More Naim clones…

Yep, I know I should be working on the HackerNAP instead, but I was just in the mood for building something else and as I had another Naim clone kit lying around, here we are 🙂

This is a NAP140 clone (or one of many actually) from ebay. I bought a cheap kit thinking I could get away with just replacing a few caps as usual, but I actually ended up replacing most of the resistors as well after a couple of them tested out of tolerance – hmm…

Also, while the listing said the 2SC2922 output transistors would be genuine after checking them I’m fairly certain they are not – at least the screen print looks wrong. The PCB is also much flimsier than usual, so actually this is one cheap kit I wouldn’t recommend that you buy 😦

Anyway, I know a couple of places that have genuine Sankens at a reasonable cost, so with a few of those and the last few caps (already on my next Mouser-order) then we’ll see if this one powers up 🙂

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Sunday morning chipamps…

It’s been some time since I did an ebay kit, but that doesn’t mean I have given up on them (in fact I bought plenty…) and a cheap kit is still a great thing to play with on a Sunday morning**

It’s a pair of power amps based on paralleled TDA7293 amplifier ICs in the correct “master/slave” configuration as per the data sheet (and this discussion on diyaudio). The TDA7293 and TDA7294 chips are among the few survivors of the “purge” of audiophile components and they should still be available. Unlike the LM38xx-series and its siblings, the TDAs have MOS-FET output stages which means they can run in parallel without resistors to limit current sharing between outputs. The parallel arrangement allows for more current into low-impedance loads, but as the TDA7293 will work on up to +/-50V rails having two ICs also makes for a fairly serious effective power output.

These kits are seriously cheap and although I’ve tried to use most of the components that came with the kit, some parts have been replaced for cosmetic reasons (because that matters to me, sorry!). Even with component replacements though, these kits are so cheap that there is no real excuse for not trying them – even if you don’t need new amplifiers at all 😉

No real sound impressions yet, but I know these chips can sound really good so I am looking forward to seeing how much of their potential can be unlocked for the same price as a takeaway meal 😉

**Yes I know it’s not Sunday today, but as Whit Monday is a holiday in Denmark it felt like Sunday morning 😀

A cheap fantasy….

Yes, it’s a not a very good joke – sorry! 🙂

Haven’t done one of these “cheap kits” for a while, but I am possibly getting a bit more picky. However, this particular board was around 20 USD for a kit (excl. tubes) and so the risk was manageable. It’s supposedly a clone of the famous Matisse “Fantasy” preamp which uses 5670 tubes. I wouldn’t know to be honest, but I have been intrigued by low(ish)-voltage tube circuits for a long time and so I took the plunge.

I’ve replaced some components (mainly the capacitors and the volume pot), but there was still plenty of kit parts left to salvage to make it worthwhile (tube sockets, semiconductors, heat sinks etc.) over buying just a blank PCB. The caps probably would have worked just fine, so that replacement was mainly cosmetic. One notably exception was the 80V rated electrolytic in a part of the circuit that sees rectified 55-60VAC – a little too close to the limit for my liking.

The tubes ‘ve bought from an Eastern European seller and they are 6n3p-E which is supposedly a long-life Russian version of the 5670. The circuit runs off 50-60VAC, so it’s what I would call a “medium-voltage” project. As usual, the instructions that came with the kit were poor (especially if you can’t read Chinese 😉 ) but with a bit of care it wasn’t a problem to put together.

Sound quality? Well, as usual with these projects I’ve only really done basic bench testing for now and so the only thing I can really confirm is that it produces sound. One of the things I did notice though was that it seems to be a well-behaved circuit. By that I mean no big turn-on/turn-off transients, no excessive noise and no microphonics from the tubes. I might just have to splurge for a proper transformer and case for this anyway…

More JLHs…

Yeah I know, I should probably stop making these at some point 🙂

We’ll do this one quickly then: Standard JLH1969 Ebay-board with upgraded components and better transistors (MJ15003). Fan-cooled heat sink with temperature control (we’ll see how well that works…). Industrial-grade 10A switching PSU per channel. Monoblock configuration in Modushop GX288 chassis.

The PSUs (Artesyn NLP250) are overkill for this application but they were cheap (surplus items). And besides, more is better – right? Not necessarily here though, because some of these industrial-grade PSUs have a reputation for being extremely noisy at low power output. As a class A amp, the max. current consumption of the JLH should be twice its quiescent current (so app. 2.6A) and each PSU will deliver four times that before the limiter kicks in. Whether this is a real problem here or not I don’t know yet, but there are no audible artifacts at all so I am not overly concerned right now.

The heat sinks were also surplus items and I am not sure exactly what their rating is. At full speed the fans are a bit too noisy for my liking (the heat sinks add some flow noise as well) but if the fan speed is lowered a little I don’t think it would be really noticeable once the amps are seated in a rack. For the time being I have installed some small temperature speed control boards for the fans (hence the somewhat messy wiring) but depending on how well that works and how hot the amplifiers get, I may go back to fixed resistors. The PSU already has a dedicated 12V fan output so the resistor doesn’t need to drop a lot of power.

The heat sinks had a cutout in the side that was just too narrow for the angle brackets to fit into. The best solution would have been to mill the ends of the brackets to fit the cutout so there is only one contact surface. Unfortunately I don’t have access to a mill anymore so I had to find another solution: A copper “heat slug” to fill the gap. Just a piece of copper bar in the right thickness cut to size and with thermal grease on both sides and that should provide the best possible thermal transfer under the circumstances.

So, will I stop building these amps? Erm, no! 😀 I am out of the ebay-boards but I do however still have my own version of the 1969 JLH that isn’t cased up yet. This build has given me some inspiration for how I can build that into small monoblocks so while it might take a while to do at least I know what parts to keep my eye out for 🙂

Distractions…

My work keeps me extremely busy at the moment, so when I finally have a free weekend I need some way to distract myself from work. Unfortunately the lack of time means that it is hard to start up any project that is even a bit complicated – however, you can always put a little kit together on a Sunday afternoon, can’t you? 🙂

The kit for this time is (supposedly) a clone of the Graham Slee Solo headamp. The circuit here seems quite traditional, an opamp for gain, a pair of transistors for output and a pair of LM7815/7915 regulators for power.

As is my custom with these builds, I have “enhanced” the ebay kit with some selected pickings from my parts bin. All PSU capacitors are now Panasonic FCs, the decoupling caps are NOS Elna Cerafines and the input caps are NOS Blackgates (they have been in storage for far too long by now so I have to use them :)) I have also replaced the volume control with an ebay stepped attenuator and the opamps have been changed from the NE5534s that came with the kit to LME49710 instead.

Sound quality is not bad and there should be room for some tailoring by swapping opamps. I don’t have time for this right now, but it’s nice to have something to do on another Sunday afternoon, right? 😀

Panda Headphone Amp

Another half-arsed half-finished project… 😀

This is a hifidiy.net HA-1 mk2 headphone amp, also known as the “Panda” amp. I bought the kit a few years ago when this amp was FOtM (“flavour of the month” – or as some would say “fad of the month” :D), but of course I don’t really need any more headamps and so it was just lying in my box of “may need at some point” unassembled kits. However, I few weeks ago I was cleaning looking through said box and found it again, and since I felt like soldering something that day I started working on it.

Unlike most “cheap” kits, this actually comes with decent components. I replaced a few components for cosmetic reasons and bought new main caps because the ones provided did look a bit worn, but other than that everything is what was provided. The amp is an all-discrete design with JFET input stage and a BJT output stage, so I had to do some matching to the input FETs, but other than that it is a straightforward build. Initial impression is that the sound is very good, but one of the reasons for the hype around this amp originally was that it is supposedly very good with AKGs and so I need to dig out my K501s and K701s to try that as well (they’re in another box..) 🙂

Now, I am still counting on the upcoming x-mas break to give me some time to finish some builds, but it’s unlikely that this will be one of them. When I started putting the board together I just wanted to do some soldering, but I didn’t have a case design in mind then. I still don’t to be honest, and since I’ve used 35mm tall heat sinks and capacitors the board is now too big to fit into a 1U modushop case – grr!

Maybe it is time to head to ebay for some “inspiration” instead then? 🙂

WCF amp completed

It’s been quite a while since I really finished a build. Sure, lots of small steps forward on lots of other projects, but nothing really finished to that fantastic moment where you can actually hear music for the first time 🙂 (or the slight less fantatic moments where you see smoke, a broken fuse or simply nothing at all… 😀 )

This is the just the WCF headphone amp I build a while ago (see this post) which has now been cased up. Instead of putting in a lot of effort on DIY mechanics I took a shortcut and bought the bespoke ebay-chassis for the design. It’s not bad, obviously fit and finished has been seen better, but given how I normally struggle to do the mechanical stuff it was still worth it. And anyway, this was a bit of a “sideline” project anyway. The transformer is from Audiophonics because they had an “off-the-shelf” model with the right specs which also was about half the price of a custom one from Toroidy.

Listening at the moment with a newly-purchased (but second-hand) Arcam rDac as the frontend and this amp is still not bad at all for the modest outlay I think 🙂

WCF tube amp…

Another installment in my “take a cheap ebay-kit and tweak it” series – a tube headphone amplifier :D. I do what I normally do with these – I prefer to buy a kit instead of a finished board (even if the price difference is very small) and then replace any parts that look “questionable” or should be upgraded.

The circuit in question is a White Cathode Follower (WCF) and the tubes needed are (equivalents of) ECC88 (input) and ECC99 (output). I haven’t actually checked if the circuit is properly calculated as a WCF, but it’s probably close enough for me… 🙂 The main attraction of this kit was that that it was simple, cheap (25 USD shipped excl. the Alps pot and the tubes) and that it needed voltages that I already had a suitable spare transformer for (200VAC and 6.3VAC). I have reused most of the components that came with the kit, diodes, resistors, screw terminals etc. The tube sockets I replaced, but the ones that came with the kit were quite good as well. For 25 USD including postage anything other than the PCB I almost consider a bonus, really 🙂

One thing I have replaced though is all the electrolytic capacitors. They looked fine on the outside, but when I checked them against the manufacturers datasheet I found problems on a couple of them –  the case size wasn’t listed for that particular capacitance/voltage combination!. This is a major warning sign that either means that they are a special-order item bought cheaply as surplus by the kit manufacturer (possible) or that they are of questionable origin, i.e. counterfeit, relabeled used caps or similar (which is sadly also definitely possible).

Since we’re dealing is a high-voltage amp I did not want to take any chances and so I purchased new electrolytics from Mouser which should be completely safe. I also chose different values (for better bass with low-impedance phones) and higher temp. rating (for increased reliability).

Soundwise this definitely sounds like a tube amp 🙂 The bigger output caps gives decent bass even with mid-impedance (60-150 ohms) phones and moving to higher impedance phones seems to improve the sound further. I have no imminent plans to case this yet, but as a cheap and cheerful build I am quite happy 😀

Resurfacing…

Things have been quiet here lately as real life once again intrudes on my build time 😉 I did however manage to finish one small project over the last couple of weeks, a clone of the Grado RA-1 headphone amplifier. Well, “clone” is maybe stretching it a bit – maybe it should be “inspired by” instead 🙂 In any case, the design is nearly identical to the “cMoy” amplifier design by Chu Moy, the founder of one of the first internet forums on headphones and headphones listening, headwize. The site is not active any more, but fortunately the excellent collection of headphone-related articles that was published there has been preserved – check it out!.

The recipe for this amp is my often-used “buy cheap ebay-kit and replace parts”, but this time I’ve probably gone a little more overboard than usual with my replacements (always nice to have lots of leftover parts in your collection ;)). The resistors are Vishay-Dale RN55 mil-spec, the electrolytics are Elna Cerafine and the input caps are Blackgate N bypassed with Mundorf M-Cap Supremes. The whole thing is powered by two 9V batteries in a Bulgin holder.

And the sound: Well, with the stock JRC4558 op-amp there’s only one word for it really – disappointing! Sharp, closed-in with very little sound stage and absolutely no way to ignore that you are wearing headphones. However, the beauty of the RA-1/cMoy design is that there is only one active part, so changing the sound by changing the op-amp is very easy. I had another look in the parts boxes and found a TI OPA2107 to try instead.

The glare and the edginess is now gone, the soundstage is wider (though there’s still no doubt you are wearing headphones) and the listening is much more enjoyable all round. I might try a few other replacement opamps as well (the AD8620 and the LM4562 would be good candidates I think) to see if it is possible to squeeze out a bit more performance. This isn’t a world-beating amplifier by any means, but with the right op-amp it is isn’t bad sounding at all.