Which amp to build for AKG K340?

[Frank M]

Hello!

So I recently (that is to say, this morning

) got an AKG K340

And that baby needs an amp - it's 400 Ohms, and 94 dB @1mW.
Unfortunately, getting a fancy headphone-amp is a bit out of the question, as my main hobby needs more funding: it look's like we'll go to the studio soon to record an album and then comes gigging. Another thing is that headphone amps are a rarity here. The shipping costs, taxes and the 240/50 power is a prohibitive factor for importing stuff.
But on the bright side, my Dad is an electro-engineer and likes doing DIY-stuff, as well.

So now that I have the phones here with me, I can say that it's not the bloated-bass version, the midrange is fine but the highs a bit recessed (or I'm not yet used to it). I have looked around on Head-fi and briefly on Headwize, as well, for some DIY amps. These are the ones that look favorable to me, as they can drive these cans or can be modded to.


Pete Millett's hybrid - getting the tubes can be the critical part - I haven't seen them around in shops that have tubes...

Wheatfield HA-4 from Pete Millett's page

Kevin Gilmore's headamp @ Headwize

JeongSeob Shin / Sijosae hybrid - simple hybrid

Greg Szekeres's headamp - easy-to-build, simple FET amp

Feel free to recommend other amps, too.
Basically, I need an amp that sounds good, clear and balanced, is at least moderately fast and doesn't lack highs. And of course one that has high enough output to power my cans

Tubes are a plus, but getting transformators for bigger plate voltage-tubes is a pain in the @$$.

Thanks in advance!

 

[chillysalsa]

The Szekeres does not provide any gain, so it may not provide enough voltage for those AKG340's, considering their high impedance.

You may want to consider building Gilmore's Dynahi instead of the smaller V1 or Dynalo, it will provide more current for those cans. I believe philodox on here has both of those in his inventory, you should PM him...

 

[aerius]

The Szekeres will not drive it. To be honest I think you'd need a voltage gain of at least 7-8 to do a decent job, I'd be happier with about 10 or so, maybe more. When philodox dropped by to test his out, I tried it out of my Gilmore (gain of ~2) and even with the volume knob wide open it was still too quiet. I have another Gilmore board where the gain is set to 10, I can test that out as soon as I can contact the guy who sold me my K340's and pick them up in person.

 

[aerius]

Well, picked up my K340 this afternoon, I can now confirm the Gilmore Dynalo is not, I repeat, NOT a good match for it, even with the gain set to ~10. The dynamics aren't there, sharp sounds such as a hard snare drum hit get softened and smoothed over, and in general it sounds a little dead. The only other amp I have on hand is the DIY tube amp from this thread. It does a much better job but I'm pretty sure there's better stuff out there. I'll have to wait till the next meet to find out what other amps it'll work well with.

 

[Frank M]

Thanks for the replies!

So then the Szekeres and the Gilmore V1 are out.
Has anyone tried the hybrids? I didn't have much time to read the threads at Headwize, but most of he time they were rather talking about the technical aspects of it.

 

[00940]

You need something with a large voltage swing at the output and some decent power. I would seriously consider a rather simple solid state amp in the line of the Meier Corda. Jan published the schematic of the HA1-MKII. It could be a nice starting point.

http://home.t-online.de/home/meier-audio/headamp.htm

 

[amb]

In the first post, Frank M stated that these cans get 94dB @ 1mW. Working with that, 128mW will get you 115dB which should be plenty for dynamic peaks. Into 400 ohms, this means the amp must swing about 7Vrms and have 18mA continuous output current capability. An M³ amplifier should have no trouble with this if it's powered by a 36V PSU with appropriate opamps installed. Same comment for the PPA or PPAv2.

 

[philodox]

That Wheatfield HA-4 looks cool, but I havent heard anything about it. I would suggest going with either a beefy tube amp [high impedence phones seem to like tubes] or go the route that I went with a KG Dynahi. [Note: Mine has not arrived yet, but I heard one at the Chicago meet and it drove the K340 effortlessly.

]

I have no experience with the M³, but I'm sure that a PPA with a high gain would do the job as well.

 

[rickcr42]

I am surprised no one metioned the SDS Labs headphone amp.It can be configured to drive anything headphone but the AKG K1000

 

[morsel]

SDS Labs was good for its time, but has an audible power supply hum problem at high output levels. M³ has 3 channel topology (active ground), better biasing, and was designed to handle this sort of headphone load.

 

[rickcr42]

Quote:

SDS Labs was good for its time, but has an audible power supply hum problem at high output levels.

good for its time ?

I did not realise there was a time limit on a headphone amp.

I have never heard any hum in any of the versions of the SDS I have built ever from the original to the latest incarnations.None.
Layout is everything and How you get hum with almost 10Kuf of supply filtration is surprising to me unless you are running the input wires unshielded right next to the AC section.
No way the power supply hums being a standard bipolar three terminal regulator bipolar supply and the output stage is no hummer either so I am baffled on this point being made ???

and any power supply/biasing issues if they were to be there are easily addressed no matter what the design topology of an amp,asuming good layout again

as an example :

My hybrid valve-Szekeres/Mosfet follower has gone through every manner of power supply and current source known to man and each had a strength and a weakness and at this time I am back to a power resistor load and split power supply @ +/- 30 VDC for the mosfet as being the best sounding (light bulb second.inductor third,CCS last).Being very power supply sensitive I use a mosfet pre-regulator to a CLC stage and then a final individual shunt regs for each device which to my ears sounds good even though overkill.the AC section and pre-reg are in a separate box so hum is off the list of possibilities entirely

My very first SDS amp used all the original parts (even the original mosfets) and it also had a remote transformer and used poinyt to point wiring (terminal strip tie points) and it never hummed even though the layout sucked and was about as ugly as an amp could be.


and for me at least the 3-ch topology is not the be-all,end-all of headphone amps even though in fashion lately.there is and never will be a "final' solution to anything audio.It seems if it does not say "xxxx" approved it don't get much play in DIY anymore and that is why this forum has become so damn boring lately.amp of the month or don't ask


(BTW-not cool, to slam anothers design [Sheldon Stokes of SDS Labs] ,a design many have built and are very happy with just because you think your design is better.Just not cool at all)

 

[morsel]

Rick, lots of amps were good for their time but are eventually eclipsed by others.

On the SDS Labs board the power transformer is right next to the input stage, and radiates 60Hz hum that can be heard and measured if you turn up the volume. Amb and I like the SDS Labs amp. It was one of the inspirations for M³, which was designed in part to overcome some of the flaws in the SDS Labs. I asked Sheldon if he wanted to do it with me, but he had already moved on and was not interested.

Perhaps you are not referring to the official SDS Labs board, but rather to a different layout that does not suffer from this problem.

Sorry if I offended you. I would not have commented, but you were (perhaps rhetorically) wondering why SDS Labs was not suggested, so I gave you an answer. Please feel free to delete our last few posts so this thread can get back on topic.

 

[amb]

Quote:

Originally Posted by rickcr42 (BTW-not cool, to slam anothers design [Sheldon Stokes of SDS Labs] ,a design many have built and are very happy with just because you think your design is better.Just not cool at all)

Yikes, relax rickr42. The M³ is a hybrid of the SDS Labs topology and the PPA plus a few other tweaks, so there is absolutely no reason for us to slam the basic design of either. In fact on my M³ web site I express our gratitute to both.

That said, Sheldon's PCB layout has some issues. Namely the opamp and input section is too close to the power transformer. The ground arrangement could also use a bit of improvement. I have built an SDS Labs amp and have done extensive measurements, and there are spikes at 60Hz and its odd harmonics in the noise spectrum that no doubt is due to the layout. I tried many things to eliminate them to no avail (short of moving the power supply section off-board). With my HD600s I can't hear the hum but it is audible with very sensitive lo-Z cans. My SDS amp runs a voltage gain of ~5, which is higher than the stock gain of 2. This may be why others are not hearing this hum as readily, but it's there.

The SDS Labs amp is a fine design with excellent sound, and I still use mine regularly. Morsel was simply stating the facts about what we found. One of the impetus for me to do the M³ project is to correct the shortcomings of the SDS board, and to make other improvements. Morsel had contacted Sheldon Stokes in the past about this but apparently he was not interested in any further work on that amp.

EDIT: Looks like Morsel was posting at the same time I was. I agree with her, this message should be deleted along with the few above. We shouldn't derail the thread in this manner.

 

[Frank M]

Quote:

Originally Posted by amb I agree with her, this message should be deleted along with the few above. We shouldn't derail the thread in this manner.

It's fine by me, at least this keeps the thread bumped back to the top

Thank you for your suggestion! I'll look into them when I'll have a bit more time. Sorry, I have to run now. See ya later!

 

[rickcr42]

It was suggested by morsel and through her amb that the above "semi" off topic posts by myself,morsel and amb be deleted befause it appears to be a bit argumentive and not on topic.

Nope.

All points made are valid and should be left up as a point of reference for anyone doing a search on any of the amps mentioned-all part of the information highway here.If everyone were to agree all the time on every aspect of amp design I would run from this joint running and screaming in an attempt to escape terminal boredom !

Back on topic :

All of the SDS amp I have built for both myself and others never had any hum issues but then I always have my AC "out of the box" and run only DC to the actual amp box.

Not just the SDS but all amps including solid state loudspeaker amp.SE tube amps I usually take a pass due to size and cost limitations but even there it would be a plus when the reduced layout pressure of the actual amp is considered.Nothing sucks more than a continous low level hum that while it may be masked when playing music will be there between cuts.
With SE tube gear it comes with the territory many times and you live with it because the plusses outweigh the minuses but with SS there is not excuse for putting up with it.none.

In the case of the SDS amp what is left once the main power supply is taken as a separate unit is an amp with a very small footprint that can be placed damn near anywhere and the power supply box can be located a distance away.to me this does not look anywhere near as cool as the original SDS layout but it works well sonically.
The ouput stage is pretty flexable also.anything from pure class-a to class A/B for speaker use all determined by the hookup scheme and biasing.Could be considered a nice way to go for a multimedia amp where with a simple flip of the switch you coulkd go from class-a headphone amp to class-A/B speaker amp and have a single amp solution on the desk top.This is how I usually do a csutom build locally.

Most of the folks I deal with are not very hung up on the
"gee whiz" part of amp design and they don't care about how parts look so the "open frame" construction is out for them.
Being nusic freaks not gear heads has its advantages and they just want an amp they can plug in and use without problems cropping up .nothing fancy,no overpriced parts,just "does it work and how does it sound"

At this time I do not have an SDS amp in house and have not for a couple of years but this thread has me wanting to do another one.One with the original look and same SDS board layout but with the RCA input jacks side mounted right before the opamp,eliminating the Two Box amp AND any possibility of transformer induced hum.The addition of 1:1 line input transformers would make it a killer multimedia amp for the desktop.

DIY means "do it yourself" and the options for any of the available amp topologies are limitless.There is no right and wrong only personal choices.The "Y" part of DIY.

cheers

Rickeraptor Rex