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CMoy and PPA

Posted 13th August 2010 at 10:37 PM by alexcp (My DIY projects)
Updated 6th April 2011 at 02:35 PM by alexcp (Added pictures)

Of course I built the ubiquitous CMoy. It was a big improvement over various built-in headphone amps (e.g. in a TV) and added headphone capability to where it did not exist (e.g. to a Playstation).

Encouraged, I built the PPA project with a Young-Jung power supply. The enclosures for both the amplifier and its power supply are from modushop.

On first power-on the amp oscillated at 12 MHz when connected to headphones. The oscillation was inaudible but clearly visible on a scope. A quick look at head-fi.org showed that PPA instability is not a new problem. I reduced the value of R11 (see PPA's schematic), which eliminated the oscillation and improved the sound. I replaced the recommended OPA627 with LME49710.

PPA is positioned as a high-end DIY headphone amp, and it is in this project that I felt how subjective "high-end" is. PPA is a nice amp, but a true high-end device like Musical Fidelity X-CANv8 simply blows it away.
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Posted in Headphone amps
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Old

BantamDAC

Posted 12th August 2010 at 08:57 PM by alexcp (My DIY projects)
Updated 15th August 2010 at 12:09 PM by alexcp

ezDAC lacked a USB input, so I leveraged my newly acquired SMD soldering skills building BantamDAC from a kit. While PCM270x-based USB DACs are rather common, BantamDAC is a compact (1" x 2"), neat version.
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Posted in Digital Sources
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Old

ezDAC

Posted 12th August 2010 at 08:39 PM by alexcp (My DIY projects)
Updated 16th August 2010 at 08:05 PM by alexcp

After power amps, speakers and a preamp I wanted to try my hand in digital sources and built a version of ezDAC. It is a fairly simple DAC with a CS8416 digital receiver, an AD1896 sampling rate converter, and a PCM1794A with a passive I/V converter for the DAC proper. Nothing fancy, but sounds as good as my DacMagic.

I used three separate 3VA toroidal transformers (for digital circuits, the DAC, and opamps) in the PSU. The enclosure is from modushop. I had to re-create ezDAC's PCB using the free version of Eagle (which I had never used before) and learn to solder SMDs.
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Posted in Digital Sources
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Old

Elekit TU-879S

Posted 12th August 2010 at 08:24 PM by alexcp (My DIY projects)
Updated 16th March 2013 at 03:02 PM by alexcp

Elekit TU-879S is the best sounding kit I have ever built. Thank you TubeDepot.com for selling these kits. With my DIY full range speakers I mentioned a couple of posts earlier, the sound is fantastic.

Update: one of the original 6L6 tubes got blue sparks inside. As this amp can use KT88, KT66, or EL34 without any adjustment or modification, I replaced both 6L6s with EL34s left from the K4040 project, but the sound deteriorated. A replacement 6L6 from TubeDepot.com restored everything.
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Posted in Tube power amps
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Old

First Watt B1 clone

Posted 12th August 2010 at 08:19 PM by alexcp (My DIY projects)
Updated 12th May 2013 at 05:09 PM by alexcp (Added photos)

What to say... B1 is a great design by Nelson Pass. Easy to build, absolutely transparent to the sound, compact, PCBs are available. I built one, using Nelson Pass' gerbers for making my own PCB, in an enclosure from diyenclosures.com (which sadly seems to be defunct now). The big blue film caps are 10uF Evox Rifa PHE426.

Update: I added a relay input selector, which reduced crosstalk between inputs. I also built another B1 clone (the last three photos), in an enclosure 1U (40mm) high.
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Posted in Preamps
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Old

Zen V4

Posted 12th August 2010 at 06:16 PM by alexcp (My DIY projects)
Updated 14th May 2013 at 01:46 PM by alexcp (Amp reworked)

Nelson Pass' Penultimate Zen (aka Zen V4) proved trickier to build than the simple schematic suggested. I used a chassis from designbuildlisten and PCBs made with the gerbers posted on passdiy.com. Initially I used some Chinese electrolytic capacitors that were easily available, but the sound was not good at all. I replaced them with ELNA for Audio, and things improved greatly. I found that the apparent simplicity of the schematic belies the difficulty of making it right.
Update: I replaced the gain stage MOSFET with a SemiSouth SiC JFET and got a noticeable improvent in both the sound and the measured performance, see a separate post.
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Old

Fostex BK-20

Posted 12th August 2010 at 06:06 PM by alexcp (My DIY projects)
Updated 15th August 2010 at 05:18 PM by alexcp

Having built a few amplifiers, I wanted to build a pair of speakers and settled on Fostex BK-20 kits from Madisound with Fostex FE-206E 8" full range drivers. I've always considered carpentry not my cup of tea, so gluing, sanding, and painting the speakers took longer than expected. However, I am very satisfied with the sound.
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Posted in Speakers
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Old

Velleman K4040

Posted 12th August 2010 at 05:53 PM by alexcp (My DIY projects)
Updated 26th May 2011 at 01:54 PM by alexcp

Then was the K4040 from Velleman. Contrary to some reviews, I found this amp sounding rather nice, particularly after I replaced the EL34 tubes in the output stage with separately purchased matched quads. However, the sound does not quite match the price, and I keep this amp mostly for its looks.

Update: I modified this amplifier, leaving little of the original design. See a later post with the details.
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Posted in Tube power amps
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Old

S5 Electronics "L" series tube amps

Posted 12th August 2010 at 05:52 PM by alexcp (My DIY projects)
Updated 16th March 2013 at 02:55 PM by alexcp

I started with a Model 8LS stereo amp from S5 electronics. Very easy to build, nice with vocals, but not quite HiFi. Later I put it into a Hammond enclosure and replaced the tranformers with Edcors. Also, built a Model 16LS, which is the same thing with a doubled output stage, giving a very similar sound. Both use a 5670 double triode in the voltage amplifier and phase splitter, and 2x6005 (4x for the 16LS) in the PP output stage.
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Posted in Tube power amps
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Old

Aleph "MJ" using SemiSouth SJEP120R100 outputs

Posted 8th August 2010 at 10:29 PM by Tea-Bag
Updated 9th August 2010 at 01:34 PM by Tea-Bag

So I believe I am finished with the Mini-A version modified for SemiSouth R100 output. The MJ is not in reference to Michael Jackson, rest his soul. Simply a reference to Mosfet input, JFET output.

Technical pieces:
R8 is a 1K pot. This allow for some DC offset adjustment.
R18, This affects drain current to differential pair. This value is lowered. I chose 220R resistor since I have a bunch of them. Papa presented this as needed on mod's in general for the lower VGS of the R100 (~1.5v)
R19, gate resistor to Power JFET R100. This is lowered to 47R. We see with F1J and F2J that gate resistors are lower.


Rail Voltage is +/-24v
Source voltage is .425v and is largely determined by the 100K pot settings and heatsinks on hand. The real value of the pot is ~ 70-80k here. I let the IRF240's run no higher than 65c and R100's no higher than 70c.


Sound

Previously I had R18 at 392 default and R19...
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