Phono PreAmp

[ashok]

Hi John,
I must start off by saying that the box you used looks really nice. Did you buy it off the shelf ? How come it is so shiny ? Looks cool.

About the CD vinyl debate. I found that vinyl sounds better in my system. Now I don't have too many CD copies of vinyl but I do have about four or five. In all these the vinyl seems to have more low level detail and a 'feel' that the CD does not.
That of course could be a problem with the DAC ! My DAC is a TDA1541 with passive filter and tube gain stage. Sounds good by itself.

I never used to believe that (newer) opamps sound different because in most cases so much feed back is used that distortion should be 'exceedingly ' low.
I was wrong . The whole character of sound can be different in some areas. I still don't know why. It is not an illusion either as I have repeatedly tested them over known pieces of music.

In view of this I will build your design to hear it ! I forgot to mention that the input impedance varies wildly at LF due to the filter but is reasonably flat in the midband . I want to see how this affects the sound. The system being compared against will be a two stage passive RIAA preamp.
I think the low impedance at LF will probably not be a problem but I want to hear it.
I have an average Denon amp (R480) with the usual RIAA feedback circuit. I put in an OPA2134 and it now sounds quite decent. BUT there is a huge difference between that and a two stage passive RIAA preamp.
Have you used a very high quality RIAA stage ( whatever that might mean !) to compare with CD ?
I also found a tubed passive RIAA preamp sounds better than the opamp version. Vinyl does sound VERY nice through the tubed preamp.
May be an area that you can explore. It will surely take away lots of your free time.
What DAC do you use?
Don't worry about boring anybody. Lots of people are reading our posts! Only some seem to reply. That's not a problem.
Cheers,
Ashok.

[Werner]

Originally posted by ashok

You are right about the unity gain limit causing the error at HF.

A Neumann cutter flattens out at 50kHz, so ...

[ashok]

A Neumann cutter flattens out at 50kHz, so ...

OK , I should have said that the error out of band is of no practical significance.
Cheers.
Ashok.

[JTT]

Oh my Gawd! Don't get me on to tubes .........

I once saw tube amps compared to a man's greatest frightener: the gorgeous blonde - Hot, Heavy, and Very Expensive! (and I bet I'm going to suffer for quoting that, even though I don't intend it to be taken seriously).

My first 'real' amp was based on the Mullard 3-3 .... and have you any idea how much it would cost to build one of those now? The second was a Beam-Echo Avantic 20w mono job (the EL84s were not too happy about that!), bought when the firm, and the prices collapsed, putting it just within my reach at £20. An aquaintence of the time bought a couple of DL75 and the stereo preamp for around £60 (I think), and my, but was I jealous of the sound he produced: via the Avantics, a 301 with an EPU100 arm, and a pair of 5 cub ft vented cabinets fitted with Wharfedale Super 12 RSDDs.

Ah, those were the days ..... queuing (how many u's in queing?) outside the doors of the Tannoy, Quad, Radford, Lowther et al demo rooms at the Audio Fairs in the Hotel Russell. But few of us had the money to buy the the gear we listened to. And those gorgeous Radford preamps .... oooooh!

Anyway, after that, I came to my senses and built my first solid state amp. OC22s in the output stage, requiring the purchase of an expensive npn transistor for the driver stage, and producing a whole 5w of power. I think it was the first transistor amp design published in Hi Fi News. Then on to a 30w Ferranti design, silicon (wow!), using a curious 100KHz square wave generator to bias the output devices; t'wasn't very stable, though I persevered with it for some months before conceding defeat. Since then, I think I've (literally) tried more than 50% of every power amp design to appear in Wireless/Electronics World. Ditto Hi Fi News. Until .... 3 or 4 years ago I came across the Leach low TID design, and that was that - and still is!

And along the way, I tried many of the phono preamp designs that were published, but not many cut the mustard. The ones that stayed the course for a significant time were the H P Walker designs (see WW May 71 and May 72, and later readers letters involving Walker, Bailey, and Lindsley-Hood), and a passively equalised design of my own making, involving .. wait for it .. a couple of TDA1034s (predecessors of the NE553x) bracketing a passive network. But I have to say that my LPs are very rarely exercised these days, for reasons I set out earlier, so I don't think I'm going to heat up the iron and make any changes to what I have now.

Except ....... that ........ I received an email list of Maplin's latest special offers over the weekend, and they're offering 12v 1.3Ah lead-acids at £4.99 a throw, so I went round and bought 3 this morning (It was on the way to a hospital appointment, so how could I ignore the coincidence?).

So, I could resurrect, and tease you, with the excellent MC preamp I used before I gave up those hum prone obscenities (it runs on 10 - 12v). So rush round to Maplin's and get your battery supplies before they run out!

Regards

JohnT

P.S. these exchanges are getting ominously longer.

[JTT]

Hi Ashok

Oh yeah, the box ......... forgot about the box ...... (do that a lot these days .... mumble ..... mumble). It's from Maplin, ref AB9, but you won't fit one o' dem 12v batteries in dere (an' I'll get more brickbats for dat, an' dis too!)

Regards

JohnT

[ingvar ahlberg]

queuing (how many u's in queing?)

Depends how many u are stading in the que, right?

[JTT]

OK, forget the queue ...........

How many n's in standin'?

JohnT

[FASTBACK]

Originally posted by JTT
I have recently had need of a free-standing Mag PU preamp, and resurrected a design I have often used in the past. It is based on the NE5532 dual low noise IC, includes a 25Hz 12db/oct HP filter, and may be powered by a couple of PP3s. It performs extremely well, despite the design being rather long in the tooth, and does not cost an arm and a leg to produce.

I thought it might be of interest to some of yous, and I have zipped up a set of files (324Kb) including the schematic and PCB layout. I'll be happy to send it on receipt of an email request. I can also provide a (higher) res image of the PCB track layout, or Gerber files (if you don't know what those are, you don't need them!) on request.

JohnT

Originally posted by ashok
Hi John,
You are right about the unity gain limit causing the error at HF. I had overlooked that till I tried to tweak some parts and looked at the actual stage gain.

That information about the electrolytic caps is interesting and reassuring. I used to get Wirless World regularly till a few years ago. I must search out the past issues .

About tweaking the parts, I am sure the improvements will probably not make any audible difference as you so rightly pointed out. Additionally deviating from standard component values is of no help as it will mean using more than one component value at one point.
However I have been working with some RIAA circuits recently and hence the "urge" to tweak spilled over to this circuit !
The RIAA error on this circuit is pretty low and as I said earlier the improvements will probably make no audible improvement.
I simulated the circuit with a cartridge modeled as a 500 ohm resistor and 0.5H inductor in series.
The response error ( deviation from RIAA curve) is attached.

Sir JTT and ashok

can you provide me the schematics of the said MM Phono Preamp inital design and the modified one.

I'm a newbie on Turntable and was searching for a DIY MM Phono Preamp.

Here is my email add:
wmg_ph@yahoo.com

Thanks.

[ashok]

Hi Fastback,
I think John (JJT) has put up his circuit on a web site with plenty of info.
Does anyone on the forum know the URL ?
I'll try to search it out also.
Cheers,
Ashok.

[ashok]

Hi Fastback,
This is John's web site. The circuit and pcb design is downloadable there. You could also ask John any questions you might have.

http://www.btinternet.com/~jaytt/

Have fun.
Ashok.