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  1. Built a Megatron. Seems to be the perfect amp to build during the seemingly unending shortage of 10m90s. I used up my final few pieces of 10m90s and C2M1000170D for this simple build, and it gave me some mild anxiety and regret for not hoarding up those sands. However, the build experience and result are worth it. Build process and after thoughts I started off with a pair of generic chassis from Taobao. 32cm wide, 8cm tall, 35cm deep. Silver and black anodised aluminium. They weren't available in other finishes but this looks clean enough to me. They do have some minor scratches and dents if you look hard enough though. The casework was done by a laser etching service provider I found on Taobao. The end result was a clean and modern appearance. Inside the PSU are a pair of +/-450V GRHV, +/- 15V GRLV, delay board and a 270VA toroidal transformer. The idea was to create a PSU that can be used by both the Megatron and the Grounded Grid amp units. These components fit the chassis nicely with little room for a third GRHV board for the 300v rail for Megatron. Outputs are split into AC and DC outputs. Transformer specs: The heatsinks for the amp unit were probably redundant since most of the heat comes off from the top. The amp board could probably fit into a smaller and lighter chassis, but I chose the same chassis as the PSU just so that they can stack. The amp build was straight forward and relatively easy compared to a Carbon build or any of the KG dynamic amp builds, due to the low component count. I did not use any boutique components in this build. The coupling caps are Wima, and the voltage rail decoupling caps are Siemens. Volume pot is an EIZZ-style stepped attenuator, internal signal wirings are pure copper. Special care was taken when routing the heater filament wires to avoid hum. Amp testing and adjustment was simple. Just ensure the all the rails are as spec'ed and that's about it. The voltage offset settles automatically after power on. No need to fiddle with any potentiometer when the amp is powered on, so it is much safer to test than the Carbon or the T2 family. Sound I used the Megatron with ES-1A, and here is my impression of the Megatron after comparing it with GG (on the same PSU), Carbon (450V GRHV 15V GRLV) and Mini T2 (triple GRHV). Currently I am using the Megatron with a quad of Mullard XF2 and PSVane EL34PH. The front end tubes are all Valvos. The sound of the Megatron is warm, slightly thick in the mids, and non fatiguing and airy in the treble. It sounds very natural and the imaging is holographic with good recordings. While it is very detailed, it does not ruin joy if the recordings are of poorer quality. Older or poorly mixed recordings have a smooth timbre and organic vibe when heard from the Megatron. While the Megatron's treble is not as extended as the Carbon's, it complements the overall signature to create a very complete soundstage and convincing sense of separation and space. What makes the Megatron standout from crowd lies in its low end - it is an amp for bassheads. It has by far the most THICC bass compared to my other amps, even more than the Carbon. The bass extends as deep as the Carbon, but the Megatron has a nice lift in the mid bass that makes my ES 1a slam extra hard. Listening to EDMs and fast pop tracks on E-Stats is finally satisfying, and I can finally stash away my planars. Carbon is like an antithesis to the Megatron. Carbon is like a clean cutting razor with little tolerance for inaccuracies where as Megatron adds a lot of joy and flavour into the listening experience. Carbon also sounds a little linear. Although the stage is wide, it is not as deep as the Megatron's. GG sounds more organic than Carbon in general. The GG's signature is quite dependent on the tubes. With the XF2s, GG is warm and clean, but doesn't deviate far from the Carbon sound. The bass isn't as tight and fast, and treble could sound stiff and slightly shrill with the wrong tubes - such as the re-issue Mullard EL34. Mini T2 sounds slightly leaner and cleaner than the Megatron, and has a much smaller bass. It is as enjoyable a listening experience for me, but the Mini T2 was much harder to build - by sheer component count. Tube placement and choices Placing the EL34s in this manner shown below allows one to use two matched quads of EL34 if matched octets are unavailable. Initially I used cheap Linlai tubes for the front end and had issues with sound imbalance and hum - turned out that the tubes were the culprits. Switched to some cheap NOS and the issues were gone. So my advice would be to use well built tubes from reputable makers. The 12AU7s affect the sound significantly. The option to roll tubes makes Megatron extra fun to use. More photos of the internals and the back of the amp coming up soon, when I am more free. I would say that the Megatron is my favourite amp - until I build the T2.
  2. The stax 007 has a more updated design and feels like it can tolerate careless handling better than the ES-1A. This might be due to the maker wishing to replicate the looks of the Omega, along with its design quirks. The ES-1A has a bendy head band that offers quite little clamping pressure. I wish the headphones could be lighter and holds on to the head more snugly.
  3. This is a repost of my impressions on another forum I've been using the ES-1a almost daily for about 4 months now. I feel that these are underrated and the audiophile community deserves to know them. Before I start my review, I just wanna declare that I have no conflict of interest with anybody in the headphone industry. I bought the ES-1a at the price of 12800HKD (1650USD) which is listed as the default price on ES Lab's web store. The ES-1a maker does not have prior knowledge about this review. A little bit about myself I like to listen to music - from pop to classical, from jazz to rock, and I am conversant in both English and Mandarin. I chanced upon this pair of headphones while I was browsing the Chinese Headfi equivalent - erji.net, and decided to purchase based on reviews of some big time Chinese audiophiles claiming that the ES-1a sits somewhere between the Stax 007 and 009s. It was a risky blind purchase (which I believe isn't uncommon among head-fi'ers), and I was just hoping that those Chinese reviewers weren't shills. The amp came in a week after I placed my orders via EMS. It came in a nice looking wooden box. Definitely an A for the effort in making the unboxing experience ceremonial, but it's a painful space-occupying lesion in my room, yet I can't bear the pain of throwing the box away. So now I'm just wondering what to do with the box. If you have any ideas, just let me know. The Chinese forum reported that the ES-1a tuning could be altered between bright and balanced by swapping earpads. I only used it with the balanced earpads, which according to the maker, was the finalised tuning. He also mentioned that the ES-1a is best paired with a solid state amp. I didn't care about his recommendations one bit. If the headphones sound good on solid state amps, wouldn't they be wonderful if I pair them with a healthy dose of tubey goodness? The ES-1a got its looks from the legendary STAX Omega. I've not seen an Omega in real life, but from Google they look pretty similar apart from the anodization color. The ES-1a is made with black anodized aluminium housing and a has aluminium ring that seemed unnecessary if not to copy the looks of the Omega. The see-through metal mesh reveals a bronze driver under the housing, and the unit is accented with some golden screws. The wire is apparently adapted from a Stax sre-725H copper cable, with a little 3D printed Y-split that bears the brand name. Now let's talk about sound. Bass- authoritative. Mids - seductive. Treble - beautiful. Imaging - stellar. Tonality - natural. That's it. I don't see the point to elaborate more because 1) my impression is subjective, and reading this review does not give you a direct idea of how the ES-1a sounds like 2) I feel that Headfi has enough overwhelmingly positive reviews on audiophile products, and this humble review wants to stand apart from the rest 3) if you insist on seeing some reviews, I would like to suggest you Google with search terms "head", "case", "es1a". Read the reviews there with discretion. Amp pairing Amps do play a significant role on the sound. With the KGHVSS Carbon ES-1a sounds more monitor-like, more detailed and more extended in both bass and treble, while with my tube amps, ES-1a sounds more holographic and trades some bass extension for a life-like presentation. Even with the lesser amps like my SRM XH, the ES-1a retains a pleasant sound signature despite detail and treble extension being completely thrown out of the window. Comparison with Stax 007A Read this section with a pinch of salt, as I clearly prefer the ES-1a over the Stax flagships. I find them comparable in terms of details when driven with some of the amps I have. I wish I have some Stax branded amps or the BHSE for the purpose of this comparison, as I believe that they are the sound many readers here can relate to. The Stax 007A here does not have the blue tac mod, as I enjoy the fun mid-bass in the Stax 007 mkii. It just makes the headphone what they are. The most obvious difference is in the treble. ES-1a is definitely brighter, and details in music are more upfront compared to the Stax 007A's slightly laidback presentation. ES-1a feels more passionate and more aggressive compared to the 007A. If you are used to the 007A/mkii sound signature, you might find the ES-1a slightly bright. If you are used to the 007mkii with blue tac mod (which I find bland), you would either find the ES-1a very fun sounding or a tad too aggressive. Bass rumbles harder on the ES-1a than on the 007A while on KGHVSS Carbon. Extension is slightly deeper too. I don't miss my planar headphones on CFA3 while I listen to Zedd or Daft Punk on the ES-1a. But I would defer listening to such tracks altogether while on the 007A. Mids on the ES-1a is detailed, but somehow the 007A does it better. On jazz tracks, 007A does things nicely by giving a smooth and slightly dark rendition to vocals. The details of the ES-1a is cuts through the overall presentation a tad too strongly. The ES-1a has a little bit of bite or impact, which might work well for some music, and backfire on some others. Soundstage feels bigger and more spread-out on the ES-1a, and this concurs with some of the Chinese reviews. Tonality-wise, both ES1a and Stax 007A sounds very natural. ES1a has slightly more defined edges and the 007A sounds smoother. Regrettably, I didn't have the chance to compare the ES1a to either the 009 or 009s for a long enough period of time to yield a reliable comparison.
  4. Finally, my mini T2 is completed. Just want to share my build experience and listening impression for those who are about to build one. Also, a huge shout-out for JoaMat, who conceptualised and designed the amp, provided me with invaluable tips when I was debugging my mini T2 and encouraged me to share my experiences here. -------------------------------- Pics or it didn't happen: -------------------------------- Build experience: Before this amp, I have built the Carbon and Grounded Grid, as well as quite a few dynamic amps including the SMD Dynalo. Overall, I am comfortable dealing with electrostatic amp voltages, but I have limited experiences working on dense and tiny SMD boards. I built the SMD Dynalo with a soldering iron, but this method was unsuitable for the Mini T2 due to the density of the components and the fact that I tend to use copious amounts of flux grease when I solder by hand - it would be too tough to clean the flux stuck underneath the tiny components. Therefore, I decided to solder the SMD parts by the solder paste and hot-air gun method. I used 1 set of mini T2 board, 3 through-hole GRHV boards and 1 delay board (warmup.zip). This amp is fast to build so long as you have a decent hot air gun (I got mine from Taobao for around 25 USD), a pair of fine tip tweezers and some patience. I used a stencil to apply solder paste on one side of the mini T2 board first, then populated all SMD components and used the hot air gun to melt the solder paste. It was quite satisfying to see the tiny parts drawn into their rightful place by the magic of surface tension. It took me about 1 hour to complete the SMD soldering for 1 side, so I'd say that this method is really efficient for the number of parts to be populated. The through-hole components and the tube sockets were populated next, and I used some terminal blocks for the power rail inputs. Just be sure to apply jumper wire for the -15V near the servo opamp. Otherwise, you risk seeing 400V at voltage offset, and frying some input tubes. The transformers I used were 130W and 87W for the HV and LV respectively. There is also a dedicated floating 12V winding for the delay board, and separate filament supply windings are used for the power tubes and input tubes for each channel. Voltage rails were pretty standard - +-15V, +220V, +400V and -460V. The warm-up time was set to 25 sec. There is no need to adjust for output current bias as in the Carbon or GG. The balance servo is activated by default, and all there is to adjust is the output voltage offset with respect to ground, and it can be easily adjusted so long as the potentiometers are soldered to the same side as the tube sockets. The amp runs cool. I used heatsinks that measure 7cm tall, 30cm deep, 5cm wide for each side of the chassis. At steady state, the amp module runs at 39 deg C, PSU runs at 35 deg C. In comparison, my 450V 20mA biased Carbon runs at 48 deg C with 15cm-tall heatsinks. Here are some errors I encountered here and the directions I took to debug. They are based on spice simulation by JoaMat. Hopefully, my tips can help builders who encounter similar issues as I did. 1. On power-up, offset voltage rises to 400V immediately after the HV kicked in. Check the jumper connection for the opamp -15v power supply. They are very short and can be easily missed. 2. 50K resistor explodes (either R11 or R12). It is likely due to an unconnected input tube or dead tube. Check input tubes and Q1A/B, Q4/5, Q11/12, Q3A/B of the same side. Also check tube sockets, because even the expensive ones can have loose connection on NOS tubes. 3. Q1A/B burns. This might not be easy to spot. The sign can be as subtle as a discoloration/fading of the silkscreen on the component surface, or a subtle exudation of flux around the collector pin of the component. This is likely due to a shorted input tube. ------------------------------ Sound impressions Take this section with a pinch of salt, for every DIY build is one-of-a-kind, and mine is no exception. For my mini T2, I used Duelund tinned copper wire as input cable, EIZZ stepped attenuator, STAX SPC earspeaker wires as output wires and a 5-pin socket ripped from a STAX extension cable. The headphone I used was the ES1a by ES Labs. I wish I had the Stax flagships to do this impression and comparison. The amp is fed by a AK4497 DAC, straight out of DAC and a coupling capacitor, bypassing any low-pass filters. For the following impression, I used decent tubes - Mullard xf2 EL34 as output, Brimar ECC88 as V1 and Sovtek 6922 as V2. Tubes do affect the sound significantly, and I will talk about that later in the discussion. My 450V 20mA bias Carbon with GRHV&LV will be a point of reference, as I am sure that this is a sound that many here are familiar with. It has the same volume pot as the mini T2 but SPC input wires and copper output wires. The mini T2 is full sounding with a natural tone. It has got a certain “WOW” factor that makes my carbon sound unimaginative in comparison. First off, the tonality of the mini T2 is warm and mildly bright such that the sound is airy but non-fatiguing, no matter how loud I cranked the volume up. The bass extends deep with a sufficient rumble where the track calls for it. The airy top end gives the amp a wide soundstage, that is paired with sufficient depth. Instrument and vocal placement are accurate and appropriate, without excessive forwardness or recess. Despite the soundstage being big, it does not sound hollow, because the music is full of details and creates a sense of well-layered space that is almost holographic. I have tested the amp briefly with other tubes and found that input and output tubes affect the sound most significantly. If input tubes have slightly mismatched sections, the balance would be too great to be zero-ed with potentiometer and balance servo. The small tubes I used are unassuming. Had I upgraded to better tubes, I guess the amp would sound better. Compared to the Carbon, the mini T2 sounds more organic, more layered and the mids are considerably warmer. It is also way more forgiving on bad recordings. The timbre sounds truer to life, soundstage is slightly larger, and feels like the music has more room to breathe. However, bass extension is not as deep as on the Carbon, and Carbon generally feels more analytical and snappier. To conclude, if there’s one word to describe this amp, it would be “fun”. It’s fun to build and definitely fun to listen to and roll tubes. I consider it as a step up from the Carbon when I use some decent tubes. Otherwise, this amp with standard new-production tubes would be at least on par as the Carbon.
  5. Congrats on your finished build! I did a similar (in terms of size and layout) single chassis build, with the amp mounted in the upper part of the heatsink. Dual 450V and 20mA. At steady state, the temps hover around 46 degrees celsius (ambient 27 deg) on the heatsinks directly behind the amp boards, 43 deg behind the GRHV, and 41 deg at other parts of the heatsink where nothing is mounted behind. Not sure about you but I feel it's quite safe to push it to 20mA if you're getting a similar temperature.
  6. I think a 10k pot a bit too low and it is more suitable for amps with bjt input. With the jfet input on carbon you can use a 50k or 100k pot.
  7. I think some of the resistors are spec'ed at 2W as per the 21st Century Maida design. Would it be ok if you replace them with SMD parts?
  8. Interesting. What's the function of the Flat jumper?
  9. Another Dynahi lives. Sigh... Heatsinks are never enough.
  10. I always wonder what makes the CFA2 sound so good and makes me choose it over the dynahi every time. Does the magic lie in the current feedback topology or the triple darlington output stage? just an idea - what happens if we parallel two or more sets of the triple darlington output for each CFA2 board? Would it be the more the merrier?
  11. That's about 2.2% lower than the 580V Stax pro bias. The slightly lower bias is unlikely cause harm to the earspeakers. In terms of sound, lower bias voltage would mean that the earspeakers are less sensitive. However at 2.2% lower, I'm not sure how much of a difference you may experience. My experience is that the bias does increase a little after warming up. I assume that your measurement was done at start-up. Perhaps you might wanna measure the bias again say, 30 minutes after turning on.
  12. Thanks @Blueman2 I would definitely consider making a chassis with heatsink sides for future projects, but for now, I have yet to source for an appropriate L-shaped aluminium thermocoupler. The transparent case is meant for prototyping only heh. It's cut to order by a seller in China. Just send them a CAD drawing and they will CNC it for you. I plan to transfer everything into a black chassis after I get a bigger heatsink. Currently it's running at a modest 14mA at 68 deg C.
  13. Another KGSSHV Carbon lives! Thanks to @sorenb @Kerry @simmconn for the help on bias voltage. I used 2 x 120v 0.5W and 2 x 130v 3W in the end. The 0.5w parts work well. Next steps: cable management, re-case, increase heatsink size.
  14. Just curious,has anyone tried using dynahi to drive a srd 7?
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