[TubeHead]

Hi all,

Just found this site, and I love it!

I want to get more into the headphile scene, and in researching amps, I'm a little confused as to when/why I might consider OTL vs. non-OTL (TC?)

For example, I've read some great things here about Woo Audio. I'm considering the WA3 or WA6 to drive a pair of Senn 650's I'll likely purchase. Which way should I lean in this case? I've read about some really interesting upgrades for the WA6 (e.g., V-caps, etc.), which I'd plan to get (and, I realize, puts the WA6 into a different price range than the WA3).

So, under what circumstances does one consider OTL or not? Is it possible to generally characterize the differences in "sound" between the two? Is one inherently better suited for low vs. high-impedance phones?

Any guidance here is greatly appreciated!

 

[Negatron]

Hi, your question regarding OTL (outputTransformerLess) implies tube amps generally. Most tube headphone amps do not use transformers partly due to the wide range of headphone impedances in the market. Transformer coupling is normaly load specific 32 ohm load uses a 32 ohm output tap 120 ohm, a 120 tap 600, 600 tap, etc. The 2 most common outputs for tube amps are single ended push-pull and cathode follower. That's a simplification but it serves here.

The output coupling is usually capacitor. Direct coupled SEPP tube amps are possible with DC servo correction but I don't know of any. Solid State amps will be DC coupled or Cap.

There are a wide field of amps to choose from, both tube and solid state and there are no shortage of opinions as to which is best. You can safely assume the first amp you buy will not be your last, so you may want to factor that into your thinking. There is a great deal of good information on this forum, there are other resources, Headwize, Hydrogenaudio Forums - search the net on headphone amps. Enjoy.....

 

[Mazuki]

I think transformer coupled tube amps give the "tube sound" most people talk about. OTL amps are faster and have different distortion characteristics. They sound almost solid state, but with more warmth.

 

[kramer5150]

I think its far too broad a topic to generalize. I have heard OTL amps (my earmax for example) that are very warm, gushing and oozing of tube harmonics. Conversely I have also heard transformer coupled amps that were very detail revealing.

 

[Negatron]

Quote:

Originally Posted by kramer5150 /img/forum/go_quote.gif I think its far too broad a topic to generalize. I have heard OTL amps (my earmax for example) that are very warm, gushing and oozing of tube harmonics. Conversely I have also heard transformer coupled amps that were very detail revealing.

Good points to make and to add to that; High guality, wide bandwith transformers are VERY expensive to make. When McIntosh went from tube to sand state amps they used output transformers behind the output transistors. Economics won out in the end though.

Sadly, 'Tube Sound' is becoming a cliche' (and marketing gimmick)

 

[fkclo]

Quote:

Originally Posted by Negatron /img/forum/go_quote.gif Good points to make and to add to that; High guality, wide bandwith transformers are VERY expensive to make. When McIntosh went from tube to sand state amps they used output transformers behind the output transistors. Economics won out in the end though.

This is an important point - not all Transformer Coupled amps are made the same. The iron plays a critical role. Regardless the design and workmanship, a bad iron can ruin a TC amp. And a good transformer for TC amp is easier said than done, especially considering the costs involved. Jack seems to hit a sweet spot with its WA6, and I believe transformer he chooses contributes a lot to the success of this amp.

F. Lo

 

[braillediver]

"Most tube headphone amps do not use transformers"???

The one All Encompassing Statement that applies to audio is- There are no All Encompassing Statements.

Depending on implementation either OTL or TL can be good, bad or indifferent.

OTL is usually more compatible with high impedance headphones- Senn HD600’s. Transformer coupled tend to be compatible with both High and Low impedance headphones- Grado’s and Senn.


Mitch

 

[TubeHead]

Thanks for the replies. I was trying to get some feel for any general differences in "performance" characteristics between the two, and it would seem there are various determining factors; therefore, a blanket, "this type is for that...that type is for this" isn't entirely reasonable.

"OTL is usually more compatible with high impedance...Transformer coupled tend to be compatible with both high and low..." is the kind of generalization I was seeking. Anything further would be appreciated, but I can live with this.

 

[slwiser]

It is all in the implementation. Cheap components and poor design degrade sound while good design and high quality components provide excellent sound no matter which design in selected.

 

[d-cee]

yeah, there's a few inaccurate posts at the beginning of this thread

i don't know of the exact tally but i don't think most tube amps are OTL (output transformerless)

OTL tube designs can usually only drive high impedance phones

adding transformers allows tube designs to drive from low to high impedances

again, a very bad and broad generalisation but:

OTL are said to have the tubier sound, whereas transformer couples amps are said to have a less tubey sound

of course there are exceptions to both situations and you should look at an amp on its individual merits rather than whether or not it's OTL

 

[sacd lover]

I have seven OTL tube amps and five transformer coupled tube amps. From my experiences, OTL amps drive ANY impedence just fine if you use an output tube with some power. In fact, my favorite amps for my low impedence MS2i's are the Singlepower OTL designs using 5687 or 6bl7gt output tubes. My transformer coupled amps .... Space Tech Lab 6AS7G/ Doge 6210 will not drive low impedence headphones like the MS2i without noticeable hum despite all the current available. My Sound Quest SQ-84 transformer coupled amp is dead quiet and extremely good sounding with the MS2i headphone; but the performance clearly falls off as the impedence rises. With the Senn 580/600 the sound paired with the SQ-84 is at best fair to good; but nothing magical like with the Grado headphones.

The tone of the Singlepower OTL amps can be rich and lush or very neutral depending how you tube the amp. My opinion is that you cant make a generalization about the tone of the SP amps. The Transformer coupled amps I have dont respond to tube changes nearly as much as the OTL SP amps and have a sameness to the sound regardless .... especially when switching just the the output tubes. The Sound Quest SQ-84 has an inherently leaner tone, while the Doge 6210 is on the richer side .... and neither of these amps seems to respond much to tube changes in regard to tonality. Neither the SQ-84 nor the 6210 nor the Space Tech transformer coupled amps resolve spatial information like the SP amps. Dynamics sound faster and more explosive in the OTL SP amps too.

I very much enjoy the transformer coupled amps and I am glad I experimented with some. But for the best sound quality and least compromise the OTL amps are superior to my ears. As long as the OTL amp in question has sufficient output power for the current demands of low impedence headphones, the OTL amps come out on top in my system using low or high impedence headphones.

 

[roastpuff]

Get something like the MG Head OTL MkII/III amplifiers - I have the MkIII, and it provides an option to switch between OTL and TC output with the flick of a switch. The best of both worlds, really!

It can drive both my 32-Ohm RS-2's and 40-Ohm W1000's alright in OTL mode, but the W1000 prefers TC mode to sound the best. The Grado's appreciate OTL more, and sound more natural that way.

The 600-Ohm Darth Beyers just LOVE OTL mode. Nothing like high impedances and tubes!

 

[Negatron]

Quote:

Originally Posted by braillediver /img/forum/go_quote.gif "Most tube headphone amps do not use transformers"??? The one All Encompassing Statement that applies to audio is- There are no All Encompassing Statements. Depending on implementation either OTL or TL can be good, bad or indifferent. OTL is usually more compatible with high impedance headphones- Senn HD600’s. Transformer coupled tend to be compatible with both High and Low impedance headphones- Grado’s and Senn. Mitch

Nothing was intended to imply better or worse and the choice of the statement "most tube amps..." It was intended to mean 'a majority of'', nothing more. I have too much iron in my house driving speakers (and sitting on shelves) to denigrate it.

I regret any misunderstanding.