Good morning!
I just bought a used AKAI AP-103C turntable. I thought that I could build a phono preamp myself without doing my research before buying the turntable.
I am not really an audiophile I just want to listen to my records. Is there any simple schematic for a phono preamp?
The basic problem that I encounter is that most schematics need +-V and ground meaning that I have to use a center tapped transformer that I CANT FIND IN ANY ESHOP in greece. Shops are closed because of covid. So I only have access to eshops and my stock of components.
If it's possible I would like a TL072 schematic (because I have a couple of them). I don't even care if it has eq or volume knobs.
(I have experience from copying effect pedals so I can transcribe schematics but I am not that experienced in understanding them)
Thanks in advance!
I just bought a used AKAI AP-103C turntable. I thought that I could build a phono preamp myself without doing my research before buying the turntable.
I am not really an audiophile I just want to listen to my records. Is there any simple schematic for a phono preamp?
The basic problem that I encounter is that most schematics need +-V and ground meaning that I have to use a center tapped transformer that I CANT FIND IN ANY ESHOP in greece. Shops are closed because of covid. So I only have access to eshops and my stock of components.
If it's possible I would like a TL072 schematic (because I have a couple of them). I don't even care if it has eq or volume knobs.
(I have experience from copying effect pedals so I can transcribe schematics but I am not that experienced in understanding them)
Thanks in advance!
Some questions:
I don't have:
1) 330uF (C3) caps. Can I replace them with 220uF or 470uF?
2) 560k (R4) res. Can I replace them with 510K?
3) 5.6nF (C4) caps. Can I replace them with 4.7nF?
4) 1.6nF (C5) caps. Can I replace them with 1.5nF?
5) 2.2uF/100V (C6) caps. Can I replace them with 2.2uF/50V?
I have all the basic values of resistors (x1, x1.5, x2.2, x3.3, x4.7, x6.8 etc) plus some x5.6, x8.2 and some random values.
I have all the basic valus of capacitors plus some random values and a few of in between values.
I have those transistors
2N5458 MPSA14 2N4401 78L05 bs170 2N3904 BC239/546B/549 2N3906 2Ν5087 7915
I have those IC's
LM324N TL072 TL082 RC4558 UA741 LF353
LM386 NE555 NE556 PT2399
And I have those diodes
1n4148 1n4733A 1N5231B 1N5404 1N4728A 1N4742A 1N5817 1N5819 1N4001 1N4002 1N4004 1N4007 bzx 15V
(yeah some are tottaly useless for this application but you never know
)
I have all the basic valus of capacitors plus some random values and a few of in between values.
I have those transistors
2N5458 MPSA14 2N4401 78L05 bs170 2N3904 BC239/546B/549 2N3906 2Ν5087 7915
I have those IC's
LM324N TL072 TL082 RC4558 UA741 LF353
LM386 NE555 NE556 PT2399
And I have those diodes
1n4148 1n4733A 1N5231B 1N5404 1N4728A 1N4742A 1N5817 1N5819 1N4001 1N4002 1N4004 1N4007 bzx 15V
(yeah some are tottaly useless for this application but you never know
)I have one of those old RadioShack phono preamp‘s. Maybe I can take it apart and take some pictures in some readings of it and find the schematics of it for you. I did open it up one time and it looked like a pretty simple layout and very minimal on the parts. And the sound is pretty decent hour one of these. I would have had a few of these and over the years some would develop a ground loop problem that I’m sure it could be fixed very easily as these are very minimal in parts. They don’t use a wall wart , if my memory serves me right. But I will find the one I have and take some pictures of the inside and see if that something that you could use ,and possibly acquire the parts for
If you replace the 330 uf cap with 220 uf, you might miss a little bass. 470 uf it might be a bit excessive.
560k resistor series a 47k resistor is pretty close to 560k.
4.7 nf parallel a 1 nf is pretty close to 5.6 nf.
1.5 nf parallal a 100 pf is 1.6 nf
Your 2.2 @ 50 v caps should be fine with a 24 v or 30 v power supply. Or less, even +12 or +9.
BTW you only need +-3 volts for a RIAA preamp going into an amp with 2 vac sensitivity for full volume. Op amps won't go closer than a volt or two to the rail, so I am splitting +18 race car transformer into +-8 v with two zener diodes to power my RIAA mixer. That gives me enough headroom to accept a 5 vac radio earphone output in the mix. +24 into +-12 is also doable. Look for wall transformers for old hedge clippers or radios or whatever. I find them at Salvation Army charity resale shop for $1 or 2. You need at least 100 ma, which is way below what most of these put out. Notice at below the rated current, they put out about 40% more than the rated voltage. You do NOT want a wall device that is a switcher power supply - those don't weigh much.
The TL072 is pretty quiet, better than a 4558 at 50x gain. ST33078 or NJM2068 would be even quieter, but would need a 33 pf cap parallel the feedback network to prevent oscillation. Also 100 nf disk caps across the power supply pins within an inch of the high gain op amp. I used one 100 nf cap for two op amps, no oscillation. MC33078 or NJM2068 are $.33 to $.50 but if you ordered some they might get lost in customs.
Happy building.
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I apologize, I edited out my error after you read it.
Yes, your parts are probably 20% tolerance so if the combo comes in 10% high it is probably no worse than anything else. If you have a cap meter, probably all modern 20% parts are 18% low; that's how precisely they make them now.
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Thanks for your response. I posted a split rail schematic in the beginning of the post. Will this work combined with the preamp?
Mjf's schematic will also work with half a 5532, which is perfect for stereo. 5532 is another quiet op amp, so cheap that it is not counterfeited. Uses a little more milliamps power than the TL072.
I don't know about that rail splitter. I used 22 ohms series 1n5344 (8 v zener) series 1n5344 series 22 ohms. That was for 4 op amps, 4558 originally and now 33078. Of course 2 filter caps, 100 uf or something, in and out.
For a splitter, you could use two resistors stacked to go to the base of one 2n2222 or so, then the virtual ground would be about .7 volts off the actual middle. Collector of 2n2222 goes to a 220 ohm resistor to + or something. I think 2n3904 will work too, that's npn isn't it?
If the bottom base resistor is a little lower value, might center the output voltage a little better. Like parallel a 10k to a 1k to make 9.1 k.
Since my mixer was in a steel box, I put a 11 turn toroid (salvaged from PCAT switcher supply) ahead of the voltage splitter to keep the lightning bolt surges and A/C motor shutoff pops out. The 100 pf cap across the input of the first schematic keeps the AM radio signals from getting in.
BTW the steel box is where the green wire from the turntable gets screwed to. My RIAA mixer isn't safety grounded to the wall plug since I used a wall transformer.
I don't know about that rail splitter. I used 22 ohms series 1n5344 (8 v zener) series 1n5344 series 22 ohms. That was for 4 op amps, 4558 originally and now 33078. Of course 2 filter caps, 100 uf or something, in and out.
For a splitter, you could use two resistors stacked to go to the base of one 2n2222 or so, then the virtual ground would be about .7 volts off the actual middle. Collector of 2n2222 goes to a 220 ohm resistor to + or something. I think 2n3904 will work too, that's npn isn't it?
If the bottom base resistor is a little lower value, might center the output voltage a little better. Like parallel a 10k to a 1k to make 9.1 k.
Since my mixer was in a steel box, I put a 11 turn toroid (salvaged from PCAT switcher supply) ahead of the voltage splitter to keep the lightning bolt surges and A/C motor shutoff pops out. The 100 pf cap across the input of the first schematic keeps the AM radio signals from getting in.
BTW the steel box is where the green wire from the turntable gets screwed to. My RIAA mixer isn't safety grounded to the wall plug since I used a wall transformer.
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