Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: btrancho on December 26, 2011, 12:44:50 PM
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I picked up the stepped attenuator shown below from eBay and want to make sure that I am wiring it correctly in my new Crack.
Can I assume that the wiring will follow the pdf instructions? The connections look to be the same as a standard pot and my meter shows all 21 steps when connected between 2 & 3 as shown below.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.trancho.net%2FHC%2Fattenuator.jpg&hash=252c4400a79861756c48f9a25ef1ba92a089e67d)
Bob
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Bob,
If you start with it fully CCW and you measure resistance from 2 to 3 you should see a descending resistance as you turn it CW. If so the schematic is right.
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Yes, that's what I get. Better safe than sorry.
Thanks Grainger!
Bob
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Finished wiring this morning - the resistance check revealed one problem and once that was resolved the voltage checks were pretty much spot on.
I haven't taken my headphones off for two hours now.
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Please, let us know if there any improvement on sound quality?
Yashin
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Yashin, I can't really tell you if there was any improvement since the attenuator was installed as part of the original build and the default pot was never used. I can tell you that it is dead quiet, even if I crank the volume to the 3 o'clock position - the 13th or 14th step - which is really beyond the pleasurable listening level for either my Beyer DT-880s or my Senn HD600s. For only $17 including shipping from Hong Kong it is certainly worth trying as an upgrade.
Reading your other post I'd recommend the Speedball before you made any other modifications - mine is on order already. I also have found rolling my tubes (to Mullard CV4003 & RCA 6AS7G) has made an appreciable improvement - more musical for sure.
Bob
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Thank you, btrancho.
have you checked the 5989 tubes for the crack? Excuse my ignorance I am new at all. Which tube is replacing which?
Yashin
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Thank you, btrancho.
have you checked the 5989 tubes for the crack? Excuse my ignorance I am new at all. Which tube is replacing which?
Yashin
Do you mean the 5998? No, as the current prices I am seeing put it out of my price range (http://www.ebay.com/itm/Tung-Sol-5998-flat-plate-vacuum-tubes-/270830363185?pt=Vintage_Electronics_R2&hash=item3f0ebf6231). I'd rather invest the $100 in the Speedball at this point. Of course, I could very well get carried away and spend the money down the line as I have a real desire to hear this in my Crack.
The Mullard CV4003 replaces the stock 12AU7 and the RCA 6AS7G replaces the stock 6080. For more tube info I suggest you read the (very long) thread entitled Tube Rolling w/Crack (http://www.bottlehead.com/smf/index.php/topic,663.0.html). (Which reminds me that I wanted to ask everyone if there is any way to search threads in this forum software - searching the entire category is a bit of a PITA)
Bob
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There is a Forum Tricks thread here:
http://www.bottlehead.com/smf/index.php/topic,83.0.html
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Please, let us know if there any improvement on sound quality?
Yashin
I have installed the same attenuator, and it works flawlesly. The sound is clearer and i really like the steps. It makes it much easier, to test different tubes and cables. As i always can find the same volume.
I think that its a good upgrade for the money.
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I should note that this attenuator is just a bit more difficult to install than the default pot. It is much smaller and the contact holes are smaller too, making multiple wire connections tricky. When screwed down, one channel sits very close to the plate, meaning you must be careful about soldering and wiring management to avoid shorting to the plate.
That said, it is easy enough to loosen or not even screw down the attenuator during construction (or upgrade) to make working with it easier. If I were doing it again, I'd also thread that first black wire from the braided set on page 21 of the manual through the two holes from the bottom, leaving a small 1/8" "post" on top to which to attach the 4 1/2" wire on page 22 that goes to the TRS terminals. This avoids having to try to get two wires through a hole that is too small.