Cheap stepped attenuator vs not so cheap potentiometer
Nov 21, 2008 at 2:41 AM Thread Starter Post #1 of 21

Navyblue

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I wonder how would cheap stepped attenuator made with cheap but decent rotary switch compares to better potentiometer like the Alps Black Beauty or the TKDs?

Would hard wired resistor path always beat good potentiometer?
 
Nov 21, 2008 at 3:00 AM Post #2 of 21

pabbi1

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Well, there are no absolutes, but generallt, the stepped resistors are better when their quality is what it ought to be. I seem to be 50-50 on cheap steppers from eBay vendors.

Ther Goldpoints are always superior to everything else I have ever tried, but I have some TKD inbount to see about that. Once you get to RK50 / Penny & Giles territory, the discussion gets more interesting.

Since the RK40 is no longer available in audio taper, the distinctions become more clear - you get what you pay for.
 
Nov 21, 2008 at 3:36 AM Post #4 of 21

rds

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Quote:

Is there any reason to spend more just to get a duller sound?


confused.gif


Personally I wouldn't spend more to get a duller sound.
 
Nov 21, 2008 at 3:51 AM Post #5 of 21

Navyblue

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From the perspective of the resistor, I believe most people wouldn't want to use carbon fixed value resistor to build anything that is in the audio signal path, if they have the choice of using metal film resistor.

So, would there be better carbon variable resistor than reputable metal film fixed resistor? But I'd expect the really good ones approaches really close. Or does the high end potentiometer use carbon at all?

Of course that is not the full picture and the quality of the switch would come into play too.
 
Nov 21, 2008 at 3:54 AM Post #6 of 21

cotdt

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Quote:

Originally Posted by Navyblue /img/forum/go_quote.gif
From the perspective of the resistor, I believe most people wouldn't want to use carbon fixed value resistor to build anything that is in the audio signal path, if they have the choice of using metal film resistor.

So, would there be better carbon variable resistor than reputable metal film fixed resistor? But I'd expect the really good ones approaches really close. Or does the high end potentiometer use carbon at all?

Of course that is not the full picture and the quality of the switch would come into play too.



The cheap carbon pots have a more analogue sound, though if you listen carefully there is some grain, which makes sense, as the carbon pots add noise. The metal film resistors are technically better (cleaner, smoother sound) but personally I prefer the sound of $1 carbon pots over $300 stepped attenuators.

BTW, how's that Beta22 sounding?
 
Nov 21, 2008 at 4:09 AM Post #8 of 21

Navyblue

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Quote:

BTW, how's that Beta22 sounding?


As of now, it has a really dark background, and I haven't even soldered anything to the boards yet, can't wait till the day I complete it.
biggrin.gif
 
Nov 21, 2008 at 6:36 AM Post #9 of 21

nikongod

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There are some nice carbon pots out there from what the reviews indicate. There are also many many plastic pots that are awesome. The channel-channel matching of anything but the very best pots is not as good as a well built stepper, but is not especially poor either: This is especially important when you consider the trend to use 2 decks of a pot to attenuate a balanced signal. Once you accept the fact that for a well built pot you will probably be spending some decent money things get interesting.

Comparing my limited selection of pots and steppers, the steppers are more likely to sound good at lower price points. The Asian steppers on ebay compare favorably with expensive pots. There are still a couple stumbling points for a stepper.

You have steps! (owned) I find myself wanting "the step between the steps" far too frequently. I personally prefer pots even with greater expense, and possibly lower SQ to steppers for this simple reason.
Quote:

Originally Posted by cotdt /img/forum/go_quote.gif
The cheap carbon pots have a more analogue sound, though if you listen carefully there is some grain


Isnt grain the typical mark of poorly reproduced digital sound? Is the sound more analog or have the transients and highs simply been dulled?

Nicer pots dont have any problems passing transients, and still sound analog when running from an analog sounding source.
Quote:

The metal film resistors are technically better (cleaner, smoother sound) but personally I prefer the sound of $1 carbon pots over $300 stepped attenuators


Is it necessary to bring exotic steppers into this discussion? There are plenty of 24-step steppers well below the $50 mark sold ready to install

If you like the sound of carbon, thats your prerogative, why not build a stepper with carbon resistors?

[sarcasm ]I suppose you would loose the superb channel-channel tracking, silence while rotating (I know steppers make some noise while switching levels, but its not the harsh screechy hiss a cheap carbon treats you to), and the superbly accurate and consistent log curve typical of cheap carbon pots. [/sarcasm ]

In all seriousness, the reviews of the Precision electronics components (PEC) pots indicate that they are a very nice carbon pot at a pretty reasonable pricepoint. all of our builds is too nice to put a worthless carbon pot directly in the signal path.
 
Nov 21, 2008 at 8:15 AM Post #10 of 21

Navyblue

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The SMD eBay stepper looks like a serial stepper (correct me if I am wrong). The non SMD eBay stepper is confusing, it mentioned that it is a serial stepper in the title and then raps the goodness of a ladder type.

If none of those are the ladder type, I'd consider building one, though I very much frowned on the amount of effort needed.

And the 20+ position rotary switch aren't cheap too, which made me look at the better potentiometers.

The cheap rotary switches normally goes upto about 12 positions. I thought of a way to overcome the limited number of steps. First build an 12 step 10k ohms stepper as usual. Then I'd have another rotary switch along the signal line which switches a 40k ohms resistor, a 10k ohms resistor, and no resistor. The first rotary switch position would essentially give me the first 12 steps of a 60 step 50k ohms stepper. The second would give me the first 12 steps of a 24 step 20k ohms stepper. And the last would give me the full range of a 10k ohms stepper. Did I miss anything?

The variable input impedance which resulted made me consider shunt type volume control with just a plain RK27. But how bad is it for the source to see a variable impedance? Afterall we can use pots ranging from 10k to 100k ohms without much harm with most modern sources, as long as the impedance is being kept at reasonable range.
 
Nov 21, 2008 at 4:33 PM Post #11 of 21

nikongod

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Quote:

Originally Posted by Navyblue /img/forum/go_quote.gif
The SMD eBay stepper looks like a serial stepper (correct me if I am wrong). The non SMD eBay stepper is confusing, it mentioned that it is a serial stepper in the title and then raps the goodness of a ladder type.

If none of those are the ladder type, I'd consider building one, though I very much frowned on the amount of effort needed.



the SMD ones on ebay are almost all serial types. MOST of the leaded resistor steppers on ebay are ladders.
Quote:

And the 20+ position rotary switch aren't cheap too, which made me look at the better potentiometers.


There are some inexpensive sources for 24-step switches in Asia, Il edit this post later.
Quote:

The cheap rotary switches normally goes upto about 12 positions. I thought of a way to overcome the limited number of steps. First build an 12 step 10k ohms stepper as usual. Then I'd have another rotary switch along the signal line which switches a 40k ohms resistor, a 10k ohms resistor, and no resistor.


What you are describing has been done. It works out very well if you need LOTS of range or very fine control with a stepper.

Check out the broskie stepper on the tubecad site for a good example. you can get closer to constant input impedance with some changes.
Quote:

The variable input impedance which resulted made me consider shunt type volume control with just a plain RK27. But how bad is it for the source to see a variable impedance?


I really like the shunted log pot. link It is an elegant solution when using inexpensive parts or if you need more attenuation than a standard pot can provide. If you are using open-loop tube stuff (or open loop SS stuff with naturally high gain), it is a very nice way to get the HIGH attenuation you may need while still using a well matched section of the pot.

The output stages in most sources are somewhat indifferent to load impedance as long as it is not BELOW a certain point. IME an input impedance which varies from 100K to 110K is not a problem for most sources that require 100K. I suppose that the arguments of "high VS low" input impedance (noise and stuff) applies when you design something with really wide variances in input impedance, but you can get around it well.
 
Nov 21, 2008 at 5:10 PM Post #13 of 21

JamesL

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SQ-wise, goldpoint and those shouldn't really make a difference... especially since the goldpoint uses a series configuration versus a ladder config. Build quality is another story.
The switches themselves can be got for $4.50-$6 from chinese/taiwanese vendors, but the resistors can get more expensive if you so choose to go with boutique resistors. What is it... 23 positions... 2 resistors per position, and 2 channels = 96 resistors? 10-20c for rn55's, 35c for PRP's.. $1 for kiwames..
 
Nov 21, 2008 at 5:19 PM Post #14 of 21

cotdt

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Quote:

Originally Posted by holland /img/forum/go_quote.gif
VOLUME CONTROL TO 12AX7 6SN7 ECC88 ECC82 ECC81 EL34 6V6 - eBay (item 320300801499 end time Dec-16-08 09:29:15 PST)

I like those, no real problems other than break before make. That's not a big problem though. If you want carbon, change the resistors and hand match to 0.1%. The MF resistors in the package work better than most cheap pots, but could also be better matched.



It's a good price. I got one, but it feels a bit stiff and I prefer the Goldpoint.
 
Nov 21, 2008 at 5:24 PM Post #15 of 21

holland

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A bit stiff, but not bad with a knob. At least I have no problems with it turning with minimal torque applied. It's not as easy as others, but YMMV. I definitely don't mind. PITA to assemble though. Series is definitely simpler and more compact.
 

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