TT Power Supplies

[Richard]

My deck's a Thorens with the later (c 1985 on) 16v AC motor as opposed to the 110v one.

Project use a similar 16v AC supply, and also offer 2 upgrade "speedbox"s instead of the AC TX. These put out synthesised AC. I tried the cheaper one (£75). Checking into the purely resistive load of a scope agreed with their pics on the box and confirmed voltage was fine. Their supplied TX (also 16v) gave a rough sine wave with a wiggle on the straights and clipped peaks. The synthesised output looked perfectly smooth sinewave.

On listening (with the Thorens) it sounded poor. Shrunken soundstage, closed in, dull. I swapped back to the TX, and swapped record tracks, but, despite wanting it to be better, there was no doubt - worse. Fortunately the shop had agreed I could take it on trial or return and refunded no problem. (I should say here that Project don't sell the box to work with Thorens and the results may be different with their own decks.)

I couldn't figure out why though. Maybe it didn't have enough power for the Thorens or maybe the amp output (for that's what it is) doesn't drive as well as a TX into a reactive motor load.

A week later, clearing a room, I found a Scalextric wall wart C912. After the initial excitement of thinking I could set up the track again I looked at the voltage and saw 16v AC at a huge 800mA . This thing is 4 times the size of the Thorens unit and even has the right plug so I had to give it a go.

Scoping confirmed voltage was fine and the sine wave was identical to the Thorens unit. (Strange that, as the Project supply TX had a worse sine wave.) Anyway, on listening, it is better than the standard Thorens unit. Not as much better as the Project was poor, but definitely clearer and more powerful sounding.

Searching the web I found that Thorens do/did their own improved supply for these decks, the TPN2000,

"The ideal power supply for all Thorens record players running on 15 - 18 Volt A/C (not the 800 Series).The transformation of a mains voltage supply (110…230V A/C) down to a smaller voltage (15…18V A/C) always generates phase shifts which in turn are the cause of increased vibration and wow and flutter in any low-voltage motors that are synchronised by the mains A/C. And, if a power transformer has to operate under a strong load, those phase shifts are even augmented. Although a well-dimensioned power transformer (e.g. torroidal transformers) can minimize phase shifts, they can not be totally eliminated. This is why the TPN 2000 comes with a massive power transformer (switchable to 100V, 115V, 230V and 240V) plus an isolation transformer, which is able to eliminate nearly all phase shifts. In addition, this combination makes an extremely effective mains filter! Many listening tests have confirmed the effectiveness of isolation transformers as part of an audio chain as the results are, generally, clearly audible.The TPN 2000 also features a phase switch on its rear panel, which can be used to determine the optimal electrical phase of the mains supply within your hi-fi system."

Quite pricey though and I've not found one for sale yet. Interesting that it's a couple of TXs rather than synthesised AC. OK, the Thorens has a mechanical speedchange whereas some of the Project attraction is for their users with manual speedchange.

The blurb suggests a better TX gives an improvement though and that certainly seems to be the case. I suspect it could be done using an amplifier but it may be very costly to do well for sound quality reason alone.

So, more knowledge and one very cheap upgrade gained