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Old 10th Aug 2020, 10:28 pm   #41
Craig Sawyers
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Default Re: Simple Op Amp RIAA preamp 1st lash up

Or imaginary.

Or purely real -exp(i x pi)
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Old 18th Aug 2020, 11:39 am   #42
bikerhifinut
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Default Re: Simple Op Amp RIAA preamp 1st lash up

version 3 now up and running and so far very good I think.

I took on board the advice in regard of an accurate RIAA EQ, I tried to work it out for myself but my head was swimming with the equations, and so I cribbed the RJM EQ as I already had the components matched up from build2 which didn't work well at all, probably due to my construction rather than any other faults.
I have a circuit to hand to build an inverse RIAA network and that will be the next job to hook the board up to my sig gen which can output down to 2.5mV so I can scope it and get an accurate (ish) idea of how it all works.

Now, I know it was disapproved that I should use the Hitachi HA12017 chip for various reasons but I'd already rashly clicked on "buy" and they arrived within 14 days and with 10 of em here I figured I had to see what I got.
Well at 50dB gain ( I shall likely drop that to 40dB if I decide to build a "neat" version as a keeper) it has a very quiet background, hiss is only audible once the volume is cranked round to antisocial/overload levels.
That is a nice, I guess, confirmation that my mania for pursuing an ultra low noise device was misguided! I did use metal films throughout to keep noise down and the EQ capacitors are all Polystyrene that I nearly threw out years ago...…….
Its fairly close to the data sheet example circuit, no real detours apart from choice of EQ and feedback ratio.
I would rebuild this on a larger board, or perhaps 2 separate boards next time as the extra parts made it quite congested although a competent PCB designer/constructor (ie not me!) would probably get it on that small board with relative ease. So apologies for the awful point to point wiring underneath, but it works.
It's playing now and the noises coming out of the Quad ESLs are very pleasing ones, no funny rustles or squeals and whistles. I used the standard 100pF loading across 47k for the ortofon 2M and I think its about right for my tastes.

Can I thank everyone for their help and forbearance. It's been fun and if I get my head round the inverse RIAA thing I might use it a testbed for different EQ configurations based around feedback.

Andy
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Old 18th Aug 2020, 11:49 am   #43
paulsherwin
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Default Re: Simple Op Amp RIAA preamp 1st lash up

I don't think anybody was suggesting that the Hitachi chip is a poor performer. It's just that it's a rather odd choice for somebody designing an RIAA preamp in 2020. Glad you're pleased with it anyway.
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Old 18th Aug 2020, 12:28 pm   #44
bikerhifinut
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I don't think anybody was suggesting that the Hitachi chip is a poor performer. It's just that it's a rather odd choice for somebody designing an RIAA preamp in 2020. Glad you're pleased with it anyway.
Thanks Paul,
I didn't mean to infer that.
I was curious after seeing an application in the R A Penfold op amp circuit book and a look at the data sheet piqued my curiosity as it was an application specific device, namely audio and in particular as an RIAA preamp, and I would imagine it saw use in some of Hitachis own kit as well as in tape replay needing EQ. Jim leSurf used the HA12017 throughout the last of the Armstrong Pre amps just before the company closed, and I figured he wouldn't use a duffer.
As people have observed, the market now for audio specific devices has all but collapsed, at least as far as the manufacturers are concerned and so a modern analogue designer has to work around more non specific chips. Although the traditional op amps are still available including in SMD, and they are probably as good as its realistically possible to get.
And the Hitachi devices are cheap as chips (oops!) and still available in their thousands, which surprised me.
Anyway Its a good result from my point of view.
And thanks for the pointer to the VSPS Paul as that's the EQ I am using, its so simple with readily available E24 resistors and easily sourced 1nF capacitors that most of us have a stash of.

Andy
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Old 18th Aug 2020, 12:38 pm   #45
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Default Re: Simple Op Amp RIAA preamp 1st lash up

Just to preserve stocks of the Hitachi devices for people with Japanese amplifiers of the period needing them at affordable prices for restoration jobs, we must all stress how slow the bass is from the Hitachi RIAA stage along with indecisive soundstaging and utterly vile amounts of granularity.... oh god the granularity. These devices also exhibit negative authority!

I suppose to make this a believable review we now need a listing of equipment used to listen to them. Of course, I used the 'Unobtainium" tri-wire speaker cables from Megablast Products.

Anyway, it seems like you've enjoyed your journey, Andy.


David
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Old 18th Aug 2020, 4:22 pm   #46
wd40addict
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Default Re: Simple Op Amp RIAA preamp 1st lash up

You could kill all demand with a simple "my wife couldn't hear the difference", the opposite of the normal Hi-Fi forum cliché!

Realistically the ESLs should show up any issues. Worth scopeing the output just to ensure there's nothing ultrasonic going on.
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Old 18th Aug 2020, 5:11 pm   #47
Ted Kendall
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Default Re: Simple Op Amp RIAA preamp 1st lash up

Just a small point to ponder - Self, having spent acres of tome on magnetic pickup input noise, quotes a disc nut whose experience he respects as never having failed to hear the background noise level rise as soon as the pickup hits the disc...
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Old 18th Aug 2020, 7:36 pm   #48
bikerhifinut
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Default Re: Simple Op Amp RIAA preamp 1st lash up

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You could kill all demand with a simple "my wife couldn't hear the difference", the opposite of the normal Hi-Fi forum cliché!

Realistically the ESLs should show up any issues. Worth scopeing the output just to ensure there's nothing ultrasonic going on.
I don't think somehow I am about to start a stampede to eBay to buy up the worlds remaining stocks!

AS you say the ESL (989 refurbished panels by OTA) do show up if anything's not right, they were my retirement present to myself second hand of course, I couldn't even dream of a new set of the current crop. And indeed these speakers gave me a new respect for the Quad 405-2, which never seems to even break sweat so to speak, I always liked them and when I bagged one at last I wasn't disappointed. The other amps are a kit integrated amp based on the KT88 at 30W and also my "Frankenstein" EL34 homebrew also 30W, both of which work well with ESLs albeit with some extra "colour" to the sound and we leave that there as I don't want to sink into the pit. I know what I like and that's it.
I have got an inverse RIAA network to assemble soon and I fully intend to do some scope measurements and I imagine I can plot a graph showing how it deviates from the standard? As this was really done out of pure curiosity rather than a need for a disc stage.

Ted's comment made me smile rather. I hope that was the intent.

A.
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Old 18th Aug 2020, 8:09 pm   #49
bikerhifinut
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Default Re: Simple Op Amp RIAA preamp 1st lash up

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Originally Posted by Radio Wrangler View Post
Just to preserve stocks of the Hitachi devices for people with Japanese amplifiers of the period needing them at affordable prices for restoration jobs, we must all stress how slow the bass is from the Hitachi RIAA stage along with indecisive soundstaging and utterly vile amounts of granularity.... oh god the granularity. These devices also exhibit negative authority!

I suppose to make this a believable review we now need a listing of equipment used to listen to them. Of course, I used the 'Unobtainium" tri-wire speaker cables from Megablast Products.

Anyway, it seems like you've enjoyed your journey, Andy.


David
Actually I rather like the bright orange double insulated 2 core flex that I salvaged from my dads old electric mower for speaker cables. Aged for 15 years in an AC environment and matured in a draughty shed.
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Old 18th Aug 2020, 8:29 pm   #50
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Default Re: Simple Op Amp RIAA preamp 1st lash up

And flexed so many times that there is no longer any single strand that is complete from end to end!

David
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Old 18th Aug 2020, 11:02 pm   #51
Ted Kendall
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Ted's comment made me smile rather. I hope that was the intent.
It was.
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