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View Full Version : Advice needed, using a volume pot as a pre amp..


Jeff Wood
23-09-2016, 07:59
Hi guys,

I've got this idea in my head about using a volume pot instead of a pre amp.

I only use one source, vinyl, so I don't need the functions of a pre amp, ie source selector.

So I'm thinking volume pot in a separate box to go between my lfd mmo phono stage and a power amp.

I could even put the volume control on the front of the phono stage, which would be convenient, but would probably trash the value of it.

(Although no plans to sell it).


So has anyone done this ?

Also any suggestions as to what pot to use, I don't spending a bit on a decent one like an Alps Black Beauty.
struth
23-09-2016, 08:59
Thats basically all a passive preamp is. If you dont need gain or connections then its fine..some say best
Firebottle
23-09-2016, 12:34
The Cosmos Tocos pots are a good quality inexpensive item, I have used them myself:

http://www.ebay.co.uk/itm/1pc-RV24YG-20S-B503-B50K-50K-x-2-COSMOS-TOCOS-Potentiometer-DUAL-Turn-24-20MM-/281856035951?hash=item419fedcc6f:g:eHYAAOSwQoFWQcv D

Alternatively you can get them from Hifi Collective, but they are out of stock and 4 times the price.

:)
Jeff Wood
23-09-2016, 12:57
Thanks, good price.

I've just this ebay seller who's got some genuine Alps Black Beauties at a reasonable price...

http://www.ebay.co.uk/itm/Alps-50KX2-potentiometer-pot-NOS-special-Quad-34-pre-amp-Black-Beauty-standards-/131868623994?hash=item1eb3fb847a:g:~psAAOSwEjFXe-O3


by the way...I quite like the idea of a phono stage with a volume control on the front, and then the power amp hidden away....

good WAF too....



(is that term still used in the world of HIFI ???)
Yomanze
23-09-2016, 15:20
Keep the signal wire lengths as short as possible...
danilo
23-09-2016, 17:09
Fit two Mono 'volume' pots as an Effective Balance control??
Don't use coax interconnects.. in the unlikely event that wasn't news to you already.
Arkless Electronics
23-09-2016, 17:16
It's fine to use coax interconnects and in fact the extra screening is important as you will have a higher output impedance than from an active pot and so it won't offer a AC low impedance to received mains hum etc;)
Jeff Wood
23-09-2016, 18:38
Two volume pots.......noooo that would annoy the Hell out of me :)

Arkless, just what I was going to say. Just kidding. And to be honest I've still got this evil plan inside my head to mount the volume pot on the front of the phone stage..

I'll post some pics of it later, there's tons of room inside..
danilo
23-09-2016, 21:46
It's fine to use coax interconnects and in fact the extra screening is important as you will have a higher output impedance than from an active pot and so it won't offer a AC low impedance to received mains hum etc;)

Another part of the world has an alternate point of view... so much so that's why God gave us buffers.
But Hey! fill yer boots :-)
struth
23-09-2016, 21:50
It is all opinions..... I like a good buffer
Arkless Electronics
24-09-2016, 01:04
Another part of the world has an alternate point of view... so much so that's why God gave us buffers.
But Hey! fill yer boots :-)

We were discussing passives I believe.... May I suggest you read some manuals such as "The Art of Electronics" by Horowitz and Hill... or maybe "The ladybird Book Of Electronics" (do you have that in the colonies?) before engaging any further in matters of a technical nature. But hey! maybe electrons spin different in the boondocks...
Macca
24-09-2016, 08:07
maybe "The ladybird Book Of Electronics" (do you have that in the colonies?) ...

Sadly no such tome exists, either here or in the Colonies. Found this one though:

http://i903.photobucket.com/albums/ac233/Macca_photos_2009/ldtbird95412e5295eb13a7c68c181b8b7acc60.jpg (http://s903.photobucket.com/user/Macca_photos_2009/media/ldtbird95412e5295eb13a7c68c181b8b7acc60.jpg.html)
CornishPasty
25-09-2016, 10:55
I would try a pot in a box first to gauge how a passive would work in your system. If it hits the spot then carry on with your idea. I can recommend the Alps pot. Forget the Tocos, a lovely sounding pot blighted with abysmal channel balance and the reason HiFi Collective no longer stock them.
Reffc
27-09-2016, 15:54
I would try a pot in a box first to gauge how a passive would work in your system. If it hits the spot then carry on with your idea. I can recommend the Alps pot. Forget the Tocos, a lovely sounding pot blighted with abysmal channel balance and the reason HiFi Collective no longer stock them.

Tocos monos are absolutely fine, and as good as Blue Alps. Alps channel balance is also not fabulous, nor are many at that end of the spectrum, but yes, Tocos stereo pot probably best avoided :)

If just going a pot in the box, just ensure that you pick a pot value which worst case offers adequate impedance for your source, and low enough for your power amp combined with source output impedance. I would advise using coax. Why would you not? Keep runs short. There are several ways to effect a ground (ground plane, star earth or switched individual earth). I prefer switched individual earthing as it keeps input signal paths discrete from input to output...a good thing.
Jeff Wood
27-09-2016, 16:32
cheers guys, tbh I've put the amp upgrade on hold for a bit and I've just spent that money on a Nessie Vinylmaster :)

I figured that was a more sensible thing to do .
Arkless Electronics
27-09-2016, 17:53
Tocos monos are absolutely fine, and as good as Blue Alps. Alps channel balance is also not fabulous, nor are many at that end of the spectrum, but yes, Tocos stereo pot probably best avoided :)

If just going a pot in the box, just ensure that you pick a pot value which worst case offers adequate impedance for your source, and low enough for your power amp combined with source output impedance. I would advise using coax. Why would you not? Keep runs short. There are several ways to effect a ground (ground plane, star earth or switched individual earth). I prefer switched individual earthing as it keeps input signal paths discrete from input to output...a good thing.

Good channel balance was the reason the blue Alps came into being and I've never found one lacking in this respect;) I have been very impressed though by a very cheap stereo pot I am trying for my new pre amp as the entry level vol control. About £1.70 but excellent channel balance and sound. Both on a par with Alps Blue for this sample. Consistency may be another matter of course!
Reffc
27-09-2016, 19:05
Good channel balance was the reason the blue Alps came into being and I've never found one lacking in this respect;) I have been very impressed though by a very cheap stereo pot I am trying for my new pre amp as the entry level vol control. About £1.70 but excellent channel balance and sound. Both on a par with Alps Blue for this sample. Consistency may be another matter of course!

I may have been unlucky Jez but have experienced poor channel matching with a range of pots including Alps. I prefer mono pots anyway but it's a personal thing. Will be trying some ladder type SMD stepped pots in due course which promise to be pretty good.
Arkless Electronics
28-09-2016, 11:29
I may have been unlucky Jez but have experienced poor channel matching with a range of pots including Alps. I prefer mono pots anyway but it's a personal thing. Will be trying some ladder type SMD stepped pots in due course which promise to be pretty good.

Maybe you got the Friday afternoon one:lol: I've never had a problem with the many Alps Blue pots I've used. I can't be doing with mono pots for my own use... kind of makes a mockery of all the trouble one goes to in channel matching if one then uses separate right and left pots...
Stepped attenuators are the bizz but unfortunately a bloody fortune!