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Hey all , so this is my first post here so sorry if its not up to par. Recently i bought a Srm-006t amp 404 signature combo . I loved the sound but it seriously lacked volume . I replaced the tubes with a new set of EH tubes .. but aside from a uptake in tone .. I didn't get any extra volume . I started searching Google for mods to this energizer and came across a post by Kevin about a cascade mod for this amp and mention of an article in Audio Express July 2017 edition by James Lin. In the thread i was reading i saw that a board had been designed (im really not a fan of point to point electronics) and messaged Kevin Gilmore about it , He said he was all out but happily sent me the screens for it and permission to get some more made . So this is the start of this roller coaster of a mod , I've learnt a pile about Stax and I've had some great help from some of the best in the bizz to produce what is a good looking addition to my amp with significant results in both volume and audio quality . So I found a place to make them and got a few made , and then populate the board with the parts listed in the article ( there was a small design change of the board from the article but ill talk about that later ) board completed ( the pot was changed to 5k and the set resister to 390ohm ) This was due to a design change from the article , The original was in series and would get scratchy over time from the current demands on it , The board mounts the resister and the trim pot in parallel meaning only a tiny portion of current is passed through it increasing reliability . So here was the first mistake ... you can't put in the wires that go down to the board after the heatsinks are installed , Also pro tip ... attach the resisters to the heatsinks and fasten them , Then install into the board as a unit .. makes it as easy as just inserting the resisters instead of trying to do paste insulators and bolts up when the back in shrouded with the previous heatsink . However it was all together and it looked great. Now to set the current limit . you can see the wires coming out the wrong way because soldering down in between the heatsink was difficult and i was lazy . So now we clear out the plate resisters , If you have never soldered before of don't know how to remove solder from a connection well ... this is not something you want to do , The boards are a little fragile and success relies on you been able to clean out the holes well . a flux pen and solder wick is your friend . I believe its been said that once you can work on a 5 layer board without damage you can work on Stax . so practice practice practice This picture also shows the 4 wires you will attach 5.1k safety resisters to in series to keep your stax safe and your head safe should the worst happen Next mistake ... mounting HV over the input side , This isnt how kevin designed this to be attached ( i think) but id ordered the standoffs and they were there .. it also worked well with how id run the wires out the top of the board , ultimately in hindsight this was just an epic fail and again i was been lazy ... however this is very unwise when you are dealing with 580v ... don't be lazy .. don't be impatient .. I knew better this this but after weeks of waiting for parts and boards i just wanted to hear what it sounded like . Also .. you cant get to the balance pot to do tube bias so in order to do the bias .. you had to remove the board from the mounting ... did i mention this was a fail in so many ways So this is when it all went wrong . I hung the assembly over the side so i could set bias .... and this is where the little things id done poorly bit me in the arse . The article says just use an insulating pad because the back of the fets are live . So i did that and plastic collets and metal fastenings (no contact to the fets were made and for anything lower volts this would of been fine ... However for 580v .. this was not ok .. it arc's through and made the heat-sink live with MUCH jumpy electrics . Luckily i hadn't touched it with my hands because in my laziness and rush . i didn't connect the earth off the board to the actual earth ... something that incredibly foolish and stupid .. but hey ... i hadn't worked on electronics like this in 20 years so i was a bit rusty in remembering the fundamentals of safety safety safety ALWAYS install your earths . The result was catastrophic the heat-sink arc'd with full force to the body of the unit . I shut it down to assess the damage The result of this was a Amp that no longer functioned , I messaged Kevin and told him exactly what happened and owned the mistake like you should . I guess he took pity on me for been stupid and organized Spritzer to send me a high res copy of the T1 schematic . As well as a few suggestions on where to start as well as the frightening reality that i may have killed the input fet , A part no longer manufactured . So i reinstalled the plate transistors (something you don't wanna be doing on a fragile board in installing and installing parts repeatedly so much care was taken . Obviously my attitude to this mod had changed from smash it through to one of respect for the gear , something i should have had from the start. So now comes the fun part .. tracking voltages and testing on gear that you are directing testing on the HV rails and components . i even changed the multimeter to one that was rated for HV rather than just the junker I use that I don't really care about . After a few hours of testing all the resistors around the d3 LED , i moved on to the power section , The great think about this amp its its discrete , so EVERYTHING has a matching part , I was lucky i had only killed one side . Slowly making my way through i found that the STAX schematic had errors in it .. That worried me a lot but luckily its a simple circuit and tracking voltages is easy ... turns out id open circuited a resister named R44 and that was all that was damaged Sadly to rebuild the board it was just easier to strip the old one apart ... and i did that destructive because reality is ... its way safer than putting lots of heat into fets to remove them from a board (10n90s is not available locally it got shipped from mouser usa ) I also could see the Dn2450 has sweated and i had a spare set to just replace them with . So we started again ... much more carefully this time and using 1kv insulation pads and fastenings on the fets [ edit .. going to move up another step to ceramic insulators and peek fastenings, following some good advice , i suggest you do the same ] Using nylon bolts and nuts and installing the fets on the heat-sink before removing the solder to help keep the heat in the fets from that process under control (i was been super careful of everything now ) Yes there is to much paste .. i wiped them down pre installation but the nylon nuts have way less clamp so i wanted to be sure there was substantial contact As you can see the wiring is now coming out the right way , Now back into testing ... and here is where it got interesting , The new batch of 10n90's (bought from Rs components as extras rather than mouser) caused the original 390ohm resister to not allow me to set my current value to .49 volts . My lowest range was .52v (approx 6 mA of draw ) while this might seam like a good idea (a little more current is a good thing ) i was thoughtful of if the transformer could supply more that so i added another 100ohms (making 490ohms) to the set resister and this put .49v set at 4.9mA draw as per the article specs All wired in and ready to mount Mounted and looking good ...... [except this isn't how it should be mounted , as pointed out mechanically the heatsinks need to be vertical so will be remounting ASAP will add updated pics as things are fixed ] Bias set and time to listen The difference this made is ASTOUNDING , It fixed all the things that annoyed me about this amp and its total lack of drive . So this was my little adventure , I hope its helpful to someone wanting to do this and also helps show some of the pitfalls and dangers of doing something that you just don't everyday Also hope it helps someone with the construction order . I really need to give credit to Kevin Gilmore for sticking with me through this and to Spritzer for giving me a high res schematic to work to, Without that i would have been dead in the water come diagnostics time as well. Also James Lin for what is basically a how to article Who should do this mod , Anyone with good soldering skills , A person that respects HV and the dangers of working with it . And also have the expectations that if something goes wrong , if you make a mistake , You COULD brick your amp in a way that makes it unrepairable and that that, is all your own fault . BTW . the guy that says he will do this for you .. is not the guy you want doing this for you . Also note edits and updates... Cheers all Wayne
Hopefully I'm at the right place this time. I want to build a kevin gilmore blue hawaii amp. As a starting point I found the original http://headwize.com/?page_id=751 and the more recent http://gilmore.chem.northwestern.edu/BlueHawaii-T2-Servo-v1-2.zip (needs LTSpice). Is there a recent version without servo, with PCB's and all that? CCS is yet partly diskussed, has someone experiance with "mu follower Output" to decouple the complex loads partly from the tubes (see schematic)? What about a PS if no 500V pnp is found? From the PSRR viewpoint I'd start with the concept: "care about higher harmonics, PSRR can start to decrease at a cut-off in the 1 kHz region. And: just in that > 1kHz range, where the measured PSRR comes in, additionally whatsoever interactions between PS and music could come in as well. So starting out with "1 V ripple on the output won't be DIRECTLY audible" could work, but I'd like to have some more safty. So what about a good old plain and simple low-pass with (no 6dB/oct, not L...) R*C*2pi=1Hz first? (Ok, R2 burns some W if some mA is needed, but there is enough space, 150R will do too.)