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Old 13th July 2012, 08:45 AM   #1
Zoodle is offline Zoodle  Australia
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Default phono preamp options

I'm looking at these options:

Hi-Fi RIAA Phono Preamp
(diagram inc.)

or this one:
RIAA PRO Correct Compensation Pre-Amplifier DIY Kit (Stereo) for Phono Turnable | eBay
(ad includes diagram)

or this:
Audio Stereo MM Phono RIAA Preamp Module, Kit, Based on OPA2134 SKU168005 | eBay
(diagram shown in ad)

or, don't laugh, this one:
Phono Preamp Pre Amp Amplifier 2inputs+ Volume Control | eBay

As you can tell, I'm looking for something low budget, but obviously I want the best sound possible :-)). I'm attracted to the last one as it's ready to go and is perhaps tweakable.. What do you think?
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Old 14th July 2012, 10:18 AM   #2
andyr is offline andyr  Australia
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A mate of mine swears by the Rod Elliott (ESP) phono stage.

Regards,

Andy
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Old 14th July 2012, 11:59 AM   #3
Calvin is offline Calvin  Germany
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Hi,

Iīd rather opt for the stage with the AD797.
The TL072 (Elliod) as well as the OPA2134 are too noisy in this application.
Also the resistance values in Elliods inputs stage are larger than itīd be good for a lownoise design. A 3-active-stages circuit like the OPA2134-circuit is unnecessary for phono-MM.
The AD797 is one of the best OPamps You could choose for a MM-input stage.

jauu
Calvin
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Old 14th July 2012, 02:19 PM   #4
mlloyd1 is offline mlloyd1  United States
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what kind of cartridge will you be using?
generally speaking, listening with cartridges attached, you will hear lower noise with a JFET input op amp (like OPA627) for MM and with a bipolar transistor input opamp (like AD797) for MC.
btw, rod's design is fine; just replace the TL072 with a "better" part.

mlloyd1
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Old 14th July 2012, 08:31 PM   #5
Calvin is offline Calvin  Germany
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Hi,

generally speaking, one couldnīt claim which is better here noisewise, JFET or bipolar. It depends on the circumstances.
Generally one can only say that JFETs show lower noisecurrent values -which dominate with high source impedances and bipolars show lower voltagenoise that dominates with lower source impedances.
The problem with MMs is that they are somewhere just on the edge.
Loaded with 47kOhms and a couple of pFs the source impedance the OPamp input īseesī will be around 1kOhm starting at dc and rising over ~5kOhms at 1kHz to maybe 30kohms at 20kHz. AFAIR the optimum source impedance for the NE5534 was ~2kOhm which prooves why it was used very often in Phono-stages. The AD797 is optimized for 200Ohms source impedance, so itīd be off of the best value and probabely no better than the NE5534, even though it features spectacular low voltagenoise figures. JFET input input OP amps have their optimum noise source impedance in the range of >>2kOhms and MOSFET Oamps even much higehr.
A OPA627 features very low voltagenoise figures for a JFET-input OP-amp, similar to the NE5534, but of course much better currentnoise figures. So itīll beat the NE5534 and the AD797 noisewise. But it is costly and as all īfastī OPamps it requires care with the power supply. A alternative with even lower noise could be the AD743 (lower voltage noise as well as lower 1/f).
I think I read in an article by J.L.Hood that a voltagenoise figure of <5nV/sqrHz were needed for acoustic ītransparencyī noisewise. A TL072 with its 18nV and high 1/f sure doesnīt fall into that category.

jauu
Calvin
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Old 14th July 2012, 08:42 PM   #6
adason is offline adason  United States
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Quote:
Originally Posted by Zoodle View Post
What do you think?
frienkly none of the above will satisfy, they will produce the sound, but far far from what is possible
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Old 14th July 2012, 09:03 PM   #7
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I tried few schematics using different opamps, but none of them sound even close to Borbely All-FET EB804/419 phono preamp - difference is dramatic.
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Old 15th July 2012, 12:19 AM   #8
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I'm having a ball with my $15 Herald Electronics Disco Mixer I found at the flea market. I then put $25 in parts in it; see this thread:www.diyaudio.com/forums/analog-line-level/164102-improving-disco-mixer-mid-fi-performance.html. I'm using ST33078 op amps. I could cut the hiss even more theoretically by increasing the RIAA cap by 10X and decreasing the feedback resistor by 10x but it sounds so good those parts are gathering dust in the bins. The advantage of a mixer, you can leave the record player, CD player, and FM radio all plugged in and balanced, you don't have to fiddle with a selector switch or a master volume pot to switch from one to the other. Just turn on the input device, it plays immediately. I converted the microphone input to an FM radio input by deleting the op amp and jumpering.
Herald is Japanese, there might be some of these RA88a's in the flea market or charity resale shop in the Southern Hemisphere, since non-computer disco is now dead. Mine had great slider pots, no complaints there, most of the stupidity was in the power supply. The NJM4558 op amps weren't much either, to start with, they hiss. They were dip package so it was easy to try replacements: I did install phosphor bronze sockets in case I want to try LM4562 or something.
Peavey also made a disco mixer which might be modifiable for more fidelity, but I've never actually seen one. Peavey has great schematic diagrams. Regular mixers don't have an RIAA input. Stay away from Behringer, they have secret schematics and use SMD parts and flat cables and that means repairs/mods must be made by gnomes or elves, in my opinion. And I have tiny Native American origin hands and fingers. I'm using a Shure M97 Era IV MM cartridge at 1.5 g.
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Last edited by indianajo; 15th July 2012 at 12:27 AM.
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Old 16th July 2012, 06:17 AM   #9
Zoodle is offline Zoodle  Australia
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I'm using a MM based on the AT95 (400 ohm coils)
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Old 16th July 2012, 06:37 AM   #10
grufti is offline grufti  United States
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The RIAA PRO - No. 2 in your list - looks surprisingly good for the money.
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