Turntable and Phono Stage

Last month, I bid on a used Marantz TT180 turntable and I won. The seller stick the platter and tone arm with tape so that it won’t move when shipped. The idea was fail, the platter move out from where it sit and hit the cartridge. Luckly it didn’t bend the tone arm. After I clean all the mess, I turn it ON, the platter is not spinning as descripe. Some troubleshooting is needed here. I found that one mechanical switch is not working, have it fixed and it start to spin now. Ooop….! It is not build in with phono stage. How to know it will sing or not?

The simplest way is to connect to your amplifier directly and turn the volume to MAX. You will hear it sing in a very low volume. OK, fine… it sing now. What to do next? the next thing to do is to make it sing louder. In order to do this we need a phono stage which is actually just another amplifier which have high gain(40 to 50 dB). We have two type of phono stage too, solid state and valve. Which one to build? Let do a search and see what is the results.

I saw someone posted a tread “Phono stage success!”at diyaudio.com. Good.. this is what I want, a success story, although I don’t have 6DJ8 but I have 6N1P and this tube is identical to the 6DJ8. Later, I found that I don’t have the power transformer and I also don’t have time to wind one too. So the idea of building a tube base phono stage have to be scrap.

From the same website (RJM Audio) as the 6Dj8 phono stage, they also have op-amp base phono stage which is very simple. I study the circuit and found that it is very interesting. Let do a test drive, I try to build a prototype first with the thing I have. I use 1% tolerence on all the resistors. My input capacitor(cap) is 1000uf and output cap is 100uf. A cheap non-polar cap for C3. I use RS207 as my power rectifier. I buy a small budget transformer with secandary voltage of 12v-0-12v writen there 1A.

This is how the prototype look like :

Prototype

Circuit build up time is 4 hours. Interfacing for RCA and PSU is 1 hour. Hehee… Where is your Op-amp? I think the board I choose screwed me up because the drill hole is not compatible with IC lead. Never mind, it just a prototype. I put the IC under the board so I can make a spider net at it.

Testing

The testing take me about an hour. Start with the main switch on. OMG, it is as quiet as a new born baby (Huming like hell…!!!). Turn it off. Check the connection. I found that the positive and negative terminal from the rectifier was inverted. Fix it and turn it on again, alright no more huge huming but I can hear hissing. This should be the grounding problem. As you see here, Im using a plastic chasis, so because of that i try to ground the pcb to the AC ground. By doing this, the hiss sound was injected into the amp. Alright I’ll remove it. After that the hissing is gone but when the volume turn more then 9 o’clock it come back again. So what is the problem now? The turntable RCA connector come with the earth wire tangling no where. I decided to connect it to the ground cable which I remove from AC ground. Oh…hissing+huming come visit me again!, look like it was not a good idea too. Then I tangle it to the RCA input ground. Hola…! finally I successfully make the new born baby sleep.

Playback

I start to spin my Long playing(LP). Skeeter Davis album “Here is the answer”. Well…well…well… a lot more moody and “silence” compare to my compact disk(CD). This is my favorite album which I brought from local flee market.

Track Listings

Stay Tune

Althought I use no fancy components but it already sound so good and quiet. Unfortunetly, RJM Audio is not selling the pcb now. I’m planning to fabricate it. Hope fully can get a better deal.

Phono Preamp Rebuild

Yeah, It feel clean and nice now with the new pcb. No more spider netting. I change the color code for each terminal to avoid unwanted mistake. Red for positive, black for negative and green for ground.

Front view

Behind

The black binding post is use to ground the grounding terminal from the turntable. It is soldered to the RCA ground just next to it.

Adeus, meu AMIGOS…….!