DIY Adjustable EQ Phono Stage

the thin end of the wedge
cytovette
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Re: DIY Adjustable EQ Phono Stage

Post by cytovette » 16 Nov 2018 19:50

ChrisfromRI wrote:
16 Nov 2018 16:11
They're the smaller body Alps pots, all four are 50K, but not the big body blue velvet Alps pots that cost $15 each.

Since you're adding it to an existing tube phono stage you might have enough extra B+ and heater supply capacity on hand to just add the 2 tube (12AX7) Bandaxall bass/treble board that's available inexpensively on ebay. It's like $20 and you stay all tube.
Thanks for the info, I looked at those boards and it would require a major overhaul. I was thinking about Alps pots as I have used the blues before for volume controls. Are the smaller Alps just as high in quality as the blue?

ChrisfromRI
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Re: DIY Adjustable EQ Phono Stage

Post by ChrisfromRI » 16 Nov 2018 21:47

Nope, but second best when comparing to other pots. They are still high quality sealed pots. The only negative about sealed pots is that many years down the road when they eventually need to be serviced they're sealed and there's nothing you can do but replace them. Some unsealed pots give you a few open ports to blast DeOxit into every few years, yet having these maintenance ports lets dust in and requires periodic maintenance. Maybe someday there will be pots with allen screws in the inspection ports so they are sealed until you need to unseal them...

cytovette
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Re: DIY Adjustable EQ Phono Stage

Post by cytovette » 16 Nov 2018 21:50

ChrisfromRI wrote:
16 Nov 2018 21:47
Nope, but second best when comparing to other pots. They are still high quality sealed pots. The only negative about sealed pots is that many years down the road when they eventually need to be serviced they're sealed and there's nothing you can do but replace them. Some unsealed pots give you a few open ports to blast DeOxit into every few years, yet having these maintenance ports lets dust in and requires periodic maintenance. Maybe someday there will be pots with allen screws in the inspection ports so they are sealed until you need to unseal them...
Would you mind posting a link where you got yours? I am seeing a lot doing searches and am not sure what is genuine.

ChrisfromRI
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Re: DIY Adjustable EQ Phono Stage

Post by ChrisfromRI » 16 Nov 2018 23:06


smee4
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Re: DIY Adjustable EQ Phono Stage

Post by smee4 » 17 Nov 2018 12:06

ChrisfromRI wrote:
08 Oct 2018 06:56

Frankly, if our high-end preamps still had bass and treble controls this would be unnecessary as we could make the correction there - problem is they took those controls away.

I agree, but you will get so many people totally opposed to tone controls. Strangely, calling it variable eq makes it more palatable.

btw, I built my own variable eq phono stage for mono playback, but I went the route of separately switchable turnover and rolloff filters. You can use those switches like tone controls if you want :)

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Re: DIY Adjustable EQ Phono Stage

Post by Philamon » 09 Sep 2019 14:50

Hi, I have just built one of these exact same opamp phono stages but have found the gain very high and also some hum, I see that you have an adjust for gain on your excellent build, would you be able to show or tell how you connected up the gain control as would like to fit one to mine.
Many thanks Phill

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Re: DIY Adjustable EQ Phono Stage

Post by ChrisfromRI » 12 Sep 2019 06:00

This assembled board from China is like the one I used. You can start with the NE5532 Op Amps it comes with, and then try substituting the better Burr Brown OPA Op Amps like I did. There are several upgrade direct replacements available. You will need a chip puller and a static free place to swap Op Amps...

https://www.ebay.com/itm/Assembled-NE55 ... Swqv5c1elZ

You will also need a center-tap transformer (18 - 0 - 18 VAC secondary) to power the board.

BTW, I put similar tone controls on my EAR834 clone phono stage as well, to adjust EQ to fix poor recordings like this Op Amp phono stage. The tube phono stage was a little bright and I appreciate having the tone controls for most recordings!