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I returned to DIY electronics in 2009 after a 20 year pause by building a few kits to get in shape. This blog is for me to keep track of my progress.
Old

How much power is enough for an amp?

Posted 2nd January 2012 at 02:09 AM by alexcp (My DIY projects)

Bruno Putzeys posted:
About power ratings, well... Normal "critical listening" levels hover around a long-term average of 85db SPL at the listening position. If we're assuming uncorrelated signals (rather inaccurate assumption but it'll do for the purpose) that is 82dB SPL for each speaker alone. Crudely calculating back from a 2m listening distance to the 1m standard measuring distance that's 88dBSPL, one speaker, one meter. It's not unusual for speakers to have an efficiency of 88dB/1w/1m so 1W is roughly the required amplifier power.

The current crop of unlistenable hypersquashed pop music has a peak to average range of around 4dB. So all it takes to reproduce pop at a reasonable level without clipping is a 4dBW (2.5W) rated amp.
Before the loudness war got into swing (say until the early 90's) peak-to-average ranges up to 14dB could be found in mainstream music. To play Sultans of Swing at the same average level requires an amp rated at 14dBW
...
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Posted in Speakers
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Old

Zen V4-J

Posted 17th December 2011 at 01:12 PM by alexcp (My DIY projects)
Updated 12th May 2013 at 04:03 PM by alexcp

Now that Nelson Pass published the details of the JFET upgrade to First Watt F2 and that Newark sells power JFETs from Semisouth, there was no excuse not to upgrade my Zen V4 with the new active device.

I replaced Q1 (see the original schematic) with SJEP120R100A; increased R5 to 130 kohm to bias the JFET correctly with Vgs of approx. 1.5V; and reduced R8 to 22 ohm.

The measured result is a nice reduction in THD+N; attached are the graphs for THD+N @ 1W into 8 ohm vs frequency, before and after the upgrade. With IRFP044 as Q1, the distortion was mostly 2nd harmonic (at -65dB), plus some traces of the 3rd harmonic. With the JFET, it is still mostly 2nd harmonic, which is now at -80..85dB, with the 3rd below my measurement floor.

Subjectively, the improvement is remarkable! There is additional detail and depth of the scene.
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Old

Zen V4, updated

Posted 13th December 2011 at 07:20 AM by alexcp (My DIY projects)
Updated 17th December 2011 at 01:41 PM by alexcp

In 2009, Penultimate Zen aka Zen V4 was my first solid state build. I used the parts that were available, did not know much about making it work well, and did not have test instruments beyond a cheap multimeter. Also, I did not have a preamplifier to work with it or speakers sensitive enough to enjoy its 25W. As a result, the amplifier turned out not quite satisfactory and for two years has been gathering dust and my wife's complaints. I was thinking about scrapping it and reusing the enclosure for something more useful. Instead, I reworked it.

I removed one of the two power transformers (moving from dual mono to stereo configuration), replaced my original dodgy Chinese PSU filter caps with Mundorf M-Lytic HC, replaced internal low voltage wiring with thick speaker wire, reconfigured grounding (so it is finally safe!) and installed balanced inputs with input transformers. What a change in sound! With my Exposure CD player, B1 clone preamp and Heresy III speakers, the amp...
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Old

My systems

Posted 4th December 2011 at 11:41 AM by alexcp (My DIY projects)
Updated 12th May 2013 at 07:41 PM by alexcp

Someone pointed out that it's interesting to see all the components in a system, rather than discuss them individually. I liked the idea - I think it also shows what projects ended up actually useful - so here are my systems (I have four with diy components).

The music I listen to is an eclectic mix of classical music (such as Rachmaninov and Tchaikovsky), opera (mostly arias), jazz (Armstrong) and some pop music.

The first system is the one I listen to the most:
  • exposure 2010S CD player with Tentlabs low-jitter clock
  • B1 clone preamp
  • F5 clone
  • Vintage Celestion DITTON 15XR speakers

The second system is the testbed for whatever project I may be working on:
  • Audio Analogue Crescendo CD player
  • B1 clone preamp
  • Zen V4 with SiC power JFET in the gain stage
  • Klipsch Heresy III speakers

The third is the best sounding so far, has the highest WAF and is likely to stay around for some time:...
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Old

CD transport

Posted 7th July 2011 at 12:48 AM by alexcp (My DIY projects)

Built from a kit. Sound lacks finesse.
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Posted in Digital Sources
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Old

24/192 DAC

Posted 7th July 2011 at 12:46 AM by alexcp (My DIY projects)
Updated 16th March 2013 at 02:33 PM by alexcp

Built from a kit. I don't like the sound at all.
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Old

Grounded Grid Preamp

Posted 7th July 2011 at 12:43 AM by alexcp (My DIY projects)
Updated 16th March 2013 at 02:35 PM by alexcp

Built from the kit from Bruce Rozenblit. Very nice one, but is not being used - it has too much gain for any of my systems. I will probably sell it.
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Posted in Preamps
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Old

Another Gain Clone

Posted 8th May 2011 at 02:07 AM by alexcp (My DIY projects)
Updated 7th July 2011 at 12:28 AM by alexcp (Added photos)

Unsatisfied with the sound of my gainclone amplifier, I re-used the enclosure and the power supply for a gainclone along the lines suggested by Bob Cordell, whose implementation of an LM3886 based amp was praised by at least one member on the NJ audio society.

I skipped both the Klever Klipper and the toroidal air core output inductor, and kept only 10,000 uF per rail in the PSU. The schematic can be found in Chapter 27 of Cordell's Designing Audio Power Amplifiers. The PCB was designed to re-use the existing mounting holes of the ChipAmp's PCB.

The result? Better than with a plain vanilla chip amp, but still not good enough for music. Perhaps I should not have limited myself to re-use of the PSU et al. but should have taken all the details of my implementation seriously.
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Old

Velleman K4040 mods

Posted 8th May 2011 at 12:32 AM by alexcp (My DIY projects)
Updated 4th May 2014 at 12:59 AM by alexcp

I posted some time ago a note about my Velleman K4040 amplifier. The sound of the amp as built from the kit was unremarkable and definitely not in line with the price. Lacking experience with tubes, I was looking for some time for well documented mods to the kit.

I found two 2006 posts here and here and implemented them rather directly. The only difference is that I used IXCP10M45S instead of a pair of J508 current sources in each channel and replaced the 1N5408 rectifiers with UF5408 instead of adding noise suppressing capacitors in parallel to them.

The mods did not leave much of the original Velleman design in place; the result, however, is a remarkable improvement in sound!

However, two problems remain: (1) I got hum that wasn't present before the mods; and (2) a two-year old running around doesn't get along with eight hot, attractively glowing tubes. The project is shelved until a better time.

For future reference: The toroidal...
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Old

Low effort Class D with ready made modules

Posted 5th April 2011 at 04:45 PM by alexcp (My DIY projects)
Updated 6th April 2011 at 01:29 PM by alexcp

To try out Class D without working too much, I picked two ready-made Class D amplifier modules: one is the $45 2*100 Watt Class-D Audio Amplifier Board from Sure Electronics with the optional $10 volume control board, the other is the $199 IRAUDAMP7S from International Rectifier.

The Sure Electronics module is based on Tripath's TK2050 chipset. Powered from a 150W 24V SMPS from Mean Well, it predictably puts out about 22W RMS to a 8 ohm load. (The declared 2*100W requires a 30V supply and a 4 ohm load.) The sound and the measurements are decidedly mediocre, although at the $45 price, the module still may be a good value. Also, the volume control board feels odd, as the knob only adjusts volume after a push; another push disconnects it again.

The IRF module requires dual rail supply, for which I chose an SMPS400A180 by hypex. With +/-40V rails, the amplifier delivers 100W RMS into a 8 ohm load. The measurements are good, and the sound is very interesting for...
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