Before I can hook up my current turntable (A J.C. Penney/Technics MCS6206) to my Silvertone 1970A (which I added a phono input to), I will need a preamp. Are there any circuits available for a simple preamp, either tube or solid-state, which I can easily and cheaply build?

A solid state opamp design is certainly the easiest. Here's one example http://phonoclone.com/diy-pho5.html

He also has a few others, including tube, on his DIY projects page http://phonoclone.com/diy.html

Before bipolar designs became the norm, I built many stereo RIAA phono preamps for broadcast use using this simple circuit. Sounded great.

Datasheet: http://www.edutek.ltd.uk/Binaries/Datas ... /LM387.PDF

Dave

Looks simple enough, but which is the input, and which is the output? Also, it would be a stereo cable in, and a stereo cable out, plugged into a short stereo-to-mono adapter cable (since that is what I have already). How would that be wired? And would a voltage doubler work well with a 12.6 volt transformer to give me the necessary 24 volts (again, I already have a 12-volt transformer)? If so, how would I build one of those?

I know you may be anxious to build something but if you've never worked with IC's and high gain circuits before, you might want to consider this $18 unit (with free shipping) that even comes with it's own power supply. Forget what the clueless dealer says in his description: With 10K Ohms load impedance, this Pyle Phono Turntable Pre-Amp provides full power to the speakers. No...I don't think so. But you can go on line and read reviews from people who say it is just what they needed for their turntables that have magnetic cartridges.

http://www.ebay.com/itm/PYLE-PP999-PYLE ... 3cc1ade631

Dave

No doubt 'Chinese speak'.

Btw, I might add that users seem to like the Pyle but vinyl heads don't. I can't say one way or the other but opted for a slightly more expensive Behringer PP400 on my 'theater' amp. My Dual 1219 is still on the old Harman Kardon receiver.

The Behringer isn't 'audiophile' quality either but you're probably looking at $100+ in that category.

Dave,
The LM387, and the similar LM381 were great low noise amplifiers, but have been obsolete for a while now. I discovered that when I went to replenish my supply, last year. Probably the best replacement would be the LM833 dual audio opamp, which is also a very low noise design. One significant difference is that it has a different pinout.
http://www.ti.com/lit/ds/symlink/lm833-n.pdf
They still give pretty much the same circuit (slightly different component values) for the RIAA preamp.

I agree there are probably better preamps out there than the Pyle but I figured it would be a good, inexpensive solution to mate Rich's Penny's turntable with his Silvertone amp. I'm not so sure I always agree with vinyl heads, though.

Dave

Well, my turntable is not working properly right now, despite cleaning. Might be a bad capacitor in the servo circuit, from what I have been told. Meanwhile, I got a good deal on a late 1960's GE RB-410-8 4-speed changer, which I will need to build a plinth for. It has a GE ceramic cartridge in it, though I will likely change the stylus as I don't know its condition, so I won't need a preamp.

I agree the Pyle is probably a good inexpensive solution. I was just throwing out another in the same category. As for 'audiophiles', there's a lot of bead rattling and voodoo that goes on but I do give them 'some' consideration... sometimes, maybe

http://www.hagtech.com If you want to build totally from scratch, get a Hagerman Bugle half kit, which is a circuit board made up with silkscreening and a parts list and assembly instructions, etc. Costs 39$. Used to be 25, as I recall. I built one of these preamps and the performance is way good. Plus you can modify it for different gains, loads, etc. I built one once and installed in a nice box. It runs on two 9 volt batteries which is an advantage for noise and hum levels. Uses two IC chips and fairly common parts otherwise. Will beat out the "econo" phono preamps using two transistors per channel and cheap parts.

That is a nice kit and their power supply is good too as it can be stacked under the phono pre board by simply using spacers.

I am not aware of any 'econo' phono preamps that use two transistors per channel. The Pyle and Behringer are classic opamp active equalization negative feedback designs similar to what Dave posted. An interior shot of the Behringer is here http://www.audioasylum.com/audio/vinyl/messages/86/861810.html

With the Hagerman Bugle you can pick components as expensive as you like, so one would expect it could perform better, but the PCB alone is double the cost of a Pyle and assembled it's $149. It better be better.

As a side note, Pyle also makes what looks almost like a clone of the Behringer PP400, the Pyle PP444.

This is the two-transistor per channel circuit used by simple, stand-alone preamps sold by Radio Shack, MCM and many others over the years. I see them on ebay at times for around $10.00. I've used them and have even homebrewed the circuit. I found it adequate for most uses. I think the newer models use an IC though.





Dave

That resembles the old Shure M61. Yeah, I've seen "2 transistor" designs but didn't know anyone was still making a commercial version. Of course, there's also "2 tube" designs, both passive and active, and almost every RCA 'Receiving Tube' Manual inludes the classic 12AX7(7025) active RIAA preamp schematic.

The RCA passive tube design has always been my favorite. I built several in the '60's for my homebrew college radio station mixing console and they performed well. I'm not sure how it would compare to modern designs. The output impedance is very high and is only suitable for feeding a high impedance input of 220K or more. I'm aware of GE's active (feedback) design but haven't seen RCA's active circuit.





Dave

Could easily use another 12AX7 as a cathode follower for the RCA circuit which will significantly lower the output impedance. Also with a design like that it requires short cables from the output to the amp so that the cable capacitance doesn't affect the RIAA eq.

Sorry, I mixed my apples and oranges. Despite saying RCA what I had in mind was the Shure M65.

I think most of the 'text book' designs were expected to be 'in box' which, at the time, meant a 10 cu ft console

Adding a CF was exactly what I intended to do back when I was toying with the idea of a 12AX7 active RIAA preamp.
(The front end network models RIAA pre-emphasis so the output should be 'flat' and is set at 5 mV in with 500 mV out)

One of the 'criticisms' I hear of active RIAA is loop phase delay but, assuming the models are valid, this is what mine plotted out as. Top is amplitude and bottom is phase.

That slight upward amplitude slope amounts to +.06 dB at 20 KHz over 1 KHz and the 'worst' phase shift is 8 degrees at 20 Hz.

I never built it though and, so, can't say how well that translates into 'reality'.