Active speaker volume control.

[Welder]

I made a truly horrendous error. I sat and listened carefully, made comparisons, opened my mind and feck me if my wallet didn’t fall out.:eek:

Ahem, I’m going active. :eyebrows:
It rather looks like everything is going except my music server and my two Dacs (I may just keep Exposure 25 RC coz I lurves it)

However, I do have a small problem and that is I would like to control the volume of my stereo without using any computer software options and without having to individual adjust each monitor and then measure for balance.

I would prefer to adjust volume on the analogue side and normally it seems a decent quality pre amp is what most use. I don’t need, or want a pre amp as such. I don’t need any type of selector switching. I just want a volume control that will operate between any Dac and active speakers.

I’m tempted to invest in a good quality stepped attenuator and just wire it up between Dac and speakers.

I was wondering what others have done and what they thought of the results.
Budget, whatever it takes within reason.

[Clive]

Dave Slagle AVC modules at $350. You do have to live pairs of controls, if you can put up with 3db steps (which is ok) then you only need the one pair of controls. Or you cold spend loads on the John Chapman RC version in a very nice box.
http://www.intactaudio.com/atten.html

[TopBalcony]

DIYParadise EVA II is what I use in my active setup. Works very well and has the advantage (to me) of remote control.

[DSJR]

T'ain't cheap any more, but it's designed for what you want -

http://www.thomann.de/gb/spl_volume_2_black.htm

Maybe this, as it's it's a A-D/D-A with line/phono input and very cheap -

http://www.promenademusic.co.uk/tascam-us100-

I haven't "listened" to either, but I believe the both of 'em will technically drive remote amps with no issues.

[Werner Berghofer]

John,


I was wondering what others have done and what they thought

I have been using this little device for a while:

http://box-designs.com/main.php?prod=prebox&cat=amplifier&lang=en

It worked pretty well, even a remote control was included, but after approximately three weeks the external PSU started to chirp in a very annoying way and did never stop.

Replaced it later by a Schiit Lyr headphone amplifier which has additional RCA line-outs on the back.

Congratulations for going active!

Werner.

[bobbasrah]

I would prefer to adjust volume on the analogue side and normally it seems a decent quality pre amp is what most use. I don’t need, or want a pre amp as such. I don’t need any type of selector switching. I just want a volume control that will operate between any Dac and active speakers.

I’m tempted to invest in a good quality stepped attenuator and just wire it up between Dac and speakers.


Maybe I am misreading this John after a few pints of Romanian beer at 40p a pint ( somebody has to suffer), but was there not a thread recently on the LED "passive" attenuator as a clone of the Lightspeed where a remote was used successfully and dirt cheap too....:scratch:

Back to the beer :cool:

[Reid Malenfant]

I made a truly horrendous error. I sat and listened carefully, made comparisons, opened my mind and feck me if my wallet didn’t fall out.:eek:

Ahem, I’m going active. :eyebrows:
:rfl:

So the man that said it's not easy has decided to take the plunge eh :D


While this won't help a great deal, the best place for the volume control is after the crossover splits the audio signal, IE between the crossover & power amps :)

That way gives you the highest signal to noise ratio as the crossover will be driven with full line voltage from the DAC, rather than a much reduced one with the volume low if it's prior to the xover.

Obviously you'd need ganged potentiometers or stepped attenuators.


Good luck John, I'm glad you have heard the angels & seen the light :eyebrows:

[Welder]

Cheers people for the various suggestions.
I've had a look at the various options and I must confess I've been left scratching my head wondering what exactly it is I would be paying for at some of the prices. :scratch:
I think I'll make my own.:eyebrows:



:rfl:

So the man that said it's not easy has decided to take the plunge eh :D


While this won't help a great deal, the best place for the volume control is after the crossover splits the audio signal, IE between the crossover & power amps :)

That way gives you the highest signal to noise ratio as the crossover will be driven with full line voltage from the DAC, rather than a much reduced one with the volume low if it's prior to the xover.

Obviously you'd need ganged potentiometers or stepped attenuators.


Good luck John, I'm glad you have heard the angels & seen the light :eyebrows:

Cheers Mark, that's where I planned to use it.

Well mate, if you're just going to buy some boxes and chuck em at the project, then perhaps it is simple.
I don't really want a whole heap of extra electronics, AD/DA conversion, banks of dodgy potentiometers, a mass of interconnects, circuitry that I don't need, and gutless amps in the mix, so I'm going to try to do the job properly this time. :eyebrows::D

[The Vinyl Adventure]

I use a valve pre ... There is a pre in my majik dsi as well as all the inputs I could ever need ... The valve pre just adds weight and body to the sound
So that's what I'd recomend ... Some them funny light bulb lookin things

[Welder]

Cheers Hamish.

I’ve got a couple of Pre amps should I find I need one.
I really don’t know if I’m right but I’m going for the KISS principle.
I don’t need any other functions than a pair line level of inputs. Everything I use is line level and I do something that apparently seems madness to many; I unplug a single set of leads and plug them into something else if I change source etc. :eyebrows:

I find this way not only do I only need one set of interconnects per link but I don’t have to worry about whether various interconnects are changing the sound. Tune by wire eh. :D

My preferred Dac outputs 4.5 Volts RMS which should be directly compatible with the power amps I’m going to use.
Hopefully I can keep a really simple chain, file data source>USB data to Dac>active crossover>paired volume controls>amps>speakers.

I’ll be continuing with my present practice of soldering direct wherever practicable thus doing away with all this connector sound stuff.;)

[The Vinyl Adventure]

Cheers Hamish.

I’ve got a couple of Pre amps should I find I need one.
I really don’t know if I’m right but I’m going for the KISS principle.
I don’t need any other functions than a pair line level of inputs. Everything I use is line level and I do something that apparently seems madness to many; I unplug a single set of leads and plug them into something else if I change source etc. :eyebrows:

I find this way not only do I only need one set of interconnects per link but I don’t have to worry about whether various interconnects are changing the sound. Tune by wire eh. :D

My preferred Dac outputs 4.5 Volts RMS which should be directly compatible with the power amps I’m going to use.
Hopefully I can keep a really simple chain, file data source>USB data to Dac>active crossover>paired volume controls>amps>speakers.

I’ll be continuing with my present practice of soldering direct wherever practicable thus doing away with all this connector sound stuff.;)

Ahhahaa ... You know it makes sense ;)

Sounds like an interesting approach ...
Why volume after the crossover?
Won't you loads of volume controls then?
My active system at the office uses an rane crossover
PC-dac/pre-crossover-4 channel amp-speakers
The speakers are dynaudio a42's I took the passive crossovers out of and the amp is a DIY (not by me) t-amp ... It sounds incredible for what it cost me and because of the active crossover we have tuned it to sound just right in the big room ...
Tbh I can't fathom why more people don't use this approach!

[Reid Malenfant]

Why volume after the crossover?
Won't you loads of volume controls then?

Volume control following the crossover means that the xover is fed constant full line level signals. As the crossover itself will generate some noise, the signal being full voltage will always be very much higher than this - so the signal to noise ratio will be much higher than if the volume control was before the crossover.

It's simple to picture if you think of lowering the volume with the control pre crossover... The music signal will be much lower & nearer to the noise generated by the xover itself.

Yes, one volume control for each output of the xover. So if it's three way as I believe Johns speakers are, he'll need six ganged volume controls :D

You think that's mad, I have thought about this for quite a while myself, but I'd need 20 ganged volume controls when my system is completed :eek: :lol:

[The Vinyl Adventure]

Ganged volume control?
Can you still have one knob that controls them all in one go?

20? If it was anyone else I'd call them a nutter ... ... ;)

[The Vinyl Adventure]

... I suppose a stereo volume knob is controlling 2 signals at the same time ... It's just like a big on of them?

[Reid Malenfant]

Ganged volume control?
Can you still have one knob that controls them all in one go?
That's precisely what ganged means :) Think team (gang) :D

A stereo control is dual gang (two channel)


As for twenty, I'd do it with digitally controlled relays with a single potentiometer controlling an ADC & the ADC feeding 7 relays per two channels.

Seventy relays might sound like a lot, but buy them in bulk & they are cheap, resistors cost next to nothing.

[The Vinyl Adventure]

I'll just have to take your word for all that matey ... There is some distance between what you just said and the top of my head ;)

[DSJR]

Stepped attenuators can be got in several gangs of switches I believe, but I would say that if the power amp gains are adjusted properly, noise shouldn't be an issue these days.

[Reid Malenfant]

I'd generally agree with that Dave, but John is going to make his own crossovers ;)

Besides which if going the DIY route there is no harm in doing it the best way for performance, in fact, you'd be daft not to if you can afford to :eyebrows:

[Reid Malenfant]

By the way John, you might well be interested to know that the Linkwitz/Riley 24dB/octave xover that you kind of copied previously & linked to in this post (http://theartofsound.net/forum/showpost.php?p=329961&postcount=23), can be done with a buffer & a single op-amp per channel.

Two per channel are not needed, you can get away with one & increase the performance, but resistors used in the single op-amp version become more critical ;)

Simple if you parallel them up to get precisely what you want.

[alexthemusicbloke]

I use a TC Electronic Level Pilot:

http://www.rockshop.co.nz/shop/media/catalog/product/cache/1/image/450x345/9df78eab33525d08d6e5fb8d27136e95/p/i/pilot_1.jpg

I A/Bd quite a few different monitor controllers and of the cheaper bunch (my budget was limited at the time) the TC was the best.

Two years down the road, it still sounds great. It can get noisy over time, but contact cleaner completely solves the issue.

[Welder]

Apparently I’m thinking about doing it wrong.:scratch:

While it seems to make sense to control the voltage between the crossover and the power amps with regard to S/N in real systems the cost and complexity just isn’t worth it.

I’m trying to avoid the situation I’ve seen with some active setups where you end up with multiple volume controls.
One possible worst case is; six volume controls on the amplifier modules (amp per driver in my case in a three way config), then another six on the crossover output with yet another six on the input crossover input side with possibly a master volume control on the crossover and yet another on a pre amp. :eek:

Having peeked in a few pre amp boxes and active/DSP units and not been very impressed with the quality of the potentiometers that came with the units and having found in the past that better quality potentiometers can make an audible difference (even if its just not having to twiddle them about to get rid of that horrible crackling sound) my rather simplistic reasoning says if they’re not there then they cant be a problem.

Given I’m not trying to set up a recording studio in my listening space and seem to have got satisfactory results for many years now without having to twiddle loads of knobs; adjusting on a regular basis individual driver output, playing with time aligning drivers (unless of course one counts the occasional bashing of the front baffle with a large hammer hoping to shift an errant tweeter back into the enclosure a few millimeters :D) and altering crossover slopes depending on the music genre and recording quality of any particular track; it seems to me that if one has got all these options but in general the approach is to set it all up and forget it, then perhaps this set it and forget it approach can be used and a load of money and uncertainty avoided.

(Phew, could I have levered a full stop in there somewhere? :scratch:)

Of course, I could be completely wrong, but I’ve read plenty of stuff about people changing the make of capacitors and resistors and hearing huge sonic improvements so I cant imagine why eliminating 20 odd cheap mechanical contacts shouldn’t give peace of mind if not an audible improvement in sound quality. :D

On recommendation of others who have tackled this problem the solution is this.
Buy three reasonable quality pots suitable for the amp modules.
Assemble the amp modules, with one set of volume pots assembled on one speaker only and connect them up.

If you’ve bought a pre built active crossover/DSP unit you’re a bit fecked here (you could open it up and hardwire) but if you’ve gone the (and imo this will give far better results) DIY route and purchased an active crossover board to populate with components with specifications of your choice and it comes with output/input voltage control options, hard wire these.

You need to initially set each driver/active channel separately using a signal generator, and SPL meter, measuring the resistance across the volume pot. I’ve been advised to measure a small range here. Then do a complete speaker (a RTA app is handy here)
Once satisfied that the frequency response is flat, re-measure the resistance across each pot and replace with an appropriate resistor/s.

Do the same with the other speaker.

You can use a pre amp in front of the active crossover unit initially to help prevent hearing damage and speaker damage.:doh:

You now have a choice. You can use two volume pots pre crossover and have a balance control, or a single pot.

Once again I don’t know if its accurate but I’m told that these days good potentiometers are capable of S/N ratios far in excess of anything we are likely to hear. After all, I haven’t noticed many posts complaining about noise from pre amps and if you’ve gone the single pre crossover pot route instead of having to split your budget over 20 pots you can spend it all on one really good one.:)

Assuming you measured a small range at the individual driver stage you will have at least some idea of what value resistors are needed to give a particular reduction in SPL which should make any adjustments you may want to make for room correction less hassle and you wont need to mess about with the crossover to achieve this.

If anyone can see a problem I’ve overlooked in the above, please shout coz I’ll be doing this next week hopefully.:eyebrows:

[DSJR]

S'cuse me butting back in, but might a compromise position regarding gain, noise and distortion be to keep the power amp input sensitivity as low as reasonably possible, and drive the crossover line amps pretty hard (especially if op-amps are used)? Keeping as much signal down the cables as possible should also aid to minimise cable "differences" too, as long as the impedance matching is done properly?

Just a thought while I'm pondering active speakers and the need to drive them properly...

[Welder]

Any comment that doesn’t state I need valves is welcome Dave. :D

I haven’t even decided which op amps to use in the crossover yet. On the one hand I read you’ve just got to have these because they’re the best and on the other I read that something else will give all the performance you’re likely to hear.
I’ll probably go with a Texas Instruments TL 072, or maybe even a Burr Brown OPA213PA. I’m still looking into it.

Once I’ve decided what components I will use in the crossover I will hopefully get some help with where best to apply gain and impedance matching from my mate Stef.

The problem as always, even with advice form people who know their stuff is after a few basics everyone has a different approach and until I’ve sorted out what my budget will allow with regard to components it is apparently difficult to state this way is better than that.

I’ll have the amps and crossover boards late this week, or early next. The next step is to build the amp boxes and get them usable. I’m going for three amps per box per speakers and keeping them out of the speaker enclosure mainly due to heat and weight problems. (I need a sack barrow to move stands and speakers as they are now.:doh:)

But, yep, most seem to agree that keeping the power amp sensitivity low and running the op amps a bit hot is sensible.

[Reid Malenfant]

What you need are some relays John. With six double pole changeover relays such as BT47 type you would be able to control two channels to within 1dB & keep a constant output impedance.

Effectively what you do is have one relay controlling 1dB, another controlling 2dB, next up is 4, then 8dB, 16db & finally 32dB.

If you didn't fancy only being able to attenuate by about 63db, then it'd be easy enough to recalculate the resistors needed to make each step 1.5dB


What you then do is knock up a circuit like I developed using an ADC. I used a single potentiometer to feed the ADC & the output of the ADC controls the relays.

You can parallel up the relays for more channels or frequency bands.

Resistors are cheap & the BT47 relays are cheap as well. They use bifurbicated gold contacts & are totally sealed. They'll last for ever at the kind of current used in audio.

[Welder]

Ello Mark. :)
Funnily enough someone else has suggested this. I’ve been reading up on it. I’m not sure if my design skills are up to it. :scratch:
1 dB steps are fine and so is probably a 63 dB range.

I’m already having problems with cascading filters for time alignment. :doh:
I may have to employ some big hammers on the baffle after all. :eek::D
Time delay is sooooo much simpler in the digital domain and that’s probably where I’ll sort it but at the sharp end.

[Reid Malenfant]

I still have your email AD fella, so I'll dig out what I can find & squirt some information your way :)

As for the time alignment, it's pretty easy. Need any help I'll be glad to lend a hand :cool:

What you are looking for is an all pass phase shifting network. It'll involve a single op-amp per delay & it'll need to be driven by a buffer.

So assuming you are going to be using your speakers, you'll need two for the mids, & two more (one for left & one for right) cascaded after the delays to the mids to feed the tweeters.

The thing with these networks is they have a 6dB loss, but depending on the design of the crossover itself you can get that back without adding extra gain stages :D

[Welder]

I may well take you up on your offer.
First I've got to get the amp packs built.:eyebrows:



(Now who exactly was it that said this stuff is simple?):D