Go Back   Home > Forums > Blogs

Old

Radio Shack Linaeum measurements

Posted 14th March 2014 at 10:40 PM by hbc

I bought a pair of these in about '95 and modified them a bit. I blocked up the ports, stuffed them with fluff, replaced the inductor with an air cored type, and rewired with CAT5. I also removed the top cages and grills which subsequently got lost, and also removed the rubber from the woofer voice coil, and put in a phase plug fashioned from some dowel.

I lived happily with these for about 10 years, ending up with an 18" subwoofer which used an equalised bass guitar speaker. The advantage of this equalisation was a degree of cancellation between the sub and the little woofers, resulting in a very smooth lump free transition in the listening position.

I found them to be an excellent tool in the development of audio stuff, it was quite easy to discern the difference between different types of cables, for me and friends, etc etc.

I bought another pair but I was wondering if the tweeters were fried as they sounded a bit dull compared to my modded...
Attached Thumbnails
Click image for larger version

Name:	pink noise.png
Views:	224
Size:	26.6 KB
ID:	1256   Click image for larger version

Name:	phase.png
Views:	241
Size:	18.1 KB
ID:	1257   Click image for larger version

Name:	impulse.png
Views:	218
Size:	6.6 KB
ID:	1258  
hbc
diyAudio Member
Posted in Uncategorized
Views 1397 Comments 2 hbc is offline
Old

Adventures in low impedance power supplies

Posted 10th March 2014 at 08:01 AM by abraxalito
Updated 17th May 2014 at 03:52 AM by abraxalito

Here's my latest crazy project, intended to answer the question 'How low can you go?' in power supply impedance. No listening tests yet, I've just finished assembling this stack of hexagon capacitor arrays out of cheap electrolytics. Total capacitance of the top 4 tiers is comfortably above 1F. The top tier is designed for lowest ESR at HF using Nichicon 1500uFs, the next tier is a trade between ESR and uF. The last two are the highest capacitance density I could find (a total of 182 4700uFs). I've yet to connect the bottom two hexagons to the upper tiers but the top two are connected by wires running through the gaps between caps.

The whole is intended to push the limits of low frequency noise in powering a couple of TDA1545s which will sit on a small PCB supported on thick wires from the centre of the top tier. I am aiming to get a capacitive reactance (at 50Hz) at the DAC supply pins below 3mohm and ESR below 1.5mohm.

Update1 : connected the bottom two tiers...
Attached Thumbnails
Click image for larger version

Name:	wedding-cake.JPG
Views:	1731
Size:	691.1 KB
ID:	1253   Click image for larger version

Name:	OST4700uF.jpg
Views:	273
Size:	171.7 KB
ID:	1254   Click image for larger version

Name:	5captier.JPG
Views:	829
Size:	673.4 KB
ID:	1255  
abraxalito's Avatar
diyAudio Member
Views 1341 Comments 4 abraxalito is offline
Old

Goodmans Magnum SL woofer distortion

Posted 5th March 2014 at 04:17 PM by hbc

I have a pair of tired Goodmans Magnum SLs. They are in reasonable condition, but one mid is blown, and they have no front covers. I tried grafting a new mid on to the broken one, expecting I would need to do some crossover work, but it really did not sound good. A very unpleasant sound that I found quite fatiguing and unpleasant to listen to coming from the upper bass lower mid area, quite a relief to turn it off actually. I put bigger and bigger choke on the woofer to try and filter it away, but that didn't work. I took of the dust cap in case that was causing it but no.


I am thinking of re-purposing the boxes now, but first did just check the woofer to make sure it has a problem. Below are some distortion plots, for a good one, the bad one and also for a Wharfedale Dovedale 3 woofer, with fixed rubber (Note the different scale). These plots were done at quite low level, like normal neighbour friendly listening levels.
Attached Thumbnails
Click image for larger version

Name:	SL good one.png
Views:	215
Size:	26.2 KB
ID:	1248   Click image for larger version

Name:	SL distortion and level.png
Views:	197
Size:	27.3 KB
ID:	1249   Click image for larger version

Name:	SL distortion.png
Views:	166
Size:	20.3 KB
ID:	1250   Click image for larger version

Name:	dovedale distortion and level.png
Views:	201
Size:	26.1 KB
ID:	1251   Click image for larger version

Name:	dovedale distortion.png
Views:	158
Size:	20.9 KB
ID:	1252  

hbc
diyAudio Member
Posted in Uncategorized
Views 838 Comments 0 hbc is offline
Old

Voltage Regulators for Line Level Audio. Part IX : Two Transistor Series Regulator

Posted 21st February 2014 at 12:50 AM by rjm (RJM Audio Blog)
Updated 4th March 2014 at 02:56 AM by rjm

Part of a series.

So you have a small handful of parts and want to build a (simple) discrete voltage regulator instead of using an IC. What to do?

For line-level audio circuits, especially op amp based (IC or discrete) preamps with high PSRR, something like the Z-reg is generally sufficient. Robust, works well, has enough ripple rejection to cut power line noise from the preamp output.

If you add just a couple more parts, however, you can add feedback to the Z-reg circuit, a simple error amplifier in the form of an additional transistor Q2, with the output-sampling voltage divider R1,R2.

The ripple rejection is not vastly superior to the circuit without the feedback unless some additional bypass capacitors are added as shown in the first version of the circuit below. The output impedance, however, improves from a few ohms to a few tenths of an ohm as a result of the feedback. Which could, in principle, be of use.

...
Attached Thumbnails
Click image for larger version

Name:	voltageregulator7 ripple.png
Views:	1169
Size:	88.8 KB
ID:	1244   Click image for larger version

Name:	voltageregulator7s ripple.png
Views:	585
Size:	89.0 KB
ID:	1245  
Attached Files
File Type: asc voltageregulator7.asc (2.3 KB, 291 views)
File Type: asc voltageregulator7s.asc (1.7 KB, 280 views)
rjm's Avatar
rjm
diyAudio Member
Views 1705 Comments 2 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part VIII : The Teddyreg

Posted 19th February 2014 at 02:44 AM by rjm (RJM Audio Blog)
Updated 19th February 2014 at 02:46 AM by rjm

Part of a series.

The circuit is described here.

I'm not going to spend too much time on this one. The idea is to increase the input impedance of the pass transistor by buffering it with a jFET so it will support a high-impedance passive CRCRC filter section that generates a low noise reference voltage. The reference is defined not by a Zener or diode stack, but by a simple voltage divider. There is a LM317 pre-regulator on the front, but it is traditionally configured and works independent of the following circuit so it is omited here together with the additional transistor that speeds up the charging of the reference voltage filter capacitors.

The basic problem is that lowering the noise of the reference cannot lower the output noise indefinitely. After a point the output noise is defined by the performance of the pass transistor instead.

As you can see from the simulation, the circuit has the same ripple rejection as the filtered zener-referenced one-transistor regulator,...
Attached Thumbnails
Click image for larger version

Name:	voltageregulator-treg ripple.png
Views:	630
Size:	98.1 KB
ID:	1241   Click image for larger version

Name:	voltageregulator-treg Zout.png
Views:	539
Size:	93.3 KB
ID:	1242  
Attached Files
File Type: asc voltageregulator-treg.asc (2.4 KB, 290 views)
rjm's Avatar
rjm
diyAudio Member
Views 1202 Comments 0 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part VII : The k-multiplier

Posted 18th February 2014 at 12:55 AM by rjm (RJM Audio Blog)
Updated 18th February 2014 at 01:08 AM by rjm

Part of a series.

This circuit is from this page by Kean Token, also referenced in his recent blog post.

Two versions are presented, one with all the protection diodes and a simplified version with extraneous components removed.

LTSpice simulation shows so-so performance into a light load, with about 70 dB of ripple rejection and a fairly high output impedance, but the drop out voltage is respectably low and we must factor in - coming directly from the Jung Super Regulator - that this is just a two transistor circuit, with no error amplifier to provide feedback.

As a frame of reference, it is quite similar in performance to the Z-reg we looked at back in part III.

The k-multipler is of a class of voltage regulators where the output is referred to the input voltage, rather than to ground. It provides "X volts less than the input", rather than the traditional regulator which provides "X volts above zero"....
Attached Thumbnails
Click image for larger version

Name:	voltageregulator-kmult ripple.png
Views:	629
Size:	97.3 KB
ID:	1235   Click image for larger version

Name:	voltageregulator-kmult Zout.png
Views:	399
Size:	98.9 KB
ID:	1236   Click image for larger version

Name:	voltageregulator-kmult simple ripple.png
Views:	353
Size:	95.3 KB
ID:	1237   Click image for larger version

Name:	voltageregulator-kmult simple Zout.png
Views:	369
Size:	95.7 KB
ID:	1238  
Attached Files
File Type: asc voltageregulator-kmult.asc (2.9 KB, 272 views)
File Type: asc voltageregulator-kmult-simple.asc (2.1 KB, 263 views)
rjm's Avatar
rjm
diyAudio Member
Views 1381 Comments 2 rjm is offline
Old

The Kmultiplier (I have a blog?)

Posted 15th February 2014 at 06:33 PM by keantoken

Well, maybe I'll start using this. I should put a link to my Kmultiplier webpage:

The K Multiplier

The Kmultiplier is as far as I know the best power filter you could possibly squeeze out of just 2 active components. Not only this, but due to its simplicity it's RF PSRR is greater than the majority of regulators. It has output impedance lower than most lytics, doesn't oscillate into film bypass, and won't glitch on fast load signals.

Click the image to open in full size.
keantoken's Avatar
diyAudio Member
Posted in Uncategorized
Views 1937 Comments 3 keantoken is offline
Old

Voltage Regulators for Line Level Audio. Part VI : The Jung Super Regulator

Posted 13th February 2014 at 05:21 AM by rjm (RJM Audio Blog)
Updated 14th February 2014 at 11:52 AM by rjm (clean up)

In the next part of the series, I'll be presenting various published regulator circuits.

Today we have the "Jung Super Regulator" (2000 version) on deck, thanks to Tangentsoft's excellent write-up.

In translating the circuit to LTSpice, I've made some concessions. While I have kept the protection diodes so as to be consistent with the original - even if they do nothing in this simulation - the op amp, transistors, voltage regulator and reference have been substituted with working equivalents from the LTSpice libraries. I've been approximate in the resistance and capacitance values, and tuned the circuit to output 10 V at 10 mA to keep in line with the previous circuits I've uploaded.

It works though, and, under simulation at least, it works extremely well. Putting it together in LTSpice gave me a new appreciation for just how much work and refinement went into its design. Now, its an open question whether such over-the-top performance...
Attached Thumbnails
Click image for larger version

Name:	voltageregulator-jung.png
Views:	2240
Size:	44.8 KB
ID:	1231   Click image for larger version

Name:	voltageregulator-jung ripple.png
Views:	710
Size:	99.0 KB
ID:	1232   Click image for larger version

Name:	voltageregulator-jung Zout.png
Views:	510
Size:	94.8 KB
ID:	1233  
Attached Files
File Type: asc voltageregulator-jung.asc (5.7 KB, 387 views)
rjm's Avatar
rjm
diyAudio Member
Views 1929 Comments 0 rjm is offline
Old

2,000W into 1 ohm

Posted 12th February 2014 at 05:10 AM by fas42
Updated 13th December 2014 at 12:52 AM by fas42

I mentioned in a thread a while ago about doing an exercise of engineering an amp capable of delivering 2k watts into a 1 ohm load, with distortion aiming at the magical ppm figure. This is still happening, and making progress ... key problem as I saw it was managing crossover distortion intelligently - I'm looking at a conventional class AB output stage at the moment - and it didn't make sense to try and control it using a classic global negative feedback approach.

By nature I'm an excellent scavenger, I look to see what ideas are already out there - so I'm trying out some concepts in using local negative feedback. This is evolving, step by step - and showing promise: in a simulation of the output stage only, getting effectively 2kW in 1R, at 200kHz with reasonable stability - and the waveform at this stressful frequency looks pretty good, there is still some crossover glitching, but I'm reducing the visible level of it steadily.

.
Banned
Posted in Uncategorized
Views 1742 Comments 19 fas42 is offline
Old

Code for dual channel DDS...

Posted 25th January 2014 at 02:37 PM by googlyone
Updated 26th January 2014 at 06:34 AM by googlyone (Incomplete)

I was asked if I would share the code for the audio DDS I was playing with.

It is here...

Ver0.1.zip

I think this is all the files you need.

To show just how lazy I am, the main function is the file titled "dig_cross.c" - as that was the main function I edited as the base of this code. There is also a file "ad1940.c" which contains a bunch of the SPI stuff. This is yet another illustration of my bone idle-ness - as this module is probably a decade old. It is used, but has nothing to do with an AD1940 IC....

No apologies

There is a bunch of comments in this, but some general overview comments are:
- About 95% of the source code is about:
- Running the user interface
- Generating the display (rather utilitarian implementation)
- Reading from the EEPROM, and doing limit checks on data
- Writing to EEPROM

...
diyAudio Member
Posted in Uncategorized
Views 1021 Comments 0 googlyone is offline

New To Site? Need Help?
Copyright ©1999-2017 diyAudio