not getting zero for resistance checks

[Armaegis]

So I think I've got a wire crossed or short somewhere, but I can't find it... here are the resistance check values that don't match the manual:

centre pin = 92k/92k (doesn't matter what the knob is set at)
#5,25 = 38 ohm
#10,30 = 38 ohm
#15,35 = 38 ohm
#17,37 = 38 ohm
#20 = 96 ohm
#40 = 290 ohm
A3,B3  = 38 ohm (all the 38's should be zero)
A4,B4= 220 to 94k

Help?

 

[Paul Joppa]

Does your meter read zero resistance when the probes are touched to each other?

 

[Armaegis]

Yes, I tried that plus various ground points which all checked out.

 

[Grainger49]

The manual is wrong, the reading from the center pin of the RCA should read ~100k (+/- 10%) regardless of the volume pot position.

I see a number of terminals that should read zero are reading 32.  It might indicate that the autoformer wiring is not right, possibly reversed.  There are two twisted wires you have to sort out with a meter to terminate them.  Is it possible you got those swapped?  Terminals 20 is attached to the autoformer also.  Your reading for terminal 40 is off by 2% so it is good.

A3 and B3 are part of the ground buss, page 27, that should be easy to check.

A4 and B4 are 6% off, that is fine.

 

[Armaegis]

Well that was embarrassing, I poo-pooed the ground buss wire on both sides (at least I'm consistent right?). The dumb part was that I caught the mistake and "fixed" it incorrectly. I somehow missed the part about connecting 17-18 together. So I wound up only doing 17. Then on the other side I connected to 38 and missed 37, look over at the other side and noticed the symmetry was off, then redid it. Sigh, that's what I get for marathoning the SEX build in one day.

Anyhow, it's all good now.

 

[Doc B]

Sigh, that's what I get for marathoning the SEX build in one day.

I spend a lot of time suggesting that builders take their time with the kits. One reason is what you experienced, it's just plain hard for the brain to stay at the level of concentration necessary to do the kit in one long haul without hiccup. The other common problem is post-construction depression - you finish the build and you wish there was more...tends to hit home on the second kit.

 

[Armaegis]

Yeah, but this was the first opportunity in nearly three weeks I had an evening to sit down and build (although that "evening" dragged on until nearly 3am). I should have split it up over a couple days, but who knows when the next opening will come around.

Also, I noticed a couple typos in the C4S manual. When mentioning removal of the 150K plate load resistors, it is from A5 and 16, not 17 (same for 36 vs 37). I think there's a similar typo later on as well, but I can't remember where. Also a random typo on p.15 where you have a random "t" in front of a B6.


Initial impressions are quite good. I prefer the Crack+Speedball with my AKG K240 Sextetts (600 ohm), but driving some of my 32 ohm cans were very nice. I find both the Crack and SEX seem to feel very spacious and mid-focuse compared to other amps. Driving some speakers, I found the sound to be almost... "bubbly" for lack of a better word. I'll need to try some more efficient speakers though.

 

[Doc B]

Not sure if you have the 120 ohm resistors in series with the headphone jack, but if you do, some 32 ohm headphones users have reported better sound when those are bypassed or replaced with wire. The 120 ohm resistors are in there so that one can put headphones of different impedance in the jack and not have to make drastic changes to the level setting. The attenuator will get more touchy if the 120 ohmers are shorted, so I would suggest trying it with a clip lead connected across the ends of each resistor before doing any hacking.

 

[Armaegis]

Hmm, I'll give that a shot and maybe try a shunt pot config next time I crack it open. Thanks!

 

[Armaegis]

I tried bypassing the 120 ohm resistors with some clip leads. It made no difference with my 600 ohm Sextetts, but with my 32 ohm cans I think it sounded better (though I can't discount the placebo effect due to it becoming louder). I did notice that the background hum became more noticeable with the resistors bypassed though (it is almost imperceptible with the resistors in).

 

[Doc B]

Yes, the noise floor will increase if you short out the 120s. That is another reason they are in there.