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In Reply to: RE: DWM Bass Panels & Sanders Magtech , " On Trial " ... posted by finbad on March 27, 2017 at 20:22:29
That is very good.
I like that you use some sidewall loading for your DWMs as well as the mains. Correct me if I gt it wrong, your placement is
1. Plain of speakers is 8ft in front of the front wall.
2. Speakers are spaced 14" from the sidewalls
3. Toe in is mild at 2" offset of tweeter side vs bass side.
4. DWM are placed each 14" in front of the mains and placed right off the sidewalls (with no significant gap)
The wiring scheme is using one set of wire traces per each DWM. Resistor adjustment and additional inductors are still in process. So far the DWMs appear to be playing a bit too high up with the original crossover and need an additional inductor to restrict their coverage to lower frequencies.
Follow Ups:
That is all correct , Satie.
A couple of insights :
Magtech : Does run hot , actually scared my forearm on the fins by reaching to its back while fishing wires , four lines of burnt skin scared -
(lol , should be added to my service record for possible "yoyo ribbon" award ).
Confirmed with Angela hot running is normal under load - Just wanted to clear-up the facts , whereas I was under the impression , read here , that the Magtech runs cool .
The Sanders Magtech Under 4ohm load driving my 3.7i @ 86 dbs @ 1m , in 78 degree ambient temperature and set alone out in the open centered between mains operates hotter to the touch than the Halo A21 though it does have much larger fin area.
Several points of interest Dr Sanders wrote to me in answer to my questions re: use of the tubed hybrid Preamp Arc LS-17se , explaining multiple reasons why I should choose unbalanced connections for the best potential sound quality with the Magtech and a tubed preamp .
I was aware "Balanced Connections" may offer no real sound quality improvements - I was never aware such connections actually could be detrimental to sound quality or at the least measures noisier and that is the case in fact .
Sanders Quote:
"
I designed my amplifiers so that they are compatible with all preamps. Tube preamps often present a problem when driving solid state amplifiers because tubes are inherently high impedance devices. The laws of physics dictate that the impedance of the source (the preamp in this case) must be lower than the load impedance (the amplifier). Ideally, there should be at least a 1:10 ratio between the two, so the amp should have an input resistance that is at least 10x higher than the preamp.
Transistors typically have low impedance while tubes have high impedance. As a result, there is often an impedance mismatch between tube preamps and solid state amps.
To solve this problem, I use FETs (Field Effect Transistors) at the input of my amps. FETs have very high input impedance similar to tubes (about 10 megohm). I stabilize the input impedance with a precision resistor to 100 Kohm. That way, even a very high output impedance tube preamp will have no trouble driving my amp.
I make this high input impedance available through the unbalanced RCA input in my amps. The balanced input has a much lower input impedance of only 1 Kohm, which would be unsuitable for most tube preamps. The balanced input will still work with the 600 ohm output impedance of your ARC preamp, but it is not ideal. You would get much better results using the unbalanced input with its 100 Kohm input impedance.
Some audiophiles believe that balanced operation is better than unbalanced operation. I suspect you are one of them. So let me explain the differences in the two systems. After I do, I think you will come to appreciate that operating your system in unbalanced mode is not only just as good as balanced, but actually better. " - End quote
Yes, impedance matching is always an issue with tube preamps. In addition to that there is the issue of the preamp being normally unbalanced in internal operation so that using balanced connections introduces crossover distortion in converting from SE to BAL and back. The Magtech solution of treating both inputs seriously with an eye to optimizing the most likely preamp options to go with each is very welcome.
Not surprised by the Magtech running hot. Running that much current for the 3.7i and the pair of DWM requires much power and is a rather low impedance load so is a very high current requirement. While the maggie spec is 86 db sensitivity, independent measurements in the full spectrum are more like 83 db sensitivity.
The EAR-Yoshino 868 line-level pre-amp provides both single-ended RCA outputs and balanced XLR ones, the balanced output achieved via transformers. EAR's designer Tim de Paravicini does a lot of work in the Pro field (for instance the Pink Floyd studio in England), where I guess that is common. Many "high-end" companies provide balanced outputs on their pre-amps via Opamps and other quality-compromising means, even Audio Research. Atma-Sphere's designer Ralph Karsten is very sold on the benefits of balanced circuits (even in domestic hi-fi's), providing only true differential balanced inputs and outputs on his pre-amps and power amps.
There is a benefit to having a transformer output to a SE tube circuit as it can lower output impedance and offer a true balanced signal with minimal added distortion since it is replacing the output capacitor. Balanced Audio Technology does produce lots of internally balanced components. But true balanced construction just doubles your parts count. So it comes as at a price.
Well that is because of the impedance matching issue he describes. He gives you a choice. I'll give you an example. I have a Cary slp98p which has about a 600 ohm impedance but that swings upward to 6k ohm at lower frequency. My amp has a 24k ohm impedance. I found lower frequencies better just running direct from my ps audio directstream to my amp. The directstream is 120 ohm flat across all frequencies. I would love to 'fix' this as I really like my Cary.
Yeah, timm .
I too enjoy running direct out of the Aurender A10 ( presents an organic tone ) a most focused image though less air and space between instruments vs the addition of the untube like sound of the LS17se (as near S.S. sounding as one can imagine , especially in its presentation of bass ) , but what it brings to the presentation is a wider larger soundstage affording more air and space between .
The A10 also matches well with placing most vocals further back so as to eliminate most outsized upfront vocals with all but the most deliberate upfront vocals - No doubt all of this is in part to the Magtechs peculiarities of presentation in total with these Maggies , in this particular room too.
Thanks for sharing your experiences.
I too have 3.7i and DWMS. The further out in the room that I bring out the mains, the more they need the DWMs. At 8 foot, the DWMs really help bring out the mid and upper bass. I just wished they rolled off faster in the midrange.
I have a wide selection of resistors and attenuators. In a smaller room the resistors are mandatory, in my larger room, not so much.
One other trick I have used to occasional success is to not aim the DWMs forward. This will help them roll off faster on the top. This is not how I am currently using them, but it has worked in some set ups. As an extreme, you can even have them run parallel to the SW. It all just depends...
The addition of the DWMs really seems to take a toll on my Pass amp -- the bias needles bounce like an earthquake with any volume. My alternative amp -- Emotiva XPA 1s rarely even get warm to the touch though.
Thank you so very much Cat with sharing your experience now and yours read elsewhere in my research .
Mr Diller sent along, at my request, two proper inductors and an assortment of standard Maggie resistors(the cost effective ones;) to get started , as you say, to roll off the mids as well as reduce the amplitude of the stronger than needed signal. Oh, at no cost to myself.
Again, I had settled on only needing to use one set of terminals and that was still a bit much due to this small room syndrome ; So, this is where I might like to further pick of your grey matter once the new panels arrive , please.
Latest Dealer inquired ETA email from Magnepan suggested 4 weeks in total, with two weeks left on that calendar.
Dealer tossed in the dress-up kit and upgraded silver material covering no cost. Of course, I can wait - I really can wait ( self talk ;)
Inquiring with Grant VanderMye on stand purchases , However my dealer was unsure, but he thought that the modification needed would void my warranty as he seemed to remember - So, I must get that issue settled with a call to Wendlle to be verified.
Speaker cables ?
Your thoughts or others opinions would be welcomed ;
Regards,
Will
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