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Here’s a close-up of a power amplifier I built around 1993, when I was 22 years old. The resolution isn’t that great, as it was taken from old photos. The output tubes on the top row are 845’s. As a perspective, the first picture shows a 12 inch desk lamp. The layout wasn't my best effort, but at 5000 volts DC, and 1800 watts… you need room for heat dissipation and safety. The tubes are choke loaded on magnequest iron! (Parafeed circuit) Parafeed was all the rage at the time.

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Note the 6 (866A tube) mercury rectifier in the bottom, operated via a timer relay for the heater warm-up period. No solid state here folks! Quite the budget for a teenager.

Dual chassis amplifier and preamplifier, I used in my 3rd system, which I built in 2016

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The amp is based on a Kit on DIY Audio: ("the first one" by user "Lazycat")

  • 160W channel at 8ohms load.

  • 500W smps power supply.

  • 10,000uf power supply capacitance per rail (not needed with SMPS… but I like overkill.)

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The preamp is fully regulated having:

  • True balanced output (DVR134 chip used)

  • Stepped attenuation volume control (R2R)

  • Fully regulated linear power supply

KRELL KSA5 clone amplifier built around 2016.

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As you probably guessed by now, I'm a huge Krell fan and eager to try more of their designs.

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Thanks to Kevin Gilmore for developing the board.

Understand that this is a genuine clone folks. Not the "improved" versions on you see on Ebay claiming to be clones and done with "cut corners".

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Some of the specs:

  • Power supply increased to 27 Vdc (original is 21Vdc).

  • 144,000uF worth of power supply capacitance!!! (lots of power amps don’t reach this level, including the 100 watt models).

  • 34,000uf capacitance on the amplifier board (178,000uf total).

  • CRC style power supply with a double rectifier bridge.

  • Power is increased to 8 watts RMS under 8 ohms. (original design was 5 watts).

  • 200VA toroidal transformer (no voltage sag here).

Some DIY amplifiers I've built.

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Being on strict budgets during the early years, some of the builds are old and in recycled chassis.

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Beyma TPL150

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Can be used as:

  • A direct radiator (worst subjective sound).

  • An open baffle with rear cover removed (quite better).

  • Custom horn loaded (very good).

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The pictures show it in a sandwich of 2 horns, which is based on a Jean Michel Le Cleach profile. (JMLC) The horn cut-off is 1.3Khz.

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Since it was to work with an open baffle type of system, we decided on 2 horns (1 front and 1 back)

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Thanks Troy for the woodwork!

his blog here

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New Tweeter amplifier !!! (2017)

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Two small mono-blocks providing a huge 12 watts rms under 8ohm.

I really LOVE this amp. I own four of them, and am building two more.

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  • Based on a Kit from DIY audio (The Wire LPUHP) but done with some personal design changes.

  • Oversized the design of the power supply (any surprise here?)

  • Added a DC servo to ensure no DC offset reaches the tweeter (my main system is a 100% DC coupled system).

  • Modified the original design to be fully balanced throughout.

  • AD797 opamp used with decoupling.

  • 8x LME49600 output driver used per channel (2A output total capacity).

Push-Pull subs (January 2018)

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Small footprint dual opposed 8" sealed. Used the Tang band W8-740P (recycled from my bass horn project above)

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Recycled materials used with minimal effort into details/finish. This was done as a possible computer subwoofer, so not a lot of overkill needed with only ½” MDF.

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Measurements were nothing to write home about, and quite expected for this style of design. The opposing subwoofer worked well at cancelling vibrations and the enclosure actually didn’t vibrate too much at all. Much less efficient than the tapered horn they used, with only 1/20 the size. Output power distortion was significant, with the project ending up in the fire pit.

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No free lunch :)

New Headphone amp (Feb 2018)

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With exactly 1/4 watt output power (at 8ohm) this is more than enough for the 300ohms Sennheiser HD650.

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Specs:

  • Dual chassis (power supply and amp section)

  • Mostly silver internal wiring.

  • Regulated power supply.

  • Double rectifier and double regulation stage.

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The unit was dead silent and quite dynamic on the modded HD650. Will roll the opamp to find the best match, and then compare it to my KSA5, which is my long-time headphone reference amp.

New Headphone amp (Feb 2018)

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With exactly 1/4 watt output power (at 8ohm) this is more than enough for the 300ohms  Sennheiser HD650.

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Specs:

  • Dual chassis (power supply and amp section)

  • Mostly silver internal wiring.

  • Regulated power supply.

  • Double rectifier and double regulation stage.

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The unit was dead silent and quite dynamic on the modded HD650. Will roll the opamp to find the best match, and then compare it to my KSA5, which is my long-time headphone reference amp.

Four new amplifiers, quasi-monoblock, for the horn system (Feb 2018)

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Specs:

  • ~3.5 watt each - measured and confirmed, 5W peak before clipping. (However, heat generation is a problem at 5 watts as the amplifier can't sustain 5watts on continuous basis, as the heatsink isn’t big enough).

  • Fully regulated (at 3 amperes continues capacity per rail).

  • Fully balanced design (XLR inputs only).

  • Fully DC coupled.

  • Integrated DC Servo.

  • Very fast slew rate capacity.

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Based on the LME49600 for output (4 LME chip used per amplifier), the driver is the excellent AD8599. 

 

I was very excited about those after the tremendous success of the 12 watts version (8x LME49600 per amp driven by a triplet of AD797)

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I expect to use 0.5 watt with those, and often much less, so I'm about 10x more powerful than required. No bigger heat sink required either.

Few simple sealed speaker test boxes for review (From left to right)

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Eton Symphony 4-212 (now SOLD)

http://www.eton-gmbh.com/fileadmin/user_upload/Produkte/Home-Hifi/Symphony_2/Datenblaetter/SYMPHONY_II_4-212_C8_25_HEX.pdf

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Eton Symphony 3-400 (solid performer from 400hz to 4khz) Owned them for a while now. (Collecting dust in storage)

http://www.eton-gmbh.com/fileadmin/user_upload/Produkte/Home-Hifi/Symphony/3_400_A8_25MG.pdf

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Eminence PRO 5W8 (Not as good as I hoped for)

http://www.eminence.com/pdf/Pro_5W_8.pdf

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Transducer Lab tweeter (2 sets of beryllium and one set of aluminum/ceramic domes)

http://transducerlab.com/

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On picture 2 (left to right)

  • Eton 3-400 again

  • Stock beryllium tweeters (tlab)

  • Waveguide loaded tlab beryllium tweeter so I can subjectively compare both versions. (waveguide salvaged from scanspeak h2606)

  • Eminence N151M mounted on B&C ME10 horn

Testing of Dipole speaker with the excellent Eton 3-400. (Winter 2019)

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Eton: 3-400 in front running full-range

Tang band: W3-315e in rear (inexpensive $20 driver)

 

In this small sealed box the frequency fell quickly below 300hz, so I brought in the W3-315E to the rescue (crossed at 200hz via simple first order crossover)

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Sitting in the middle of room, and accessing YouTube and TV videos, it’s quite satisfactory. However, when equalization was added, it sounded surprisingly good, with a nice soundstage. 

 

Subwoofer added below 100hz (no chest pounding expected from a pair of 3")

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The KSA5 amplifier clone does run a bit short on power, as it pushes only 7 watts, and speakers are about 87db efficient. Add that they drop to 4ohms under 300hertz, I may add a tweeter on top. For TV dialog content though, this works just fine.

Class D (5th attempt - 2019)

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I usually don’t like Class D (including Tripath and similar variation). In the HiFi shows I attended, I consistently disliked what I heard, including some very expensive systems. Perhaps technology will improve someday, to maybe outperform the AB Class amplifier. Seems like people have been saying this for over 10 years now. Here’s hoping…

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With a budget in mind, I decided to build three class D amplifiers for a TV system. (one is currently undergoing testing as a subwoofer amp)

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They are:

  • Cheap Ebay bought 24V SMPS at 6 Amperes supply, 100% stock, 1 per case feeding both channela. (Mar 2019 update, 2 failed in less than 6 months)

  • 2x TDA3116 based board per channel (bridged, so ~100W per channel under 4 ohms, 100 watts claimed being very optimistic...)

  • XLR inputs

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Whilst they do work, I haven't yet assessed the sound quality. Stay tuned for that.

2nd set of LPUHP monoblocks. (May 2019)

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Liked the first one so much, I bought a 2nd set of boards.

These two were built slightly different:

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  • OPA1611 opamp used (original was the AD797)

  • No DC servo, as I plan on using those on woofers (and less than 3mv of offset is negligible on a big 4" voice coil)

  • Different brand of capacitor on the PSU

  • Better quality speaker posts (not sure if it helps the sound or not, but I had them anyway)

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Subjective comparison between both to come.

DIY Dual channel, very high quality microphone preamplifier

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High quality parts used throughout, with a recycled chassis from APC.

 

Specs:

  • ​AD SSM2019 receiver

  • BB OPA2134 (gain and DC Servo)

  • AD SSM2142 XLR output buffer

  • Dual LM7815 regulators with lots of capacitance added.

  • +48Vdc phantom power via a SMPS module (up to 2 amperes output)

  • 30,000uf worth of filtration :)

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