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Marantz discrete op amp (line stage or headphone amp)

Posted 10th November 2013 at 11:00 AM by rjm
Updated 10th November 2013 at 01:11 PM by rjm

Last one for today.

I was having problems getting this to work, the key seems to be adjusting R6 to null the voltage offset. Works fine now, but this is just a rough reverse engineer of the diagram, the parts values and the type of transistors are essentially placeholders.

The input jFET is shown as a dual package. The output bias current is most likely much lower than the 100 mA I configured, so the class A output power is proportionately smaller. For the rest of the currents and the types of transistors used, your guess is as good as mine.

edit: R7 should most likely be closer to 47 ohms, while another 5p capacitor should go in parallel with the feedback resistor, R17.
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Old

The Pentamond

Posted 10th November 2013 at 05:17 AM by rjm

A rainy and cold afternoon here in Kyoto. The mind turns to audio circuits... headphone amplifiers... diamond buffers...

This is an answer to the question of how you scale up the basic diamond buffer circuit to higher output currents without making any modifications to the driving transistor pair.

You just add more outputs in parallel.

It seems to work pretty well under simulation.
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Old

Another diamond buffer variant

Posted 9th November 2013 at 11:42 PM by rjm

Browsing through an old issue of MJ (No. 1076), I found some sketches of the Marantz SA 11S3 SACD player analog circuitry which seemed interesting.

The are two discrete op amp "modules", one is used for the I/V converter and low pass filter, the other design is applied to both the line output and headphone outputs.

The parts and values are not given, so the circuit below is just a working mock up in LTSpice based on the published diagrams.

The output stage from the headphone / line driver op amp is attached below. There's a JFET input and BJT gain stage as well, and the whole thing is wrapped up in a feedback loop. The buffer itself, being unity gain, works just fine as a standalone circuit element.
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Old

PIC Microcontroller as a potential DSP / DDS Element

Posted 3rd November 2013 at 02:29 AM by googlyone
Updated 3rd November 2013 at 02:31 AM by googlyone

I noted that the new PIC32 series micro controllers include I2S along with the SPI interface. Well at least a few in the range do. This got me to thinking:
- A 32 bit micro using a fairly efficient RISC architecture
- With I2S in and out
- That runs at 80MHz.

I chose the PIC32MX450F256H.

Surely to god I can do something fun with this. But what?

Ultimately I will try chucking some IIR filters in here to see how they go (there is heaps of processing time available). But in the first instance I want to do a DDS. Reason being that I have more active crossovers than I have speakers (and that is saying something! - ask my long suffering wife!).

One thing that I have been on the look out for is a decent DDS synthesister for audio band that has really low distortion. My current Audio synthesiser uses the AD9952 DDS chip. OK, this runs at 400MHz, but it does use a 14bit DAC, and can be run right down into the...
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Old

Ironamp Project Video Posted

Posted 1st November 2013 at 12:56 AM by Michael Rothacher
Updated 2nd November 2013 at 05:52 PM by Michael Rothacher

Ironamp project video posted here:

https://www.youtube.com/watch?v=FZymAeaVsAg

I hope you enjoy it.

I updated the captions if you want to try Youtube's translation option - should be funny
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Old

Jig to help soldering SMD components

Posted 31st October 2013 at 10:12 PM by tauro0221

Hi,
I was searching for a jig that to help me soldering SMD components to the board but unsuccessfully was unable to find one. Specially when your are an older person with checking hands like me. So I decided if you do not find it built it. Checking my junk box found some parts that allowed me to came out with this SMD holding down jig. It worked so good for me that I decided to share it with the diyAudio members.

To fabricate it I used a 1 x 8 inches aluminum strip and bent it like a square with one leg side cut out. Drilled a hole at the end of one of the leg and installed a 2 inches screw thru the hole and used one spring and holding it with a nut to applied pressure from the tip of the screw to the other side leg of the square. I think that a picture it is better than words specially when you are not a technical writer like me.
Attached it is a picture showing the final SMD soldering holding jig.
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Old

TI marches steadily down the road to oblivion

Posted 23rd October 2013 at 12:20 AM by abraxalito

But hey, its stock is 30% up on the year!

http://www.testosteronepit.com/home/...verpriced.html

Wolf is a little bit too polite in his analysis of TI's woes - #1 is crappy strategic thinking.
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Old

Prototype stereo balanced passive filter for Ozone

Posted 14th October 2013 at 06:57 AM by abraxalito
Updated 27th November 2013 at 01:42 AM by abraxalito

Here's my first stab at an affordable yet screened passive filter using off-the-shelf inductors. Its a 17th order quasi-Chebyshev using 8 equal valued series L and 9 shunt caps achieving slightly better than 50dB rejection at 24.1kHz.

Update - this might be the first and last filter I build with these Coilcraft inductors. (If anyone's interested, the part no. is LPS6235-335). Reason being - on trying to order more, the price got hiked more than 100%. Originally these were attractive because on Taobao there was a source selling well below the manufacturer's list, but that seems to have dried up. At the list price in USD, there are other alternatives potentially better value. However none with the same inductance (3.3mH). The key feature is the Q - the Coilcrafts have a Q around 40 at 20kHz - this is very hard to beat in such a small package. As a reference, my pot-core hand-wound inductors have a Q about 160 but they're huge in comparison, so these tiny inductors are actually...
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Old

Wharfedale Dovedale cone rubber repair

Posted 10th October 2013 at 11:28 PM by hbc

After the Magisters went I started missing them. Much irrational thought later I decided that I needed some Dovedales. It may be some left over residual memory of some super 8s I had when I was young, they were very nice despite the lack of tweeter (retrospective young thought). The big Dovedale woofers look similar with the green felt, bit nervous of those strange pink domes though... Anyway, eventually "won" some with mint drivers slightly tatty boxes. Long story short the rubber had got stiff, but not yet brittle.

Sulk, got the Magnums... (must have bass now). After much research and thought, the Dovedales don't seem to be a standard size for foam, and I had got to the point of contemplating cutting away some of the cone to fit a flat foam. I was tidying up the garden when I found a 700 inner tube I had changed recently.
At this point I thought what have I got to loose, so gave it a good wash, (lots of washing up liquid applied neat), chopped out the valve...
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