[markC]

Well, here I go chasing my tail again... I just built and installed a pair of dual mono Gold point mini L stepped attenuators. Good improvement in sound quality, but I seem to have lost some db's? These were installed in a dual mono tubed pre where the usual volume setting was between 11 o'clock, (faily low listening level), and 3 o'clock, (pretty much max. listening level). Now, the normal level has gone to within 2 clicks of max. I'm thinking here that 0 db is 0 db, right? How can an attenuator change a "straight through" signal? Any thoughts ? Could I have done something wrong?

[mgalusha]

Mark,

The attenuators (and your original volume pots) act as a voltage divider and depending on the resistors you choose the listening range will be controled by those values. That said, it should not be acting as you describe.

A few questions.

What value were the original pots? 10K? 25K? 50K?
Are the Goldpoints the same value?

How many dB of attenuation did you order with the attenuators or did you buy the resistors seperately? It may be that the resistor values are incorrect.

Are you sure everything is wired correctly? If the resistors are in the wrong locations it could easily cause the behaviour you describe. Looking at the resistor chart on the Goldpoint site two clicks from the top should provide -6 dB. That should be nearly full power depending on the gain of you preamp and amp.

I have a Goldpoint mini H and it's behaviour with regard to level has been fine. My preamp has 12dB of gain and about the highest I see on the level contol is about 2 o'clock and that's the "holy crap is that loud" point. Normally it lives in the 9 to 11 o'clock range.

Mike G.

[markC]

Hi Mike,
The Goldpoints are 50k, the same as the original pots. I ordered the -64 db, as per the chart suggesstion on line. I checked the resistor values 3 times b4 I soldered them, and unless I'm really dumb, they're installed correctly.The only thing that I did different from the original set-up was to run both grounds from the attenuators back to star ground seperatly. Originally, 1 ground was joined to the other pot and then a single wire was run to star ground. I'm somewhat baffled at this point, I guess I'll open it up again and double check my wiring.

[mgalusha]

Mark,

Hmm.. it sounds like everything should be happy. The star ground certainly wouldn't have changed the gain. If you have an ohm meter try measuring the resistance on of the original pots from the center terminal to each side while the pot is set at 12 o'clock. If they were linear pots this would be about 25k-0-25k but they probably have a log taper and should not be symmetrical at 12 o'clock.

Then measure one of the attenuators and compare were it has to be set to provide approximately the same values on either side of center. It shouldn't be much different than the pot assuming a log taper.

Just had a thought. It's possible, though unlikely, that linear pots were used and a shunt resistor was placed across the pot to make it act like a log type pot. If so, this would play hell with your new attenuators. By chance was there a resistor soldered across the terminals of the old pots?

Luck!

Mike G.

[markC]

No resistor, but there is a switch connecting the 2 halves of the pot. Switching takes the 100k pot from 50k to 25k.

[mgalusha]

No resistor, but there is a switch connecting the 2 halves of the pot. Switching takes the 100k pot from 50k to 25k.

Not quite sure what you mean. You indicated the original pots were 50K but above it says 100K.

If the image below were your pot/attenuator, how is the switch connected? Have you tried disconnecting the switch from the circuit?



The diagram is how most volume pots are connected. Was your wired this way?

Mike

[markC]

Hi Mike;
Yes the pots are wired that way, (except no circuit board), the output goes to a switch which allows a normal or high gain choice. The switch is then wired to the tubes, (6N1P triodes). The old pots are marked Alps 625N 100kx4. There are two sections to the pot. one front and one back with 4 legs on each section, (only 3 legs are connected). The back section was connected to the input/output/ground. The front input to ground measures 99k, the rear input to ground measures 47k. Flipping the switch, (which is an on/on type and is connected to the input/output only-the ground is common between front and back sections), results in the front changing to 31.8k and the rear also changing to 31.8k.  On the inside of the pre, it was marked 50k/25k beside the pots. I've always used the normal gain setting as the high gain introduces some noise. Thanks for your help, by the way.
Mark