ASL MG Head OTL MKII For Senn HD580's?
Jan 14, 2006 at 7:01 PM Thread Starter Post #1 of 20

scm207

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I'm currently using an SR-71 to drive my HD580's and I'm curious about trying a tube amp just to hear their sound. Upscale audio has an MG Head OTL MKII for $275. Anyone have an opinion on the MG Head/580 combo or on the price Upscale wants for the MKII ??
580smile.gif
 
Jan 14, 2006 at 7:49 PM Post #2 of 20

mkmelt

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The MG Head is a good match for use with HD-580 headphones. There is a ton of information on this unit in the Amplification forum. Just search for 'MG Head'. The MG Head will draw you into tube rolling, where changing either the single driver tube and/or the pair of output tubes will noticably change the sound of the amplifier (hopefully for the better). Price seems ok. See if you can audition the unit and return within 14 days if not satisfied. What type of warranty will they provide with the unit?
 
Jan 14, 2006 at 7:54 PM Post #3 of 20

scm207

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Upscale Audio is offering "Guaranteed against DOA only". Their website doesn't say whether or not they would accept a return though, I suppose, there are headfier's who may be interested in purchasing it.
 
Jan 16, 2006 at 8:54 AM Post #6 of 20

Bruce Henness

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I purchased a Mark III exactly one year ago and have put about 300 hours on it without any hiccups. I also got a pair of 580's at the same time and find the sound to be very warm and enjoyable. The OTL position sounds better IMO also. This is by far the best experience I have ever had with headphones.
I have no experience with the II version but I suspect that changes were made for both audio and marketing reasons. You only build what you can sell and the end product reflects what the customer feels is in fashion. I do not know how good the OE tubes are but I do know that the EH 12AX7 and the Sovtek 6BQ5's supplied are the absolute lowest cost items available to complete the circuit. If you don't roll tubes on this puppy you will miss out on half the fun.
I can't imagine anything out there that offers as much for the money. However there is the Millett from Shellbrook Lab that I have not listened to yet but offers real audio tubes in a platform that will also double as a preamp (the MkIII will not cut it as a pre). I like to stick to audio tubes as my experience with 6DJ8's (a multi mega hertz, front end tube for TV's that was never designed for audio) has been less than enjoyable.
Happy Hunting!
 
Jan 16, 2006 at 3:18 PM Post #7 of 20

milesbeyondjazz

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I use my MK 111 with my Senn 600s and my AKG K501s and I have to say it is a perfect match for both of these phones.Im still useing the stock tubes with mine since I am new to tube amps and really dont have any idea what tubes to try with them.It also powers my 325is pretty good to,even though I still prefer my Gilmore lite for them.
 
Jan 16, 2006 at 6:09 PM Post #8 of 20

Zealot261

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I absolutely love my MG Head MkII. It does a wonderful job with the Senn580. Another pro is the ability to tube swap. It has allowed me to fine tune the sound to my liking. There are plenty of online sources that describe which tubes do what best. The tubes are also fairly easy to come by. The only problem is, tube rolling is more addictive then opamp rolling.

The OTL feature is also quite nice. The ability to engage the output transformers for phones with low impedance adds to the adaptibility of the amp. Granted, mine always stays in OTL for the senns.
 
Jan 16, 2006 at 7:01 PM Post #9 of 20

saint.panda

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The Mg Head OTL MKII / HD 580 setup is probably the warmest headphone combo I've ever heard other than the HD 600 with the Audiovalve RKV, although less hifi in all regards. Very pleasant and organic sound with a good punch in the bass although it somewhat lacks in transparency and liveliness. The bass was also a bit loose and the treble lacked some air. And the transient response was bordering on sluggish with the notes not hitting hard enough for certain musical material. On the positive side, the bass and midrange created an enthralling experience like falling back into a comfy sofa, and issues like sibilance or listening fatigue or leanness of sound are non-issues with the MG Head. A soft but full-bodied sound with lots of bloom in the midrange if that makes sense.

I bought my MG Head OTL MKII for about $150 with shipping back then on ebay and probably wouldn't pay more than around $250 including shipping. While it's a good starter tube combo with lots of choices for tube-rolling, eventually all my music started to sound pretty similiar, i.e. a but too sirupy, not very snappy and just not very transparent overall, even compared to other albeit more expensive tube amps. Unfortunately, the number of inexpensive and commercial tube amps is very small. So if you want to go tubes without spending a fortune, the MG Head becomes one of the main candidates by default.

But with all said, I thought it's a great combo for chilling out to some relaxing jazz or soothing vocals - even compared to more pricey setup, and certainly a good overall value due to its availability on the used market, especially with the HD 580, which I think holds the best value in the high end realm anyway.
 
Jan 17, 2006 at 4:06 AM Post #11 of 20

Bruce Henness

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Quote:

Originally Posted by Blasyrkh
can anyone explain to me exaclty which is the difference between the DT and OTL mode?


saint.panda, are there any tubes that can kill the siroupy sound on the mg head?



DT puts transformers in the output, OTL is "output transformerless". As to how they sound, it will depend on the phones attached, the source, material listened to and your mood at the time. One will tend to be louder than the other also. Horses for courses. Syrupy is what this puppy is all about. The cure for it is called an "opamp" but sticking a Telefunken 12AX7 in the lead slot will probably lean it out a bit compared to a Mullard.
 
Jan 17, 2006 at 4:29 AM Post #12 of 20

mkmelt

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The original model was the MG Head DT. I believe DT stands for Divergent Technologies, the original North American (actually Canadian) importer of this product. OTL stands for output transformerless operation. This feature was added to later versions of the MG Head. In an amplifier that features OTL operation the final output stage of the amplifier does not use transformers to match the impedance of the amplifier to the load impedance of the speaker or headphones.

OTL circuits are rare, but occassionally seen, in tube amplifiers designed for driving loads more typical of loudspeakers than headphones. By bypassing the output transformer any sonic impact of the transformer (they all have some effect) is removed from the audio chain. Also gone is the possibility of applying global feedback to the circuit design.

In the MG Head the OTL mode should only be used with high impedance, i.e. 250 ohm or greater, headphones such as the Sennheiser HD-580, HD-600, and HD-650. It works because while there is still large mismatch between the output stage of the amplifier, perhaps 15X the input impedance of these headphones, enough power (approx. 120~150mw) is still able to be delivered to drive the headphones to full or nearly full output without clipping the signal.

The output transformers used in the MG Head are somewhat limited in bandwidth, resulting in rolloff off the bass and the upper octaves. When the amplifier is used in OTL mode the bandwidth is wider and flatter, but the bass is less controlled because there is no global feedback in the circuit. Global feedback in a tube amplifier is normally achieved by tapping the signal at the output transformer and comparing this to the original signal, so it is not possible in OTL operation.

If you operate the MG Head using the transformer coupled output, you can switch the feedback circuit in and out to compare the sound. When feedback is engaged there will be a corresponding drop in the audio signal level equal to the amount of feedback being applied. To compare the audio with and without feedback requires adjusting the volume levels to match. Normally there is sufficient unused gain in the line stage of the MG Head, the part of the amplifier powered by the dual triode 12AX7 tube, that this is not a problem.

In normal operation the frequency response of the MG Head looks something like this - '^', in OTL operation it more closely resembles a flat line '--' within a frequency range of perhaps 50Hz - 10KHz.
 
Jan 17, 2006 at 3:40 PM Post #14 of 20

Finch&Music

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Quote:

Originally Posted by Blasyrkh
understood, thanks for your answers!


I hope you all understand that in this thread there is only discussion on the mk II version. Only on that version (I do not know if it already was a two box version at that time) you can switch between feedback levels.

In the MK III version (two boxes!) you have the choice between driving in OTL form or via OutPutTransformer. For the latter there is only one setting available (at least in the 230V version I own myself). Untill now I have no complaints on technical behaviour, no hiss, no hum or things like that.

I have tried a low and high Z can (High End Grado and Senn 650) on it and I really think you should use the OTL output, but always with a headphone with at least 250 ohm (like Senn's or Beyers). In that case the MG Head OTL MkIII really can 'sing' and is at that price point for me a good instrument to make music happen (for my ears and with classic/jazz, that is).

When using higher impedance cans in combination with the OTL setting the lowest frequencies have a good chance, because in that case the output cap of only 100 mf is just enough to give the music an enjoyable low end. All of this with respect to price/performance level! I have good musical expierence with low pedal organ, piano, cello, opera and also enjoyed Pink Floyd and Freddy Queen.

With lower Z cans you can better use the drive option with the outputtransformer (again with MkIII version). Not version I or II, I could never listen to them (not available in Holland/Germany as far as I know).

At an higher pricepoint there are certainly better alternatives. Look around at headfi. So in the end it is your wallet and your personal ambitions that will decide on how you perceive the value of a MG Head.
 
Jan 17, 2006 at 4:00 PM Post #15 of 20

Hirsch

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Quote:

Originally Posted by mkmelt
Also gone is the possibility of applying global feedback to the circuit design.

In the MG Head the OTL mode should only be used with high impedance, i.e. 250 ohm or greater, headphones such as the Sennheiser HD-580, HD-600, and HD-650. It works because while there is still large mismatch between the output stage of the amplifier, perhaps 15X the input impedance of these headphones, enough power (approx. 120~150mw) is still able to be delivered to drive the headphones to full or nearly full output without clipping the signal.



It is very possible to use global feedback in a OTL design. It is rarely useful, but it is possible (I've got the option on two amps).

When the output impedance of the amp is greater than the impedance of the headphone, the amp will normally not have the power to drive the load. The result can be noise or distortion. However, the EL84 has a fair amount of power (the MG Head, running OTL, can drive K-1000's, which are both inefficient and well below 250 ohms). That excess of power makes up for a great deal of the impedance mismatch. I prefer to run OTL, and have only really seen a benefit in the use of the transformer for low-impedance (30-40 ohm) headphones.
 

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