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March 24, 2019, 06:21:19 am

Author Topic: Rebuilding a Broken Crack  (Read 451 times)

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Offline TypodCrow

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Re: Rebuilding a Broken Crack
« Reply #15 on: March 02, 2019, 04:13:06 am »
At least get a quote from Bottlehead, keep it in the family as it were.

Contacted the ream; will probably hear back Monday or Teusday. Until then I've taken the other suggestions and compiled a cart which I can easily checkout. I've also asked Maxhawk if he can kindly throw in a few feed of colored hookup wire (of the right kind) when he sends me the tube switching board. If this works out, then I'll be able to avoid dealing with 97' of white hookup wire sitting around until I need it in a few years.

OP has been updated with the suggestions I've taken from everyone here. Thanks again guys, I appreciate your input so far.

Offline TypodCrow

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Re: Rebuilding a Broken Crack
« Reply #16 on: March 16, 2019, 06:51:30 pm »
Asking for some more help:

As I get ready to plan out the output transformer circuits, I'm realizing how  many things will need to be switched when changing from tube output to OT output.

To simplify this, can I wire the ground/-ve of the primary and the ground/0ohm of the secondary on the output transformer together? Or should I keep these separate? What am I sacrificing (besides an isolated ground) by connecting them together?

Offline Paul Birkeland

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Re: Rebuilding a Broken Crack
« Reply #17 on: March 17, 2019, 06:34:32 am »
As I get ready to plan out the output transformer circuits, I'm realizing how  many things will need to be switched when changing from tube output to OT output.
I would listen to them before you commit to adding them to the circuit.  FWIW, we have never heard a Hammond transformer that we were happy with. 

To simplify this, can I wire the ground/-ve of the primary and the ground/0ohm of the secondary on the output transformer together?
Yes.

Or should I keep these separate? What am I sacrificing (besides an isolated ground) by connecting them together?
No, I would connect them together.  This is a little safer, but you can try it either way.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline TypodCrow

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Re: Rebuilding a Broken Crack
« Reply #18 on: March 17, 2019, 08:34:28 am »
Thanks Paul; saves me another thing to switch on and off if I commit to them. I'll definitely listen first, but will most likely need to keep them on since I have low impedance cans and I'm fairly committed to the crack for now.

Offline TypodCrow

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Re: Rebuilding a Broken Crack
« Reply #19 on: March 18, 2019, 09:25:30 am »
Doing resistance and voltage checks now and getting some failures. The entire Crack has been rebuilt to as-recieved state (see first post for details). I have not plugged in headphones yet.

How might I debug what's going on? At first glance it seems the output caps are just not filtering out any DC?

Full voltage and resistance tables below. Inconsistencies with instructions highlighted:

Voltage (with tubes):
177
2182
30
4182
577
6108
7108
80
9108
10108
110
120
13180
140
15200

200
21218

A177
A20
A40
A50
A677
A70
A90

B177
B2180
B3108
B477
B5180
B6108
B70
B80

Resistance (without tubes, just in case it helps:

meter leads alone1.2

1inf
2inf
31.2
4inf
5inf
6inf
7inf
81.2
9inf
10inf

121.2
13*See note below*
141.2

201.2
221.2

B3inf
B6inf

RCA: GND1.2
RCA: L89
RCA: R90

Note on 13: slowly climbs to 200kohm when MM set to 200kohm limit; declines slowly to 0 when I flip multimeter to 2Mohm limit
« Last Edit: March 18, 2019, 09:32:36 am by TypodCrow »

Offline Paul Birkeland

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Re: Rebuilding a Broken Crack
« Reply #20 on: March 18, 2019, 10:02:42 am »
I have not plugged in headphones yet.
That's a relief.  This amp will destroy any headphones you plug into it.

Are the 2.49K resistors present on the headphone jack?  Can you post some photos of your work?  Is the headphone jack grounded exactly as it is in the manual?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline TypodCrow

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Re: Rebuilding a Broken Crack
« Reply #21 on: March 18, 2019, 10:31:26 am »
Pictures are a little hard to snap with the massive caps and the Speedball boards in the way but I'll do my best with the angles I can sneak in. The pictures are taken with Maxhawk's tube switching speedball board installed but the state is the exact same if I use the stock Speedball board. I have ensured I am in 12AU7 mode on the switching board.

Note: All 6 LED's are lit.

Are the 2.49K resistors present on the headphone jack?

Yes they are (picture attached).

Is the headphone jack grounded exactly as it is in the manual?

No. The jack's S terminals (both) are connected to 12. It is also grounded to 3 (which routes to the volume pot's ground terminal) instead of pulling a wire all the way across from the pot's ground directly. 3 also grounds both speedball boards (that is all ther connections at 3).

The T and R connections of the headphone jack are hooked up to 10 and 6, which are only wired to their respective output caps.
« Last Edit: March 18, 2019, 10:41:13 am by TypodCrow »

Offline TypodCrow

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Re: Rebuilding a Broken Crack
« Reply #22 on: March 18, 2019, 10:59:20 am »
I think i know what it is. The resistors only cut across the headphone jack, but don't ground to the sleeve pin. I'm going to short the three right side pins of the headphone jack (view orientation of the picture attached in my last reply to this thread). That will solve it.

Dumb derp; my apologies.

Offline Paul Birkeland

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Re: Rebuilding a Broken Crack
« Reply #23 on: March 18, 2019, 12:50:22 pm »
Yes, that's the issue.  In Crack 1.0, these resistors go down diagonally to the sleeve terminal, then in 1.1 we ground out all of the terminals that are shorted when no headphones are plugged in, then connect the resistors to this ground. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline TypodCrow

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Re: Rebuilding a Broken Crack
« Reply #24 on: March 18, 2019, 12:58:27 pm »
It's a great feeling finally hearing this beauty. The OPT's I can't judge yes since I only have low impedance loads hut I'll definitely borrow my friend's HD600 to get an understanding of how they're affecting SQ.