DIY Audio Projects Forum

Hi Everyone, I'm planning to build myself a new headphone preamp, the unit will also incase a revised passive attenuator and input/output selectors.

I'm getting a little fat and lazy as the years crack on and am getting tired of standing up and walking across the room every time i need to make a volume adjustment.

I've always used a stepped attenuator using an Elma rotary switch as it was a reasonably affordable way of doing things.
I'm not really into the idea of spending around £400 on one of the kits for the relay controlled stepped attenuator, so am considering the idea of doing the dirty and using a motorised pot (Alps Blue or TDK 2CP) as all in with the motorised pot and controller it can be done for around £150.

What I'm wandering is, is a good quality pot really that bad? how much of a notable difference would I get compared to the stepped attenuator?

For reference it'll be sitting between a Forewatt preamp build and either my KT88 Oddblock builds or the new headphone preamp (Bruce's design).

cheers
Josh

For what your doing the quality of the amps is not worth spending cash on expensive pots.

But for the top stuff where is currently not for sale you want the best pot.

For majority of amps on the market the amp distortiots way more than the pot.

For the top stuff the components and pot distortiorts more than the amp.
At the top level your comparing sound that is all mudded hard and scattred to none of that with expensive pots.
Bourns91 10k vs a 10k with takuman carbon resistors.

Theres a good reason why luxman and mcliton etc all of those do not use ERSE pulse X or more epxneisve and do not use stepped pots.

Because you can't hear the diffrence and is waste of time with the poor construction and design quality.

You will hear diffrences in reagards to better component quality regardless of amplfier used.

But lower quality amps is not so obvious though you may hear a tiny diffrence.

But with better amps the diffrence is very obvious.

Goes down to how much money you want to spend.

For the cash savings on a cheaper pot will get you HIFI resistors and HIFI capacitors for a whole amp rebuild which will result in more sound quality compared to a single expensive pot.

You could look at doing something like this! https://www.waste.org/~knobs/arduino_remote_stereo_volume_control.html
Might not be pretty, but you could implement it in some sort of way that's visually appealing to you, and I suppose depending on what kind of stepper motor and belts you use you could potentially adjust a stepped attenuator.

I built one of these and put it in a little black hammond enclosure that sits beside the preamp chassis, and uses GT2 belts and pulleys to adjust the volume. It looks a bit weird, but I like it, and it works great.
Here's a pic.. Sorry for the low quality of the picture.

You can use cable tie as a cheap alrenative to a custom size rubber belt.

I tried a bunch of different options before ordering a belt, and none really consistently worked properly.. Everything I tried slipped or kind of walked around front to back on the pulleys or knobs. Also with the belt and it's teeth you don't need to have much tension on the belt. Which I think would prolong the life of the stepper motor and pot or attenuator, not having a high shear force on the shaft of the pot, attenuator or stepper motor.

The belts and pulleys are fairly cheap:
https://3dprintingcanada.com/collections/belts
https://3dprintingcanada.com/collection ... lt-pulleys

They've got just about any length of pre-made belt that you could need. Just tie a piece of string around either pulley and get the exact length that you need.
And as for the pulleys, you can get them with a 5mm bore for the stepper motors, and they also have 6.35mm bore for the pot.

Hi,

I just used a Velleman 2 channel infrared and a pulse width modulator to drive a small DC motor driving an extension shaft.
Then I could use whatever pot I wanted.

If you really wanted to use a relay attenuator then de-bounce the input to a decade counter and drive relays.
But I don't use stepped attenuators I'm not a great fan, and prefer pots.

Another analogue way to do it is to drive a pot then input the dc signal from the pot into an LED bar graph driver then drive relays from that. If you didn't like computer based systems. Or use a SS volume control into a bar driver etc.

They are just off the cuff ideas.

Regards
M. Gregg

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