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Old 14th June 2004, 09:10 AM   #1
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Default Stepped attenuator

I'm going to build a Cleo V for a customer.
http://www.triodedick.com/cleo_5_deel_1.htm

I have offered a noble pot (You know the ones by Bill Fitzpatrick) with the detents. But was thinking...if the customer gets a DACT or other brand stepped attenuator...what kind of gains wil he get...in other words .......

is a stepped attenuator really a step up......?!?

Does anyone have any experience in upgrading to a stepped attenuator? And which one is best for the money?

Asking here because the premium is very high..DACT = 180$,
Noble is 25$

Cheers,
Bas
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Old 14th June 2004, 09:49 AM   #2
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Bas,

The noise factor of the metal chip resistors DACT uses is superior to conductive plastic. However, the Noble detented controls are NOT junk.

FWIW, Gordon Rankin prefers Penny & Giles conductive plastic to stepped attenuators. P&G pots. carry a hefty price tag.
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Old 14th June 2004, 09:50 AM   #3
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Hi Bas,

I just recently changed from ALPS bluepot (I now call it the Blue Basstard) to a stepped attenuator from Schuro (Elma switch with Dale resistances).

The increase in low-level detail was astonishing. It changed my sound from flat to 3D. Basses were somehow deeper, background- and dubbed vocal can now be easily followed, voices sound more natural.

I can only say that is a major step up. Much more than I had expected. Now, when I see a picture of a DIYer using a bluepot, I can't help to feel sorry for him, especially when he's build an otherwise perfect amp (like an expensive Aleph).

Hope this helps.





Beware: This only a comparison between ALPS bluepot against Schuro stepped attenuator kitset.
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Old 14th June 2004, 09:53 AM   #4
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Quote:
The noise factor of the metal chip resistors DACT uses is superior to conductive plastic. However, the Noble detented controls are NOT junk.
Thanks Eli


Quote:
The increase in low-level detail was astonishing.
That confirms what others have told me! Thanks.
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Old 14th June 2004, 01:05 PM   #5
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Same experiences with a blue Alps to a DACT. Very much worth the extra $$.
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Old 14th June 2004, 01:48 PM   #6
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Thanks Ralph. I appreciate all the input by people that have actually upgraded their pots. So much more than the marketing.

Cheers,
Bas
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Old 15th June 2004, 03:33 AM   #7
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Hi,

Bas,

Since this is for a valve circuit I'd recommend one of the series type attenuators as these provide a constant impedance to the circuit.
This can be critical if the designer had this in mind and chose the value of the potentiometer accordingly (value of g' in formulae).

If you want to avoid putting all resistors in series as you attenuate further down (lumped Johnson noise), add the R values of such series attenuator as you'd move position (R2' = R1 +R2, R3' = R1+R2+R3 and so on) and use a double deck switch.
Most likely you'll need the E96 series range of 1% resistor values for a precision steps of 2-3 dB/step.

By doing so you'll never have more than one resistor in the signal path but instead you'll have a second switching contact.
Given the high contact integraty of the ELMA, Shallco and Seiden switches I have not noticed any degradation of sonic quality because of that.

If money's no object I'd choose the naked Vishay bulkfoils, followed by Dale, Caddock, Beyschlag (Dutch ), Resista, old style Holco...plain good quality carbon films work surprisingly well too.

The shunt part resistors aren't really an issue here, use decent MF and you're done.

Also keep in mind that those switches and resistors should not carry more than say, 20 VDC for highest reliability.

On a final note, in real life and with my system, I hardly ever use more than 3-4 positions. So you know where I spend the hard earned Euros.

Use of Ag doped silver (2%, preferably 4%) is highly recommended especially since the solder lugs of the switches are goldflashed in case you use the hardwire version, not the PCB. Besides the better sonics it's a doddle to use too.

Naturally, the above description applies to a single channel only.

Cheers,
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Old 15th June 2004, 04:03 AM   #8
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I have just built a Goldpoint Shunt attenuator, with Vishay S102 as series resistor and Dales as shunt resistors.
No pot can come close to this!!
No need for a Dact, as there are kits from Percy and others that cost way less.
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Old 15th June 2004, 04:09 AM   #9
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Quote:
Originally posted by fdegrove
The shunt part resistors aren't really an issue here, use decent MF and you're done.
Don't underestimate those. In my tests they were as important as series resistors (if not more).
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Old 15th June 2004, 05:41 AM   #10
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stvnharr's flicking phalanges formulated:

Quote:
No pot can come close to this!!
No comment...

Seriously--thanks for the tips. The percyaudio.com
and goldpt.com sites are groovy.

Best,

George "Cheech" Ferguson
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