TC-750 Phono Pre-Amp (Continued)

Pardon a noob question, but after I thought I had finished all the mods, I realized that I haven't bypassed the diode. I not sure how to do that, can I just rip it out? I have listened to it and it sounds much better than my mani already. Is bypassing the diode going to make it sound even better, or is there some other reason for it?

 

Does it look that bad?

 

Hi,
I designed and built a 18V near-zero-noise psu. 2x9V battery and a capacitance multiplier. If anyone can help how to upload the pictures here (now I can only insert hyperlinks). Thanks in advance.

 

The photos are:
https://pasteboard.co/J2SMYo5.jpg

 

18V Zero Noise PSU for TC-750 RIAA preamp

Here is the schematic:
https://pasteboard.co/J31WDFE.jpg

Operation:
The two 9V battery in series creates 18V. The ON/OFF switch is in the + side. A 2200uF cap improves the dynamic behavior and shunts the battery internal noise. Next stage is the capacitance multiplier with one NPN transistor. It reduces noise and makes the output impedance low and constant in the frequency range. The 1N4007 diode protects the transistor from reverse voltage (it is connected in "normally closed" direction). Finally there is a 4,7uF cap for stability.
Suitable transistor is NPN, can handle 100mA or more and has hFE 350 or more. BC337-40 is cheap and very good for this purpose - it has low Vce_sat, also.

Build
I placed the components to a pcb board just the same way as on the schematic. Dont forget the switch. If there is a risk of short, use a fuse holder and a fuse (100mA, slow), before the switch. The 2200uF cap is also glued to its position, not just soldered (see photo).
Output voltage is about 0,65V lower than the double batteries has.

There are some 18V cordless tools - that rechargeable batteries can be used, too.

Good luck and enjoy the music! Please share your experiences.

 

Hey! I did the Sola psu but I have a 12v 3a gell cell from a security panel that I am looking at hooking up. I bought a step down converter to charge the battery. I'm wondering how long it will last, and how far below 12v it can get before the unit doesn't have enough power.
I'm thinking about sticking the 750 in a chassis with the battery and a panel mounted battery meter, but I'm not sure if that will just be wasted juice to run the screen.

 

Hi Folks,
Just looking for a bit of clarification on this - I have done this TC-750 mod. My TC-750 also came with version 3.0 of the PCB - the output caps were 10uf and the input caps were 4.7uf. I replaced the output caps with Jantzen 10uf and the input caps with Jantzen 3.9uf caps. All is good, but I notice from this post and some other photos posted in this thread that some people seem to be replacing the input caps with the 10uf caps, and the output with the lower value caps. Has that worked better for this mod?

Thanks in advance.

 

Thanks for the quick answer. I also have a very low level hum on the left channel (even with no turntable hookup). Can't hear it with a record playing and doesn't impact much other than it becomes my total focus because it isn't dead quiet.

In one of the posts you mentioned that you had a bit of a hum and were going to remove the 1k resistor to see if that made a difference. Did that solve the problem?

Thanks again.

 

I was coming here to see if people still felt 750 with mods was better than Mani and
Finally getting my vinyl back in action in our new home...I can't just have open boxes strewn about with a curious toddler but I'll be damned if this doesn't make me want to do it right and put it in a new case. Sola PSU price made me blink and I'm just not in a place where I can mess with soldering right now.

I read the last few pages of the thread but am currently debating these options:

• Buy Mani, wait until I have time to tinker, mess with TC, sell Mani
• Buy TC with upgraded adapter (from TC, not a Sola or whatever), tinker when I get around to it.

"until I have time to tinker" could be a long while. Any opinions on TC + upgraded wall-wart vs Mani?

 

I have a high output MC (Denon DL-110) so it sounds like Mani might be a safer bet.

 

Thank you all for this inspiring thread! Modded my tiny TC-750 this week into a real nice sounding phono preamp.

 

Hi all. New member here.
I recently bought a cheap TC-750 and found this thread. I was thinking of doing theese easy upgrades shown here.
I upgraded to 12v battery supply and sound improved alot. Mostly in the bass.

When i opened the unit i see alot is different in my unit. Perhaps it is newer.
I was thinking about changing caps and removing diode and the 220uF filter caps.
https://imgur.com/N5k8JeL

The Front and back of my unit looks like this:
https://imgur.com/3URRsx1
https://imgur.com/30ffp3d

I was thinking of starting with changing caps to better quality but the same values.
Any thoughts?

Best Regards, TiGgR.

 

I “needed” another phono preamp for head-amp comparisons so I did one of these mods.

• Output caps replaced with Jantzen superior 4uF
• Input caps replaced with Jantzen superior 10uF
• Input loading caps replaced with sockets so I can experiment with various values. Current installed caps are WIMA 100pF ceramic
• Bypassed diode D1
• Removed power filtering caps
• Grounded RCAs to the chassis ground

I dropped it into an aluminum box that could hold the board and the caps, extended the LED to the front of the box.

Power is a SOLAHD SLS‑12‑034T in a separate chassis. No power switch, probably should have added one but the umbilical can be removed from the back of the preamp.

After basic testing of the circuit I was holding off putting it in the system until I could run an analyser on it, I broke down today and just threw it in. Sounds good!

 

Just sighed up here due to this thread.

I picked one of these up just for the sport of it. $20 on eBay with free shipping, figured not much to lose if I don't like it.

I did pull the load capacitors as I'm using an Audio Technica cartridge and don't want any more capacitance than necessary.

I also used a decent 12v power supply that is normally used to power a Parks Budgie (a tube phono stage w/ a DC to DC built into it for the voltage required by the tubes).

My first listening impression of the TC-750 is, "where is the bass?" Nowhere near the bass of the Budgie or my Mofi StudioPhono.

NOTE THAT the unit I got has the variable gain control, I think this is the LC model? Maybe that has something to do with it?

Will removing the filter caps on the power input help in the bass department?

Why would one want to remove the power filter caps? I think mine are rated for 25v, can I use an 18v or 24v power supply just to see how that sounds, w/o having to remove those caps first? Or is 24v too close to the 25v rating of the caps?

I'm interested in learning a little as I do this, so any pointers/advice for how each of the changes may effect the sound quality would be helpful.