Goldpoint stepped attenuators

markC · « **on:** 11 Nov 2003, 03:36 pm »

Anyone have experience with these? I'm thinking of upgrading the volume pots. in my tubed dual mono pre to stepped ladder types. I've heard of some problems with "popping" as the attenuators are rotated, but am wondering if this is an impedance mis-match problem. It seems like matching the attenuators impedance to the amps input impedance is the way to avoid this problem, but it is just what I have read, and was wondering if anyone had experience in this area.

Curt · « **Reply #1 on:** 11 Nov 2003, 08:34 pm »

The slight popping is not a problem, it's a normal characterstic of ladder attenuators. It only happens when your adjusting the volume, not when your listening to music, and can't hurt anything. Ladders are great.

A snip from our website FAQ:

A precision ladder step attenuator is a wonderful device. Only two resistors in the signal path at any one time and the lowest added noise factor possible. The ladder step attenuator is the most desired and most expensive volume control available in high-end audio today.

There is only one issue with ladder attenuators, an occasional slight click when changing volume levels. These occasional clicks are not harmful in anyway, such a small noise compared to the actual music program, simply a characteristic of ladder step circuits.

The sonic benefits of a ladder attenuator far outweigh the slight occasional, harmless click produced when changing the volume level.

mgalusha · « **Reply #2 on:** 11 Nov 2003, 10:27 pm »

Mark,

I have a Goldpoint ladder attenuator and it does sound very nice. I have to disagree with Curt slightly. In some circuits the pop is more than slight. It seems to depend on how much DC is present in the source and how sensitive the input of the preamp is to DC. I do agree with him that ladder attenuators sound very good.

I tried the Goldpoint in a Grounded Grid and the poppng was pretty loud. I can't say how many dB but it was loud enough to cause concern. One thing that will reduce or eliminate the popping is to provide a constant path for the signal to ground. Arn makes mention of this on the Goldpoint site but doesn't go into detail. I am using a 500K resistor from the wiper to ground. This is high enough not to interfere with the attenuator but still provides a constant signal path to ground.

Voltsecond has similar info on his site as well.

Mike G.

_scotty_ · « **Reply #3 on:** 11 Nov 2003, 11:42 pm »

deleted server double posted

_scotty_ · « **Reply #4 on:** 11 Nov 2003, 11:48 pm »

Contact bounce when switching positions can cause a click to a pop depending on how long the bounce takes to happen. DC should not be present at the input of the pot as rotation of the pot across the switch contacts and the variation in resistance ratios modulates the DC present
and gives you a signal to hear. The DC should have hit a blocking cap somewhere ahead of the pot. I have had excellent results with the Danish Audio ConnecT stepped attenuator in my projects. The resistors used are surface mount devices with no lead inductance to affect the sound, also the physical size in smaller than some designs. It is available from
http://www.nutshellhifi.com/

mgalusha · « **Reply #5 on:** 12 Nov 2003, 12:17 am »

Scotty,

I agree, DC should not be present but this is not always the case. (sadly) You make a good point about the contact bounce. I forgot to mention that in my earlier post. Since the DACT attenuators are series wired, they don't seem to be bothered by contact bounce as the signal always has a path to ground.

I'm currently using a DACT wired in shunt mode instead of the normal series mode. It seems to be quieter and somewhat cleaner. The signal only has 1 series resistor as opposed to 23 (at low levels) when wired per the usual practice.

Mike G.

_scotty_ · « **Reply #6 on:** 12 Nov 2003, 02:29 am »

The shunt to ground trick is the way to go if you have the input voltage to spare. You hear 70% of the single series resistor and the DACT contributes
the other 30%. I am using a zero gain discrete active buffer. I don't have the gain to spare from my sources.

markC · « **Reply #7 on:** 12 Nov 2003, 03:51 am »

Thanks for the replies. I think that if I'm going to upgrade, might as well go with the ladder type for the extra $. It seems that the fewer resistors in the signal path the better. Now, what about impedance of the control? Do I stick with the value of the existing pots. ,(which I believe are 50k), or match the input impedance of my amp, (which I believe is 10k)? By the way, the specs. for the pre are 48k input impedance and 600 ohm output.

mgalusha · « **Reply #8 on:** 12 Nov 2003, 04:52 am »

Mark,

Go with the 50K since that is what your pre is designed for. In many tube preamps the value of the input pot is what sets the input impedance.

Since this is an active pre, the value of the input attenuator will have little if any affect on the output impedance.

Mike G.

mgalusha · « **Reply #9 on:** 12 Nov 2003, 04:57 am »

Scotty,

I used the same value for my input resistor as the origianl pot and don't notice any gain loss. I didn't measure it but it's very similar to having the dact wired in series mode. I may have to put it on the bench just to see what the difference is. You have me curious.

Mike G.

_scotty_ · « **Reply #10 on:** 12 Nov 2003, 05:16 am »

I may be on the wrong page. If you have a series resistor between the pot and the load and the pot connected as a variable shunt to ground the total load impedance seen by the source will vary and you also have a resistive voltage dividing network with the resistor to ground being the variable element. What I am trying to say is that you now have an insertion loss due to the network. But I could be wrong. I think if you have 10k in series and the pot to ground set to 10k in its rotation you now have shunted half the voltage to ground best case scenario. This should be a 6db insertion loss, I think.

Curt · « **Reply #11 on:** 12 Nov 2003, 07:49 am »

Quote from: mgalusha

Mark,

I have a Goldpoint ladder attenuator and it does sound very nice. I have to disagree with Curt slightly. In some circuits the pop is more than slight. It seems to depend on how much DC is present in the source and how sensitive the input of the preamp is to DC. I do agree with him that ladder attenuators sound very good.

I tried the Goldpoint in a Grounded Grid and the poppng was pretty loud. I can't say how many dB but it was loud enough to cause concern. One thing that will reduce or eliminate ...

I consider DC, at the ladder attenuator, a defect and did not mention it.

Curt · « **Reply #12 on:** 12 Nov 2003, 08:02 am »

Quote from: _scotty_

Contact bounce when switching positions can cause a click to a pop depending on how long the bounce takes to happen. DC should not be present at the input of the pot as rotation of the pot across the switch contacts and the variation in resistance ratios modulates the DC present
and gives you a signal to hear. The DC should have hit a blocking cap somewhere ahead of the pot. I have had excellent results with the Danish Audio ConnecT stepped attenuator in my projects. The resistors used are surface mount ...

Contact bounce is not the problem with ladder attenuators.

A ladder step attenuator is a different circuit from a series step attenuator.

With a ladder step each switch step, due to the switch's MBB (make-before-break) configuration, halves (or worse) the units resistance to the source (for an instant) then drops it back to the next step's real value (usually about double the resistance or more) this is what makes the clicking sound. This is caused by paralleling the two volume control steps resistors before releasing the old value and taking on the new value resistors. This is the ladder characteristic I was speaking about above.

Switching a ladder very slow can accent the clicking sound, I try to switch at a good rate of speed. All-in-all a very trivial price to pay for the benifits of the ladder step design. IMO a ladder step is the ultimate choice but it is also much more expensive and more difficult to design and manufacture.

Popping from a series step attenuator could be caused from switch bounce, but in fact this is rare.

Curt · « **Reply #13 on:** 12 Nov 2003, 08:08 am »

Quote from: mgalusha

Mark,

Go with the 50K since that is what your pre is designed for. In many tube preamps the value of the input pot is what sets the input impedance.

Since this is an active pre, the value of the input attenuator will have little if any affect on the output impedance.

Mike G.

If your feeding the source signal directly to the attenuator 50k ohms is an excellent choice, probably the most common choice also. It will work great with both tube and SS source output stages.

Make sure there is no resistor in parallel with the attenuator or the 50k value will be reduced to the parallel combination's value. This is a trick used to make a linear taper pot function as a audio taper pot, but not needed with a properly designed step attenuator.

markC · « **Reply #14 on:** 12 Nov 2003, 10:18 pm »

Thanks for all the help Curt, Mike & Scotty! Before I actually order the attenuators, I'll open up the pre again and have a carefull look for any resistors in the path or anything else that I don't fully understand. It is a pretty straight forward design, all point to point wiring, so hopefully an intermediate like myself will be able to pull it off without a hitch. Now just to decide if I'm brave enough to order the kit and take on the many, many solder connections. I believe that will be 192 for the kits and 6 more to put 'em in the circuit.