A Valve Preamp with Phono Stage and Tone Controls.

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Cressy Snr
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#46 Re: A Valve Preamp with Phono Stage and Tone Controls.

Post by Cressy Snr »

Rather than do the cathode follower, I’ll probably go 1uF cap, 10K feedback resistor, 0.22uF cap, 1 Meg resistor, then output terminal. otherwise it’ll be a delicate balancing act to elevate the heaters to the right level. With just a couple of followers 100V above the heaters, it’ll be easier all round. It’s a lot of work just to avoid one cap.
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#47 Re: A Valve Preamp with Phono Stage and Tone Controls.

Post by Cressy Snr »

izzy wizzy wrote: Sat Sep 19, 2020 5:46 pm I have a prejudice that phono stages should have a high gain first stage. And with this, a two stage design is enough. There are a number of ways to do that. I don't know for sure, but I would imagine a number of cascaded low gain stages will result in quite high noise. A high gain first stage could be a cascode 88, a 12AX7 in say a CCDA stage or a pentode. I think an 88 as stage 1 will sound a bit wimpy; lacking drive and voom so a bit dynamically flat. But that's a guess. This is why you see a lot of 12AX7 in commercial offerings.
That’s the problem I face with this stuff. The number of different ways to make a phono stage, is staggering, and not just anybody can build one. It’s difficult not to become discouraged when faced with so many alternatives. I’m seriously thinking of wimping out and just building the line stage part. I’m going in circles at the moment and need to step back.

The best policy might be to just get on with it, and see what the result is. Cant evaluate anything if I don’t actually build something.
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#48 Re: A Valve Preamp with Phono Stage and Tone Controls.

Post by Ant »

Breadboard the line stage then do the phono stage once youre happy with the line stage

The phono stage is not directly related to the line stage as far as i can see so build it in stages
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#49 Re: A Valve Preamp with Phono Stage and Tone Controls.

Post by pre65 »

Ant wrote: Sat Sep 19, 2020 6:27 pm Breadboard the line stage then do the phono stage once you're happy with the line stage

The phono stage is not directly related to the line stage as far as i can see so build it in stages
I'll second that Steve.
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#50 Re: A Valve Preamp with Phono Stage and Tone Controls.

Post by Cressy Snr »

Might be the best plan as you both say to build the line stage and forget the phono for now. It’s just going to get silly otherwise.
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#51 Re: A Valve Preamp with Phono Stage and Tone Controls.

Post by Mike H »

Sorry late to the party.

Whenever I messed with tone controls ideas in recent years I found the biggest problem was the quality of the pots. And the quality of the caps. And the quality of the resistors ... I remember one I made with slider pots that was really awful ... and for some reason, it seems you can't get the pot values you want also with the quality you want. Also passive (incl. Baxandall network) needs log pots, at least if you want the spindles to be mechanically in the centre of the total end-to-end travel, at the 'zero' positions. But active Baxandall uses linear pots so I think this is the way to go. The next problem you going to have then, is the gain of the amplifying valve, if memory serves the last time I was thinking about this sort of thing I was looking at something like a EF86 pentode to get the gain, with a cathode follower on its output, the latter not only to provide a low impedance drive to the output of the preamp, but also to drive the network which can present a low impedance at whichever end the pot wipers are turned to minimum resistance. I remember a Quad preamp doing similar, but using a ECC83 with a very large value anode resistor, 470k, as the Voltage amplifier.
 
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#52 Re: A Valve Preamp with Phono Stage and Tone Controls.

Post by izzy wizzy »

Cressy Snr wrote: Sat Sep 19, 2020 6:47 pm Might be the best plan as you both say to build the line stage and forget the phono for now. It’s just going to get silly otherwise.
Best way to start. You want to have the line absolutely silent before introducing the phono. Also you can gauge the effect of the tone controls from the sources you already know.

It might be an idea to consider a two box solution maybe as we all know projects tend to grow and take up more room than we had planned at the outset. Cramming things in on a phono with a PSU as well is a very tricky thing to do as space is your friend here.
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#53 Re: A Valve Preamp with Phono Stage and Tone Controls.

Post by Cressy Snr »

OK,
Suggestions have been taken on board re separating the two functions. The two-box, separate power supply option will be used.

So....here's the line stage:
UGBuffer.jpg
Designed by Max Robinson of the Angefire website: http://www.angelfire.com/electronic/fun ... one-A.html (fig 6.1.)
It is effectively a unity gain device with tone controls. It’s made up of a cathode follower input stage, tone stack and an op-amp output stage.
I don't really need gain, what with having the 2 stage power amp with choke loaded drivers, so the unity gain preamp with tone stack option, is the best for what I want to be able to do.

Response curves:
IMG_0480.gif
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#54 Oh dear. :|

Post by Cressy Snr »

Well this is embarrassing!

I’ve spent over ten years trying to get rid of starkness/sterility on my old ‘50s and ‘60s digital files. It has involved changing virtually everything in my system. I mean, the turntable/arm/cartridge is different, the CD player is different, the speakers are different, the streaming is different, I’ve had too many amps to mention, and I started this thread in desperation really, as including some degree of tone-control has seemed to be the only way out of this situation.

There has been a lot of success and the system is nowhere near as bad as it was; and with each ‘improvement’ I’ve made, I’ve believed I’d solved the sterility problem, only for it to rear its head six months later, and start the whole chasing-the-tail merry-go-round up again. Entertaining I suppose, but bloody frustrating in the long term!

A notable success on the analogue side has been the addition of the 50-odd year-old Shure M55E cartridge to the turntable/arm/cartridge mix. The sound out of this combination is diametrically opposed to the godawful noise that caused me to abandon vinyl completely for several years. If not for our Ant getting into resurrecting old idler-drive record players, I would have still been bereft of the black stuff, and none the wiser as to just how nice it can sound.

But back to the digital side, and aside from the bass lightness of some of the older recordings, which can be explained by the fact that they were often engineered to be played on Dansettes, we still had the problem of excessive forwardness and in-your-face ness rearing its ugly head at times. After so many years of fighting with this syndrome, I’d decided enough was enough, hence the desire on my part to move over to tone controls.

Our An, and Ed before him, buying the Topping E30 DAC and reporting good results, got me thinking, always dangerous, but looking at the system as a whole and the way it had evolved over a decade, the one constant in the whole setup was the presence of a Musical Fidelity M1 DAC.

I’d bought the M1 because I’d blown up my Beresford TC-7510 mk6 DAC by buggering around trying to bypass the op-amp analogue output stage with capacitors (idiot.) The M1 had to be better because it was £400 (2010 prices) was from an established company, and the dealer said it was good. There it was, and there it stayed, sitting steadfast, in the digital side of the system, thoroughly reliable, never missing a beat and there seemed to be little reason to change it.

So our Ant had bought this Topping DAC and I had an old Beresford TC-7510 (the last update before Stanley brought in the Caiman series) going spare and gathering dust. The wall-wart, however didn’t work, so I needed a 12V DC supply. Luckily our Ant had a very cheap, universal 600mA variable voltage wall-wart with a plug end that fitted the input socket on the back of the old Beresford DAC, so I procured that and got the old Beresford to light up once more.

As soon as the first song started, I knew what had been responsible for the starkness - the M1. The Beresford was playing the music without fuss or favour and there was no sign of hardness/sterility whatsoever on old records. And it got better as it warmed through. I’ve been running it for three days now and have no complaints at all. It’s nice and warm and analogue sounding.

I can concentrate on building a phono stage now, so this thread is not entirely useless.
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pre65
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#55 Re: A Valve Preamp with Phono Stage and Tone Controls.

Post by pre65 »

A tale with a happy ending. :D

Put the M1 on Ebay, better cash in hand than rubbish in loft. (old Yorkshire saying)
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#56 Re: A Valve Preamp with Phono Stage and Tone Controls.

Post by IslandPink »

It must be a house sound with Musical Fidelity, Steve. I remember hearing a couple of their power amps at shows, and they were hard and charmless.
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#57 Re: A Valve Preamp with Phono Stage and Tone Controls.

Post by Cressy Snr »

Interestingly, there was one person who suggested a few years ago, that the problem of hardness/sterility in my system at the time, might have been down to the M1 DAC. That person was Andrew L.

Should’ve listened.
Maybe I should also have entered the M1 into the infamous Owston DAC comparison using that Eurythmics track. :lol: :lol:

Anyway, it’s fixed now - a bit late in the day, but never mind.
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