO to biamp., posted on February 16, 2017 at 18:28:58
andyr
Manufacturer

Posts: 11419
Location: Melbourne
Joined: September 2, 2000
Agree with what Satie said. Now, some would say Magnepan could've chosen to continue on with the parallel XOs of the 3.6 - just changed the slopes - but they didn't ... so the series XO version must sound better.

The truth of that I cannot comment on - but I'd stake my 'left one' that a 3.7 that had its passive XO excised and replaced by a 3-way active XO ... would sound much better! :-))


Andy

PS: and if you ask Wendill about replacing a Maggie's MDF frame with a hardwood frame, he will give you a similar brush-off comment. :-))

 

RE: "sanctioned" conversion of the XO to biamp., posted on February 17, 2017 at 05:21:37
neolith
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Posts: 3762
Location: Virginia
Joined: February 21, 2002
Contributor
  Since:
December 2, 2004
No disagreement there. I am just not up to it at this time.



I married the perfect woman. The downside is everything that goes wrong is my fault.



 

RE: wattage, more than low impedance.. Tweeters use a few watts max., posted on March 3, 2017 at 15:50:19
pictureguy
Audiophile

Posts: 7084
Location: SoCal
Joined: October 19, 2008
right as far as you go.
But 'Stats also typically have HUGE phase angles as frequency rises.
This means that to get 10 watts to the tweeter, you need Far More power to yield the 10 you need.
1.4x @45 degrees and INFINITE at 90 degrees where no power is delivered. The 'tell' is you use the cosine of the phase angle. @60 degrees, you deliver only 1/2 the amps power to the load.
Too much is never enough

 

RE: Tweeters use a few watts max ..., posted on March 3, 2017 at 15:51:53
pictureguy
Audiophile

Posts: 7084
Location: SoCal
Joined: October 19, 2008
Any idea of Phase Data?
Too much is never enough

 

RE: "sanctioned" conversion of the XO to biamp., posted on March 3, 2017 at 15:57:36
pictureguy
Audiophile

Posts: 7084
Location: SoCal
Joined: October 19, 2008
Exactly the perfect place to Start.

Plenty of time ot clown around later!


Too much is never enough

 

RE: No, sorry. nt, posted on March 3, 2017 at 16:32:41
andyr
Manufacturer

Posts: 11419
Location: Melbourne
Joined: September 2, 2000
.

 

RE: Making my amp happy, posted on March 6, 2017 at 11:45:43
jimf42
Audiophile

Posts: 2
Joined: May 21, 2002
I have been biamping my MGIIIa s for years using the passive XOs from Magnepan and a pair of Bryston 3B amps. Works great. Amps stay nice and cool and it sounds great. If I was really worried about amp capacity, I would switch the two amps to mono and one from each channel.

 

RE: Making my amp happy, posted on March 7, 2017 at 11:36:35
Norman M
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Posts: 778
Location: NYC Suburb
Joined: December 9, 2012
I'm with you on that. I use (and actually prefer) Magnepan's XO-1 over my Marchand 'active' XM44-2 when bi-amping a Tympani IV-A. I'm using a pair of Bryston 7BSTs on their woofer panels and a Bryston 4BSST to drive their T/M panels. Due to an oversight on my part, I learned that contrary to Magnepan's XO-1 instructions, I enjoy these speakers more when I omit the IV-A external X-O box (as done when using an active X-O), which in fact had the indicated connection clipped. For one thing, very much less listener fatigue.

 

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