Hot-Rodded Crack

Since I can't leave well enough alone for longer than 5 minutes, I opted to add a Triad C7X choke to the power supply in the final resistor position. I think I'm done :)

Choke-1.jpg


Choke-2.jpg
 
Indeed, it sounds very good. My musical memory isn't good enough to pinpoint the differences between the unit with and w/o the choke, but I'm very pleased with the current sound. Since the choke, standoffs and spiked feet only ran about $25, it was a relatively cheap upgrade.
 
There's some interesting reading about chokes in power supplies here and elsewhere; I very much like the idea of rejecting as much mains noise as possible from the amplifier.

Hmm, it looks like I'm going to have to add another item to my upgrade list. Thanks alot! At least it's cheap enough to try :)

 
Okay, so this is my first post/question here or anywhere, so here it goes.  I really like all the things you have changed on this amp, e.g., Kiwames and all the nice caps.
I have a couple questions though; Forgive me if they're obvious as I'm new to this.  First, how did you match up the values for the Kiwame resistors? I can't seem to
find values that match the values in the kit.  Did you round up or down to the closest available value (did you use a 2.40K in place of the 2.49K)?
My second question is about the Obbligato 1uF Copper coupling caps you added.  I don't fully understand their purpose or what they are connected to. 
Are they bypassing the Solen 100uF Caps, and if so, are they just connected in parallel to the Solens?
Thanks,
Austin
 
Welcome Austin, I am sure Bryan will answer soon, but as I made similar mods and Bryan advised me I will try to answer your questions. I used Takman carbon film resistors but the method is the same. I bought a large number of resistors at values close to the stock values, and measured them using the ones that their actual value was closest to the stock, they can vary by 10% from their rated value. Bypassing is usually done with a higher quality smaller value cap to add it's sound signature to a ,usually, inferior large cap. The solens are good caps though, but I think Bryan likes what the obligattos do to the sound. As far as bypass cap values, it is usually best to go with a cap that is 1% of the larger caps value. The advice of all the Bottlehead folks is to build stock, listen for awhile before mods, to help appreciate what the mods do to the sound. Hope this helps.

Cheers,
Shawn
 
Hi Austin. Shawn is correct on all accounts. The best thing to do is to purchase a few resistors that are close to the value and use the one that's closest. Kiwames are usually pretty close to their marked value (within 1-2%), if you get Koa Speers from Mouser, they can vary a little bit more. Paul can state which resistors need to be close and which can vary quite a bit from the suggested value.

The Obbligatos were used to bypass the Solens at a 1% ratio. Bypassing is a bit of a black art, some feel it's beneficial and some do not, 1% is merely a rule of thumb and I've seen many other ratios out there. Solens are great caps if you need a large value film cap to fit in a relatively small area. There are better sounding caps, but for more money of course. Obbligato caps are quite good for the money, probably the best bang-for-the-buck caps out there aside from maybe the Russian PIO and PTFE caps.
 
Thanks both of you for the help. It's now clearer to me what I need to do with the resistors.  Bryan, I'm still a little foggy with the Obbligatos. When you say
you're bypassing the Solens, does that mean they are connected in parallel with the Solens? 

Shawn, thanks for the advice and the suggestion about building stock then listening for the changes.  I've got two kits.  I plan to keep one stock and do upgrades to the other so I can A/B them for that exact reason.  I'm not sure I would be able to remember the differences without being able to give one a good listen and then the other, but who knows, maybe I will.

I'm on a pretty tight budget so best bang-for-the-buck is what I'm looking for right now, so, about those resistors, how many Kiwames/Takman resistors did either of you have to go through and how close were either of you able to get to the kit values?

Thanks for the help,
Austin
 
Yes, in parallel. When caps are wired in parallel you add the capacitance together. When caps are wired in series, they act like resistors do in parallel and decreases your total value, so if you wired a 100uF and 1uF cap in series, you'd be left with something slightly less than 1uF capacitance total.

Regarding the resistors, I have a tray of assorted values from Koa Speers that I bought back when they were 16 cents a pop, so I probably had 6-10 or so of each value to test before using. Now they cost around 50 cents a pop and a number of values are sold out. Again, some of the resistor values aren't critical. I think there's a thread floating around somewhere on here where Paul states appropriate variances for resistors in the Crack circuit. Personally, I try to use resistors within 1-2% of the suggested value, and when I'm matching channels, I like to be nearly exact on each side (~0.1-0.2%), but that's just me being anal ;)
 
The crack follows the KISS method of design.  It uses a minimum of parts.

The only resistor considered (classically) in the signal path is the volume pot.  The 2 power supply resistors, 270 ohms, could be replaced with chokes.  Other than that there is the driver plate resistor, the output cathode resistor and the bleeder resistors.  Those are not usually considered in the audio path.

There might be a resistor in the PJCCS that would benefit from a thick metal film resistor, I don't know.
 
You must log in or register to reply here.

Similar threads

H
Hot-Rodded Dynaco ST-35
Replies
8
Views
6K
TonyMc
T
H
Hot Rodded Bottlehead S.E.X.
Replies
18
Views
9K
HF9
H
H
Hot Rodded Dynaco ST-70
Replies
11
Views
10K
Doc B
Doc B
H
Hot-Rodded Seduction
Replies
17
Views
6K
Dobs
D
Back
Top