DIY volume control

[ROTECH]

When I was at DIYNE, Dave Ralph (DLR) was using a DIY volume control. He said it consisted of IIRC a 10k pot, with RCA in and RCA out. The unit he had was very nicely done- and I wanted one.

I would like to think it must be a simple solution to make this.... would it be as easy as using the pot terminals to sweep the positive conductor in the RCA wire-jack?

Any help would be great, I would love to get one made up

[dcibel]

Re: DIY volume control

That's right, all you need is a box, a 2-pole logarithmic potentiometer, some panel-mount RCA connectors, wire and solder. Best solution is to put a buffer on the end of it, but that's adding a lot more complexity.

Search for "Alps blue-velvet". That will be the best audio pot for your money. Very good tracking and will last a very long time.

[Face]

Re: DIY volume control

Just avoid carbon and no-name pots and you'll be ok.

Alps makes a good attenuator. If you want to get fancy, check out Goldpoint's stepped attenuators.

[tom_s]

Re: DIY volume control

Best solution is to put a buffer on the end of it, but that's adding a lot more complexity.

There are probably better options these days, but here's what Corey Greenberg came up with in 1995-

http://www.stereophile.com/content/a...ier-schematics

[dcibel]

Re: DIY volume control

Maybe "best solution" wasn't the right words..."better solution".

I had build a DIY pre-amp in the past. Came from here and was called Kookaburra I think (no longer made). I was an analog pot connected to a microcontroller. The micro activated a digital volume control in the signal path, with a buffer on the end. This solution meant you could use a cheap and common single pole carbon pot, and would not get scratchy over time since the pot is not in the signal path.

The site I linked to above btw, is run by a couple guys on DIYAudio. It is a community effort, the site made as an alternative to "group-buys". It is completely non-profit AFAIK.

[john trials]

Re: DIY volume control

With a plain pot or stepped attenuator, it can be hit or miss, depending on your source and amp impedance interactions. If there is an impedance mismatch problem (which can happen with a pot or stepped attenuator), it would be better to make a buffer preamp (like the Pass B1 that was used at Exojam's). See PassDIY.com

[mzisserson]

Re: DIY volume control

With a plain pot or stepped attenuator, it can be hit or miss, depending on your source and amp impedance interactions. If there is an impedance mismatch problem (which can happen with a pot or stepped attenuator), it would be better to make a buffer preamp (like the Pass B1 that was used at Exojam's). See PassDIY.com

+1,111,543,321

I find straight passive attenuation causes more problems than it cures. Exo's pass was very nice. Yes, power factor still counts at small signal and impedance mismatching causes big issues sonically. You want your voltage and current arriving at the same time...

[AJ]

Re: DIY volume control

If you'd like to build something more 21st century how about this:

http://www.tauntek.com/irvc2-ir-mast...me-control.htm

I haven't built one yet but the kit looks good. You can even control relays (on a seperate board) for source selection. But, all you need to get it running is a case and a power supply.

[ROTECH]

Re: DIY volume control

All great info, I may try one of the simpler, yet still buffered options mentioned for a near future custom application. Though for now it sound that a used rotel or adcom preamp off CL for bout $100 sounds like a great idea for quick-simple-EASY.

[dcibel]

Re: DIY volume control

Solid solution. Look at NAD as well, their integrated amps have external connections to separate the preamp and power amp, so you can feed the pre-amp into any external amp, and you can feed any external source directly into the power amp, bypassing the pre stage.

I think Rotel does the same, not certain though.

[mzisserson]

Re: DIY volume control

If you you'd like to build something more 21st century how about this:

http://www.tauntek.com/irvc2-ir-mast...me-control.htm

I haven't built one yet but the kit looks good. You can even control relays (on a seperate board) for source selection. But, all you need to get it running is a case and a power supply.

I would love to see more on this (testing?) It is very cool.

[AJ]

Re: DIY volume control

I haven't seen any completed units using his board/kit, but I'm sure it works fine. The Burr-Brown PGA2310 is proven, and the logic required to run it isn't really complicated. His "learning remote" feature is what makes me want his board/micro-controller.

A drawback to his design is that it doesn't have output buffers after the PGA2310. This doesn't matter to me as I'm going to have (when I actually build a preamp) a balanced output converter/output board, but it could be for some people that want to use it standalone.

[OlderMongrel]

Re: DIY volume control

If you decide to go with a plain old POT, see this first:

http://sound.westhost.com/project01.htm

John

[neildavis]

Re: DIY volume control

I haven't built one yet but the kit looks good. You can even control relays (on a seperate board) for source selection. But, all you need to get it running is a case and a power supply.

It's a fair price and it looks like a nice DIY project. However, if you are OK with buying the import stuff, this one on Ebay from hiamplifier is a better buy:

http://www.ebay.com/itm/NEW-Version-...item19cb7d713c

I got one and the case for it, and I'm working on a replacement CPU board to make it a volume-compensated A/B switch box.

[stujonesmd]

Re: DIY volume control

For an inexpensive control preamp (one with input selector, volume, balance, tone controls) there are a number of possibilities:

A used high quality (e.g. NAD) preamp.
A new Pyramid or Gemini control preamp (yes, these are sold as 'pro' equipment but seem to work OK for hifi use, and cost on the order of $100. I own a Gemini PA7000 and it is a surprisingly nice piece of equipment for the price. Internally, it is built using high quality op-amp circuitry, and the controls work decently well. The Gemini has gotten decent reviews. I would stay away from Pyle stuff--the reviews range from mediocre to horrible.

DIY possibilities abound, from various kit boards from China (via E-bay), as well as 2 good preamp kits, one from Velleman (K8084), available now from Parts Express, and one from Kits 'r Us (sold as the K100 from Carl's Kits and several other vendors. Both can be modified slightly to deliver true audiophile quality, but work nicely as supplied. However, neither of these should be attempted by a kit building neophyte, especially not the Velleman, which also requires a grounded metal case for good results. The Velleman requires an external (preferably far-away external) 24V center tapped power transformer (12-0-12), also available from PE. The Velleman kit does not have a balance control. The Kits 'r' Us runs on DC 12V and includes a 12V regulator circuit that must be fed from a 15-20VDC source (but is easily bypassed to run from battery or 12V regulated wall wart). This kit is based on a Philips preamp IC which uses voltage controlled amplifier circuits for volume, balance and tone controls and supplies 20 dB voltage gain from input. This Philips IC yields very good results, with slightly greater output noise than the Velleman design. The Velleman can easily be altered, however, to add a balance control, and the (already very good) TL072 op amps can be replaced by NE5532 or Burr Brown op amps without changing the rest of the circuits, for even lower noise and distortion.

Using LM322 or LM324 op amps (which are designed to run using a single DC supply), it is relatively easy to build a buffered volume/balance control for line level inputs, and also relatively easy to put together a line level mixer. The key is to use low noise metal film resistors, as well as high quality metal film pots for the volume/balance controls. A number of circuits have been published on the web. It is probably a good idea to breadboard one of these before hard wiring, since results can vary significantly depending on component (particularly resistor and capacitor) performance. 1% tolerance resistors aren't necessary as long as a good VOHMmeter (very inexpensive these days, PE has plenty) is available for matching parts. 1% caps are overkill as long as appropriately high values are used for coupling, at least in my experience.