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Remote tweaking

Posted 25th March 2015 at 11:13 PM by fas42

A thought has popped into my head ... I enjoy the process - well, most of the time, :D! - of refining systems so that they deliver what I call convincing sound - a quality beyond what people typically achieve with audio systems assembled and "optimised" in conventional ways. And I've been able to help others at times move in the right directions, to advance what they're currently achieving.

So, I'm curious whether there are any out there, lurking :), interested in having a one to one interaction with me in having a go at getting something better out of their systems. Before wasting any more time on pursuing a silly idea, I would be curious if anybody is interested? And if you don't like to "expose" yourself to the great unwashed, :D, just send me a PM!

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Mid-life crisis turntable purchase and speaker build and who knows what else?!

Posted 25th March 2015 at 04:14 AM by Mike94531

Not sure why, but about a month ago I decided that I wanted to buy a turntable and get into listening to albums. So I did some research and bought an old used Technics SL-BD22 and a Sansui R99-Z.

Now I have been hitting up Goodwill looking for albums and I found an actual record only store about 45 minutes from me and I bought some records from them over the weekend.

The bad news is that I don't have any decent speakers, I used to have some old Yamaha home entertainment speakers for our old CD player however I sold them at a garage sale 3 years ago or so.

How have I been listening to my new to me albums? Well, I am using my speaker setup with subwoofer that supposed to be in my office connected to my computer. My kids are not happy to be watching YouTube videos with the old stock computer speakers!

Speaking of speakers, I bought the Parts Express MTM TriTrix speaker kit...without the wood.

Below are some pictures of my stuff...
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TDA8946AJ headphone amplifier

Posted 20th March 2015 at 04:13 AM by abraxalito
Updated 23rd March 2015 at 06:40 AM by abraxalito

I built this up to see how the TDA8946AJ DC-controlled volume element sounds. According to the datasheet and comparing the figures with those for the same amp minus the volume control (TDA8946J) there's some additional THD so I was curious to hear how transparent it is.

There are transformers both on the input and the output of this. On the input to match levels (4:1 step down) and to do unbal-bal conversion. On the output again for the same reasons, except bal-unbal to drive my phones which I've not modified for 4 wire operation. The trafos are ferrite (=very cheap) RM10 for the input (under the board) and RM12 for output (behind the board). In order to be able to match a variety of phones, I've wound 4 identical secondaries so they can be combined in series or parallel.

From the pic you'll see the customary array of caps - I need to order up some lowESR (preferably NCC) 1800uF caps to do better justice to the rails. Last night I experimented with some ceramics...
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Posted in Power chip amps
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Doin' a "Gilmore" : a discrete transistor headphone amplifier

Posted 10th March 2015 at 12:17 AM by rjm (RJM Audio Blog)
Updated 13th March 2015 at 10:42 PM by rjm

Recently I spent some time updating the diamond buffer of Sapphire headphone amp circuit. Later I stumbled on Kevin Gilmore's headphone amp circuit. Well, I'd read it before, but it had slipped my mind.

On seeing the Gilmore circuit again the thought process re. a Sapphire+Gilmore went something as follows,

"Toss out op amp, convert the Gilmore dual-LTP front end to bipolar, bolt the Sapphire3 buffer stage to the back, and substitute in the Sapphire3 current sources. Wrap in a mild feedback loop."

The result is shown attached. The Vbe multiplier is still a simple resistor (R33) ... that may need to be refined to add thermal throttling. The offset servo is not shown, but the action is shown as Vadj. Alternatively a trim pot would be placed between R30 and R32 to provide a small measure of offset adjustment. Most of the open loop gain is controlled by R14,R15 ... it seems to me that some work could still be done in that area. Despite going...
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Schitt's flagship DAC uses a not-for-audio DAC chip.

Posted 7th March 2015 at 07:43 AM by abraxalito
Updated 12th May 2016 at 02:56 AM by abraxalito

The Schitt Yggy DAC has already created something of a stir over on Head-Fi amongst those who've heard pre-production prototypes. Its of interest not just because of the pre-launch buzz but also because the designer (Mike Moffat) is one of the long-time seasoned guys in the field. He says this is the best practical DAC he knows how to build. And its priced ISTM very reasonably given the amount of tech it embodies ($2300) - the DAC chips come from ADI and are $64 a piece on the manu's website. He's using 4 of them but says he had to address the glitching of the DAC without using a sample-hold which sounds like ***.

The chip is the AD5791BRUZ which ADI designed for industrial/scientific/medical applications rather than for audio. Datasheet attached.

Having looked over the DS what strikes me as interesting is that this is a 20bit DAC (1ppm) yet the 1kHz THD performance (p4) isn't anything to write home about (-97dB) and that figure is given at a very low sample rate...
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dantimax (contact information)

Posted 25th February 2015 at 02:56 PM by djg440

Was wondering if any one can help with how to contact...
I have placed a order for three remote boards and three motorized alps pots.
all of the contact links do not go through that is supplied on his sights. Hopefully someone has a email address or contact information that has worked for them and can share it.
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Which is better, Sennheiser HD600 or AKG K702?

Posted 25th February 2015 at 12:24 PM by rjm (RJM Audio Blog)
Updated 25th February 2015 at 11:41 PM by rjm

The HD600s.

Ok, so why donít you like the K702s?

I didnít say I didnít like them. Just that I think the HD600s are better.

Itís pretty simple really:

The K702s have a strident, hard upper-midrange "bump" that I find disagreeable. Yes, it makes tracks sound more ďliveĒ, but itís also fatiguing and a bit clinical, and - as many others before have noted - makes the sound overall somewhat thin. In direct comparison the HD600s seem full the point of boominess, but I'm willing to accept that midbass plumpness for the Sennheiser's warmer, luxurious midrange. In imaging, the K702s trend to a wide, distant, airy soundstage while the HD600s run towards a closed in, intimate presentation. In that sense the K702 are more like listening to speakers, and I can certainly see people being attracted to that.

These are both top-shelf headphones at the top of their game, I don't mean to imply that the AKGs are bad. The two...
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Random hippie checking out the waffle amp. Er, and his new bass.

Posted 24th February 2015 at 06:21 AM by mlise

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Z-reg II improved simple Zener voltage regulator

Posted 22nd February 2015 at 01:24 AM by rjm (RJM Audio Blog)
Updated 28th February 2015 at 06:17 AM by rjm

I've added an additional RC filter stage (R3, C4 in the schematic below) before the Zener diode, substantially reducing the amount or ripple on the transistor base by cleaning up the voltage applied to the Zener reference. (The original Z-reg is described here.)

Circuit shows C2 with a value of 300 uF. Typically much larger values are used. I kept the filter capacitance to a minimum here to show circuit working with a reasonably high ripple (1 V p-p) on the input. The rectifier diodes used here are of no particular consequence, I just wanted the simulation to generate a realistic sawtooth for the input.


OK, this doesn't do as much as I originally thought. The improvement is mostly below 100 Hz, whereas the ripple is mostly in the 100Hz-1kHz band. There's perhaps 3 dB less output ripple, but that's about it. You can verify this yourself in LTSpice, just cut the wire between C4 and the junction or R1-R3 and rerun the sim.
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Where I'm standing today, DIY F4's to begin soon.

Posted 17th February 2015 at 09:02 PM by Jeffs
Updated 17th February 2015 at 09:10 PM by Jeffs

Here goes!
This all got rolling after checking CL then picking up some 30+ year old 4 ohm speakers I had wanted since I could drive to a store and drool. Sure, might rather have some old Polk SDA's like the ones briefly owned in 1989, but am happy with what I got and the price.
I started reading DIY Audio a few years ago, and a couple of years ago was sure I was going to build one of the F5 Turbo variations one day. After disappearing for a few hundred hours to read all of the treads I was confused and it was time to buy a new roof, and spend a couple of months in India... so had to quickly forget about the idea.
I should have done an Amp Camp project to learn more about what does what.

This morning I ordered JFET's and MOSFET's from Alex (Alweit), has an eBay store and is a member on the forums.
I picked up the F4 boards from the DIYAudio store a few months ago, probably after Jim (6L6 on the boards) initially read about my ideas of...
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