**Edit**

Instead of leaving this post with info what will slightly disagree with the updates I’ve decided to correct it to follow the design changes.  The new Amp fits in as Amp8S (even numbers are balanced, odd numbers are SE).

With the success of Amp1S and the enjoyment I got out of the process, the build and the customer feedback I received, I’ve decided to step it up and develop a higher end battery powered balanced desktop amplifier.  The electrical design for this amp has been in the works for years, now it’s time to make it a reality.

Unlike Amp1S where they sold before I was able to keep one for myself, this time the amp is as much for me as anyone else.  This will be the amp I want with the design and features that I’m looking for.  As it happens, I’m probably not the only person who this will appeal to.  Target quantity is only 5 pieces possibly 6 (0 of 5 will be mine) with each having the number engraved either on the front or back.. 1 of 5, 2 of 5 etc… if I do make the 6th unit it will be 0 of 5 and the unit I keep.  Given the roadmap I have for various amplifier designs and styles, and price ranges, this will likely become Amp8S.  The S refers to the Stepped attenuator and Special edition nature of this amp the same way it did in Amp1S, the 8 is where it fits into my master plan.

Design goals:

– Lithium battery powered
– 50+ hour battery life
– Automatic built in battery charging
– Standard RCA and 3pin XLR balanced inputs
– 1/4″ and 4pin XLR outputs (I’m doing some final testing of a dedicated 3.5mm IEM output jack with low noise, low gain)
– High output current (would drive small speakers)
– Drive headphones like the HE-5/6, LCD2/3 with authority/clarity
– Use balanced stepped attenuator
– Simple, solid, attractive enclosure
– Dual mono balanced construction, including separate battery packs and a physical division between the channels.

The Amp1 enclosure was based on cost effective design, simple assembly, inspiration derived from Bosch Rexroth extruded aluminium.  I still love the design, of course it’s mine, however with more freedom I think I can create something much more interesting.  I love the look of machined aluminium, a recent piece I milled for a new charger I’m building for the Electric Porsche has revived my interest in designing a nice thick aluminium face.

With a target quantity of 5-6 units instead of a small production run in the 100’s I have more freedom from cost, and it’s within the means of my CNC router that is normally reserved just for prototypes.  This means I will have complete control over the finished product, but it also means it could take awhile.

I have a pair of Amp1 Upgrades that I use for my personal use, and for the past year they’ve been powered by a lithium battery.  This battery appeared in my first blog post and is something I use for all of my testing, the final revisions to Amp1S were done powering it with this battery.  The problem is that even though Amp1S sounds wonderful with the included power brick, it actually sounds better when powered by the battery.  I contemplated turning this stand alone battery into a product, however it’s better to simply incorporate it into the amplifier design from the start.  Amp8S will not have a battery that plugs in the back in place of the power brick, the amps entire power supply will be designed around the battery being an integral part of the Amplifier.  Actually two batteries to be specific, each channel will have a separate battery, when used with the balanced 4 pin xlr output the two channels will be physically and electrically separate.  Due to the battery monitoring and charging system I was unable to keep the batteries separate, but the single battery is twice the size and very stable.  They will share the same face plate and volume control (Quad stepped attenuator), however the enclosure will be constructed from physically independant “boxes”.  One advantage of the dual mono approach is simplicity of execution, I design one balanced channel/battery/power supply and build two of them to make an amp.

The PCB/Battery/Enclosure designs are all underway, I will post the progress as I have more to show.  Pricing will be announced once I have a firm handle on both the PCB design, Enclosure and BOM.  Although the price will be quite a bit higher than any of the versions of Amp1 it will still provide very good value for money.  And like Amp1S, once they’re gone they’re gone!

The LD2.24M was put on the back burner due to issues with my enclosure manufacturer.  I made a hand full of enclosures on my CNC mill that I use for prototyping, it isn’t a production machine, which makes the process quite slow.  This is fine for prototyping but not for manufacturing in any quantity.

I was recently approached by a small US metalworking company (who is already tied to the car audio industry) who will be manufacturing enclosures and assembling the finished product.  The electronics will still be manufactured and tested by RW Audio.

I will be updating the website with purchasing information for the line drivers, all USA sales will be handled through Toolmakers Metalworkz.

Stepped Attenuator   –   check
1/4″ output jack   –   check
RCA Inputs   –   check

Since a picture is worth a thousand words, here are a few pictures to get started.

Limited Edition 2013

Uses existing PCB, side extrusions, top, bottom, feet and hardware.

1/4″ output jack and RCA inputs.

I’m very happy with the final product, and honestly the sound quality using these larger jacks and stepped attenuation is much better than I had expected!

As a prototype I have the parts to assemble three Amp1S’s (I will likely keep one) if there is enough interest I will put this into production as a real product.

I decided to try a different direction for a possible upgrade.  This time using a small stepped attenuator, instead of the very large Alps RK27.  This allows the original PCB to remain with only slight modifications.  It still uses a 1/4″ headphone jack and can either keep the existing 3.5mm inputs or be swapped out for RCA inputs.  Since the original PCB remains this modification could be implemented by skilled Amp1 owners on any existing Amp1 or Amp1 Upgrade.  The key to making this work is flipping the PCB upside down within the enclosure which gives enough clearance for both the stepped attenuator and 1/4″ jack to fit in the stock locations.  The existing hole for the 3.5mm headphone jack must be enlarged to mount the 1/4″ jack but that is the only enclosure modification required.  If RCA inputs are desired the existing holes will also require modification, this can be easily done with a drill press or even hand held drill once the amp is disassembled.  The power LED if kept would require glue/epoxy to mount it to the front panel.

Let’s try this again, before even posting this update on the possible change there is another change.  I didn’t like the amount of work required to make these modifications, (drilling/milling) and the requirement to flip the board upside down within the enclosure.  The best solution is to use a new front panel if changing the pot/output jack, and/or change the rear panel if switching from 3.5mm jacks to RCA’s.  So by adjusting the mounting location of the new stepped attenuator and 1/4″ output jack the main PCB remains in the stock location with only small wiring changes.  To allow quick updates and without locking myself into another front/rear panel design to have EDM cut, milled, engraved, anodized, paint filled (with minimum quantities of course), I’ve opted to try a different solution.

Above is a rendering of the new front panel showing the new amp dubbed Amp1S with the “S” referencing the “stepped attenuator”.  This will bolt up to the current Amp1 enclosure/PCB but now raises the volume control and output jack high enough to clear the PCB.  The LED now stays in the stock location and doesn’t require modification.  I’ve found the stock pot and headphone output are difficult to desolder from the PCB, for this reason I won’t be selling an upgrade “kit” at the moment, I will just be selling complete Limited Edition Amp1S amplifiers with the stepped attenuator, 1/4″ output jack and RCA inputs.

The single most common question I’ve received over the years regarding Amp1 is can I buy a version with RCA inputs and a 1/4″ headphone jack.  The answer has always been no, because there simply wasn’t room inside the enclosure with the existing PCB.  The 2nd most common question, usually from customers putting the amp together themselves was can I buy a better volume pot for Amp1, again the simple answer is no, I’m using arguably the best volume pot in this size range.  Then they would ask can I fit in a different pot, and once again there simply isn’t room with the existing PCB.

The most recent person to ask this question was Matt, he posed very simple questions, and as always the answer was no there is no other volume pot that will fit.  This started to make me think WHY is it there no other volume pot would fit.  When I designed Amp1 the best compact pots available (with very similar performance), were the Alps RK09 and the Panasonic EVJ, I had used the Panasonic in my line drivers for years but with similar performance the Alps included a switch.  This switch simplified the design of Amp1 eliminating the need for a separate power switch somewhere on Amp1.  Ironically I recommend that people leave Amp1 on for best performance (why do we need a power switch again?).

So I need a volume pot, I don’t really need a power switch, I want RCA inputs and a 1/4″ output, this simply won’t fit!  Actually I’ve never tried to make it fit (without the PCB installed).  After thinking about it for a few days I rummaged through the parts bin and I had some decent panel mount RCA jacks, an Alps Blue (RK27) Pot and a very cheap generic 1/4″ jack.  I enlarged the input/output holes in the back and the RCA jacks mounted very nicely, same with the pot and headphone jack, enlarging the holes allowed proper mounting, although the shaft on the RK27 is too long it would need to be cut down, and the 1/4″ jack is VERY close to the pot, but all of the headphones I have on hand work.  The headphone jack will be moved down and to the right to give more clearance and leave the headphone label visible.

The PCB is sitting below the amp due to the obvious lack of space and the reason I had been saying no all these years.

I don’t like the quality of the 1/4″ jack but I have found a better quality version from one of my vendors that has terminals out the end that wouldn’t allow PCB mounting but short air wires would let it connect to a PCB.  Same goes for the Pot, there simply isn’t room for PCB mounting, if you look close the pcb terminals are sticking out the left side with air wires connecting it to the PCB.  Now the PCB is obviously way too long!  Portable1 is similar in design to Amp1 but mainly surface mount, what if I switched the resistors/capacitors and anything else that made sense to surface mount, much of this could go on the underside of the PCB.

After a bit of fiddling in my spare time I have an Amp1 PCB design that is 1.08″ sorter to allow clearance for the Pot and 1/4″ jack.  The RCA jacks sit above the board so they simply need new connection points.  Amp1 was designed with the high gain setting, the low gain was added for compatibility, however it’s always worked better, cleaner, quieter in the high gain setting.  Axe the low gain, switches, capacitors detract from quality, eliminate them (and the space they took up on the PCB).  What we are left with is an entirely redesigned Amp1 with the same power supply, there are  TO-99 footprints nestled into the DIP locations directly on the board.  This means that my recommended LME49720HA can be inserted and soldered directly to the board with no adapters or sockets.  The signal path of Amp1 is sorter than the original version, and the left and right channels are as symmetrical as the space would allow.

This new PCB fits the existing enclosure and mounts to the bottom panel as usual.  The two front mounting holes are gone, requiring a new hole to be drilled in the bottom panel, not too difficult.  Because of the size of the Alps RK27 the bottom panel won’t mount properly to the enclosure side panels, this means spacers will be used to “lower” the bottom to allow clearance.  This won’t be noticeable from the front as it will still sit behind the front panel, however a small gap will be visible in the rear.  The alternative is cutting a relief in the bottom to allow the “side” of the volume pot to stick through.  The pot uses the existing location on the front and once the shaft is cut down slightly the knob will fit properly and look like any other Amp1.  The difference on the front will be the 1/4″ jack, this will require a slight movement to the right, so the hole will have to be both enlarged and moved.  This can easily be done on a CNC milling machine.

I’ve been listening to this new Amp1 (just a modified stock Amp1 PCB) on the bench for awhile now (stock op-amps) and the new pot is a pleasure to use and sounds wonderful.  I’ve just started testing with the Lithium battery that I mentioned in the previous blog post, the results are simply awesome, I love this volume pot, and it’s quite convenient to be able to use RCA inputs and not requiring an adapter to use 1/4″ headphones.  About 8 hours have passed since the previous comments, I’ve since swapped to the HD650’s which sound equally as good as the K240 Monitors.  The 2nd switch is from the stock op-amps to the LME49720HA, this really brings out the top end in the HD650’s which are known for being quite dark.  The op-amps are fully “broken in” already as they were pulled from one of my other personal amps, once they warm up I will switch back to the K240’s for an update on performance.  Back to the K240’s like the HD650’s there is a new top end and level of detail that simply doesn’t exist with the stock op-amp.  Even the Alessandro MS1’s have a smooth detailed appearance and the volume pot gives a nicer range for this low impedance headphone.

After some more testing I will have a sample batch of PCB’s made and if they meet my expectations I’ll produce a new version of Amp1 with RCA inputs, Alps RK27 volume pot, and 1/4″ output jack all in the existing enclosure, by default it will likely come with the TO-99 LME49720HA op-amps soldered directly to the board, however for those who must swap them I will make it available with dip sockets instead.