Crack Upgrade Path?

[levlhed]

I suppose the result is similar, but I'm not sure it was necessarily less warm.  I should have spent more time going back and forth, but once I went to the upgraded one I never went back and listened to the stock one!  And I was back in there three or four times hooking my modded Nano up to it to steal another listen.
I think ironbut can help characterize it better as he has probably spent more time comparing the two.

[tdogzthmn]

I am thinking of wiring my amp with cotton insulated copper wire.  If the wire is unshielded will that cause problems and noise during use?   

[Paul Birkeland]

The stock wire is not shielded, just insulated.  If you do buy cotton covered wire, be sure to get solid core.  I've seen a few builds go really badly because stranded wire was employed. 

My preferred cloth covered solid core wire can be found here:
http://www.tubedepot.com/wire.html

Just be sure to pay attention carefully, as stranded and solid wire types are listed side by side.  I especially like this wire because the cotton is bonded to the PVC underneath, so you can strip this as though it is normal PVC coated wire.  Another nice aspect is that a little bit of overheating will make the PVC shrink away a bit, but the cotton will remain. 

[tdogzthmn]

I found the wire on hifi collective.  Its solid core copper AWG 28, 6N cotton insulated.  Its all white so I would have to label each strand during wiring so I dont loose track of the connections.   

[Paul Birkeland]

That should work OK for everything but the heater connections, where it will be pretty thin to get the job done IMO.

[grufti]

Wow! Speedball!

[nsorens]

Yes, WOW Speedball.
I used to feel that my Enhanced Sex/Hammer Dynamics speaker setup was a more involving listening experience, but now with the speedball upgrade the Crack /DT770(600 ohm) combo comes much closer to being in the "listening room".

[Doc B.]

Thanks guys! The cathode follower setup on the 6080 is a really neat way to get the output impedance down to where it can run a pretty broad range of high impedance headphones, but the CF is kind of an imperfect beast in terms of distortion with an ordinary resistive load. Remembering the dramatic improvements we heard when we added a C⁴S load to the CF in the Foreplay preamp oh, so many years ago made it a certainty that I would try one on the 6080 in a Crack just about as soon as the solder was cool on the prototype. PB found a nice beefy transistor for the job in the form of the TIP50, and the project was a go. Gotta admit in this case the end result exceeded my expectations, and I've been using the C⁴S circuit for something like 15 years.

[mrarroyo]

nsorens were those huge caps part of the kit or an upgrade you installed? Thanks.

[nsorens]

Those are definitely non-stock....  They are the AXON True Cap 100uF / 250VDC caps that JREBMAN found at PartsConnexion, thanks JREBMAN! 
I built Crack stock at first and listened to the electrolytics that came with the kit. The stock parts are very good and the AXON's only make a subtle improvement. 
The Speedball upgrade is NOT subtle, it is huge improvement as everyone is reporting. 

[grufti]

Here's another one upside down.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fimg13.imageshack.us%2Fimg13%2F83%2Fdsc2932crop640.jpg&hash=79fcdca4f4b5bf33c87742e1348ce4d46b150c3a)

Most of the "extras" make up a regulated 12.6V DC heater supply for the driver tube. Mind you, the reason is not that I disliked the 6.3V AC heater supply. It works great. I just wanted more constant working conditions for the cathode follower independent of my choice of driver tube and its heater current draw [and vice versa].

You can also see the additional B+ supply capacitor and resistor. At this point everything still fits inside the chassis, sort of.

I haven't measured anything yet. I'm enjoying the music way too much.

[grufti]

I couldn't resist.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fimg532.imageshack.us%2Fimg532%2F7758%2Fcrackleftat1v1khzoutwit.jpg&hash=10a82d9b7c33db876d4924420dbfd260872377a4)

This is again at 1V rms out - Crack with Speedball upgrade left channel blue - control red.

S/N improved to better than -70dB. THD improved to just above 0.1%. 2nd still dominant, 3rd at roughly -90dB, all higher harmonics buried in the noise, power supply completely inaudible.

That's only part of the story really, because the music just sounds incredibly "right".

[Paul Birkeland]

Here's another one upside down.
Most of the "extras" make up a regulated 12.6V DC heater supply for the driver tube. Mind you, the reason is not that I disliked the 6.3V AC heater supply. It works great. I just wanted more constant working conditions for the cathode follower independent of my choice of driver tube and its heater current draw [and vice versa].

You do realize that there is some headroom for heater current in the PT3?  You could probably draw up to another .5 to 1 amp on that winding without huge issues...

I'm glad to see that the PEC pot fits nicely!

[nsorens]

Nice PEC pot, where did you find it? Been looking for another one of those for this amp but they are getting harder to find...

[grufti]

Digikey has them. I just checked.

This one came out of my box of goodies.

Nice PEC pot, where did you find it? Been looking for another one of those for this amp but they are getting harder to find...