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Old 15th February 2009, 06:42 AM   #1
stl is offline stl  United States
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Default Resistors for Stepped Attenuator

Hello,

I want to use a hybrid stepped attenuator for the S-5 K16LS amp from Glassware Audio Link and they have two types of resistors carbon and metal film.

Q: With respect to sound quality and clarity which ones are better?

Also, would changing resistors on the main circuit make any difference in terms of sound quality?

Thanks.

Frank
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Old 15th February 2009, 12:32 PM   #2
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Stl,

Traditionally carbon resistors are more noisy - but to what extent that would be a factor will depend on the position in the circuit of the attenuator. But the choice is not really there. Metal film resistors go to 1% tolerance and cost is no real issue in terms of that of the amplifier.

Changing the resistors in the main circuit will be advisable depending on how old they are. If older 5/10% carbon types, they can drift with the years, and again in the light of the negligible cost penalty, I would change.

I am not very sold on the 'sound' of components; that is often an overrated topic.
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Old 15th February 2009, 12:48 PM   #3
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You really gonna use a 3-knob gizmo for volume? Obviously they got a great deal on those 6-position switches but is this going to make an acceptable volume control?

Your resistor question is impossible for anyone to answer. Apparently some people are completely immune to differences between passive (or active) parts and maybe you are lucky to be one of them Of course then you won't be needing no fancy attenuators anyway.
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Old 15th February 2009, 09:02 PM   #4
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John Broskie's 3 knob attenuator looks interesting to me. Cost effective, allows fine db adjust, and doubles as a balance control....

I have not tried one, so I have no idea how they sound/work.

I am soldering in one of his little 3-way input selectors into my Aikido as I type this.
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Old 15th February 2009, 09:12 PM   #5
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Quote:
Originally posted by analog_sa
You really gonna use a 3-knob gizmo for volume? Obviously they got a great deal on those 6-position switches but is this going to make an acceptable volume control?
I was going to ask the same question (cant recall why not). For quality controls I use Elma 24 position switches (e.g. type 04-2100) for volume controls. Those are 'shorting' types, thus giving 47 steps, which at 2 dB each are almost inaudible as steps. In addition you can model your own law, taps, etc. and have a tractability of <2%. They are expensive (don't know how they compare to the above), but hardly more than some other fancy stuff on the market. One can lessen the step spring tension for easy rotation, or remove it altogether.

Quote:
Your resistor question is impossible for anyone to answer. Apparently some people are completely immune to differences between passive (or active) parts and maybe you are lucky to be one of them Of course then you won't be needing no fancy attenuators anyway.
Mmmmm .... I think that is a bit 'digitally' put. One acknowledges those differences; as a past research engineer I too often had to reckon with exactly that or else .... But it has also been abundantly demonstrated that certain "beliefs' are not supported by practical tests; on the contrary. One also needs to acknowledge that.

The question is whether these differences are of consequence in audio. If resistors are to be used at sub-mV level of signal, I would be careful. But it is hardly likely that a volume control would operate at below 100s of mV.
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Old 15th February 2009, 09:49 PM   #6
AndrewT is online now AndrewT  Scotland
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http://www.diyaudio.com/forums/showt...40#post1100140

beware the poor choice of switch impedances.

The three knob solution is a brilliantly simple solution that is operationally very convenient.

The resistors in the first sections must be replaced with values much lower to achieve the 10:1 ratio from source to first attenuator, then 10:1 from first attenuator to second attenuator and finally 10:1 ratio from final attenuator to load.
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Old 16th February 2009, 12:46 AM   #7
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Hi Andrew!

Y-e-e-e-s....

I have not really considered this seriously, but thanks for the wake-up call. The contacts on the Elma switches are quite close-spaced, and I guess I was rather fortunate in mounting the resistors directly on the contacts instead of an intermediary pc board. Then with a log law I also bypassed to common at certain points to keep the last (top) resistors from getting too high in value. I will certainly do a frequency spectrum up to -3dB before using this again - guess I was fortunate up to now as no h.f. droop was noticed!

Regards
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Old 16th February 2009, 04:30 AM   #8
stl is offline stl  United States
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Quote:
Originally posted by AndrewT
http://www.diyaudio.com/forums/showt...40#post1100140

beware the poor choice of switch impedances.

The three knob solution is a brilliantly simple solution that is operationally very convenient.

The resistors in the first sections must be replaced with values much lower to achieve the 10:1 ratio from source to first attenuator, then 10:1 from first attenuator to second attenuator and finally 10:1 ratio from final attenuator to load.

Hi Andrew,

Thanks for your quick response.

The "log law" is something I don't understand yet , but I do know that this attenuator will be replacing a 100K pot for a 4 Ohm output impedance amplifier. The source will be a dvd player or a computer, I'm not of sure of the source impedance.

So considering my lack of understanding of electrical theory, can I just solder the resistors that come with the kit to replace the 100K pot? or do I have the calculate the values myself?

Also, did you receive any information on how to wire the attenuator to the amp? The original pot has six leads, and I have'nt the slightest clue how I will be doing the wiring with this attenuator.

Finally, in your experience, is the hybrid attenuator worth its trouble or is a pre-soldered ladder type from eBay good enough for the job?

Thanks a tonne!

-Frank
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Old 16th February 2009, 05:11 AM   #9
Will is offline Will  Malaysia
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Default Re: Resistors for Stepped Attenuator

Quote:
Originally posted by stl
Hello,

I want to use a hybrid stepped attenuator for the S-5 K16LS amp from Glassware Audio Link and they have two types of resistors carbon and metal film.

Q: With respect to sound quality and clarity which ones are better?

Also, would changing resistors on the main circuit make any difference in terms of sound quality?

Thanks.

Frank

Why don't you just buy one of these?

http://cgi.ebay.com/100K-Stepped-Att...3A1%7C294%3A50



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Will
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Old 16th February 2009, 08:04 AM   #10
AndrewT is online now AndrewT  Scotland
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the three knob attenuator is TWO ATTENUATORS in SERIES.

The kit comes with a full set of resistors and a comprehensive tables of values for other impedances.

The problem as I see it is that the standard kit resistors give nearly equal Zin for all the attenuators and ignores the rule of 10:1 that works for so many systems.

I suggest you look at resistor values that stagger the Zin for the first and second attenuators. They are all printed in the sheet. But it even tells you how to calculate resistor values for both types of attenuator for any Zin.
Read the instructions. Someone in Glassware knew what they were doing. Someone else came up with the standard resistor values. Change them.
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