301/401 power regulation

[jimangus]

Hi i have just read the article on the 301/401 and was wondering if any one has any thoughts on how to build a vairiable power supply as per the following quote.

"A major upgrade is to remove the eddy current brake completely and fit a dedicated variable frequency power supply. The problem is that there are not too many power supplies capable of supplying on 80-90 volt sine wave variable between 45 and 60 hz at a power of over 12 watts. Reducing motor voltage means the deck takes a second or so longer to reach full speed. Big deal, in practice this is just not that serious an inconvenience."

It would in practice be a major upgrade. Opposed to using the light bulb method.


Just a thought.

Jim

[NealG]

Where did that quote come from?

I've tried my own DIY PSU on my Lenco and at EFIII had a chance to try it on Greg's 401. We found (and I find the same at home) the supply sits on dynamics. Bass is lighter and lacks the impact of deck without PSU. However, at home I note better separation of fine detail vs no PSU, it was not that apparent at EFIII in the large hall. On the whole I prefer my Lenco without it.

This is not say though that you won't have better success, you may. I suspect the slight impedance a supply must introduce kills one of the main dynamic appeals of an idler deck and that is bass impact and speed.

[jimangus]

Originally Posted by NealG

Where did that quote come from?

Sorry neal, out of the useful links bit under 301/401 article posting.

So you found that a regulated power supply detracted from the sound.

Hmm some people have also comented that the light bulb method of reducing voltage also is different and not better in many ways.

I wonder as a way of testing the reduced voltage if power resistors on the power feed would be the way to go for expermental purposes. That is of cource if you can put them on mains , i'm not certain you can , can you ?

Cheers
Jim

[Greg.]

Hi Jim,

I disagree with Haden Boardman (Neal, see Useful links, 301/401 article)on this issue. I spent quite some time trying the 40W or 60W lightbulb tweak. In my experience reducing voltage, as Neal says, reduces dynamics, mainly noticable by a dulling of the authority of the sound and dulling the speed and attack on notes which is afterall the main feature that has caused many of us to convert from belt drive. Speed stability is also harder to set and maintain. If I theorise, and I'm no expert so maybe wrong, I recon to reduce the voltage reduces the torque of the motor. If the contol system is to brake the speed of the motor with the eddy brake, surely there will be better control and accuracy with less speeding or slowing of the platter as the record plays if the brake is applied when the motor generates best torque. Mark (Islandpink) built the Imbabi power supply but could not get it to produce more than 190 volts and had problems with implimentation and the White Noise PSU also had similar issues. Neal and I tend to hear music similarly and we agreed on his observation above. Clive takes the view that the eddy brake contributes to the Garrard sound and I also agree, finding it a positive feature.

Generally I agree with the rest of Haden's points in his article although I think he's being a bit pedantic on his comments about the wiring loom hanging spring. I think Garrard got alot right with this TT and personally prefer full mains on the motor and the original hard rubber mat is also best.

Best wishes,

Greg

[NealG]

Ah! OK got it.

I don't think is just the drop in voltage, I strongly suspect that adding impedance into the motor supply is the main reason for the softening of dynamics. My PSU is adjustable, it will quite happily drive my Lenco up to 255v, we had it running at 235v at EFIII with Greg's 401, the effect was the same. Lowering voltage just makes the effect worse IMHO.

I may try reconfiguring it to parallel the o/p devices to lower impedance and increase current capability but his will mean a new stepup TX...

I agree with Greg, the eddy brake is best used with the motor at full torque with the least impedance in the supply. Perhaps a suitable rated step down transformer would be a better idea if you want to experiment with lower voltages?

[Clive]

It looks like we're getting to an understanding of this but there are more questions. A psu that can supply 240V, possibly over-rated, maybe 30W might be what we need. Applying the brake seems to "steady" the motor in some way. Reducing the voltage reduces vibration but would we see the same from a steady 50Hz 240V but with better dynamics and detail?

Re the mat, I'm back to the standard 301 mat which I've glued with spray mount. It works well, so I'm with Greg on this.

Clive