Need a good Phono pre:

[Dmeister]

Hello everyone. I need a MM phono preamp, because the one on my amp is horrible, and I can't stand it anymore. I was thinking of making it myself, since I've got two transformers that I think could be used for the power supply (I don't want to buy a new transformer). One has a 12V 4,2A secondary, and the other has a 9V 1A secondary. Can anyone please recommend me a schematic ? Thanks.

Regards, David.

[kevinkr]

Look for anything by Salas..

[Dmeister]

Originally Posted by kevinkr

Look for anything by Salas..

I have no idea who, or what, Salas is . Could you give me some schematics/links ?

EDIT: I see, he's a member here. I saw his schematic but it requires 40V, which I don't think any of my transformers could supply.

[indianajo]

You can split the 12V supply with two 5.1V zener diodes to make a fake signal ground, then build any op amp circuit. Here is a hum elimination tip - put the power transformer in a different steel box than the op amps, RCA jacks and volume pots. Lots of mixer schematics on analog source here. Here is one diy dj mixer I think MM is the common type of phono cartridge, isn't it? I've got a shure M97 era Iv cartridge.
I found a herald disco mixer with great slide pots and a nice steel box, and ****y 4558 op amps inside. I improved the bypassing, including putting ceramic caps on the power supplies and op amp sockets, and got really good results with cheap old 33078 op amps. I understand LM4560's are even better. JRC4560's (differnet part, also sold by TI as RC4560) works the same as the 33078 to my ear.
+-5.1 power supply, vs +-15 v power supply, is a non- issue to me. I'm using an 18V slot car wall transformer to make +- 8.1 VDC, but that is because I have an FM radio input (off the earphone jack) that hisses too much if I make the FM put out less than 5 VAC. I have the radio, phono, CD all inputs to the mixer, and turning down the slider doesn't make the slight noise any less- so I am really happy with it. I put the classy but hot tube PAS2 preamp back in the attic.

[dangus]

Hagerman Technology LLC: Bugle Opamp Moving Magnet Budget Phonostage DIY Kit is supposed to be good. The schematic is there if you want to build from scratch; you can also buy just the PC board. I've sometimes seen kits on eBay.

I intend to build a copy of the UREI 1622 phono preamp card. The schematic can be found easily, and there's some pictures of the original cards that make the layout clear. It originally used the TL084, but it would be interesting to try the TL074, or build a card with two dual opamps instead which would allow even more choice.

[Dmeister]

Originally Posted by dangus

Hagerman Technology LLC: Bugle Opamp Moving Magnet Budget Phonostage DIY Kit is supposed to be good. The schematic is there if you want to build from scratch; you can also buy just the PC board. I've sometimes seen kits on eBay.

I intend to build a copy of the UREI 1622 phono preamp card. The schematic can be found easily, and there's some pictures of the original cards that make the layout clear. It originally used the TL084, but it would be interesting to try the TL074, or build a card with two dual opamps instead which would allow even more choice.

I can't find the schematics for the UREI 1622, but the Bugle project seems quite good. Although, I have a problem. The power supply requires -9V and +9V and my transformers only have one secondary. What can be done ? I'm 15, and still somewhat of a beginner, please keep that in mind. Thank you

[vgeorge]

Originally Posted by Dmeister

I have no idea who, or what, Salas is . Could you give me some schematics/links ?

EDIT: I see, he's a member here. I saw his schematic but it requires 40V, which I don't think any of my transformers could supply.

His 43dB MM schematic needs +28V. It wouldn' t hurt to have a better look at the pdf here: Simplistic NJFET RIAA

[quadtech]

Originally Posted by Dmeister

I can't find the schematics for the UREI 1622, but the Bugle project seems quite good. Although, I have a problem. The power supply requires -9V and +9V and my transformers only have one secondary. What can be done ? I'm 15, and still somewhat of a beginner, please keep that in mind. Thank you

You can go with a couple of 9V batteries, or 12V lantern style
batteries, and in fact, will benefit the sonics.

[Dmeister]

Originally Posted by quadtech

You can go with a couple of 9V batteries, or 12V lantern style
batteries, and in fact, will benefit the sonics.

Okay, I could use two batteries, it's the simplest solution, but the circuit needs -9V and ground. Should I just use signal ground as the ground ?

[indianajo]

Batteries are so stone age, particularly used for a mm cartridge mounted on a turntable plugged in the wall. Have been listening all day to a mm cartridge driving op amps powered by a single winding transformer. (no center tap) Driving my ST70 tube amp and my SP2XT speakers, oddly enough.
If your transformer is 12 vAC, get a bridge rectifier and a 15 V-up to 100V electrolytic cap, 500-5000 uf, make a simple DC supply. Plus of rectifier to cap plus, minus of rectifier to cap minus, two transformer secondary windings to the AC terminals of the rectifier. Be cool put a fuse on the input for the transformer (unless it is a wall transformer). If your wall transformer is DC out, forget the bridge rectifier, just hook the + and - of the cord to the + and - of the filter cap. A .1 uf 25 V or above ceramic cap in parallel (one to each lead) with the electrolytic cap is cool (for pop elimination). I get my wall transformers for $1 in a grocery cart at the Salvation Army resale shop. My mixer runs on a slot car transformer, 18 VDC. Watch buying non-transformer supplies, they may be fine for printers but squeal into hifi circuits.
Measure the open circuit voltage Vo from + to - of the cap. Buy two 1N4733 zeners, 5.1 V 1.3 W. Solder the band of one to the unband of the other. The middle point is the signal ground of the op amps and the ring of the RCA jacks in and out. You want about 200 ma (milliamp) through these to keep under the 1.3 W rating, so Vo-10.2v/0.2amp=2*R in ohms. The resistance that you get, put one between the unband end of the two zeners to minus of the DC filter cap. Put another resistor between the line of the two zeners to the plus of the DC filter cap. Op amp plus goes to the line end of the two zeners, op amp minus goes to the unline end of the two zeners. If you use more op amps than draw 100 ma, then use higher power zener diodes and smaller resistor. I'm using 4 ea 33078 op amps and 5 W zeners, and 22 ohm resistors, in my disco mixer. Like I say, having a wall transformer 6' away from the steel box with the op amps in it keeps the hum down.
If you are hung up on the word "mixer" a 1 input preamp is a mixer with only one input op amp, not more than one.
Datasheets on op amps are at datasheetcatalog.com. I like 8 pin DIP op amps, you can get the sockets and drill holes for them on a piece of lexan or something. When I'm not reworking an existing mixer or something, I drill holes for the resistors and pots in the op amp circuit and solder them together. Don't forget bypass .1 disk caps on the op amp socket back between +v and -V if you use anything faster than a 4558. Lots of band & disco mixers use 4558's, they hiss to much for me listening to hifi sources with any more high frequencies than a guitar. I find the 101 and 741 op amps sold in kits by various vendors to be pathetic attempts to get your money- those are the reason so many people built fet or bjt transistor preamps with 80-100 parts. 33078, 2068, tl072, rc4560 make very good hifi, maybe even NE5532, but tl072 locks up if your input pops (from the light switch) so I don't use it.