Feb 3, 2019 13:09:04 GMT 12 beeman said:

Graham - could this suit our next potential build?

Errr, yeah, naah.

Correct me if I'm wrong Colin, but IMO all we need is big mutha transformer to provide the 90 - 100 volts ac that the huge synchronous motor in the Denon needs.

From memory I think the motor is 30 watts ( most turntables are about 3 watts ) and massively heavy therefore plenty of inertia. Also the 14 inch cast platter provides plenty of inertia .

We found on both the previous builds that rpm on 50 hz was spot on and rock steady, so no real need for hz/speed adjustment.

The transformers we used last time however are no longer available from Jaycar but I think I have a suitable one here salvaged from a dead Pioneer amp.

Cheers

Ok, I’ll assume it’s a Japanese version Denon set for 100v 50Hz operation.
If it’s 50Hz you can use a step down transformer with 100v output. It doesn’t need to be too big, as long as it is rated for 30w (VA in transformer speak) or more continuously. 50va should do it.
Different transformers have different amounts of transformer regulation ie, the output voltage tends to increase less proportionately with increasing input voltage, and so it tends to remain at the same voltage. In this case 100v. But with a transformer that has a high amount of regulation the AC waveform tends to become more distorted at the peaks of the sinusoidal waveform that the mains is meant to be. For a shaded pole motor like the Garrard and Denon that means the power output is still varying despite the tendency for less varying output voltage, and that means....ta da, more vibration and similar flutter! You can see how the mains voltage flutters and wows on an oscilloscope, with the scope input displaying the mains waveform (safely via an isolation transformer!!!) and the trigger input connected to a quartz stabilised 50Hz source. In Nelson when I was there it fluttered quite a bit, one of the reasons why I wanted a 50Hz power supply box that runs my 301 motor with lower distortion on the waveform.
My Garrard 301 draws about 11w at the reduced voltage I run it on, 200v rather than 230v. In the 100v Denon that would be about 87v. I run it on lower voltage to reduce the vibration coming off the motor. Having it run on synthesised AC means the flutter reduces over running it on the mains, and to me it sounds more calm with better soundstaging.
In the big Denon, the platter’s larger inertia might smooth out the flutter from the mains better than the Garrard. As the motor in the Denon looks like a shaded pole type like in the Garrard, only bigger, reducing the voltage to it might slow it down a little and so you might need to run it at increased frequency, say 51 to 53Hz to compensate (the speed needs to be measured).
I designed the DDS-1 to run 12w max, but the low voltage synthesised 50Hz generator in it could be the basis for a more powerful version capable of over 30w, at increased size and cost. I’d still make the frequency adjustable so that it can be increased to get the right speed with its intentionally designed-in output voltage reduction.
Hope this helps!

AMR-iFi R&D

Ah So. I concede to your superior knowledge and experience .
Maybe one of your PSU would be an upgrade for Beemans Denon.
Yes they were designed originally for Japans 100 volts 50 hz mains power supply.
I did find reducing the transformers output to 90 volts ( with a huge dropping resistor ) seemed to result in quieter operation with no drop in rpm.
Cheers

In the 90s I used to run my 301 through a 25w incandescent light bulb to reduce the voltage to the motor. It’s better than a resistor as it has non-ohmic resistance which helps regulate the power to the motor. It glowed dimly. On the 100v Denon you’d use a higher wattage globe, 75w to 200w (230v rated globe) or so incandescent light bulb to reduce the voltage to it from 100v. Actually you could even use a 230v globe to reduce the voltage from 230v to 90v across the Denon without using a transformer. You’d need to experiment with which wattage bulb would achieve that. (Safely!) The globe will glow softly like it has been dimmed.
But synthesised AC power is still better to reduce the flutter.

AMR-iFi R&D

colinf can you tell me more about the DDS2?

Difference to DDS1, benefits, ease of installation?

Sure, the DDS-1 was my first attempt at a variable-frequency power supply for the 301/401. At that time I used the MCU chip to do everything…control the display, read the buttons and generate the digital sinewave all in sequence. Which made changing the speed a little quirky, but once set it worked ok. In the DDS-2 I made the digital sinewave generator separate so the MCU could concentrate on the display and reading the buttons, and send code to the sinewave generator for the correct accumulator calculation. Also the digital resolution is better, 10 bit vs 8 bit. So speed change was seamless. Also a change to a switchmode power supply with an even more stable output voltage, which makes it possible to use anywhere in the world. After experimenting with his 401s, Peter at Reference Audio asked me to see if I could increase the range of frequency, limited to 62Hz in the DDS-1, to allow the use of no pulley on the motor. That meant operation around 67Hz for 33 and 88Hz for 45, so I increased the range from 42Hz to 100Hz. That allows you to run 60Hz turntables as well. And I managed to fit everything into a slightly larger box than the 2 smaller box DDS-1. The new box also has heatsinking for the amplifier module, which I found to be running a little too warm on the DDS-1. Also provision on the circuit board for torque adjustment by setting the output voltage.
Phew! I have done a bit to it haven’t I!
The first version also used a switch on the 301 speed lever shaft so that when you turn it to 45 you could set the frequency independently of that needed for 33. But it was a fiddle to install so I did away with that and now it just has a standard Aus/NZ socket on the back to plug the motor into.
To install it on the 401, the 401 has a strobe which will indicate the wrong frequency when not run independently from a 50Hz source, so you need to either remove the neon bulb or separate out the wiring and have it run from the mains 50Hz.
Oh yes…and a change to LCD display instead of Oled like the ‘1. That’s to prevent screen-burn that the oled display was prone to. 

AMR-iFi R&D

You can also change the display colour from green (pictured) to blue or red (Peter says it’s orange!) or turn the display off while listening.

AMR-iFi R&D

Hi Colin - and what does "allow the use of no pulley on the motor" mean in a 401 context - I didn't think it had a pulley. Thanks.

Ok - I know it as a capstan - but see it is described online as the motor pulley. Should have googled first...

The motor shaft has a stepped pulley (or capstan? I never know the correct term for it!) attached to it with grub screws for the different speeds. By removing it the diameter is less and to get the same speed at 33 as with the pulley on, the motor needs to run at 67Hz or so. The spindle itself is machined to a closer tolerance than the pulley so there can be less flutter. Removing the eddy current brake disc also results in less vibration and flutter, and having the motor run at higher speed makes it more efficient, so you can use less power to run it, as well as the lower gearing that lets you reduce the power to the motor a little bit more to reduce vibration even further.

AMR-iFi R&D