[adydula]

Birthday gift coming next week a Bottlehead Crack OTL and I swore never back to tube amps for my headphones!!

%^$*)^&(&#)&#^&%^&%(

HA!!

Here we go again!

Alex

[adydula]

Ok I got the kit from Bottlehead on Friday and spent 3 hrs on it on sat and 3 hrs this sunday am.

Did all the resistance checks ok, fired it up all voltage checks were spot on.

Hooked us a DAC and tired my Beyer DT90's (the reason I bought this kit in the first place for).
So many people reccomenf this amp with these higher impedance DT90's.

So only after a few hours of listening I am really happy with the way this amp and the Beyer D90's pair.

Such a wonderful lush musical sound....just fantastic.

Tried my DT 1350's (82 Ohms or so)...they sounded like crap...as would be expected for an OTL amp designed to be used
with 300 ohm and higher cans.

For a tube amp its dead silent!! Very surprised.

A little microphonic if you tap the tubes, but why would you do that anyway when listening. LOL

I havent finished the wood base, and will post some pix later when done.

Reccomend this amp kit for those that want to try a DIY for the first time....a real easy kit to build.

OK later.
Alex

[adydula]

Hey Dale...

Power transformer gets warm, but not hot, the top aluminum plate has two large high wattage resistors that get hot and the top plate gets slightly warm, nowhere unpleasant
at all.

The case is wood, there is a small ventilation on the top, and the feet on the bottom raise the amp about 3/8 inch to allow for airflow.

Been listening for a solid 3 hrs now and  this amp is "cool" to me compared to many others I have used.

I can grab the power xfmer and its just mildly warm. the top mounting plate is also slightly warm where the large plate resistors are locates, but
this is in a very small area.

I have the speedball upgrade coming and these resistors are removed...so this will be really cool.

The upgrade is a constant current source for the amp and its components, have large heatsinks 90 deg to the main mounting plate.

This amp is a keeper for my Beyers!!

Its really that good.

Alex

This am even makes my really bright, brittle Chicago cd's sound great and its amazing on whats in these recordings!!! HA!!

[adydula]

Some quick pix:










Still sounds great this am!!

Alex

[krikor]

Nice clean work on the build. Is that the stock power tube that came with yours... which one is it? What's the input tube?

I got my Crack with Speedball built last year, plus a few tweaks. And yes, it really does sound fantastic, especially for the price.

[adydula]

Hello,

This is the third time I have tried to reply to your post!! Keep hitting the backspace key and loose everything!!!!!!!!!

Your Crack looks very nice as well!

The signal tube is a 12AU7, its an old tube for sure but has no discernible image that would identify what the manufacturer might be.

The Power tube was shipped with the kit, its not a 6080 but might be a 6AS7G tube, its has RCA Electron Tube on the base and made in USA. There are no other markings to tell what it is, and I have crawled over it many times trying to find one.

That said this combination with the Beyer DT90s are absolutely amazing and I thought that after the newness wore off it would be just another good amp. But this am it still sounds really great....

The soundstage and overall presentation is just wonderful....

The only worst it has are these to me:

1. Slightly microphonic. If you tap on the top metal mounting plate you can hear the ting, ting taps via the tubes etc. But when you listen there is no issue, why would you tap etch when listening....LOL.

2. The gain with these tubes and cans only allow me to barely crack open the volume control to at best 9-9:30 am position. Hasn't been a real issue but am concerned with the Speedball update this may worsen.... that said there is a fix for this that I will try with 4 resistors in the RCA input lines and resistors across the pots.

Even with these minor issues this is indeed a classic OTL tube amp that works very very well with high impedance headphones!






Alex

[adydula]

OK I just finished the basic Bottlehead Crack project and finished the wooden enclosure.
I used a Dark Mission Oak Minwax stain, 4 coats sanded in between and it came out nice.

I also added 4 resistors in a voltage divider arrangemment in the RCA inputs and across the 100k volume pots. This mod is described
on the BH Crack forum FAQ's. Some people depending on the impeadance of the headphones and how hot source material is can only turn the
volume control a small amount, this makes this issue go away.....I can fully utilize the vol pot now, away from low settings where channel imbalances are noticeable.

Here's some pix of it and the Beyer T90's. Its a really nice solution for listening to music with these cans!!

PIX:








Alex......whats next install the Speedball Upgrade when it come in...a constant current source to make things even better!

[adydula]

Hey Dale,

I never go to meets around here there arent that many that I know of....

If I did  would put it in bubble wrap and in a large box and into the car etc....carefully.

My ODA is small enough and sturdy enough to easily transport if I elected to do so.

This little amp is about as simple as a tube amp gets and works so well for these cans.

The O2 and ODA also work very well and I have listend to them all and its hard to tell the differences but with the Crack
the difference is great than with the O2 and ODA.....it must be the tube harmonics etc...

All are keepers!
Alex

[JimJ]

That's a beautiful looking system.  One thought I had was - do you ever transport your gear, like to meets or anything?  And if so, how do you protect it?

I hauled tube gear up and down I-95 when I was in my nomadic mode a few years ago. Didn't require anything more specialized than an open cardboard box and a layer of bubble wrap or a blanket underneath it. Worked for everything from a Bottlehead Foreplay to 40lb triode monos...

[adydula]

I have one 6AS7G coke bottle RCA from 1953 that is a new NOS tube... its very sensitive and touchy and has a little buzz in the background... after its one for several minutes it sometimes goes away and sometimes not...I can gently tap the tube in the top and it goes away and might come back and might not... ah the wonders of vacuum tubes!!

So I asked the seller to replace the tube and they did no questions asked and it arrives yesterday. A 1953 JAN version of the same tube... it went in and right away it worked very well... not sensitive, good sound and I am a happy camper...

I ordered two more of these JAN types to hopefully have a few tubes that are stable and work well for my future use.

These older large style coke bottle tubes really look cool, but they are not without issues....

I have several other amps, receivers, players and many pcs... one that I built and posted here in the circle is my ODA, a desktop version of the O2 amok with more power and much more versatility... its my gold standard for a close to perfect SS amp.

I listened to the Crack with the new JAN 6AS7G tube and the sound was absolutely stellar with a set of Beyer T90's. After an hour of listening I plugged into the ODA and I was really surprised how well it played, just as good as the crack but different to my ears.

I thought that with that new tube that the sound experience was head and shoulders above anything I have heard, until I tried the SS ODA!!! Ha!

Amazing how are brains and mind can affect our experiences!

The good thing is they both are stellar and great examples of lower cost stuff that can compete with stuff that costs much more..... and there is a great satisfaction that I built both the ODA and the Crack....

So we have wonderful nice looking finger burning tubes that glow in the dark contrasted with a most advanced desktop ODA!

Life is Good!
Alex

[adydula]

Ok Update ...I just added the Speedball upgrade to the Bottlhead Crack...

What is that you ask?

Well here is BH's explanation:

“A Camille Cascode Constant Current Source is applied to each triode—both halves of the 12AU7 voltage amplifiers and both halves of the 6080 cathode followers. By loading a triode voltage amplifier with a high impedance, such as an active current source, it operates in a more linear region and produces less distortion. A second advantage, not as widely appreciated, is that the current source provides a great deal of isolation from the power supply. A good current source will provide a high impedance over a wide range of frequencies including radio frequency interference. It is otherwise extremely difficult to stop RFI that is carried on the power line, because power supply chokes have a leakage capacitance and the large capacitors used will also have some inductance at high frequencies. Isolation from the power supply also removes the power supply capacitors from the signal current loop.”

Here is what it looks like:




Its three small PCB's with a dozen or so parts, resistors, Led diodes, transistors etc...

There was a $20 upgrade deal last month and I bought the kit.

It took me about 2.5 hours or so to populate and wire it in.
Fairly easy to do if you know how to solder etc...common sense.

All voltages checked out the first time and it played very well from the get go.

With my BeyerDynamic T-90's the spound is SUPERB....I cant imagine it getting it any better.

Totally black silent background, awesome soundstage, detail etc...all those superlatives..the kick drum is so dang good, taunt, deep etc..

The problem is now I will spend way too much time re-listening to all my music again...and thats fine with me!!!

Alex
Smiling alot!

[adydula]

Weeks have gone by and the Crack is still working out very well.....I just got 5 USN NOS 5963 tubes and they are pretty great with this amp!

A friend alluded to these tubes measured the least in the noise department and I should try them...they were bought for about $8 each on the bay, not bas considering all the high priced NOS tubes out there etc......I have a budget and these tubes are affordable still...at least for now!!

One of the five is truly exceptional.....I don't have a clue as to why, wish I has a good tester to see if its subjective sonic qualities perceived by me relates to any measureable data points.

That said it really is a very very good three dimensional tube, very transparent and very low cost!!

Listening here and liking these USN 5963's a lot!

Alex

[Rocket]

Hi Alex,

Really glad that the speedball upgrade has worked out well for you and thanks for your update.  Sure wish I could do electronics as I would buy a bottle head crack.

Cheers Rod

[adydula]

Rod,

they do sell them completed I think for a fee, I think its $250 or so?

If your interested I would build it for you.....let me know ..pm me etc...

Alex