Output Coupling Capacitors

[Dr. Toobz]

Or get a 600:8 ohm transformer;

Better yet, get a S.E.X. amp. That's what we designed that amp to do - headphones or speakers. You'll see a lot more power output into 8 ohms. On another forum someone was asking about comparisons of Crack with a $1200 headphone amp that a competitor makes. If that is a reasonable budget and one is willing to build their own gear one could buy a Crack, a Speedball, a S.E.X. amp and the MQ iron upgrade for S.E.X. for less than the price of the competitor's amp, and have all sorts of fun.

Already have all of those! But the temptation to keep messing around with them is hard to resist. Maybe the Stereomour should be next....

[grufti]

Please take a look at these new -3dB tables [... removed because they contained errors]. 100uF really sticks out as the best value to chose.

[Just_Joe]

The newer Sennheiser 595's are rated at 50 ohm impedance. I've enjoyed the cans for some time with the S.E.X. amp and other gear. The fact that the Crack amp was designed for high impedance cans did not hinder the desire to own one, not one little bit. If the amp didn't perform well with the 595's, there would simply be new cans in the collection.

There were no serious performance issues with the stock Crack amp and the 595's. This combo managed to slap a stupid grin on my face and actually brought tears of joy to my eyes, but the lower freqs did seem a little gentle.

I managed to salvage the 220uF PS filters from the rail that came off the FPIII upgrade and used them to replace the 100uF coupling caps on the Crack. Now all things are very much where I like them. New cans can wait until I burn the 595's up.

-Joe Sengl

[ironbut]

Thanks for those charts grufti! Excellent stuff.
Hmm,.. I have to guess that you have a pair of MB Quarts?

I aways wondered if MB Quart is part of the same company that makes the MBHO microphones?

[grufti]

You guessed it. I do own a set of MB-Quart headphones and still like them roughly twenty years after I bought them. Too bad MB didn't survive intact.

MBHO was founded by Herbert Haun, who had been at MB from the start as a technical director. He went back to his microphone roots. There is a wiki article available at:

http://wiki.faust3d.com/wiki//index.php?title=PMB_/_MB_Quart

A company called GermanMAESTRO picked up some of the pieces and still produces headphones that are similar to the MB-Quarts.

[tdogzthmn]

Would you be able to explain what is going on in the charts you posted?  I dont have an engineering background but I am interested in your findings.

[Dr. Toobz]

Nice graphs, but I'm confused. The graph labeled as "6AS7" shows lower -3dB values for a given impedance, with the 5998 graph being opposite. For example, JH16 Pro (18 ohms) is listed as needing a coupling cap of 47uF to get a -3dB point of 25Hz with the 6AS7, yet the same value is listed as yielding a higher (36Hz) point with the lower resistance 5998. Since the 5998 has a lower Rp than the 6AS7, shouldn't the -3dB be lower for any given impedance/cap combo? Maybe the graph labels were reversed?

[grufti]

There is nothing really special going in the charts/tables.

The coupling cap (100uF/160V in the kit) influences the low frequency roll-off in the frequency response of the amp. The formula for calculating the frequency at which the output is reduced by 3dB popped up somewhere way back in this thread. At first I computed the table based on that formula, but that is correct only for a voltage source.

The latest two charts/tables use what I hope is the correct way to calculate the bass roll-off frequency. Any value under 20Hz (better yet 10Hz) and greater than 2Hz is very good. All the values in the tables are frequencies in Hz by the way. The column for the 100uF capacitor has ideal values for just about any headphone on the market, between 12Hz and 2Hz for the 6080 output tube in the kit.

The Bottlehead crew fortunately takes care of this kind of design work before they sell their amps to you and me, so we usually don't have to worry. And it turns out that they got it right yet again. It's just for some very unusual headphones that a different capacitor might make a difference.

I hope this helps.

Would you be able to explain what is going on in the charts you posted?  I dont have an engineering background but I am interested in your findings.

[Jim R.]

Steve K.,

How large are those Obligato PS caps?  I just checked out the diyhfs pages and they don't list the dimensions of most of the caps.

Has your impression of them changed any?

-- Jim

[grufti]

It isn't that, but you're right.

Sloppy thinking on my part. I'll modify my post as soon as I have more than just a minute to do it. In the meantime ignore the two new tables.

Nice graphs, but I'm confused. The graph labeled as "6AS7" shows lower -3dB values for a given impedance, with the 5998 graph being opposite. For example, JH16 Pro (18 ohms) is listed as needing a coupling cap of 47uF to get a -3dB point of 25Hz with the 6AS7, yet the same value is listed as yielding a higher (36Hz) point with the lower resistance 5998. Since the 5998 has a lower Rp than the 6AS7, shouldn't the -3dB be lower for any given impedance/cap combo? Maybe the graph labels were reversed?

[ironbut]

Hi Jim,
They're pretty big. About 4x1.5 inches.
I'm still going to give them another day or two before I do any critical listening. I guess I have about 150 hours on them so far and they've gone through the regular film cap changes (I check them about once or twice a day) and they've seemed to settled down for the most part.
I'll post something in a day or two how they compare to the stock Panasonics.

This is with a stock unit and however they turn out, I'm sure it won't be as positive an improvement as the Speedball is (I seriously doubt that any component change will do that).

[Jim R.]

Steve,

Ah, thought this was with the speedball installed.

With all the great things people said about the upgrade, I'm thinking the BGs as coupling caps would be quickly taking me into the territory of rapidly diminishing returns and might find themselves better used n something else.  Stereomour?

Then again, maybe finding a nice bypass for the stock caps would be enough.

-- Jim

[ironbut]

Well, after around 250 hours of 24/7 burn in, I can't really say the the Obbligatto caps are full burned in yet. Most of the warts that that sprung up during break in have receded so I think I can say where it'll eventually get to.

With the tube set that I enjoyed the most with the old caps was a Tungsram E80cc and a Sylvania 6080WB the differences with the new caps were pretty subtle. This is with my Audio Technica AD2000's and computer based rig.
Then I tried a Tung-sol 5998 with a CBS/Hytron 5814a which I found to be a nice pairing. Wow,.. I still need to re-install the Panasonics to double check but I'm listening to a 24/96 download of Raising Sand with the Pure Music player on my Mac/Metric Halo and this is the best depth and realistic soundstage I've heard with digital. I've used "Trampled Rose" for demo's of my headphone rig for more than a year and this is way-way better than it's ever sounded. I have to admit that I've heard a more analog sound with digital but you don't even want to know what that was done with! But for a "sane" system,.. not bad at all.

Tomorrow when I have time, I'll hook it up to my Tape Project rig and that should be pretty scary.
So, like I said, I'll roll the stock caps back in this weekend but right now, I'm just in hog heaven!

[ironbut]

I went ahead and switched back to the stock Panasonics and listened today.  I still have to say that I'm amazed how good those things sound.
Then I switched back to the Obbligatto PS film caps. (BTW I used some solid copper 18AWG wire I get from Chris Venhaus for the leads)
Once again, these listening tests were done with a pair of ATH AD2000's my digital system and a Tung-sol 5998 CTL top getters (1958 I think) and a CBS 5814a.

Everything seems a touch more defined like a layer of fuzz has been eliminated. Not huge by itself in any particular frequency range.
The soundstage is much more 3D with these caps. Maybe better than I recall it was with the Speedball (It's been a while but I can't remember being blown away by stage depth. Maybe the combo of the 5998/5814 with the Speedball will, I'll have to wait and see).
I think the level of the perceived bass is a touch less but it's better defined just like with the Speedball. The Speedball did add a half octave or so to the lower extension and did a similar job of cleaning up the lower frequencies. The definition of the lows was also better with the Speedball.

So, I'm pretty certain that these caps will stay in the Crack for a while even after I get the Speedball.
They don't seem to add anything bad and seem to do a better job of getting out of the way than the stock caps. Pretty subtle stuff but it may be more pronounced with the Speedball (or less?). We'll see.

[ironbut]

I feel a little weird replying to my last reply to myself,.. on second though, no I'm not.

Just wanted to let you guys know that I got the Speedball yesterday and installed it. I burned it in overnight so it's probably got around 20 hours on it right now.
So, with the Obbligatto PS caps and the same signal chain as the two previous posts, all is wonderful and killerliciousness!
One of the great things about this combo (other than the price) is the sound seems improved on all genres of music. It doesn't improve a bad recording of course but it also doesn't call a lot attention to the worts either.
IMHO the improved soundstage and imaging is worth the cost alone.
Very engaging too,.. (I've been trying to write this post for about an hour now).