Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: akis on May 22, 2015, 06:06:21 AM

Title: Are these UK voltages ok (seem very high) ??? [solved]
Post by: akis on May 22, 2015, 06:06:21 AM

Crack + Speedball. 

 Measured voltages as follows:

1   71.6v
2   187.6v
3   0
4   187.7v
5   182.9v
6   0
7   113.4v
8   0
9   180.6v
10 0
11 0
12 0
13 187v
14 0
15 205v
20 0
21 223v

All v dc.

Measure much higher than the manual suggests ?! I would have thought the transformer supplied for the UK kit drops the voltages to be the same as US ?

Thanks in advance.

Title: Re: Are these UK voltages ok (seem very high) ???
Post by: Paul Birkeland on May 22, 2015, 06:15:10 AM

Your voltage at 5 suggests that half of the 12AU7 is not operating properly.  Are both LED's on the 9 pin socket glowing?  Are both halves of the 12AU7 glowing? 

When both halves of your 6080 are allowed to draw adequate current (which requires proper operation of your 12AU7), then you will find that your voltages will align with more precision to those specified in the manual.

-PB

Title: Re: Are these UK voltages ok (seem very high) ???
Post by: akis on May 22, 2015, 07:00:46 AM

Thank you. I'll check. Certainly one was dimmer than the other - I noticed when measuring.

Of course they are the fiddliest components to get to.

Title: Re: Are these UK voltages ok (seem very high) ???
Post by: Paul Birkeland on May 22, 2015, 09:29:10 AM

Quote from: akis on May 22, 2015, 07:00:46 AM

Thank you. I'll check. Certainly one was dimmer than the other - I noticed when measuring.

Of course they are the fiddliest components to get to.

I suspect that you have incorrect R1 resistors on some of your boards.  Do measure them with your meter before powering the Crack up again.

Title: Re: Are these UK voltages ok (seem very high) ???
Post by: akis on May 22, 2015, 09:36:33 AM

Both diodes across A3 to A8 measure ok: 1.504v and 1.511v. These LEDs both light up and both sides of the 12AU7 glow (and equally).

Short of replacing the LED's I'm stuck on what to do next.

I don't fancy removing the PCB's to replace the LED's for no reason.

Is there anything else it could be that I can check?

I did plug in my headphones and have a listen. The Left Channel is lower output (I'll do the resistor mod once I've sorted the voltages).

The sound is more muffled somehow compared to pre-Speedball and less dynamic. There seems to be a greater level of distortion than before and it saturates at lower volumes??

Title: Re: Are these UK voltages ok (seem very high) ???
Post by: akis on May 22, 2015, 09:42:20 AM

Yep you're right. And I thought I'd been so thorough !! What a numpty !!!

I've switched one of the R1's with PCB B. Will rectify that now and re-measure.

Title: Re: Are these UK voltages ok (seem very high) ???
Post by: Grainger49 on May 22, 2015, 09:54:22 AM

Wait till you get where you can't read the colors.  Then you have to use a meter to find your resistors.  But a smart man won't wait that long. 

I pretty much got lost with 5 band resistors and went to measuring them all before presbyopia.

Title: Re: Are these UK voltages ok (seem very high) ???
Post by: akis on May 22, 2015, 10:54:52 AM

Ok so that's how long it took to swap across 2 resistors.

Check and check again ! Use a meter as Grainger says.

New readings:

1    74v
2    180v
3    0
4    180v
5    74v
6    0
7    104v
8    0
9    106v
10  0
11  0
12  0
13  180v
14  0
15  200v
20  0
21  200v

Much better. Now let's see how it sounds.

Title: Re: Are these UK voltages ok (seem very high) ??? [solved]
Post by: akis on May 22, 2015, 11:13:50 AM

WOW WOW WOW !!!

Awesome sound. Don't think about it, if you can, you must buy yourself a Crack.

What did I learn on the build:

Crack: the LED's between A3 and A8 are very fragile (I broke one and had to find replacements) but that's about it.

Speedball: 2 things a) the 24swg i.e thin cable needs a really good wire cutter to not damage the core, b) read the resistors carefully!

Thanks for your quick and helpful responses.

 :) :) :)