Finished build. Voltages and Bass...

Sp33ls · 2489

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Offline Sp33ls

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on: March 29, 2017, 07:46:47 AM
Hey all,

This is my first post here, and I have to say that the community seems great : )

As you may hopefully notice in the attachments (along with the dust and messy cable management  :P), my Crackatwoa is operational!

It sounds pretty great. They're paired with HD650s.

The only interesting tidbit is that after installing the TwoQuiet attenuators, my first observation was that the bass didn't seem quite as present. But, that could just be a volume discrepancy.

Here are my measured voltages. The left-hand voltage is the expected value, and the right-hand side is the measured value.

Terminal     Voltage (DC)

Low Current C4S
IA        150V   (150)
OA 60-90V   (77.3)
KregA  3-6V   (5)
bRegA 150V    (150)
IB        150V   (150)
OB   60-90V   (73.6)
KregB   3-6V   (5.7)
bRegB   150V   (150)
High Current C4S
IA         190V   (197)
OA        150V   (150)
bA         0V   (0)
IB          0V   (0)
OB  90-110V   (98)
bB        150V   (150)
Headphone Jack
Tip          0V    (0)
Ring        0V    (0)


Will the difference in OA and OB cause any imbalances? Also, what are your experiences in using the HD650s with the Crackatwoa in terms of overall bass "presence"? I can certainly reach the level I desire, but need to use an equalizer to do so.

Btw, thanks for the kit, Bottlehead! I love having the option to (potentially) save some coin and have the accomplishment of DIY. It looks really cool.

EDIT: Btw, I'm using a Telefunken 12AU7 and Bendix 6080WB at the moment. I noticed that the Bendix's bass was more punchy and tight when compared to the 6AS7GA's lush (definitely present) and more relaxed presentation.

A side note about the the Sylvania tube that came with the kit, I believe there may be something faulty with the tube. I've noticed a spark a time or two from within the tube (and a resulting noise output in the headphones), and I've been given a slight shock when touching the chassis (even tho I passed the resistance tests), and it seemed that the tube was shorting itself and after I was lightly shocked, it resumed working. I've not had that with the 6080WB. Thoughts?
« Last Edit: March 29, 2017, 07:55:11 AM by Sp33ls »



Offline Paul Birkeland

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Reply #1 on: March 29, 2017, 08:57:12 AM
The only interesting tidbit is that after installing the TwoQuiet attenuators, my first observation was that the bass didn't seem quite as present.

I've been given a slight shock when touching the chassis (even tho I passed the resistance tests),
You very, very, very likely have an unsoldered joint in your amp or a very cold solder joint.  This is easily heard as weaker than normal bass response, and getting a shock from the chassis plate is a sure sign that the amplifier is not finished yet and shouldn't be used. 

Just out of curiosity, do you have grounded outlets where you are using this Crack? 

I'd go over the whole build and reheat all the solder joints, focusing specifically on those solder joints on terminals that are supposed to have 0 Ohms of resistance.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Sp33ls

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Reply #2 on: March 29, 2017, 12:34:45 PM
Thanks for the words of advice, PB! I'll go through and reheat the joints.

Just out of curiosity, how much bass response should I expect to hear with this HP/amp combo? Subjectively speaking, as I have no real objective means of measuring it here.



Offline TurbOSquiD77

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Reply #3 on: March 30, 2017, 04:10:51 PM
Hey Sp33ls,

From my experience the Crackatwoa gives a "normal" amount of bass presence with just about any headphone I've used. Although, the amount of bass does follow that of the headphone more than that of the amp driving the headphones.

With the HD650 and Crackatwoa I hear more of what I call "clean" bass, rather than a lot of bass quantity. I notice the HD650's have an overall warm signature, but just a bit less bass presence than usual. Say, if normal is just the right amount of bass, above normal sounds as if one used an equalizer to add bass, and below normal sounds thin, then the HD650 C2A combo is right in the middle.

This is difficult to explain, wow I'm fatigued.

Too little bass to one person may be too much to another.

-T



Offline Sp33ls

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Reply #4 on: April 07, 2017, 10:38:10 AM
Thanks for the replies. I do agree with you, T.

I went through and re-heated the solder joints. It sounds amazing! :)

I'm actually going to run my turntable and a hifiberry DAC through a vintage Marantz receiver that I had recently re-capped and replaced the resistors on the pre-amp board in order to get some extra tone control in the line.

I'll report back after giving that a test.



Offline TurbOSquiD77

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Reply #5 on: April 09, 2017, 05:34:27 AM
Nice  8)

What turntable are you spinning, and how do you like the hifiberry? I think I read there are quite a few options for firmware as well. What do you run?

Best!