diyAudio - rjm
Go Back   Home > Forums > Blogs

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Old

Which soldering station should I buy?

Posted 17th May 2013 at 08:47 AM by rjm
Updated 20th May 2013 at 06:20 AM by rjm

Thinking I should get a new soldering station.

I've had my eye on a Weller station for the longest time, but put off getting one for one reason or another.

Looking at the selection, I think the choice comes down to the two following models, or, indeed the equivalent made by another company:

WTCPT (link)

WES51 (link)

The main difference is in the WTCPT the tip temperature is fixed, but rigorously controlled, while the WES51 has user adjustable power but the tip temperature is left unregulated.

I'm leaning towards the WES51 as being slightly more in line with my own style of work: I'm more likely to want higher or lower temperatures depending on the job at hand than I am to require "700F" exactly.

Update 1.

A little concerned the WES51 is only 50W max. That's less than the maximum I use now for the tough stuff.

Hakko has two models in the price...
rjm's Avatar
rjm
diyAudio Member
Posted in Uncategorized
Views 653 Comments 6 rjm is offline
Old

Audacity sucks.

Posted 9th May 2013 at 03:50 PM by rjm
Updated 10th May 2013 at 04:35 AM by rjm

Under windows at least, Audacity is unable to record audio at bitrates above 16 bit.

It will seem to, all right, but the data is quantized at 16 bit (30 microvolt LSB), regardless of the settings chosen.

The attached images show the same source, the first recording is made in Audacity, supposedly 24 bit, but actually only 16 bit, while the second is recorded with a program than actually supports 24 bit, exported, and imported into Audacity. The data is amplified +70dB in both cases to make the difference visible.

Audacity will happily manipulate and save high bit rate data, but as a result of licensing restrictions and on account of it being freeware, it does not support the actual recording of this data.

***

Any internet search will confirm that the Windows version of Audacity is limited to 16 bit recording. And yes, it's more of a limitation of Windows than it is of Audacity. My irritation, however, is chiefly with Audacity...
Attached Thumbnails
Click image for larger version

Name:	16bitLSB.png
Views:	135
Size:	102.3 KB
ID:	987   Click image for larger version

Name:	24bitLSB.png
Views:	163
Size:	55.0 KB
ID:	988  
rjm's Avatar
rjm
diyAudio Member
Views 542 Comments 0 rjm is offline
Old

J-Mo Mk. II vs. Szekeres, distortion comparison

Posted 3rd May 2013 at 09:24 AM by rjm
Updated 6th May 2013 at 12:52 AM by rjm

Two headphone amplifiers sharing the same basic MOSFET source follower output stage.

When the source current and source resistance are optimized for the given headphone load and similar maximum output power (~50 mW at 1% THD), the distortion pattern vs. output power is remarkably similar.

One plot below is simulation, the other measurements. The J-Mo 2 simulation closely matched the actual measurements, it wasn't worth my while to generate a full simulated data set when I already had the measurements on hand. No reason to suspect that the Szekeres sim is inaccurate, either.

The take home message is the distortion characteristic of a MOSFET follower is what it is, and unavoidable. Take it or leave it, as it were. However - and this is key - if you don't optimize the stage for the headphone impedance, the distortion for a given output power will increase significantly.

As an aside: Greg did his homework with the original circuit....
Attached Thumbnails
Click image for larger version

Name:	szekeres THD sim.png
Views:	210
Size:	27.4 KB
ID:	980   Click image for larger version

Name:	jmo2 thd sim.png
Views:	238
Size:	32.1 KB
ID:	981   Click image for larger version

Name:	IMGP6429 1280.jpg
Views:	269
Size:	386.1 KB
ID:	982   Click image for larger version

Name:	IMGP6436 1280.jpg
Views:	339
Size:	408.4 KB
ID:	983  
rjm's Avatar
rjm
diyAudio Member
Views 742 Comments 0 rjm is offline
Old

Szekeres Headphone Driver, distortion simulation

Posted 3rd May 2013 at 09:11 AM by rjm
Updated 3rd May 2013 at 09:15 AM by rjm

I've always enjoyed the sound of the Greg Szekeres' Headphone Driver (buffer) and derivatives sharing the MOSFET source follower output stage.

I've often wondered however, whether it's distinctive sound is because it is unusually free from noise and artifacts, or because its unusually prone to heavy second harmonic distortion.

It's not hard to set this up in LTSpice, but I haven't seen it done before. So, for your education and enlightenment, I present the harmonic distortion vs. output power data for the original "classic" circuit as uploaded to Headwize all those years ago. The LTSpice asc file is also included I you want to play along. The harmonic data is generated by hand, reading the FFT peaks for 10 or so different input voltages.
Attached Thumbnails
Click image for larger version

Name:	szekeres sim circuit.png
Views:	292
Size:	50.6 KB
ID:	976   Click image for larger version

Name:	szekeres THD sim 2.png
Views:	207
Size:	28.2 KB
ID:	978   Click image for larger version

Name:	szeke2.gif
Views:	536
Size:	6.0 KB
ID:	979  
Attached Files
File Type: asc Szekeres.asc (2.1 KB, 175 views)
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 823 Comments 0 rjm is offline
Old

Discrete transistor line amplifier stage mod 1

Posted 19th April 2013 at 11:24 PM by rjm
Updated 20th April 2013 at 06:04 AM by rjm

Changed the collector load on the voltage amplifier stage to a current source (Q3), as per the Marantz SR2285B circuit.

Also increased the resistance of the feedback connection, R6+R8, there seemed to be no obvious advantage in making it much smaller than the typical load (>10k). The compensation capacitor C2 is increased to match, to flatten the HF response.

The circuit can drive light loads to +20 dB. Of course that's not much of a challenge for this general class of circuit.

I'm a bit stumped as to what the next logical step is from here. Seems to me to depend on what you actually want the circuit to do.
Attached Thumbnails
Click image for larger version

Name:	RJM discrete mod1.png
Views:	736
Size:	59.2 KB
ID:	963  
Attached Files
File Type: asc RJM discrete mod1.asc (3.5 KB, 115 views)
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 769 Comments 0 rjm is offline
Old

Discrete transistor line amplifier stage

Posted 16th April 2013 at 02:18 AM by rjm
Updated 16th April 2013 at 01:23 PM by rjm

Over the last couple of years most of my interest in audio has been with transistors. I've been slowly teaching myself to read and understand the circuits.

Circuits like this one for example. Not hard, but still a bit too complicated for me to understand without the helpful wikipedia markup attached.

Instead I've looked at primarily at the schematics I have for discrete audio preamplfiers, 1970's vintage typically. Based on what I've learnt so far, I've done up a "test mule" in LTSPICE, shown below.

It's not a circuit you should build. It's for pedagogical purposes, though it does actually work reasonably well - in simulation anyway. Its just a simple starting point to observe how the different parts interact under simulation.
Attached Thumbnails
Click image for larger version

Name:	RJM discrete.png
Views:	434
Size:	93.4 KB
ID:	959  
Attached Files
File Type: asc RJM discrete.asc (3.2 KB, 112 views)
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 763 Comments 0 rjm is offline
Old

A poll. Basic electronics and DIY audio.

Posted 2nd April 2013 at 02:46 AM by rjm
Updated 4th May 2013 at 11:54 PM by rjm

It came up at the help desk, but I want to put this before diyaudio.com members generally:

I feel strongly that people who build audio equipment as a hobby should take it upon themselves to obtain a basic understanding of both the practical and theoretical aspects of electronics. Take a trip to the library and read through the first couple of chapters of electronics textbooks, that kind of thing.

It's more than just the safety aspect, I think of it as a basic necessity...

So, how many people here are familiar with the following statement?

The impedance of a capacitor is -j/([omega]C)

Familiar as dirt? Never heard of it before?
rjm's Avatar
rjm
diyAudio Member
Views 562 Comments 2 rjm is offline
Old

Preamps are not line level.

Posted 1st April 2013 at 05:57 AM by rjm

If you don't think about it too hard, you'd imagine that the signals in the phono stage would be smaller than the signals in the line level preamplifier stage that follows it. Or that the signals in the DAC/CD player would be about the same level or slightly lower than the signal in the preamplifier.

As usual, the answer is "it depends". It depends on the sensitivity of your speakers, how loud you are listening, and the voltage gain of the amplifier. It also depends on whether we are talking about a MM phono stage or low output MC.

My point is simply this: the volume control is an attenuator, and at the typical "9 o'clock" position the input signal is reduced in magnitude by about 35 dB.

That cuts it back down to being comparable to the output of a moving magnet cart, and much, much smaller than anything found in a DAC stage.

It means you absolutely, definitely, positively must spend as much effort and care...
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 560 Comments 4 rjm is offline
Old

Marantz SR2285B Receiver : Phono Stage Model Response

Posted 19th March 2013 at 07:02 AM by rjm
Updated 20th March 2013 at 02:54 AM by rjm

Mid-range 1970's stereo receiver.

I was curious to find out a) what the phono circuit was, and b) how tight the RIAA response might have been.

The answer is "four transistors" and "pretty damn good", respectively.

We are impressed. These Japanese engineers knew a thing or two. I would like to see some of these old circuits resurrected as discrete phono stages with modern components to see just what they are capable of.
Attached Thumbnails
Click image for larger version

Name:	Marantz SR2285B phono.png
Views:	731
Size:	39.9 KB
ID:	917   Click image for larger version

Name:	Marantz SR2285B ps.png
Views:	1212
Size:	52.6 KB
ID:	918   Click image for larger version

Name:	Marantz SR2285B sim2.png
Views:	867
Size:	17.9 KB
ID:	919   Click image for larger version

Name:	simluated results.png
Views:	407
Size:	32.8 KB
ID:	920  
Attached Files
File Type: zip Marantz LTSPICE.zip (1.5 KB, 95 views)
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 1189 Comments 2 rjm is offline
Old

X-reg voltage stabilizer LTSPICE file

Posted 15th March 2013 at 02:54 AM by rjm
Updated 20th March 2013 at 02:47 AM by rjm

I did up the X-reg circuit in LTSpice.

Results shown below, together with the LTSpice .asc file you can use to play around with this yourself.

First attached image shows FFT for the rectified DC (green), reference voltage (red) and X-reg output (blue) for the designed-for 10 mA output (top) and a more punishing 100 mA (bottom).

Second image shows an LTSpice screengrab for the LT1086 with bypassed adj pin under comparable loading. Input voltage in blue, output in green. This is a reasonable approximation of a "good" IC regulator.

Last image shows a plot of the exported LTSpice FFT data for the X-reg and the LT1086-12V (Cin 1000uF, Cout 100uF) both at nominal currents of 10 mA. The LT1086-12V is a reasonable substitute for a generic LM7812, i.e. a "bad" IC regulator.

A typical op amp will have sufficient PSRR to mop of the residual noise from the bypassed LT1086. The fixed LT1086-12V, on the...
Attached Thumbnails
Click image for larger version

Name:	xreg 01.png
Views:	2160
Size:	104.8 KB
ID:	910   Click image for larger version

Name:	LT1086.png
Views:	842
Size:	56.0 KB
ID:	912   Click image for larger version

Name:	Regulator Comparison.png
Views:	507
Size:	50.4 KB
ID:	914  
Attached Files
File Type: zip xreg 01.zip (1.9 KB, 151 views)
rjm's Avatar
rjm
diyAudio Member
Views 1935 Comments 2 rjm is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 08:34 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2