Crack Upgrade Path?

[dumbo]

First kit, first post, already feeling greedy.  Wondering what success others have had upgrading the Crack.  I have the Speedball on order.  Silver wire?, stepped attenuator?, etc.  I understand these items may eclipse the price of the kit, just curious if anyone has tried.       

[Paul Birkeland]

A stepped attenuator isn't a bad idea. You can also upgrade the 160uf caps at the output (voltage rating needs to be 150 or greater).

Better wire and RCA jacks are other decent options. I would go with continuous cast copper wire over silver, and maybe switch to cardas RCA jacks if you're comfortable drilling out the chassis holes a little.

Fortunately, the Crack performs well enough for these upgrades to be sensible.

[grufti]

Just based on the decription and without having built it for the Crack, I would say install the BH Speedball upgrade kit above all else.

Next in terms of how much the sound of your Crack might change would be different tubes. You have lots of choice.

I am personally very much into "quiet" amps and I will try to reduce anything resembling hum and noise ... always.

I have changed out the RCA jacks, but mostly because I wanted more robust ones, not so much because I expect better sound.

I will probably cut more holes into the top plate in order to increase air flow. Any decrease in temperature inside the chassis will slow the ageing of parts and will keep your Crack sounding great longer.

Finally, how about better headphones?

[dumbo]

Finally, how about better headphones?
[/quote]

Got a pair of HD800s.  Not sure I will be upgrading those anytime soon.  How about the headphone jack?  Anyone have a good replacement?

[eeyore]

Got my kit today and looking forward to building it. My plan for upgrading is to build the kit as is, without any modifications. The 'upgrades' I have in mind include;

• Speedball
• Replace the headphone jack with a high quality locking Neutrik type
• Replace all resistors with Tantalums or non-inductive film types
• Replace all capacitors with film types, even on the PSU
• Replace sockets with teflon
• Replace volume control with DACT or Goldpt
• Replace IEC inlet with one that has both filter and fuse
• Replace RCA with a Neutrik XLR
• Replace cabling with solid silver or solid copper

Actually, that is pretty much everything! The joys of DIY!!! Looking forward to first listening!

[Grainger49]

The threads in the Crack folder have a lot of improvements.  My favorite is an improved signal path cap at the output.  That is the capacitor you listen through.  Bottlehead has selected the best capacitor they can afford to put in the kit at the price point they sell it for but it can be made better.

The stepped attenuator will also be in the signal path.  PJ has appropriately pointed out that any amplifying device only modulates the power supply, therefore the power supply is in the signal path.  Bottlehead is very careful about selecting the power supply for specific properties.  Check here before modifying the power supply, but do that for sure.

[Doc B.]

Got my kit today and looking forward to building it. My plan for upgrading is to build the kit as is, without any modifications. The 'upgrades' I have in mind include;

• Speedball

This should have the greatest impact, along with tube rolling. I'm liking a 5998 right now.

• Replace the headphone jack with a high quality locking Neutrik type

I'd suggest modifying the headphone plug to a Neitrik rigtht angle plug if you are going to bother with this.

• Replace all resistors with Tantalums or non-inductive film types

Careful here, you need to know what design parameters determined the composition of each of the original resistor. Resistors in the power supply must have an adequate voltage and power rating, resistors on the PC boards must in some cases be very precise metal film resistors, in other cases once again power and voltage ratings are critical. Grid stoppers may be best if left as carbon composition. Really other than that there aren't that many resistors in the circuit once speedball is in place.

• Replace all capacitors with film types, even on the PSU

You will need to add "make much bigger chassis to hold them. Much bigger." I do however think this might be somewhat audible.

• Replace sockets with teflon

This is probably fine. I had heard years ago of Teflon sockets that were getting loose due to cold flow, but I haven't heard that recently.

• Replace volume control with DACT or Goldpt

IME the Goldpoint with Dale resistors sounds best. It might be interesting to try transformer volume controls. Figure on calling up the architect for another addition on that chassis plan.Sometimes it's easier to add another story than to add a room. A very tall box might hold all this extra stuff.

• Replace IEC inlet with one that has both filter and fuse

Those little Corcom style things are only for frequencies that are higher than we really need to worry about. Probably better off with a bigger outboard power conditioner that filters down to something like 50kHz. Or you might find just as good a result from putting one of those little Panasonic CMCs and a couple of AC rated caps around 10uF or so at the transformer primary. By now it may just make sense to call a commercial contractor to build your chassis...

• Replace RCA with a Neutrik XLR

Yeah, if you have converted to XLRs in your system this is a good idea.

• Replace cabling with solid silver or solid copper

The wire is all solid copper as-is.
[/list]

Actually, that is pretty much everything! The joys of DIY!!! Looking forward to first listening!

[tdogzthmn]

What are some good stepped attenuators that are reasonably priced and where could I find them.  I also wanted to buy a metal knob for the volume control and wanted to know what the shaft dimensions were.

Thanks,

Tom

[dmatt]

Replace all capacitors with film types, even on the PSU
You will need to add "make much bigger chassis to hold them. Much bigger." I do however think this might be somewhat audible.

You're not kidding.

The two 100uF and three 220uF Solens I have coming are 2.2" by 2.8" and 2.4" by 4.5" respectively.  I may need a second chassis for these puppies (or a taller base).

Looks like the DACT CT2 attenuator will fit with the Speedball mods though.

[dmatt]

tdogzthmn,

I am not sure what you consider "reasonably priced" but here are two stepped attentuators (the websites list the dimensions) for around $150-$175:

Goldpoint (you can order from the website):
http://www.goldpt.com/compare.html

DACT CT2 (you can order from DIYCable.com http://www.diycable.com/main/product_info.php?cPath=31_71&products_id=274 ):
http://www.dact.com/html/attenuators.html

[tdogzthmn]

I was thinking under $45.  I saw some goldpoints listed on ebay but for those prices I would much rather buy the speedball.

[grufti]

I have used stepped attenuators from two auction site sellers located in the Far East: vintage_audio_lab and gigawork. They always have some items listed on the site and more in their stores.

Their prices are definitely reasonable and the units that I received worked just fine.

What are some good stepped attenuators that are reasonably priced and where could I find them.  I also wanted to buy a metal knob for the volume control and wanted to know what the shaft dimensions were.

Thanks,

Tom

[Paul Birkeland]

In the power supply, fitting three 220uf film caps will be tough. Instead, run the stock first and second caps with the resistor between them, then use a Triad C7X and a 47-100uf cap after. This will impart 90 percent of the benefits of big film caps without the crazy space requirements. The C7X should knock the noise down enough to get away with this.

[dumbo]

Awesome responses.  Exactly what I was hoping for.  Thank you very much.  I plan to build the kit stock at first except for upgrading to silver wire (don't want to wire it twice) and then upgrade each part one at a time.  Should be a fun learning experience. 

[grufti]

The Schurter 1A power entry module with line filter has approximately 30dB of attenuation at 50khHz for common modulation [and nearly 0dB for differential]. That's not bad. In addition to that it keeps all the RF crap out that might cause trouble.

The reason why I don't always use them is that they are really best at keeping noise from inside the device away from the line [the Crack isn't causing any as far as I can tell], plus there is a potential for ground loops when these filters live in more than one device, plus Doc's proposal to use some X2 caps etc is more flexible and effective.

Schurter filter graph attached, solid line is common, dotted is differential:

• Replace IEC inlet with one that has both filter and fuse

Those little Corcom style things are only for frequencies that are higher than we really need to worry about. Probably better off with a bigger outboard power conditioner that filters down to something like 50kHz. Or you might find just as good a result from putting one of those little Panasonic CMCs and a couple of AC rated caps around 10uF or so at the transformer primary. By now it may just make sense to call a commercial contractor to build your chassis...