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Showing posts with label Tube Amp. Show all posts
Showing posts with label Tube Amp. Show all posts

November 15, 2019

Linear Tube Audio MicroZOTL MZ3 Headphone Amp

The Best Headphone Amp I Have Heard At Any Price

Like most of you, I’ve been doing this audio thing for a while. I’m privileged to be in the MD/DC/VA corridor so I’m able to attend meets and audio shows regularly and sample a lot of different equipment. Generally, at any show there’s plenty of gear that sounds very good, and there are a 2-3 special pieces of equipment that leave a strong, lasting impression. These are usually priced like a new car, but every now and then you find a performance outlier, something that’s disruptive in its price range and should frankly cost far more. One such performance outlier is the subject of this review.

About a year ago I attended Capital Audio Fest (goes by CAF for short) which has a small but ample headphone presence. There I saw Linear Tube Audio’s booth and wandered over. I was familiar with LTA’s MZ2 headphone amp based on David Berning’s ZOTL technology, having previously listened to it at a meet in its stand-alone state without the power supply upgrade. The unit’s visuals with transparent top harkened back to the original blue Berning headphone amplifier I listened to at a meet many moons ago (its Plexi side window presented the unique topology like a PC enthusiasts rig).

New at the booth for 2018 was a pre-production MicroZOTL pre-amplifier with a headphone output. I took a look and was a little dismayed it didn’t have a balanced output, but I sat down and had a listen anyway, plugging in a nearby MrSpeakers Aeon Flow (if you’re not familiar, it’s a very good value planar magnetic headphone under $1K) and choosing a song on Tidal. Everything sounded good and well until I heard the strumming of a guitar. It’s hard to describe how incredible it sounded, just crisp, natural and telegraphic, like the acoustic guitar was right there next to me and I needed to turn to my side to confirm it wasn’t. The acoustics of the song had more presence and detail than I was accustomed.

The gent running the booth, Josh Levi, let me know that MicroZOTL pre-amplifier was based on their new MZ3 headphone amp which would be out shortly, price TBA. Not being content with only a smattering of details, and knowing LTA is a local brand, I reached out to owner Mark Schneider and scheduled time for a visit to the LTA listening room/manufacturing area.

Mark has a calm and approachable demeanor and is a true engineer. I’m quite certain he has a complete virtual catalog of all the various audio parts available in his brain. We chatted at length on our preferences for various audio jacks, capacitors, resistors, what made an audible difference and what didn’t. Given the length of time I’ve been experimenting with various audio builds, I was almost perplexed that Mark had tried as many different items that he has.

Besides the parts, Mark was experimenting with myriad other design elements, picking up small but noteworthy improvements in sound. From expensive ceramic circuit boards to non-magnetic transformer covers, everything was there for a reason… sonic improvement. At this point I realized nothing here was getting phoned in, these devices were meticulously designed and likely engineered more carefully than most audio equipment on the market.

If this were the only thing going for LTA, they’d still be ahead of the pack, but the most unique thing about these amps is the technology. David Berning’s technology is completely unique. You will not find anything like it on the market. I’ve put together countless amps, solid state, tube (both with output transformers and OTL), hybrid, etc. The innards of MicroZOTL amplifiers look completely alien, with hand-wound magnet doughnuts and small towers of diodes residing above them flanked with wires on each side. I’ve read the white paper on how this works, but quite frankly it went above my head. Ultimately, for you and I the listener, we can say “who cares what’s going on inside, all I care about is the sound”. There’s certainly nothing wrong with that approach, but some niceties with this design are reduced heat, much longer tube life, and the units aren’t overly heavy from bulky output transformers. They also have a remarkably black background that you won’t hear in most tube amps.
Love the volume control display

Long story short, I helped out Mark with some marketing for several months while he finalized the MZ3 and a few months ago took one home. To say that the MZ3 is better than my highly modified Bottlehead Mainline is an incredible understatement. Not that I was dissatisfied with the Mainline, I found it to be a nice step up in terms of clarity from the Bottlehead S.E.X. and it held its own against other amps like the Torpedo, Budgie S.E., a high-voltage octal Aikido build and other various amps that have come through the listening room. The difference, however, is truly palpable. It’s very rare that I’ve changed a piece of gear and it’s just night-and-day better… like almost two decades ago when I shelved some $30 Sony headphones for the Sennheiser HD600s, or when I set aside a pair of HD650s for my first planar magnetic headphones, the Audeze LCD-2.
The MZ3 is not lacking in connectivity

Listening with my Audeze LCD-4, the MZ3 has a sound that is slightly more neutral than a typical tube amp, but it is still natural sounding. I personally would consider it neutral; others may consider it ever-so-slightly warm. It’s also, full, enveloping, and easy to get lost in the sound and just not think about anything else. Soundstage is precise and crisp. Every detail is there but not obtrusive or overly sharp. I believe what this amp has more than anything else is it just sounds so natural. I was starting to lose interest in headphone listening to speakers, however the MZ3 rekindled that joy so acutely that I often lose track of time playing track after track.

Bottom line, this is a phenomenal amp, truly the best headphone amp I have ever personally heard at any price. It is not the cheapest amp; however, the price is incredibly reasonable for the performance and all the detail that went into its creation. It’s not a balanced amp, but after hearing it, I honestly don’t care. I think building headphone amps can finally take a rest, as I don’t think I could ever make one that sounds this good. If you are a headphone enthusiast and can swing it, I highly recommend auditioning the MZ3. Even if you need to double your budget, save yourself some time and buy your forever amp. I know if for whatever reason I suddenly needed to rebuild my rig from the ground up, I would be at Mark’s office tomorrow with my credit card in hand.

PROS
  • Beautiful, neutral and engaging sound
  • Super black background
  • Attractive chassis
  • Cool, satisfying haptic-touch volume control
  • Includes a remote control
  • Has speaker outputs for high-efficiency speakers
  • Multiple inputs and pre-amp outputs
  • Price is very reasonable for performance level

CONS
  • Not a warm and syrupy tube amp if you are looking for that
  • Only comes in black

Note: I didn't get into some of the features of the amp as I'll only be using it as a headphone amp with its standard settings using the controls on the chassis... but others will be pleased to know there are three selectable inputs, a pre-amp output, speaker outputs for VERY efficient speakers (the output is about 1 watt), and a remote control that allows you to switch inputs, adjust balance, etc.

Setup:
Audeze LCD-4 Headphones w/Ballista Headphone Cable
PC w/Amazon Music HD Unlimited > Chord USB Cable > Schiit EITR > 110 Ohm Zynsonix Coax Cable > AudioNote DAC 2.1 > Zynsonix RCAs






Disclosure: The author provided marketing services for Linear Tube Audio from Sept 2018 to Mar 2019 in exchange for product credit. All views herein are the true opinion of the author and are not the result of any compensation or business arrangement.

April 19, 2012

DIYTube 6L6 Clementine Single Ended Tube Amp

Shannon Parks, owner of DIYTube, has made a number of projects available since 2003 when the DIYTube ST35 clone was made available. DIYTube is both Shannon's small business located in central Illinois and a close-knit forum featuring a handful of helpful and prolific members. Projects on DIYTube include the 60 watt Eiclone amplifier to driver boards for Dynacos to stand-alone single-ended amplifiers like the Clementine and Get Set Go. The projects are all well documented and feature circuit boards for easy building.

The Clementine can be configured to use with 1626 Darling tubes (hence the cute name... oh my darling Clementine) to output 3/4 of a watt or with 6L6 tubes (equivalents: 6L6GC / 807 / 1625 / 6BG6) for a fruitful yield of 5 watts (see what I did there?). This post is dedicated to the building of the 6L6 Clementine.

DIYTube Clementine Schematic

The transformers used for this build aren't quite as fancy as the Transcendars found in the Get*Set*Go build, these would be the tried and true Edcor XPWR005-120 power and GXSE15-8-5K outputs. If you aren't familiar with Edcor, they're likely one of the best-value transformer manufacturers in the U.S. They've been around since 1971 and have been offering distinctive "True Blue" transformers to hobbyists for decades. All of their transformers are made-to-order, so there's usually a 4-6 week waiting period before you get your order, which really isn't so bad considering their pricing.

Edcor power and output transformers

Deviations to the BoM (bill of materials) include the typical Kiwame / Koa Speers carbon film resistors, along with a pair of matched Mundorf Supreme 0.22uF capacitors. Barely squeezed in was a pair of 100uF 100V Elna Silmic IIs. Also packed in was a little bit more capacitance in the power section using 150uF caps and a pair of 2.2uF Solen film bypass caps. Lots of green and red on this board, looks like Christmas time ;)

Top of the populated Clementine board

Important to note is the 8 pin sockets need to be carefully lined up before and during soldering. It's possible to end up with them at a slight angle, which will cause the tubes to jut out at an angle on the top of the chassis. With a bit of heating the joints and shifting, I was able to get them nice and parallel with the board. Once everything was placed, a nice scrub-down with a toothbrush and rubbing alcohol was in order to get all the rosin flux off the board.

Bottom of the populated Clementine board

For the chassis, Keith (po1019 on Ebay) fabricated me a very nice one made from aluminum and walnut side panels. Keith's work is very professional and I hope to continue using his chassis for my future endeavors.

Custom chassis with walnut side panels

One of the more time consuming parts of a build is creating all the necessary holes in the chassis using a combination of the drill press, Greenlee die punches for the tube holes and a Dremel cutting disc for the IEC inlet. Below is the chassis ready to head over to the powdercoater.

Prepped chassis top plate

Chassis bottom plate with vent holes

The chassis was then powdercoated a nice cream color. 

Powdercoated Clementine Chassis

...and the transformer bells a dark red. The transformers also got some brand new nylon screw insulators and brass hardware. I'm not sure why, but often times the nylon insulators that come with transformers are worn looking and discolored. This process is a decent amount of work. The original hardware has to be removed, the bells sanded and taken to the powdercoater, the nylon insulators squeezed into place, then the brass screws trimmed down to fit, then the acorn nuts tightened in place, all for the sake of presentation.
A beautified Edcor transformer

The next task is to add some rubber grommets to the chassis where the wire from the transformers runs inside. This is to protect the wire from rubbing up against a potentially sharp edge on the hole and shorting to the chassis metal. It's an added precaution for the sake of safety. 

Rubber grommets on the chassis holes

The next process was to add the switch, pilot light, power inlet, signal input RCAs and output binding posts. The RCAs are Cardas GRFA, the binding posts are Cardas Economy ACBP, which are still on the pricey side in my humble opinion but not as much as the CCBP copper posts I typically use. Nearly all these items are installed with a socket wrench.

Chassis-mount items in place

The PCB and choke were then installed. The PCB was installed using standoffs, screws and lockwashers to prevent anything from coming loose down the line. The choke was installed using rubber washers underneath to damp any vibrations from making their way to the chassis, along with size #6 hardware.

Chassis and PCB in place

Next the Edcor transformers can be installed. Only two were added at this point as one of the bells was a little shy on the paint from the powdercoater and it needed a respray. The transformers also get rubber washers underneath, along with size #8 hardware, including lock washer, washer, nut and screw.

Two of the Edcor transformers in place

The Edcors were wired into place. I've seen a number of members double up the 6.3V taps in order to use other tubes, but for this particular build I only plan on using 6L6s so I won't be performing that mod. The extra 6.3V tap (brown) will be dedicated to the pilot light. The power wiring and front switch was also wired up during this step. Directly after the fuse is a GE Thermistor wired on solder tabs (the little black circle in the middle of the photo below). A thermistor is a resistor which has a resistance that varies depending on temperature. In this case, the NTC thermistor is used for inrush-current limiting. A higher resistance is provided initially which prevents large currents right after turning the amp on. Once it has heated up, the resistance is much lower, allowing higher current flow. 

Transformers and power wired up

UPDATE: After a lengthy delay waiting to get the transformer bells resprayed, I've finally finished up this wonderful little amp. I used a pair of Svetlana 6L6 tubes and a NOS coin-base 6SL7. The Clementine sounds like a champ, surprisingly resolving. For my personal tastes, I like to run it with a subwoofer to get some additional bottom-end extension.

A rear photo of the unit with Cardas binding posts and RCAs

Front photo of the unit

Detail photo of the wood side panel 

Below is the detail of my custom designed and engraved Clementine logo with clipped cornes on a brass plate. This logo was designed in Illustrator (vector) and sent to a trophy maker for engraving.

Clementine custom engraved logo

I hope you enjoyed this build. I highly recommend checking out Shannon Park's offerings at DIYTube and Parks Audio. Also be sure to check out my matching Get Set Go amplifier.

Need a custom audio cable to take your rig's sound to the next level? Contact Zynsonix Audio for smart solutions.

The Fine Print:
Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 
 



March 17, 2011

The Bottlehead Single Ended Experimenters (S.E.X.) Amplifier

If you've read my other posts, you'd know that I enjoy building Bottlehead gear. I have both a Bottlehead Crack high impedance headphone amp and Seduction phono preamp, both with the obligatory C4S upgrades. The Crack is excellent for high impedance cans (~300 ohms), but can't really handle the low impedance ones. The solution was to build a S.E.X for those more demanding headphones. ;) 

The S.E.X. kit
is a stereo integrated single-ended-triode amplifier with 2 watts per channel output and has been available since 2004. From the Bottlehead site: The two stage zero feedback RC coupled circuit uses parallel feed (a.k.a. parafeed) output, a topology championed for use in modern single ended amplifiers by Bottlehead and MagneQuest. Parafeed output assures articulate, musical bass, great high frequency extension and minimizes the influence of the power supply on the sound. 

The Bottlehead S.E.X. Kit
There are a few special upgrades available for the S.E.X., including the C4S Constant Current upgrade which consists of a pair of small PCBs with mounted MOSFETs, LEDs and resistors (currently $45), and some higher quality MagneQuest transformers and chokes ($300-450 depending on nickel content). And of course you can throw in the nicer caps and such as well.

Building the amp is the typical Bottlehead affair; there's a wooden base to assemble and stain, a top plate made of aluminum you can paint or leave bare, and a nice big instruction manual that makes things easy for beginners. Because my build included the aforementioned upgrades, I had three manuals to look at.

My first concern was the MagneQuest transformers. They may be well made, but they aren't much to look at in my humble opinion. The chokes hide beneath the plate but the outputs would be visible. I sanded down the metal frame, taped off the center with painters tape, and spritzed it with metal primer, copper hammerite paint, a layer of clear coat, then more hammerite paint. It gives it almost a leather looking texture when the clear coat reacts with the hammerite. I then wrapped the center with some thin black leather (Doc's advice). You can see the difference below between the original look (left) and the modded look (right).

Magnequest choke, transformer and stock bell
I got the plate back from the powdercoater with my favorite antique copper finish, so the next step was to begin populating the plate. I had made a few enlarged holes for the Neutrik locking jack, Cardas RCAs and binding posts, Goldpoint attenuator and vintage lamp.

Teflon 8 pin sockets and boards, Goldpoint attenuator


The Goldpoint attenuator required a little bit of work to fit. In the stock hole position, it butted up against the wood frame and the plate couldn't be seated. The hole had to be enlarged vertically to allow clearance. A couple of the little solder strips required mounting to #8 screws to be enlarged. I recommend one takes their time if they use a drill for this, as I broke two of them :P

Further population included a few little tweaks to the stock kit, including rubber washers for the transformers and chokes, shielded Cardas output wire, bypass film caps for the power supply caps, a few nicer Nichicon caps, thicker shielded wire for the power switch, another solder strip for the Neutrik locking plug to keep the installation clean, and some big hulking paper in oil AmpOhm caps, which required the addition of a set of 2" standoffs. Below are a few progress pics of the amp being built. 

Getting Started

Additional solder post used for headphone output

Solen caps placed temporarily for resistance checks
One thing about the build that was a little difficult was soldering the bottom of two of the power supply caps. There were three or so things going into the top hole of terminal 4 with that little solder strip which made it quite difficult to ascertain whether you had a good solder joint or not. With a flashlight a couple minutes of investigation, it could be seen. 

C4S boards fitted

The little C4S boards got in the way of the standoffs for the large caps, so I flipped them 180 degrees and dremmelled into the unused part of the board for clearance. It's almost comical how large the AmpOhm caps are at a mere 2.2uF.

Finished inside - Front

There's a lot of parts shoehorned in here

Finished inside - Back


There's a lot packed into this little chassis, every inch counts ;) I originally had a set of EAR feet on the bottom of the wood frame, but the caps protrude far enough that I had to get larger feet. I initially entertained the idea of some little brass spikes, but the company selling them wanted $80 for a set of four 1" x 1" threaded brass spikes. I picked up a set of 1" black steel spikes and 1" rubber feet (both under a dollar each) from PartsExpress. I ended up liking the black spikes better, so I drilled out the bottom of the wood frame and threaded it for them.

This amp lets it's business hang out ;)

Finished Back

Finished Front
The emblem on the front I had custom made (I had two made in total). I created the logo and sent it off to a promotional company that makes the little metal emblems. 

UPDATE (3/22/11) I got to have a listen to this yesterday, Eileen got me a replacement set of RCA tubes, and I had a pair of Sylvania coin-bases arrive from another supplier. Sound is really excellent, even before burn-in. No lack in the bass department, a nice powerful sound with just enough detail.

I'm currently using a very special custom 10-3 right angle power cord with this kit (my own recipe). Take a look at the details here.

Wondering where I got all my parts for this build? Check out a list of my favorite online vendors here.

UPDATE (3/29/11) Replaced the stock sandcast 0.1 ohm 5W resistor with a Vishay Dale wirewound in the power supply. Can't tell if it made a sonic difference, but would likely be a little more reliable over the years.


The Fine Print:
Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 


March 5, 2011

The Millett DCPP Engineers Amplifier

Another great project from the man himself, Pete Millett. The Engineer's Amplifier is a distortion canceling push-pull amplifier that makes use of low-cost TV tubes, namely four 6JM6s and 6CB6s. If you prefer the top cap look, you can substitute 6JN6s for the 6JM6s. The amplifier puts out about 18 watts in stock configuration, or well over a hundred with some tweaking (take a look at TubeLab posts especially). As seems to be the recent tradition from Pete, the board is large and bright red, and makes use of a compliment of Edcor transformers. The audio path is pure tube except for the CCS in the LTP tail, a few tube purists may take issue with that but they'd be missing out on a great amp ;)
There they are! Fairchild FQPF8N60C
Some nice concessions to us vintage parts lovers are the lovely green Koa Speers carbon film and traditional carbon comp resistors, the latter being used as grid stoppers. There's also some good old silver mica caps in there. I decided that I wanted this build to be unique, and had some interesting ideas in mind, including a nice Zebrawood wood base with an illuminated slot for the logo and a copper / antique copper powdercoat scheme.


Board top with ceramic tube sockets
Board bottom with resistors populated


I initially build this amp with Russian paper in oil caps:


Russian PIO
But eventually settled on AmpOhm aluminum paper in Oil.

AmpOhm aluminum foil paper in oil capacitors
Here's some final photos of the build:




Orangey Red LCDs
Cardas copper binding posts and Vampire RCAs

The illuminated logo was achieved by using a piece of perforated powdercoated metal as the base, then fastening the "Millett" brass logo I designed on the front. Lighting the logo from behind is a small circuit featuring 16 diffused orange LEDs that runs at 6.3V off the heater. The nice top plate with cool little perforations around the MOSFETs was made by Bob Collins (DIYAudio member PPP6l6gc) for a very reasonable price.

Some other fun little upgrades from the stock build were:
  • Cardas Copper Binding Posts
  • Vampire RCAs
  • Kimber and Oyaide Wiring
  • AmpOhm Paper in Oil Aluminum Capacitors
The sound is very detailed and engaging. Quite the opposite from the lush Dynaco ST70. Another recommended build from Pete Millett.


Wondering where I got all my parts for this build? Check out a list of my favorite online vendors here.



The Fine Print:
Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 


February 21, 2011

The Millett Jonokuchi Headphone & Speaker Amplifier

Our industrious friend Pete Millett has released another build of note, the Jonokuchi headphone / speaker amp. The Jonokuchi, like the Engineers Amplifier, makes use of a compliment of very reasonably priced Edcor transformers. Unfortunately, or fortunately depending on your tastes, the Edcor iron is only available with Royal Blue powdercoated bells, so if you'd prefer another color, be prepared to pay for your local shop to sandblast it off or purchase some unpainted bells of the same size.

The Jonokuchi, like the Engineers Amplifier, makes use of old television tubes that are cheap and readily available. It's a single-ended affair that uses 13EM7 tubes with 13V heaters. As stated on Pete's page: the amp design was optimized for headphone use, but still makes a fine amp to drive small speakers to reasonable levels. This is a relatively low cost build at approximately $200 in parts, just add a chassis. Assuming you make use of the PCB, you'll want to go with an 8" x 12" chassis as it should fit everything perfectly. Hammond makes a cheap one for ~$30, or you could get something more exotic like...

... a Hammond Chassis with Walnut Side Panels
...or a custom chassis from ebay seller po1019
Pete also put up plans for a Front Panel Express Chassis that comes with all the holes already trimmed out and labeled, but for nearly $300 for the chassis alone, I think I'll pass ;)

Jonokuchi with custom FPE panels
I was able to pick up my red board just recently from Pete and I've dropped a few parts on it so far.

The lovely red Jonokuchi board

Mostly populated, a few things left to source
I'll update in the coming weeks as the remaining parts arrive. Should be a fun little project. Now which film caps should I use... Obbligato, Mundorf, Sonicraft... oh the possibilities :)


UPDATE (3/05/11): I decided to go with the Hammond Chassis and AmpOhm Paper in Oil caps. Yes... the AmpOhm caps are a bit large, but with some creative mounting, they didn't pose a problem. Pete has the hole layouts in PDF on his website, so download and either print out yourself on a couple pieces of paper and line them up with tape or let Kinkos or Staples handle it on larger format paper. 


Chassis with drilling holes laid out on top
Drilling out the holes on the drill press.
I had Staples print the CAD drawings on the 11x17 paper, but despite saying not to resize in the instructions, they did anyway and I killed the first chassis, so be sure to measure the drawings first no matter what.


Mouting the AmpOhm PIO Caps

UPDATE (4/18/11): I finally finished up drilling the Hammond chassis, there were quite a few holes for tubes, transformers, a pilot light, the IEC inlet and the PCB mounting standoffs.

Front of the Chassis
Rear of the Chassis with oversized holes for Cardas RCAs

Bottom Plate

All holes were drilled with a trusty low-cost drill press and de-burred with a dremel tool. The rectangular opening in the back of the chassis was cut using a dremel metal cutting disc and then filed manually. Once complete, I gave the whole thing a once-over with 180 grit sandpaper.

UPDATE (7/8/11): Finally got the chassis back from my overly busy powder-coater. Now things are finally starting to come together. In place of the 5 watt 220 ohm resistor I placed a Hammond 157J filter choke (205 ohm) that was primed, painted and wrapped with leather. Cardas RCAs were installed on the back panel, along with some nice thick gold-plated binding posts that Parts Connexion was clearancing. I didn't want to splurge on Cardas posts as this amp will likely see a lot more duty as a headphone amp.

Board fitted in the powdercoated chassis

I designed a nice custom plate with the Japanese Kanji from Pete's Front Panel file and copperplate font spelling out "Jonokuchi". These little touches make the amp feel a little more polished and complete. The screws connected to the aluminum standoffs surrounding the tubes were depth-mounted as I'll be placing some decorative metal surrounds around them.

Custom plate embellishes the top of the chassis

UPDATE (8/2/11): The bell-ends are done being powdercoated in lovely a copper color and have been reassembled to the Edcor iron using my typical brass hardware and acorn nuts. I actually take the time to trim down each screw with a rotary tool to ensure that it's the proper length for the acorn. A few extra minutes of effort here and there goes a long way on the finished product.

The transformers were then mounted and the set of copper colored tube surrounds were screwed in place using very short screws as there is very little clearance between the chassis and the board. A jewel pilot light with a 12V LED was mounted on the left and connected to the tube heater pins on one side.

One the Jonokuchi was completely assembled and measurements checked for D.C., the amp was plugged in to verify the LEDs were lighting and the tube heaters were warming up. I then plugged in my trusty Panasonic tester headphones and had a listen. Unfortunately there was a bit of static noise depending on the position of the potentiometer. I ran a connection from the back screw of the Alps Blue Velvet pot to the chassis ground to ensure proper grounding, but that did not solve the issue. In Pete's design, the JP1 connection is used to connect AC ground to signal ground. After shorting JP1 with a short piece of buss wire, the noise was gone.

The amp itsself is on the lively side in my humble opinion, it possessed a detailed sound with taut bass and no rolling off of the high frequencies that I could detect. Unfortunately I was only able to source one pair of 13EM7 tubes (Raytheons), they tend to be a difficult tube type to find in the usual places. I feel that with the right compliment (some warmer tubes), I'll be pretty happy with the Jonokuchi.

UPDATE (8/8/11): I was able to get some custom engraved brass plates for the front of the unit detailing the operation of the push buttons, so those will be the final touch. Here's some final photos:

Jonokuchi Front
Jonokuchi Rear

Jonokuchi Side

Jonokuchi Inside

The Fine Print:
Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind.