I'm going to use one of these: http://www.partsconnexion.com/tkd_64186.html with a 50k series resistor.

Meh. Just get this...

DACT CT2 50K Stereo Stepped Attenuator (New) on eBay.ca (item 280537303175 end time 18-Oct-10 10:37:40 EDT)

You'll never have to second guess the quality of your pot.

posty doesnt have to worry about the 2399 anymore. :facepalm: it is in safe hands. (well not yet).

ps. posty is super cool.

pps. would that dact pot require any sort of resistors is series/parallel? or just drop it in and go to town. also any ideas on whether the stock hole in the top plate will accept the dact pot. same question for the tkd pot.

Meh. Just get this...

DACT CT2 50K Stereo Stepped Attenuator (New) on eBay.ca (item 280537303175 end time 18-Oct-10 10:37:40 EDT)

You'll never have to second guess the quality of your pot.

I listen fairly quietly; a DACT doesn't have nearly enough steps.

pps. would that dact pot require any sort of resistors is series/parallel? or just drop it in and go to town. also any ideas on whether the stock hole in the top plate will accept the dact pot. same question for the tkd pot.

You should try and keep the input impedance at 100k, so a 50k series resistor is a good idea with a 50k pot.

The TKD requires a new mounting hole, and I suspect that the DACT would too.

Why not just get a 100K pot instead? If'n you're shopping.

I went that way because the 50k pot with 50k series resistor gives me ~6dB of pre-attenuation, increasing the usable range of the pot. Also, if I ever gut the amp a 50k pot will probably be more useful to me.

yeah that preattentuation is really useful. you tell him beefy.

there might be a renewed interest in the no electrolytic crack amp after all. found another guy with a cnc machine on campus. speaking with him on Monday.

Ok, so I bought a TKD 2CP2511 50k pot for my Crack build, and I need a sanity check. Resistance across input (pin 1) to gnd (pin C) is a constant 43kohm regardless of pot rotation, which makes perfect sense. But the resistances across the input and gnd to the output (pin 2) while turning the pot are baking my noodle.

When moving from minimum volume up, pin 1 to pin 2 increases in resistance from 43kohm to a maximum of 59kohm at about 1/3 of the pot travel, then drops steadily to 10ohm.

Pin 2 to pin C jumps very fast from 10ohm at minimum volume to about 3kohm in the first few degrees of rotation, then moves steadily up to 43kohm for the remainder of the rotation.

Clearly, these TKD's don't behave like normal pots, and there is a PDF on their website explaining that their rotary faders are 'ladder' circuits. Is this the full explanation for what I am seeing, or am I just going nuts?

Useful references: datasheet and an explanation of their ladder curve.

Edited February 8, 201214 yr by Beefy

Finally got around to taking proper photos of my Crack......

Highlights:

TKD 2CP2511 50kohm pot

50kohm 1W PRP resistors in series with the pot for approx -6dB pre-attenuation

Cardas RCA jacks (rhodium plating is a BITCH to solder)

Teflon tube sockets plus PCBs (Woo Audio branded)

2.2

bloody hell beefy. thats a nice looking build.

Thanks, CJ. It took an embarrassingly long amount of time to keep it clean, but definitely worth the effort

Congrats, it looks damn nice. I wish you enjoy it

Thanks, CJ. It took an embarrassingly long amount of time to keep it clean, but definitely worth the effort

it was my second ever build. i just wanted it to work. no time was spent trying to keep it clean. i doubt i could have done any better even if i tried. looks fantastic sir.

...... and here is the last pic I will post this week, I promise!

My Crack with Speedball and Axon film output caps installed:

Any thoughts on the crack with the nicer caps? I'm about to put in another order for odds and ends for the dcpp. Wouldn't mind throwing in a pair of caps if the difference is noticeably between stock and upgraded caps.

Edited January 20, 201115 yr by crappyjones123

Paging dsavitsk. Dsavitsk, please pick up a white courtesy handset.

Yes, crappy. The answer is yes.

Exemplary work on that amp, Beefy. Looks like textbook work for a Bottlehead project. Doc B. would be proud. Congrats!

Edited January 20, 201115 yr by bhjazz

new caps are otw. just got the wood case back from the guy i had asked to glue it and give it a clear coat. looks rather nice without the packing tape i must say

on a side note, past few weeks i had been listening to the jh16s exclusively. just went back to the 650 after 3 weeks. jh16s seem so closed by comparison perhaps its just the new toy syndrome all over again. resolution is far better on the jh16s but the feeling of music not playing inside my head is not present. me likey. me likey very much.

for the past 2 days ive noticed this really high pitched whiny noise coming out of the right channel. audible without music. with music i just know its there because the music doesnt have any notes that high. if i unplug the headphones and plug them back in, it goes away for like a minute but then comes back again. using 421a and amperex 12au7 (bugle boy). any thoughts?

new caps are otw. just got the wood case back from the guy i had asked to glue it and give it a clear coat. looks rather nice without the packing tape i must say

on a side note, past few weeks i had been listening to the jh16s exclusively. just went back to the 650 after 3 weeks. jh16s seem so closed by comparison perhaps its just the new toy syndrome all over again. resolution is far better on the jh16s but the feeling of music not playing inside my head is not present. me likey. me likey very much.

This is why I can never get into IEMs, they all sound so closed in (inc JH universals).

for the past 2 days ive noticed this really high pitched whiny noise coming out of the right channel. audible without music. with music i just know its there because the music doesnt have any notes that high. if i unplug the headphones and plug them back in, it goes away for like a minute but then comes back again. using 421a and amperex 12au7 (bugle boy). any thoughts?

Aside from trying different tubes...... are you perhaps getting DC leakage through the caps? Check the DC offset.

for the past 2 days ive noticed this really high pitched whiny noise coming out of the right channel. audible without music. with music i just know its there because the music doesnt have any notes that high. if i unplug the headphones and plug them back in, it goes away for like a minute but then comes back again. using 421a and amperex 12au7 (bugle boy). any thoughts?

Try switching tubes, cables, channels on your source to isolate the problem.

Also, take your set up into a distant room and try it there. It could be airborne digital or something that's leaking into your grounds on that household circuit( a different house would be definitive).

changed the bugle boy to a mullard. changed channels but whiny noise remains even with the cables switched and unplugged. problem is either with power or within the amp itself. i dearly pray it isnt the 421a. all else is cheap and easily replaceable.

Hi guys,

Got a Crack coming in as my first DIY build to write an article on. I'll do the basic build first, then the Speedball upgrade.

Then I'll no doubt re-read this thread and start making a friggen $1000 amp out of it with all the good ideas here.

Thanks for the great thread! No noise Head-Case FTMFW.

Cool beans. Would really be interested to see how the articles turn out!

Hi guys,

Got a Crack coming in as my first DIY build to write an article on. I'll do the basic build first, then the Speedball upgrade.

Then I'll no doubt re-read this thread and start making a friggen $1000 amp out of it with all the good ideas here.

Thanks for the great thread! No noise Head-Case FTMFW.

lol you need we 421a's first. and some bugle boys. and mullards. and hytrons. and rca's. and 5998s. and 6080s. and 6as7g's. and moar 421a's. thats like $1000 right there

post pix dood. it is quite good for a cheap(ish) amp.

ps. completely forgot about using motor run caps throughout the amp.

Edited February 19, 201115 yr by crappyjones123