Bryston BP26 preamp clone…

Even though my pile of finished (and half-finished, and not-even-started-yet…) projects seem to be steadily growing, I can’t help but keep an eye on eBay for new and interesting designs to add to it. I’m not sure I can describe fully what makes a design “interesting” to me, but something about how it looks, how well thought-out it seems to be in terms of features, whether it seems to be well-engineered and also whether it’s fully-assembled or PCB/kit so I can influence component choices etc. myself – and of course whether it looks like good value.

The latest thing I stumbled upon was a blank PCB of a (supposed) clone of a Bryston BP26 preamp. To be honest Bryston is one of those brands that I know about but have never really had any particular opinion about. I get the impression that their stuff is solid and well-engineered, but their representation in Europe is sketchy and the design of their products has never really managed to catch my eye. However, regardless of the supposed provenance of this kit – you never really know how close to the original these “clones” actually are – a fully discrete preamp design with both balanced and SE inputs is definitely interesting. The board looked good on the pictures and as I had most of the expensive components (connectors, relays etc. ) and quite a bit of the other stuff on hand already, I decided to take a chance on it.

Normally the quality of these ebay-offerings is a bit hit-and-miss to say the least, but this one I’d place firmly in the “hit” category. The board is good quality and it is supplied with documentation that is well above average for what you can expect. Full, readable pdf-schematic, full BoM (with just a few untranslated comments in Chinese that you have to work out), a basic adjustment procedure (only one trimpot per channel) and – something completely unheard of – a mechanical drawing of the rear panel cutouts for the connectors!.

The board came together quite easily, and although it took a while for me to operate the input selector correctly during testing to actually get sound (…) there were no real issues getting it to work. The board seems stable and well-behaved in initial testing, meaning no nasty turn-on/turn-off thumps, no noise and no unexpected spikes in DC-offset or bias at any point.

Normally I’d try and finish the full pre as quickly as possible, but this time I’ve chosen a slightly different strategy. I’m going to listen to the board in my own system before i decide if I want to commit the extra money for the final enclosure (mostly because a customised back panel is probably going to cost about the same as all the other components combined). While I am waiting for a PSU board that should be here in a couple of weeks, I’ve repurposed an old bottom plate into a makeshift test bottom. Let’s see and hear what this thing can really do then 🙂

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Music Box…

For some time now I have been using Raspberry Pi-based music streamers in combination with Volumio as my primary signal sources. On the hardware front I have both analog and digital versions of the Hifiberry Pro+, an Allo Mini Boss and an ES9018-based DAC HAT. However, to see if I could push the quality up even further I wanted to try and do something myself as well.

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Wooden amps…

Well, not completely wooden of course! Some years ago I showed a plan to make a set of amps with wooden front panels, because I picked up some pre-cut wood in the right dimension on one of my trips to Japan. A while back the plan was resurrected, but then immediately brought to a halt because I had to enlarge some already-drilled holes and managed to destroy one of the panels in the process – bummer!

However, in the mean time I’ve found a local place that sells wood trim pieces for professional craftsmen and in their assortment I found a pre-made profile in the right dimension for a 1U panel and in several different kinds of wood. I chose oak as it is more my thing than the darker wood types and it goes well with both black and silver fittings. I’ve recently invested in a better drill press, so redoing the panels were without accidents this time and I also managed to overcome my fear (or is it loathing) of doing cabling to finally complete the set 🙂

The set consists of a DCB-1 preamp (on a clone board), meaning a DC-coupled version of the classic B1 buffer circuit, and a Hifimediy T4 Tripath-style class D power amp. The power supply is a surplus N2 XL375-type which I bought a small stash of some years ago.

No detailed listening impressions from my main system yet, but on test speakers it sounds excellent as I expected from what is basically an “evolution” of my old B1/125ASX bedroom system. Both components include relays to minimise turn-on and turn-off thumps and so as a set they are well-behaved enough for daily use (which is always one of my success criteria). As far as the looks are concerned, I could honestly see this being something I will want to try again in the future…

Buying “suspicious” parts…

With the current trend in audiophile parts being that all the “old” audio grade parts that we know and love are either being discontinued outright or at least replaced with something in impossibly small surface mount packages, it’s almost inevitable that we all at some point face a choice between giving up on a project and sourcing parts from “questionable” channels such as eBay or Aliexpress.

Here are the questions I personally ask myself before buying something and while they are definitely not a guarantee against wasting your money, they might help someone decide when to take a (calculated) risk and when to pass up what otherwise looks like a good opportunity.

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The last F5?

I’ve built a couple variations of the F5 already and I have a couple more that haven’t been finished yet, but the last one of them is here. It’s a pair of mono blocks with fan cooling and a large power supply 🙂

This project was of course driven by the fact that I really liked my original F5 build, but also by the fact that I had some suitable heatsinks and that I got a good offer on a couple of transformers that were really meant for a Pass/FirstWatt mono block build (2x18V/250VA each). The heatsinks actually turned out to be a mixed blessing, because they are just a millimeter or two too tall for most of the readily available enclosures, so I had to go up to a 3U size. I also decided to choose a slightly larger footprint instead of trying to shoehorn everything into a “real” half-width box. That annoyed me in the beginning, but to be honest I am not regretting that now.

Design-wise, you should be able to see the inspiration of some of my other projects in this one and that is no coincidence – there were some concepts I wanted to “recycle”. That last piece to arrive of what you see now was the rear panels which showed up a few days ago. Fitting them was a quick job, but they are quite expensive and so I can’t help but breathe a sigh of relief when they fit as I intended the first time. No matter how many checks and paper mock-ups I have done in the creation process it’s always a huge relief when everything works…

Still a bit of a way to go, but getting this far was very satisfying 🙂

The BoSoZ…

When I started to look around for balanced preamp designs some time ago, the BBA3FE wasn’t the only design that turned up. Another candidate was a sort of “predecessor” for it, namely the Pass Balanced Zen Line Stage (aka BoSoZ). I was a little slower getting started on this one so the BBA3FE came first, but a few weeks later inspiration struck and I managed to finish the layouts for both the BoSoZ and the matching PSU as well.

I chose a mono configuration for the amp board to maximize flexibility and minimize board cost. I’ve only made some minor changes to the schematic, but you should be able to see the resemblance to the BBA3FE layout easily. My prototype version uses 27.5mm output caps because I had some I wanted to use, but the “real” version of the board has space for 37.5mm caps as well and is only slightly larger (app. 5mm deeper).

As you can see I’ve actually also made good headway on the mechanicals of the design so what you can see now is really a semi-completed amplifier. Other than the new amp/psu boards I’ve picked components “off-the-shelf”, i.e. input selectors, an output relay board and an aux PSU that I have previously done, so putting it all together wasn’t that hard to do.

I need to pull myself together a little and get the wiring done before it will play music for real, but other than that it’s looking very promising – and the initial sound quality tests definitely match that as well 🙂

A Christmas present in March…

Yes, it’s this season’s last (or the year’s first) Christmas present which finally turned up 🙂 It’s a partial kit version of the “B1 Korg” preamp circuit, which is to say B1 that Nelson Pass modified to use a Korg “Nutube”.

The “Santa” who was kind enough to send the package is none other than Nelson himself who a couple of months ago offered a limited batch of boards and JFETs for just the cost of postage. Naturally I jumped on this and somewhere along the line a Nutube was thrown in the package as well. The only downside was a longer wait, but I would be an idiot if I complained about that – so I don’t! 🙂

The Nutube is basically a solid-state version of a triode tube, meaning it doesn’t require high voltage, doesn’t use (and waste) a lot of power and and doesn’t have a relatively short lifespan. What it retains is the tube “character”, meaning a relatively high and almost completely 2nd harmonic distortion level. I have actually been looking at the Nutube during my trips to Japan, but it seemed a bit expensive on its own and there were no designs available that seemed to scream “build me” as a looked at them. However, now there really was no excuse for not trying it and as regular readers will know I have been a big fan of the original B1 design and its derivatives.

I don’t have all the parts in stock, but I’ll be picking up my list again this weekend and trying to get an order out the door as quickly as possible. The board and the Nutubes are now for sale in the diyaudio store (also courtesy of Nelson) so even if you didn’t get a free kit you can still get in on the action 🙂

Nudging projects forward…

Sometimes my projects are “stationary” for a very long time, and then a small nudge from another project is just what was needed to get them going again.

The current example is this (eBay) clone of an Ray Samuels Audio XP-7 headphone amp, which has been needing a custom front panel for several years now. Originally I tried drilling the case myself with a stepped bit, but that simply wasn’t accurate enough and so I needed to remeasure and do a custom panel instead. I’d been dreading this because of the frustration I feel when it doesn’t work out (and custom front panels are not cheap), but spurred on by my recent success of doing the back panel for the ES9038 dac I decided to give it a go, and this time it actually also worked on the first try 🙂

The XP-7 is a pretty straightforward headamp design with an opamp and a BUF634 output buffer in the feedback loop, as was the “state of the art” around 15 years ago 😀 . The only things that stand out in the clone design are the feedback resistor values that are lower than usual (which means lower noise) and then the chosen opamp which is an AD797 that also has very low noise. Together they should make a very dynamic amplifier and I remember being pleasantly surprised when I tested the bare board. However, putting it in a case should make is easier to try again (although to be honest I do next to no headphone listening these days).

The battery supply is two 9V batteries which is normally very impractical, but it does also have some benefits and I actually use a battery-powered CMoy-style headamp for a lot of testing (no risk of ground loops etc.). There’s still a bit of wiring to do here, but it’s always a nice feeling to move something along that has been sitting on the shelf for far too long 🙂

Power-delay timer for 5/12V triggers

This small design is actually a solution to a problem I have, but as it’s also one I’ve seen others describe from time to time I still find it worth sharing.

My current preamp is discrete and has a 15-second delay before the output is turned on (to allow it to stabilise).  This means that the poweramps I use will turn on before the preamp and consequently I get a bit of a turn-on thump in the speakers when the preamp turns on. There is a 12V trigger output on the preamp, but even if there was a trigger input on the poweramps as well (and there isn’t) the 12V trigger is active immediately and so that doesn’t really help.

Of course you can solve this manually by waiting for the preamp to switch on fully, but 15 seconds feels like a long time when you’re just waiting and so I decided to do something to address this terrible hardship… 😉

The easiest way to fix it – introduce a longer delay before turning on the power amps – only required a modification of my previous delay circuit to power a bigger relay, so that’s what I did. The relay I’ve chosen is an Omron G5LE which is rated app. 5A with a reactive load, so that should be fine for most amps in the power range that I normally use. Not all manufacturers publish the specs of their 12V triggers, but those that do generally state a max. current capability of 100-150mA. As a single 12V board draws app. 45mA with the relay engaged powering one board should be fine and even adding a second should be trouble-free as well.

When I made the board I only really could see the point of a 12V version, but afterwards I realized that a 5V version would be able to work with USB-power and that might be worthwhile as well. On 5V the current consumption should be just under 100mA, which pretty much any (non-portable) USB source should be able to provide.

I’ve tested the circuit and it works as expected, so apart from still being on the lookout for suitable case it’s more or less “mission accomplished” for this one 🙂

Desktop DAC with a cheap ES9038-board…

Last year I mentioned that I had bought a cheap ES9038 DAC-board and now that’s starting to come together. This will be used as a controller to feed a pair of active monitors on my desk (that’s the “need” I mentioned in the original post) where it will save me a box as I currently have a separate USB DAC and passive pre). To make the box a bit more versatile (and to use some of that empty space inside…) I am thinking about including a Raspberry Pi Zero W in the box and connecting it to the I2S-input of the DAC plus add a potentiometer for volume control (digital on the DAC via an onboard uC). The ES9038Q2M DAC is asynchronous with its own clock so perfect for use with the RPi and this combination would give a Volumio-based source with two additional digital inputs and a volume control. That means that can be connected directly to a power amplifier input or active speakers – perfect for the desktop or a second system!.

The slightly unusual power arrangement with 5V input to a DC-DC converter is to support this setup. It will allow the RPi to be powered on constantly while the DAC power can then be switched on and off. I bought an early (”first generation”) of the ES9038 board with a slightly different power setup than the current version and crucially no DC input connector that I did not need (of course the newer versions of the DAC board can be used as well). Check the diyaudio-thread for the board for loads more examples of how people have been hacking this by the way – some of them are close to unrecognisable.

The original idea was basically to allow the power source to be a cheap 2A USB-charger, but reality seems to have thrown a spanner in the works here – none of the chargers I have tried will actually let the DC-converter start properly because of the high inrush-current it draws. Using a slightly more beefy 5V supply fixes the problem though, so the concept is more or less intact anyway 😀

Part of what drew me to this DAC-board originally were the on-board connectors, but as I couldn’t find any mechanical drawings having to make the back panel by hand seemed a bit of a risk. Using my own measurements and the datasheets of the connectors I managed to trace it out and with judicious use of paper printouts from Frontpanel Express to check the dimensions against the physical board it actually fits well for a first time attempts – although this is definitely an occasion where I would wish for a 3D-printer or a laser cutter to make prototypes before betting my money on ordering “the real thing” from Schaeffer/FPX (they are becoming quite expensive I think).

Soundwise this seems quite close to the other ESS-based DACs that I have tried. I am not sure that is such a good thing to be honest, but I am prepared to compromise a little bit on my desk where convenience is important and the differences aren’t night and day anyway 🙂