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
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
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.
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.
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.
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.
analog_sa said:
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.
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
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.
http://www.diyaudio.com/forums/showthread.php?postid=1100140#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.
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!
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
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
AndrewT said:
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
stl said:
Why don't you just buy one of these?
http://cgi.ebay.com/100K-Stepped-At...4|66:2|65:12|39:1|240:1318|301:1|293:1|294:50
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.
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.
Andrew,
So I gather it would be better to order the attenuator without resistors (hopefully it comes with instructions) and figure out the values of resistors I need and purchase them separately? Would these resistors have to be high voltage rating for the tubes?
Also, by 'first' and 'second' attenuator you mean 'first' as in the two mono Left/Right channel and 'second' attenuator as in the Stereo attenuator in the middle? Is this right?
Also how might one go about finding the Zin for a tube amp connected to a DVD player?
Thanks very much.
So I gather it would be better to order the attenuator without resistors (hopefully it comes with instructions) and figure out the values of resistors I need and purchase them separately? Would these resistors have to be high voltage rating for the tubes?
Also, by 'first' and 'second' attenuator you mean 'first' as in the two mono Left/Right channel and 'second' attenuator as in the Stereo attenuator in the middle? Is this right?
Also how might one go about finding the Zin for a tube amp connected to a DVD player?
Thanks very much.
The DvD player should give the output impedance (Zout or Rs') in the specification
The tube amp should give the input impedance (Zin''') in the specification.
The first stage attenuator (L&R balance/fine setting) is the series version and I suggest it has Zin' <=Second stage / 5
This gives a 20:1 ratio of Zout'' to Zin''.
The second stage is the shunt attenuator.
This should also be <=Zin''' of the tube amp. again this will give the 20:1 ratio of Zout''' to Zin'''.
eg.
Tube amp Zin (input impedance) =100k
second stage Zin'' = 100k / 5 =20k
The maximum output impedance is [20k+Rs''] / 4 ~ 5k5 This is ~ 18:1 to the tube input.
The first stage Zin' = 20k / 5 = 4k
The maximum output impedance is [4k+Rs'] / 4 ~1k1 This is ~ 18:1 to the second stage.
Finally If the DvD has Rs' (output impedance) is 200r then the ratio is 20:1
I hope this long winded reply makes some sense. But trying to achieve that rule 10:1 or better as the signal goes from one stage to the next.
Voltage rating to suit the tube amp is not affected here.
The tube amp should have near zero volts offset at it's input.
The attenuator will be handling 10s to 100s of mVac.
You can use ordinary 1% metal film resistors 250mW to 600mW rating and <=50ppm temp coef.
The thought of using the new 24position master control with 1dB balance control is attractive, but unfortunately much more expensive and because it uses many more resistors in the shunt attenuator has many more soldered joints in the audio circuit and if you adopt exotic resistors will bump up the bill even higher.
Choices, why do we need them?
The tube amp should give the input impedance (Zin''') in the specification.
The first stage attenuator (L&R balance/fine setting) is the series version and I suggest it has Zin' <=Second stage / 5
This gives a 20:1 ratio of Zout'' to Zin''.
The second stage is the shunt attenuator.
This should also be <=Zin''' of the tube amp. again this will give the 20:1 ratio of Zout''' to Zin'''.
eg.
Tube amp Zin (input impedance) =100k
second stage Zin'' = 100k / 5 =20k
The maximum output impedance is [20k+Rs''] / 4 ~ 5k5 This is ~ 18:1 to the tube input.
The first stage Zin' = 20k / 5 = 4k
The maximum output impedance is [4k+Rs'] / 4 ~1k1 This is ~ 18:1 to the second stage.
Finally If the DvD has Rs' (output impedance) is 200r then the ratio is 20:1
I hope this long winded reply makes some sense. But trying to achieve that rule 10:1 or better as the signal goes from one stage to the next.
Voltage rating to suit the tube amp is not affected here.
The tube amp should have near zero volts offset at it's input.
The attenuator will be handling 10s to 100s of mVac.
You can use ordinary 1% metal film resistors 250mW to 600mW rating and <=50ppm temp coef.
The thought of using the new 24position master control with 1dB balance control is attractive, but unfortunately much more expensive and because it uses many more resistors in the shunt attenuator has many more soldered joints in the audio circuit and if you adopt exotic resistors will bump up the bill even higher.
Choices, why do we need them?
There is a substantial difference between the sonics of carbon composition resistors, carbon film resistors and metal film resistors. There are also significant sonic differences between different brands of metal film resistors.
Besides the high noise of a carbon resistor, they also have a very high voltage coefficient. In other words, the resistance of a carbon resistor changes with the voltage applied to the resistors. This is NOt good!
Additionally the temperature coefficient of a carbon resistors is magnitudes higher than a metal film resistor. On other words the resistance of a carbon resistor changes significantly with temperature. In one particular tube amplifier it took approximately 7 minutes for the driver circuit to stabilize with carbon resistors. It only took about 30 seconds to stabilize with metal film resistors. This also means that the bias of a circuit can often shift during louder music passages depending on the circuit.
The only thing carbon resistors are good for is covering up other flaws in the system, which is a back assward approach. EVERY component that you use will affect the sonics of the electronics. There are also non-inductive metal film resistors made by Caddock. Metal oxide resistors don't sounds as good as metal film in general. Metal foil resistors are considered some of the very best resistors, and also some of the most expensive. Wirewound resistors have their pros and cons. They are more expensive than metal film resistors. but they also have a fairly high inductance. There are tradeoffs when using them.
The differences in the end cap construction of different brands of metal film resistors can make a noticeable difference in the sound quality.
Using metal film resistors in a phono stage can eliminate much of the hiss.
Just say NO to carbon resistors!
Scott Novak
Besides the high noise of a carbon resistor, they also have a very high voltage coefficient. In other words, the resistance of a carbon resistor changes with the voltage applied to the resistors. This is NOt good!
Additionally the temperature coefficient of a carbon resistors is magnitudes higher than a metal film resistor. On other words the resistance of a carbon resistor changes significantly with temperature. In one particular tube amplifier it took approximately 7 minutes for the driver circuit to stabilize with carbon resistors. It only took about 30 seconds to stabilize with metal film resistors. This also means that the bias of a circuit can often shift during louder music passages depending on the circuit.
The only thing carbon resistors are good for is covering up other flaws in the system, which is a back assward approach. EVERY component that you use will affect the sonics of the electronics. There are also non-inductive metal film resistors made by Caddock. Metal oxide resistors don't sounds as good as metal film in general. Metal foil resistors are considered some of the very best resistors, and also some of the most expensive. Wirewound resistors have their pros and cons. They are more expensive than metal film resistors. but they also have a fairly high inductance. There are tradeoffs when using them.
The differences in the end cap construction of different brands of metal film resistors can make a noticeable difference in the sound quality.
Using metal film resistors in a phono stage can eliminate much of the hiss.
Just say NO to carbon resistors!
Scott Novak
AndrewT said:
Thanks, that explains a lot.
The Zin for the tube amp is 100k and the DVD player Zout is a 100k.
So would the instructions that come with the attenuator guide me to finding the right value resistors? In terms of the ratio, how much off the mark are the stock resisitors that come with the attenuator, if I'm using source Zout, amp Zin at 100k?
I'm about to order the attenuator without the resistors, will probably need your help when I'm putting it together.
Thanks
"Carbon" resistors
There is a big difference between carbon comp resistors, and carbon film resistors. Good carbon films are not noisy, and don't drift like carbon comp resistors. IMO metal film resistors sound cold and sterile.
Also there is a difference between the cheap carbon films made for Radio Shack, and a better quality ones like KOA Speers (available at Mouser). Some say they are the same thing as a Kiwame resistor. I don't know, but they do sound very similar, at 3 cents each (in quantaties of 100) they are hard to beat. Rikens sound very good, but are getting hard to find because manufacture has ceased for these, plus they are pretty pricy at $4.00 each. The Takmans are new carbon film types, and are designed for audio use, reports are that they sound great, and are priced pretty fairly.
I prefer carbon films over metal films any day, but I avoid carbon comps, except as grid stops, where their non-inductive design makes them superior for this duty.
twystd
There is a big difference between carbon comp resistors, and carbon film resistors. Good carbon films are not noisy, and don't drift like carbon comp resistors. IMO metal film resistors sound cold and sterile.
Also there is a difference between the cheap carbon films made for Radio Shack, and a better quality ones like KOA Speers (available at Mouser). Some say they are the same thing as a Kiwame resistor. I don't know, but they do sound very similar, at 3 cents each (in quantaties of 100) they are hard to beat. Rikens sound very good, but are getting hard to find because manufacture has ceased for these, plus they are pretty pricy at $4.00 each. The Takmans are new carbon film types, and are designed for audio use, reports are that they sound great, and are priced pretty fairly.
I prefer carbon films over metal films any day, but I avoid carbon comps, except as grid stops, where their non-inductive design makes them superior for this duty.
twystd
stl said:The "log law" is something I don't understand yet
Perhaps I can have a try here (getting jealous of Andrew
)It has to do with the way we hear different sound intensities, which is logarithmic. That is, equal steps of subjective loudness are not steps in output of say 2W, 4W, 6W, 8W, 10W and so on. These are equal steps in electrical output, thus linear.
If you advance a volume control in what will appear to you to be 'equal' steps of loudness, an output meter attached to the amplifer will register (say) 1/2W, 1W, 2W, 4W, 8W, 16W and so on.
That means that the 'law' that an 'even' (logarithmic) volume control will have to follow will be to first increase the signal in small steps, becoming larger all the time. You might have experienced the 'quickly loud' sensation in e.g. portable transistor radios, where a linear control increases loudness as per my first example. (Linear controls are cheaper to make.)
If you measure a center-tapped potentiometer, a linear pot will show 50% of the total resistance from each end of the pot, but a log pot will show only 10% of the total resistance from the 'cold' side. (As a true log scale does not have a zero or maximum, log pots are tapered off close to each end.)
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