SteveLuck Posted December 28, 2012 Posted December 28, 2012 I want to reduce the sensitivity of my volume control (Integrated Valve amp) my new speakers are super efficient and super loud I had a quick e-mail to Dr Tube who knows about my model amp he suggested putting a couple of 220K resistors in series with the volume knob but he also recommended replacing it with an ALPs blue model. Which is a squeeze but fits. Current Spec is a 470K log if i replace it with a 1m Alps log Pot would that increase the angle required to raise the volume small amounts to start reducing as you get round the dial to zero resistance and full signal? Am i understanding how this works correctly.(more or less) He's also recommended by-passing the balance pot also 470k but with a center detent. Id like to keep the balance pot, If I can find a dual gang steped attenuator for the balance say a 24 step one i might get one small enough to fit. Would that be a step in the right direction. A small number of steps on the balance would be OK but obviously not on the volume. "The amp is too sensitive for your requirements. All though it can be a good idea to incorporate a better volume control in this amp (to improve the sonics) that will not solve your problem. You need to reduce the sensitivity of the amp. The easiest method is by adding two resistors in series with the volume potmeter. Two 220k resistors will probably do nicely. Alternatively you can remove the twoo 100uF electrolytics in the cathodes of V3. That'll also reduce the gain and improve linearity. While you're at it, remove or disconnect the balance pot (unless you really need it) and fit a better quality volume pot. An Alps Blue Velvet wil just fit in there." - DR TUBE Any Ideas. Thanks Steve
Milo Posted December 28, 2012 Posted December 28, 2012 Hi Steve, I've heard of using resistors with the volume control but I can't comment on the tech stuff. I have heard of attenuators that you can get to put on cables. Someone will know more about it.
ophool Posted December 28, 2012 Posted December 28, 2012 (edited) Hi Steve, Alternatively you can remove the twoo 100uF electrolytics in the cathodes of V3. That'll also reduce the gain and improve linearity. Think I would be trying that option, looks like a win-win, no parts required and improved linearity. There are better sounding pots than Alps Blue, but 470K is not a common value from what I see around. You could also try shunt wiring the pot using some nice Vishay/Charcroft Z-foil resistors. Edited December 28, 2012 by ophool
davewantsmoore Posted December 28, 2012 Posted December 28, 2012 "Alternatively you can remove the twoo 100uF electrolytics in the cathodes of V3. That'll also reduce the gain and improve linearity. If DRTube is correct, then this would sound like the best route. I'd want to understand the circuit first though.
RoHo Posted January 6, 2013 Posted January 6, 2013 I would certainly try it without those 100uF cathode caps which will reduce the gain and will probably sound better. Getting rid of a big electro cap right in the middle of the signal current is a good thing. If it doesn't suit your taste try replacing them with higher quality items. If that doesn't give enough gain reduction then add the two resistors, technically known as a voltage divider. Again, no downside really. I would do this before changing the pot which may or may not do what you want.
Owen Y Posted January 7, 2013 Posted January 7, 2013 Sorry, chiming in a bit late here... - Removing the cath bypasses would lose you a few dB & better sonically too IME - getting rid of electrocaps (any cap really) if you can, is a good thing. Better tonality, more natural. - Changing the vol pot from 470k to 1M would not have much effect, probably tend to make things worse. - Putting the addit Rs in front would do the trick, raising the vol setting for the same spkr SPL - make those good quality Rs, to your audiophile taste - I have used dual vol controls before, which allows balance control at same time - if you are thinking resistor attenuators, then the DACT ones are quite good, IME. (They do dual gang jobs also).
SteveLuck Posted January 7, 2013 Author Posted January 7, 2013 I still like these as a way of limiting the volume without doing surgery on my amp even with the cost involved. It would also allow me to reduce the signal going to the Lowthers without reducing the signal going to high pass on the hypex plate amps if i needed too. These are transformer L Pads so the the amp doesn't see the increase in resistance: If the volume im getting from 9 watts is anything to go by then even just 3 watts from some SET's into some of the massive horns out there would still need some attenuation! I'd be surprised if there weren't other gizmos out there like these.
Monkeyboi Posted January 7, 2013 Posted January 7, 2013 (edited) I still like these as a way of limiting the volume without doing surgery on my amp even with the cost involved. It would also allow me to reduce the signal going to the Lowthers without reducing the signal going to high pass on the hypex plate amps if i needed too. These are transformer L Pads so the the amp doesn't see the increase in resistance: Foste attenuator.jpg If the volume im getting from 9 watts is anything to go by then even just 3 watts from some SET's into some of the massive horns out there would still need some attenuation! I'd be surprised if there weren't other gizmos out there like these. I believe the OP would be far better off attenuating the input to his amplifier rather than attenuating the output. The attenuators you've shown are intended to go between the output of the amplifier and the speakers. This won't give him any additional control over the volume he's seeking to acheive, just dissipate a lot of power unnecessarily in the output. The initial suggestion of adding a 220k resistor in series with the input of the volume control for each channel is a simple, inexpensive and effective solution. Steve need only purchase a couple of inexpensive 0.6W metal film resistors from his local electronics parts shop to see if the method acheived the desired result in giving him more low level volume control. He may then wish to explore the option of using more expensive "audiophile" grade resistors if he feels the "tone" isn't to his liking. If it were me and I was unsure as to exactly how much pre-attenuation I needed, I'd probably get some 330k and 470k resistors as well just to try out. The only cost a few cents each. 470k will give him 6dB attenuation if used with his existing 470k potentiometer (volume control). Cheers, Alan R. Edited January 7, 2013 by Monkeyboi
VanArn Posted January 7, 2013 Posted January 7, 2013 A correctly specified volume control should not require additional attenuators or add-ons if you wish to avoid the intrusion of unwanted capacitive losses (H.F. roll-off) and noise. An answer to your problem would require knowledge of the output impedance of the source(,i.e. pre- amplifier) and input impedances of your amplifier.The modern approach for valve based equipment is to use 100k Ohm log pots. for volume control providing the circuitry suits this application.
Owen Y Posted January 7, 2013 Posted January 7, 2013 Steve, I've used Lowthers in past, for maybe 10+yrs, in front horns & basshorns. And yes, they are super sensitive, up to ~105dB in a horn, requiring less than a watt to make your ears bleed. Your problem is either/or: - Too powerful an amp (for the spkrs). - Too sensitive spkrs (for the amp)! - Amp with too high input sensitivity. - Preamp (if separate) too high output - should not be the case. That's my take on it... What are your amp/s, spkrs? Cheers. I still like these as a way of limiting the volume without doing surgery on my amp even with the cost involved. It would also allow me to reduce the signal going to the Lowthers without reducing the signal going to high pass on the hypex plate amps if i needed too. These are transformer L Pads so the the amp doesn't see the increase in resistance: Foste attenuator.jpg If the volume im getting from 9 watts is anything to go by then even just 3 watts from some SET's into some of the massive horns out there would still need some attenuation! I'd be surprised if there weren't other gizmos out there like these.
Owen Y Posted January 7, 2013 Posted January 7, 2013 PS. Whilst you may technically need only less than 1 watt to create adequate SPLs with your spkrs, 9 wpc may be necessary for adequate power headroom in hand to reproduce musical dynamics.
SteveLuck Posted January 9, 2013 Author Posted January 9, 2013 Some one at work suggested i just need a bigger knob!!!!
SteveLuck Posted January 13, 2013 Author Posted January 13, 2013 Thanks for all the advice - having now had a chat with an eceptionally smart Electrical Engineer who kindly sketched out whats been dicussed in this thread and explained that volume pots are more like current dividers than just variable resistance I now undertand the advice given above much better! Tantalum resistors for high end audio: http://www.hificollective.co.uk/components/resistors.html I'd still like to replace the volume pot if i'm going to take a screwdriver and soldering iron to my much loved amp. I'll ignore the advice about bypassing the balance pot (too usefull for testing things are working) but will fit a better quality one. Audio note now make their own for a reasonable price only 100k though: http://www.hificollective.co.uk/components/potentiometers.html Cheers
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