luvdunhill

What Are You Building Today

173 posts in this topic

Had a pupil once that suggested mV stands for miniVolt. Cute isn’t?

Anyhow - this is what I’ve done today:

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Current in mA – milliampere.

Regarding Watt.  You know what Miniwatt is?

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Regarding Watt.  You know what Miniwatt is?


A vacuum tube?

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11 hours ago, JoaMat said:

Regarding Watt.  You know what Miniwatt is?

The opposite of a Hiwatt?

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A really small riot in the LA area.

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16 hours ago, JoaMat said:

Regarding Watt.  You know what Miniwatt is?

I have some Philip Miniwatt tubes.

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On 17/02/2017 at 8:21 AM, JoaMat said:

(snip)

Regarding Watt.  You know what Miniwatt is?

Watt....?

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Just a few more holes here and there - need a fuse holder on the rear panel, then four PCB mounting screws and the transformer - hoping to get the mechanical stuff done during the three-day weekend!

1707b31dc3a0e188bfedf7909354c30b.jpg

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What, no 78?

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Thats the middle setting 78 = 45 + 33?

Not really.

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8 minutes ago, luvdunhill said:

Just a few more holes here and there - need a fuse holder on the rear panel, then four PCB mounting screws and the transformer - hoping to get the mechanical stuff done during the three-day weekend!

1707b31dc3a0e188bfedf7909354c30b.jpg

Why not follow the high-end audio industry practice and just use duck tape. They supposed to sound better that way! 

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Ok, added holes and screws. Next need to make a cable, perform some turntable modifications and then the software side of the project.

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On 10/19/2016 at 11:13 PM, luvdunhill said:

A small discrete buffer - prototypes have been created, will fire them up tomorrow.

b855f1b2e52508c90f201d9d767900c9.jpg

 

On 10/20/2016 at 11:27 AM, luvdunhill said:

 


Perhaps something like this?

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What connectors are you using in the top pic (buffers), and what are they plugging into in the bottom pic? Bottom pic looks kinda like a torpedo amp, though it isn't.

1 hour ago, luvdunhill said:

Ok, added holes and screws. Next need to make a cable, perform some turntable modifications and then the software side of the project.

9d78369d0795e39c85405e02cfc20cb6.jpg

870228c3a5d01a8141d6ef4a3656917c.jpg

 

I see the micro hanging on the USB port... what is this and the software for? Cool project? What kind of TT?

 

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I made this. It is a usb dac with a headphone driver built in. I made it as I was tired of having lots of boxes and cables all over my desk. Obviously it still needs a case.

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Chris, those parts are made by FCI. Search for BergStik. They are rather nice board to board connectors.

 

Actually, what is hanging on the USB is a cheap USB serial uart bridge, based on the CP210x. You can get them on eBay for a few dollars. It makes for a nice multiplatform software option, as you can get Mac, Linux and even .NET support. There is a three wire connection to an Atmel microprocessor.

 

Well, now I can change he phase of the outputs via software.

 

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To

 

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Now the question is how to convert a frequency of the output sine wave to rotational frequency of the platter. That seems to need some maths.

 

Oh and here is the four pin DIN cable that has way more parts to assemble then it needs. It's kinda nice spring loaded mechanism when it's all said and done. It will interface directly with the connector on my Rega turntable. Crazy Brits.

 

faa2302da0f33ddf6f4a847ad418b421.jpg

 

 

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Ahh, so that's what the software is for... now onto the maths! Very cool!

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For my Parasound. Getting it to bias was like resistor sudoku.

3zd4jaW.png

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What I/V stage is that?


Sent from my iPhone using Tapatalk

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Blue IVY?

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It's my own, but very similar to @cetoole's. It's a folded cascode, with differential filtering and a discrete Sallen-Key filter. Trimmers instead of an op amp servo, and a nickel sandwich on the output.

Using some nice TO220 parts that let me bias it very hot.

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Cool (or rather, hot?)! What DAC did you put this in and how does it sound? Any reason going discrete for the Sallen-Key? Also, thoughts on 3rd order GIC filter like in the pcm1704 datasheet? Most DACs seem to stick with the standard SK opamp

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It's going into a Parasound D/AC 1600. It's still a work in progress-- I needed to replace the DAC power supplies because the stock ones were remarkably derpy. Pulling the I/V stage causes the regulator output voltage to go up. I put in some shunt regs and ripped out approximately a million bypass caps that were to far from the load to do anything.

tGewsgg.png

 

I don't like GICs/FDNRs. That's what the Parasound had. The big problem I see is that the op amps don't have sufficient gain at frequencies that we care about (352.8KHz and multiples) to actually work. The PCM1702 specs this fellow, which has just 30dB of gain that rolls off very quickly at 300KHz+. Not only is the impedance driving the shunt op amps going to be sort of high, it will also change with frequency.

I like Sallen-Key filters because they can be built around an emitter/source follower. Those are much more dependable. By cascading it with an RC pole, you can build a third order filter with just a current sink and a BJT as active devices, and it seems to work well into the lower MHz without doing anything weird.

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I agree with the SK approach!

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Milled a couple of small board 0.8 x 1.15 in. Put a cheap USB microscope on CNC machine.

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Easy to move microscope over the board. Took this picture, optical magnification x40.

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