Crack Upgrade Path?

[TonyMc]

The Alps seems to have perfect tracking all the way down. The stock pot didn't sound bad at all, but it didn't track as good as the Alps. With the stock pot the right side would kick in before the left. Not really a big deal as I never listen to levels that low and it didn't seem to affect the upper volume at all.
I would still like to try one of the Chinese attenuators from e-bay. I tell you though the little pins on the Alps are a PITA to see and solder.
The caps I installed are the AXON 91

 

[Noskipallwd]

I agree with Dr. Toobz, the speedball is by far the most effective upgrade. I settled on the 5998 as well, along with a Mullard CV4003. The 5998 provided some gain as well as giving the bass more control, less thump and more clarity. I replaced the output and the last cap in the PSU with Mundorf MKPs, as well as bypassing the other PSU caps with 2.2 uf MKPs. I think the biggest bang for the buck upgrade for me was the filter choke in the PSU, about $14 from Mouser, but it takes some creativity to fit it on the plate.

Shawn P.

 

[levlhed]

I already have Speedball and ran a 5998 for about a year until I hosed it on accident.  Now I run a 7236, a 'computer' version of the 5998, which sounds exactly the same if not a tiny tiny bit better. Tele smooth plate on the front end....So, upgrading the vol pot to a PEC and may as well do the caps if it's not too much trouble anyway, knowing it will only be a subtle improvement....not much else to upgrade without serious modification...I'm still trying to figure out what to do there though.

 

[Laudanum]

I agree 100% that Speedball provides a more signifigant change in sound than the Film output caps and also agree about the potential changes/improvement being greater with tube rolling.
I installed the film caps BEFORE I did the Speedball upgrade.  Just guessing that this could have impacted my perception of their impact, but by strict definition, I cant exactly call the change "subtle" in that I didnt have to listen intensely to recognize the change in sound.  But again, I am in total agreement that it isnt as signifigant as the other upgrades/changes mentioned.  "Smoother" is probably the best single description of the film caps affect.  As I mentioned previously, I think the stock caps sound good and in retrospect, I could happily enjoy Crack with them, and did so for a while.  But the film caps are a worthwhile addition to the upgrade path IMHO.  Just not on the top of the food chain so to speak, when prioritizing.

 

[Beefy]

Now I run a 7236, a 'computer' version of the 5998, which sounds exactly the same if not a tiny tiny bit better.

The 7236 is actually a computer rated 5998A, which is a slightly different tube to the 5998. It looks like it uses the flat plates of the 6080/6AS7 rather than the dimpled plates of the 5998, but still has the higher gain and slightly lower heater current of the 5998.

*

Back to the more recent upgrade questions, I'd put in a vote for the TKD 2CP2511 or 2508 pots. They track and sound better than an Alps, even to my tin ears. And I've personally avoided PEC pots because of numerous reports that they can be noisy and scratchy, particularly at low volumes.

 

[levlhed]

Thank you for the clarification on the 7236.  I highly recommend it as a cheaper alternative (though not a sexy ST shaped) to a 5998.

The TKD pot fits in there ok?

 

[tubeglow]

Thank you for the clarification on the 7236.  I highly recommend it as a cheaper alternative (though not a sexy ST shaped) to a 5998.

The TKD pot fits in there ok?

I used a TKD and except for having to enlarge the hole it fits fine. I can't compare it to any other potentiometer because I installed it during the original build but I can't hear any issues with it at all and it's very smooth.

 

[Natural Sound]

I installed a Goldpoint 'Mini-V' in my Crack, but only because I had it around from a project I wasn't satisfied with and tore down for parts. I don't think I would have spent the $140 just for this amp. It does sound great, much better than the Alps blue I originally installed. I don't have any experience with the PEC so I can't compare the Goldpoint with it.

Shawn P.

Hi Shawn,

Are you using the speedball upgrade? It doesn't look like there would be enough room between the Mini-V and the C4S board.

Tom

 

[levlhed]

TKD pot and Mundorf MKP's output caps installed by a tech friend of mine, I only just got the amp back at lunchtime....won't have time to listen until later tonight.

 

[levlhed]

Um...YES.  A definite improvement.  As other's have said, not night vs. day but noticeable.  Nicey nice.

 

[Laudanum]

Um...YES.  A definite improvement.  As other's have said, not night vs. day but noticeable.  Nicey nice.

I dont know about the pot but I like the Caps.  Not bad at all for affordable "basic" MKP's.

 

[grausch]

Reviving an old thread again, but this has some solid info in it and hoping to keep all of it in a relevant place.

I am planning on putting in the Belton tube sockets, and since this means some major rework, I plan on replacing some parts as I go along. I was just going to order resistors, but read the following and would just like to double-check before I order incorrect parts.

I am quoting DocB from the first page of this thread: "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."

I do not have Speedball installed, but will be replacing the metal film resistors and probably the power supply resistors. Resistance will stay the same, I plan on slightly increasing the wattage, but am not sure about the "voltage and power ratings" mentioned in the above quote. Would a 500V rating be sufficient? I also know that an increased wattage leads to a bigger resistor and potential mounting issues. Anything else I need to be aware of?

 

[Paul Birkeland]

The 270 Ohm resistors need to have long leads so that you can mount the one between the two 6 lug terminal strips on the power transformer.  Most 270 Ohm 5W resistors won't work here, so you'll probably need one 10W and one 5W part here.  These are not particularly audible in my experience.

I can't see any reason to change the 270K 1W resistor, but if you need a new one, any 270K 1W resistor will work fine.

The 22.1K resistors are chosen for good quality and adequate power dissipation.  You could spend a lot of money on nicer resistors, but they won't deliver the performance that the Speedball does.  (Same goes for the 3K cathode resistors)

-PB

 

[grausch]

Hi PB,

Thanks for the response. These changes are purely cosmetic in nature and I feel that I can do a better job now than I initially did. Plus, I really like working on the Crack. It is a really simple, yet elegant design that makes it very easy to experiment.

I will be replacing all the metal-film resistors with the mustard coloured Vishay / Dale ones on Mouser. Not very expensive and purely cosmetic.

Regarding the 270 ohm resistor, I was thinking of either using the Stereomour trick of using insulation from another wire to cover the exposed wire, or just make fly leads and solder the resistor to that. Again, purely a cosmetic change.

For the 270K resistor, still undecided. In any case, for both of the last 2, I will look up their specs and find something that can handle the 500V minimum.

Once all of these changes are implemented, I will have the base Crack built exactly like I want it, and can probably add Speedball at that point.

 

[Paul Birkeland]

I will be replacing all the metal-film resistors with the mustard coloured Vishay / Dale ones on Mouser. Not very expensive and purely cosmetic.

The two 22.1K resistors should carry at least a 1 Watt rating. 

Regarding the 270 ohm resistor, I was thinking of either using the Stereomour trick of using insulation from another wire to cover the exposed wire, or just make fly leads and solder the resistor to that. Again, purely a cosmetic change.

A 10W part will actually look better back there.

For the 270K resistor, still undecided. In any case, for both of the last 2, I will look up their specs and find something that can handle the 500V minimum.

Any old 270K 1W part should work, the 500V rating isn't necessary. 

 

[Colin]

How is the sound quality changed if all the crack's stock cable changed with pure silver core cable? I'm a newbie in diy, very interest when hear the silver core cable interconect sound character. But a little fatigue in high tone, its get sibilance and 'overload' in treble. So is it possible to get the best sound when apply all the stock cable with it?

 

[bocosb]

I just noticed that my bottlehead crack has reversed left-right channels (i bought it already built some time ago) - I would like to fix this and also upgrade the volume pot if i'm anyway taking it to an electrician.. any suggestions for a good value pot?

 

[borism]

The Valab 100K ladder type attenuator has been used by a number of people here. It's only $33 on eBay.