DIY Audio Projects Forum

PWM fitted,

I removed the electrolytic cap it wasn't required.
The motor wires go through a ferrite bead.
The N20 motor is quite loud (to me) in operation running it with PWM is much better.
However I'll complete the project and see if its OK with the enclosure in place.
The Pot drive works but a few "alterations" are required..

Regards
M. Gregg

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What is the sound of one hand clapping?

I have been looking at the brass couplings,

Here is an experimental flexible coupling, its obvious that reinforced hose would make a good coupling but the jubilee clips you see used on the internet is just pants. So after a while I thought what about using thick transformer wire. I will look at this and see what it looks like with a small amount of metal epoxy to just cover the termination (just twist it with pliers and cut it with two twists left).

Anyway it might be of interest...I'm not a fan of the brass fixed couplings.
NB just black out any printing on the hose with a sharpie indelible pen and colour in the nylon braid on the ends.

Regards
M. Gregg

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What is the sound of one hand clapping?

I have fitted a mechanical stop,

So its not possible to over drive the volume Pot, It took a bit of filing with a needle file to get the travel to match the Pot track from end to end.
I mounted the fixed stop on the brass bush nut with JB weld, and Drilled the pulley and mounted the striker plate.
But it works.
Next is the main preamp board build on the PTFE board.

Regards

M. Gregg

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What is the sound of one hand clapping?

I have just installed the input indicator wiring.

The indicators are on a separate circuit so they are all on at low level and just show the selected input.
I just used a 1.5A T fuse but wanted to keep the facility of using Polyswitch fusing.
I found a couple of wire ended adaptors and fitted them to the fuse.


Regards
M. Gregg

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What is the sound of one hand clapping?

Would an expandable coupling work here. https://www.homedepot.com/p/Hillman-3-8 ... /204775505 Some fancy threads may be required.

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John

The main requirements of the coupling are to allow flexibility/ stop vibration and shock and a controlled twist to stop any shear forces on the control potentiometer. I have seen other flexible couplings and might have a look.
So any fixed coupling wouldn't work. If the chassis moves even slightly due to expansion then the alignment between the shaft and the Pot can move with no "give" in the drive chain that causes stress on the Pot shaft.
The motor drive is working well at the moment with enough "slip" on the drive belt to give a clutch effect so you can turn the Volume manually and still motor the Pot all the way to each end of the stop. The striker plate has to be cut to size to match the ends of the Pot track so you don't get overdrive past the end points but still get full operation. So the stop is a single point and the striker represents the gap in rotation between the two end points IE the pot isn't 360 degrees so the coupling can only be allowed to rotate as far as the Pot does. But there can be no "slip on the coupling" the coupling must always match the pot position to the coupling stop position.

So its nothing special its just the same as any positional control on a machine or CNC.
The PWM is better than a straight LM317 I can control the motor speed down to a crawl, the Velleman IR allows for toggle action or pulse so I selected the pulse which allows for a 1.5-2sec pulse that gives steps, but the pulse stops if you release the control so you have variable toggle time but a maximum of 1.5-2sec that represents about seven steps from one end of the pot travel to the other.
NB using the pulse means the dog stands on the remote it won't drive to full volume because the pulse toggle just times out.
I have loaded the TV settings etc and IR volume into a programmable handset from the velleman control fob.

It would be interesting to do proportional control with a control pot on a handset and as you turn the pot on the handset it motors the pot to mirror it but I don't have the time at the moment. There is lots that could be done with something like a Arduino but I didn't want to spend time programming.. So standard servo control would also work well the same as RC cars or planes. You could do volume, balance, bass, treble ,tilt etc.. LMAO and not use electronic control just Pots. I guess it depends on how you feel about TV set type SS tone stacks.
Its interesting that it would be just like a control desk in a mixing studio.

I should add that the shafts touch each other inside the coupling there is no air gap. So only the slightest flexibility.

Regards
M. Gregg

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What is the sound of one hand clapping?

Output capacitors just arrived.

So the next step is to fit the output clamping Zener's and 1Meg resistors to the output phono socket connections.
Then look at the heater wiring connections on the preamp board. I will look at using a couple of resistors to create a false centre across the heater terminals at the tube end of the heater ramp and attach the reference lift voltage at that point. This should lift both sides of the heater supply to give the same potential on both the + and 0V rail above Gnd. With a bit of luck this will prevent the DC heater supply from biasing the filament at either end.

I fitted the reference resistors in place of the 470K discharge resistor which gives a 120K discharge path so there was no point in using a 470K as well and saves some space.

This is the first try of Copper foil and wax that I have tried so I'll see how it goes. I have used the bees wax Jupiter's in the past and they were OK (but they melt if you don't position with care ). I also have some copper in oil Audio note from a previous build that I quite like the sound of but I'm interested in the reviews for the copper and wax.

Regards
M. Gregg

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What is the sound of one hand clapping?

I was looking at the bypass cap for the 5687 cathode resistor,

I found a couple of Black Gate caps in my parts box, I remember ripping them out after about 10 mins in a test.
I was going to use Kaisei caps but I will bite the bullet and give these a try.
It goes against the grain a bit but..

Regards
M. Gregg

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What is the sound of one hand clapping?

Main board completed,

There is a bit of tidying up and cleaning to do.
I used the Black Gates and wired in silver with Teflon insulation using Audio Note solder then terminating on the edge of the board.
I screened the input wires to the tube grids. The board is PTFE and resistors are AMRG 2W and Tantalum 1 W.
I still have reservations about the black gates I'm not a great fan and prefer Kaisei.
Still quite a lot to do but I wanted to get the main board done so I can run up the supply and see how the voltage levels are with current being drawn. It means I can look at the volume pot wiring and balance control.
The heater wires are lifted away from the board but its hard to see in the picture, the capacitors and resistors are spaced off the board with glass beads.

Regards
M. Gregg

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What is the sound of one hand clapping?

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