Replacement Power Adapter for a TC-750LC Pre-Amp

[dylan_k]

I've read that there can be improvements by upgrading the power supply for a phono pre-amp like my TCC TC-750LC.
What I'm having trouble finding, though, is the make and model number of any power supplies that can provide this improvement, or any specifications.
The power supply that came with my unit is a AD-35120200D, pictured below. It is labeled "Input: 120V AC 60Hz0.1A Output 12V DC200mA"


I've also read suggestions to look for a power supply that is linear, and regulated. These seem rare but supposedly better.

All this leads to some specific questions:

1. What is the size of the yellow tip on the barrel connector? Knowing, that, I can find another with a compatible tip.
2. What specs should I look for in a power supply that will make any improvement? The goal for this improvement is less noise, if possible.
3. Does anyone know the specific make/model of a power supply that is compatible and provides an improvement?

(I know that there are many better routes to explore for improvements, but I'd like to focus this thread on this particular route, please. Most other threads on this topic have strayed from it without any of the specifics above.)

Thanks in advance to anybody who can help me through these confusing questions.

 

[w3jn]

That looks like a linear power supply already. Does it have some heft to it, or does it weigh only a few ounces.

What "improvements" are you looking for?

 

[dylan_k]

There's really no heft to it at all.

I don't know how to tell if a power supply is linear, or regulated, but it seems those qualities are better?

My goal for this improvement is less noise, or to prevent electrical noise. That seems to be the results described by others who have done this upgrade.

 

[Sgt Shultz]

There's really no heft to it at all.

I don't know how to tell if a power supply is linear, or regulated, but it seems those qualities are better?

My goal for this improvement is less noise, or to prevent electrical noise. That seems to be the results described by others who have done this upgrade.

TCC offers an improved 500ma power supply for these, I purchased it when I purchased the preamp, have you checked their site?

I see it's now standard when you purchase the preamp.

Technolink (TEC) TC-750LC RIAA Moving Magnet (MM) Phono Preamp (Preamplifier)

 

[w3jn]

You can tell if it's a linear or switch-mode by taking an ohmmeter and putting the leads across the AC input prongs. If you see a relatively low resistance that doesn't gradually increase it's likely a linear. If you get infinite resistance or a resistance that increases as the internal capacitors charge it's likely a SMPS.

Usually a SMPS will be labeled 100-240V or the like, and also state "regulated" which is why I'm thinking this might be a linear supply.

 

[dylan_k]

have you checked their site?

I have checked their site, but I have questions 1, 2, and 3 as they pertain to that upgrade model.

You see, my pre-amp is quite old now, and there's a reference to a different barrel size on the older models. I sent them an email asking for clarification and will post to this thread with whatever findings might come from that.

From their site, this is what I can find about the "standard" and "upgraded" power supplies, offered by them.

PREMIUM High Output AC Adaptor:
- 100-240VAC 50/60Hz
- REGULATED output 12VDC, 1.5 Amps
- SMPS

STANDARD AC Adaptor:
- 100-240VAC 50/60Hz
- REGULATED output 12VDC, 500mA
- SMPS

So, yes, @w3jn it seems they are both regulated, which is a good thing from what I can tell.
How much does "linear" make any difference vs switching.SMPS? I see some conflicting takes on that.

​

 

[w3jn]

That's not what you have, though.... yours isn't regulated, and it's 12V 200 mA.

A switchmode power supply takes the incoming AC, rectifies it, and an internal pulse-width modulated oscillator running at 40-100 KHz drives a transistor which in turn drives a transformer. The voltage and current is fed back to the controller IC to maintain the 12V (or whatever voltage) and shut down in case of overcurrent.

A linear power supply has none of that. Just the AC directly feeding a transformer, and the voltage on the secondary is rectified into DC and filtered. If regulated, it's usually via a linear regulator chip such as a 7812.

A well-designed SMPS can be as quiet as a linear which is *usually* inherently quiet.... but the linear is more expensive due to the larger transformer (60 Hz needing a bigger core than 100 KHz).

Badly designed linear power supplies can be problematic as well.

 

[dylan_k]

That's not what you have, though.

I think this is becuase my pre-amp is old. Since I got mine, they started shipping it with better power supplies. (@Sgt Shultz mentioned this via the screenshot above.) So it seems that either one of the current offerings could offer some improvement over what I have now. I'm still curious to know whether those barrel plugs will even fit in to the back of mine, though.

Thank you for helping me to understand the various terms involved, @w3jn. It seems I can do without the linear aspect, if the switching models can be just as quiet, and quiet is my goal, here.

Is Jameco a good brand? I found that they have one that could work as an upgrade. It's the Jameco ReliaPro 12V 1000ma AC to DC Linear Regulated Power Supply (DDU120100H4480). This one is listed as both linear and regulated, though I still don't know if a 2.1mm x 5.5mm plug will fit into my pre-amp or not.

 

[Sgt Shultz]

I think this is becuase my pre-amp is old. Since I got mine, they started shipping it with better power supplies. (@Sgt Shultz mentioned this via the screenshot above.) So it seems that either one of the current offerings could offer some improvement over what I have now. I'm still curious to know whether those barrel plugs will even fit in to the back of mine, though.

Thank you for helping me to understand the various terms involved, @w3jn. It seems I can do without the linear aspect, if the switching models can be just as quiet, and quiet is my goal, here.

Is Jameco a good brand? I found that they have one that could work as an upgrade. It's the Jameco ReliaPro 12V 1000ma AC to DC Linear Regulated Power Supply (DDU120100H4480). This one is listed as both linear and regulated, though I still don't know if a 2.1mm x 5.5mm plug will fit into my pre-amp or not.

I purchased my first TC-750 about 6yrs ago (for one of my sons) and they offered the 500ma version as an upgrade (I purchased it), if your 750 Is newer than that then I'm thinking the upgrade supply will work.

Purchased a TC-760LC about 2yrs ago (for a budget LOMC phono pre shootout I posted here) and again purchased the 500ma supply in lieu of the 200ma, I believe you're safe getting this.

At the time of purchase I believe the upgrade was about $10, how much do they want for it alone? I should add I'm sure you could return it if it's not compatible eh.

 

[Sgt Shultz]

Ok, took some pictures and measurements, the connector is 3.5mm, do you have a means of measuring the connector on your power supply?

 

[w3jn]

Jameco is a reputable supplier but who knows who actually makes that power supply. I certainly can't give a recommendation on whether it will improve noise or not.

It doesn't seem that a 1 amp power supply is necessary when the 200 mA power supply works. This is a phono preamp that probably draws 10 mA, if that - it has all of 6 transistors in it. An extra 800 mA capacity isn't going to help with noise one way or the other.

I'm earnestly hoping you're not planning on pursuing some mods I found in the process of trying to find a picture of the inside of this thing..... I really had to laugh at this guy's claims. His work speaks for itself....

 

[dylan_k]

Holy, McGuiver, Batman! That's a lot of weird-looking zipstrips. No, I'm not looking to mod. I was just looking to understand whatever benefits there were or could be, from an upgraded power supply. If there were any, I was curious to know how/why. If there aren't any, then I guess I'm good with what I have. Thank you for helping me to learn.

FWIW I did learn the measurements of that barrel plug. For anyone looking to replace the power supply... Someone from Phonopreamps.com told me by email that the TC-750LC's power supply has an "EC 60130-10 Type E 3.4 mm OD, 1.3 mm ID, tip positive" plug. @Sgt Shultz thanks for measuring, and it seems similar to these specs. I don't have a good way to measure that inner diameter, unfortunately.

 

[Scott75s1974]

You could just rig a board in a box (or just inline with some wide shrink tubing with a filter cap on the PS you have-5000 or 10000uf would be more than enough. That would quiet it down. But I suppose there is already one in the amp box?

 

[Sgt Shultz]

Holy, McGuiver, Batman! That's a lot of weird-looking zipstrips. No, I'm not looking to mod. I was just looking to understand whatever benefits there were or could be, from an upgraded power supply. If there were any, I was curious to know how/why. If there aren't any, then I guess I'm good with what I have. Thank you for helping me to learn.

FWIW I did learn the measurements of that barrel plug. For anyone looking to replace the power supply... Someone from Phonopreamps.com told me by email that the TC-750LC's power supply has an "EC 60130-10 Type E 3.4 mm OD, 1.3 mm ID, tip positive" plug. @Sgt Shultz thanks for measuring, and it seems similar to these specs. I don't have a good way to measure that inner diameter, unfortunately.

I'm sure it's the same plug, I would look into the upgraded power supply.

I've only heard it with the upgraded but others here have heard it with both and say it's an improvement. It's not the noise floor but the headroom for the preamp is my understanding.

 

[dylan_k]

OK so I went for it. An upgraded power supply arrived today, along with a barrel adapter so that I can plug it in.

I could have just bought the one that's sold by phonopreamps (via the bay), but I opted to get a power supply with slightly better specs, just for the sake of experimenting.

I did my best at an A : B test, understanding that there is such a thing as confirmation bias. So, take this with a grain of salt, but I think it made a noticeable difference. The difference wasn't earth-shattering, but it was noticeable. The pre-amp seems a bit louder with the new power supply, and I noticed a bit more of both the low and the high notes. I tested it with my well-worn copy of Nancy Sinatra's Not the Lovin' Kind. With the upgraded power supply, I could hear the bassline better, as I mentioned, but also the pop sounds from the record's old condition showed up a little bit more. Overall, though, I think it's an improvement!

For anyone else who might have the same questions I did, about the current model of TC-750LC pre-amp, I'll put down the answers that I found.

1. What is the size of the yellow tip on the barrel connector? Knowing, that, I can find another with a compatible tip.

The barrel connector is a IEC 60130-10 Type E coaxial power connector. This type has a 3.4 mm outer diameter and a 1.3 mm inner diameter. The tip is positive. It's worth pointing out, too, that you can get adapters to convert one connector size to another, but make sure the power supply's electrical specs are correct for your particular device before doing so.

2. What specs should I look for in a power supply that will make any improvement? The goal for this improvement is less noise, if possible.

There doesn't seem to be anything 100% conclusive on this, but I did find some recommendations. I think it helps to look for something made by a reputable manufacturer, with published specifications, not just flashy-sounding descriptions. From among those specs, it's said to be helpful when the power supply is regulated. Some suggest that linear power supplies can offer some advantages, although well-made switching power supplies are probably fine, too. The specs I went with were 12V 1000ma AC to DC Linear Regulated Power Supply.

Batter power is apparently another way to go, but I couldn't find enough clear information on how to do it.

3. Does anyone know the specific make/model of a power supply that is compatible and provides an improvement?

I got a Jameco DDU120100H4480, along with an adapter, for its 2.1mm inner diameter plug to fit into the pre-amp's 1.3mm inner diameter socket. The "upgraded" supply offered by the preamp's seller would probably have worked just as well without the need for an adapter, though.

So I guess that's a wrap for this little learning exercise of mine. Thanks to everyone who helped me and I hope this proves useful or at least interesting to anyone else later on.

 

[hucklecat]

Good job @dylan_k thank you for gathering this information for other users. Can confirm that the stock power connector is 3.4x1.35mm.

You can buy "DC plug connector tip kits" at the usual online places that have adapters from standard 5.5x2.1mm to various other sizes, including 3.4x1.35mm. I used one of these to adapt a 12v 2A wall wart from my box of old power supplies, and it works well.

I know folks on other forums have experimented with higher voltage supplies, but be warned that many of the stock capacitors are only rated to 16v. Of course that can be fixed.

I have seen some pretty extreme mods attempted on this little guy. I don't think most of them are really necessary. The measured stock frequency response is modestly rising, but fairly flat. Here's what I did beyond using a higher-current power adapter:

1. Replace the first 220uF power supply smoothing cap with the biggest one you can fit comfortably. I had a 1000uF 16V that, bent over creatively, fits perfectly in the stock chassis. If you're going to re-case this guy, I think your efforts to improve the power supply filtering will be rewarded.

This SIGNIFICANTLY and measurably reduced power supply noise, which is probably the biggest problem with this preamp.

I do not think removing the reverse-voltage protection diode is worth doing unless you're comprehensively rethinking the power supply, which I don't think is worth the effort here. But don't let that stop you from experimenting.

2. Remove the 1K resistors (R1) from the input and jumper those connections.

3. Depending on your input capacitance needs, you can probably remove the 220pF loading capacitors (C1) and maybe socket the 47K resistor (R2) if you want to be able to change the loading.

4. Remove/jumper the output volume pot.

5. Maybe think about replacing the input and output coupling caps (C2 and C8) with something of better quality. I'm really not sure this is necessary. I've seen folks put some really expensive caps in here. If you're going to play this game, start with something reasonable like a Nichicon Muse.