spritzer

Spent all day battling with the 3GS I bought from Mike, upgrading it to 3.1.2 and then jailbreaking/unlocking it. It works now but damn I don't like Apple one bit...

SRM-XH I've gotten a few PM's asking how to convert the small Stax amps to balanced operation and there really isn't much to it besides the issue of a 4 gang pot and finding inputs which fit the chassis. Now the SRM-XH I had used the green double layer PCB but some have a singe layer board and I haven't tested that as if yet. The whole point is to mimic the input as it is now and copy that to the other side of the 2SJ109. Here is how the input looked in my amp: Now I just ordered some 1/8W resistors and a cap and mounted this underneath the board using the holes which the 100R resistor used previously. I also replaced all the electrolytic caps in the amp with higher rated units and ran the amp at 14VDC and people quite liked it at CanJam even with it sitting next to the T2.

Given the outcry for some documentation on how to build some of these ESP amps I think it is time for a thread on the subject. Now the plan is to post here a summary of the parts needed to build a KGSS amp using the boards from Headamp.com plus what ever build/mods of Stax amps come to mind. KGSS Now for some time people have claimed that the KGSS is somehow hard to build when it really couldn't be further from the truth. My first DIY amp was a KGSS with those horrible old PCB's using offboard heatsinks and caps but after blowing up a couple of boards and PSU's (I really didn't have a clue as to what I was doing) I had two working amps. Now the new boards make life a lot easier and they are pretty much self explainatory (as all the values are printed on the boards) but there are a few things that are good to keep in mind. Given the way the boards are made (i.e. with a full groundplanes and traces carrying very high voltage running right under the heatshinks) it is a very good idea to raise the boards a bit using plastic washers (or nylon or some other non conductive material) on the pins before soldering them in place. Doing this you aren't simply relying on the solder mask to be the insulatior as it really isn't a good idea. A second point would be to pick the correct LED's for the amp and PSU boards. You need LED's which have a nominal voltage drop of 1.7V. Mouser part# 859-LTL-307ELC is the one I use (also for the BH) but you can use other LED's but it will have an effect on the standing power of the amp and thus how much heat it gives off. With large enough heatsinks you could go crazy but lets not stray off the path. So lets start off with the PSU and here is a picture of the PSU board which shows all of the parts needed. Not shown is the transformer needed which has to be custom made. KG and I use SumR in Canada with great results and here are the specs (two 0-280V/140mA windings, one 36VCT/200ma) plus I'd go with a core band and two 0-117V primaries for international use. For the diode bridge in the LT supply (+/-15V) I use the RS402 unit as it fits and I've always used it with these boards. The small caps are 0.1uf/50V with a 5mm pitch such as these. 1N4007's are very common but you can also use UF4007's here. As for the transistors, the board offers two good choices for the first spot (and you only have to use one, the two spots are there just to offer a choice given the different pinout) but I use a third, cheaper option (at least when I bought my stash), the 2SA1831. It is alsmost identical to the 2SA1968 but has less voltage tolerance but that's not an issue here. It also goes in the spot marked for the 1968. As for the Mosfet, I use the IRFBC30 but there are other options. Both of these transistors should be easy to find but I get mine from bdent.com The caps for the bias supply are 0.1uf/1000V MKP with a 22.5mm pitch and the bias adjustment pot is the standard Bourns 3296W (straight line of pins on the bottom and with top mounted adjustment). For the bias resistor I use Xicon's which are rated at 500V but you could use a 1/2W unit which is rated at 700V. Anything between 4.7M and 5M is just fine for a Stax headphone. For Sennheiser's they need an additional 5M resistor but you can add that inline later on or find a 10M resistor at Mouser. To adjust the bias you must measure before the resistor so raising the bias resistor is a good idea so you can addatch a measuring probe to it. One should also know that not all multimeters are created equal and you need one with a real 10M input imedance to measure the bias accurately. The cheap VC99 appears to work ok for this but a Fluke is a good choice. For the rest of the parts they are all pretty easy to find. There are dozens and dozens of choices when it comes to terminal blocks so pick one which fits you budget. The mains PSU caps are all the standard size, I've used Nichicon and CDE which both fit well. The resistors are Vishay RN60D for the smaller ones which I'll cover in the next section. For the larger units I've never actually used 180K/5W but rather 100K/10W units I had here. Mostly due to me reading the board wrong but they have been fine for years of heavy use. AMP section Here is a picture of the amp board. The majority of the parts here are Vishay RN60D resistors which you can get from pretty much anywhere. Mouser is a good choice and there is a rather good way of buying all the values you need. Just do a search for 71-RN60D-F- and find the values you need from the drop down box and you are set. I always order resistors in multiples of 100 but you don't need so many here. The larger 3W resistors are also Vishay such as this one and this one. The 22pF caps on the board are 500V silver mica caps from CDE such as these. The heatsinks used in this amp are these and you also need something like this to insulate and mount the transistors. Trimpots are 3296W Bourns like the PSU. Now the only real problem here is the input transistor but as it often is, it's not a problem at all. The dual 2SK389 has been discontinued and the current LSK389 uses a very different package. The good part though is that you only need matched 2SK170's and the spot for them on the board has already been marked. You can buy these matched from AMB so it isn't a problem. Now lets say you have built the amp and then you need to adjust it. Like any of the SS amps you measure at the Stax terminals and there are two pots on the board, one for balance and one for offset. The one next to the 2SK389/2SK170 is the balance pot so put the probes between the + and - output and adjust for 0VDC. The pot towards the "back" of the board is the offse so put a probe between the + output and ground and adjuse for 0VDC. Simple really...

I think it is time for an electrostatic amp build thread... Yup missing the comma but not being at CJ you don't get the context either i.e. me drunk as a skunk yelling at Ed while holding the camcorder...

I seriously doubt it. I've met a lot of bakers from the US over the years and they are shocked at the range of products we can get. One guy from Vermont who makes pancake mixes and the like was bowled over that we have 4 different types of fresh yeast to choose from, flown in every week. Now Ireks might be in the US since they are by far the largest supplier of this stuff in the world.

I'd send you some but somehow I don't think customs takes too kindly to some white powder (well slight yellow tint) in a bag being shipped... The manufacturer bags are also too big since you could make about 1000 pieces from a 30pound bag.

Have you ever even looked at the KGSS PCB pictures Justin posted? All values are printed on there and the majority are easy to find on Mouser simply by looking up the RN60D's and selecting the right value or doing a search. I mean 180K/5w isn't hard to find nor is 300K/3W etc. I could also post the whole email dialogue between me and Robert (rbarth) which would be a complete noob guide to how one goes about building a KGSS, down to the smallest detail such as the K after a resistor number is really important... There were three individuals who contacted me with blown PSU's. Always the same problem, it ran without a load and blew up. Then there is the whole issue which is probably down to flaky bias supplies which I will test once I get my PCB's... Now the KGSS supply can run for days without a load and even if you do something really stupid (like I did, mixed up the wires) only a single resistor blew up and the PSU worked just fine without it.

Ireks Hvedebag as it is known in the Scandinavian market. Basically wheat sour dough in powder form.

It's ciabatta, you can always just burst the largest gas bubbles and it will still rise. That said our dough has something which makes it a lot easier to manage...

NICE!!!! Very nice price too if you bought it from Richer Sounds...

Exactly!! Knowing Fairchild though they've probably discontinued it already...

Mmmm ciabatta. Ambient temp is a real issue for me as well since we let ours settle for about 4 hours each morning before cutting it up and it can get a bit big...

So you think any of this gets posted on the forums? I take it you just registered on HF yesterday? Once people realize the main thread is just one major wankfest with idiots like NoNoNoNoNoNo acting like experts they turn to people like me and KG. Hyperbole or not this design falls way short of the intended target. It was never supposed to be the end all amp design but to come up with something that measures far worse then the Stax designs it is ripping off while being about as expensive in parts alone is simply retarded. Hell much more expensive considering what I just paid for that SRM-1 Mk2 P.P. Ahhh a good quad at 7-8ma wasn't a problem but at 10ma+, not so much...

Try two months... Not happy about that but it is mostly fixed now. Oscillations and wild drifts are the nature of the beast when you use 1970's era PCB's and cutting all the wrong corners on the design. As for problems, what about unstable PSU's and the need for 50+ jfets to get a good quad which seems a bit silly given that this is supposed to be a budget design. Now all of this is gone once the new PCB's will land as they are probperly designed and no matching is needed. Plus the whole buisness of distortion being a few orders of magnitude lower and all that... Stax bitches!!!!

You would have to do quite a bit of modding to the main board to do the newest upgrades and using the old PSU isn't really an option IMO. Personally I'd just build the KGSS stock and then sell it. It's a great project and going by the exstata thread on HF, a hell of a lot less trouble then building the Exstata. I didn't have them both at the same time sadly. A used 323 would be a good budget option though and the A model I had was easy to change the voltage on...

First off, take the top off the amp. You will notice two PCB's standing upright in the amp, one for each channel. These have pots marked TVR1 and TVR2 which you can adjust via holes in the side of the chassis. Now the TVR1 pot is the balance and the TVR2 pot is the offset. What you have to do is take a voltmeter, set it to about 30VDC range (or if you have an auto-ranging unit, just set it to DC) and measure at the Stax sockets on the front. Use the diaphragm above and put the red and black probes into + and - for one channel and adjust the balance pot (TVR1) for 0VDC. Now remove the probe from the - output and hook the lead to any exposed part of the chassis for a ground connection. Now adjust the offset pot (TVR2) for 0VDC. You will have to go back and forth between the two adjustments a few times and then repeat for the other channel. Normally it is best to do this after the amp has warmed up for a bit (say and hour or two) but you can set it instantly after power on and then readjust later on. Now there is a relay bank on the output of the amp (the soft "tick" sound you hear when powering up the amp) and if they don't engage then you can't measure at the Stax sockets. This makes things just a little bit trickier though...

Could also be the slightly over reactive protection circuit. Listen for the output relays... Yup and I'm guessing Larry didn't bother to check the offset/balance either... There are number of designs cooking, all of which are better then the Exstata. As for being easy to build, I for one think an amp could be made a lot easier then the Exstata but that maybe just me... I had the 323 once and it is indeed great.

How about adding some simple regulator like a 317HV to the stock PSU? One could use shorter caps and place the whole thing above the stock PSU inside the box... Happy to help and I'm pretty sure the SRM-Monitor is a SRM-1 Mk2 with the EQ added. Certainly appears to be the case with the SRA-14S as well but without great pics one can never be too sure.

...and your point is? Does any iron made today match the quality of for instance the old Peerless iron? I certainly don't think so...

SRM-1 Mk2 schematic. This includes the Pro bias supply in case somebody wants to modify a non Pro unit...

You would be correct as the exstata version which measures properly is very similar to the SRM-1Mk2 design. Now the PSU lacks regulation in the Stax amps but with fresh caps and a stable line voltage it shouldn't be a big deal. You certainly will get a lot cleaner, more transparent sound from the Stax amps. Now speaking of the SRM-1Mk2, it appears I've just bought one and the tasty P.P. version at that. I see some mods in its future, adding balanced inputs and I might even try to add some regulation to the PSU...

The only "real" hurdle with any of these amps is getting output transformers good enough. With that sorted you can build almost anything you'd like.

As Kevin has pointed out, we aren't normal but I for one don't get the point of 3rd party amps if aren't getting any real improvements for your money. My SRM-Xh has the same voltage swing and a lot less distortion in a tiny box. The SRM-1 Mk2 (not the Mk1, very different design) is mostly identical to the SRM-313 except different parts used. This isn't a bad amp but comparing a stock unit to anything modern is madness since the PSU caps will be way past their sell by date. As for the SRM-T1, it's a good circuit built on the cheap and with the wrong tubes. The ECC99's should solve some of the compression issues but the real "fix" is the KGST. 6S4A tubes with a 10M90 CCS which I should have up and running as soon as I place a new order with Mouser. I'm as you all know certifiable so I'm running it at +/-400V for added effect...

Your best bet really would be to sell the boards and wait for the next release as it will be far, far better. The short story is that KG and I both built our P-P versions of the amp (not using the stock PSU which is IMO rather terrible but rather a known benchmark which is the BH supply) and we were not happy with the results. Now KG measured the build and it wasn't pretty, distortion many orders of magnitude higher then the KGSS (1%!!!!!) but until an amp had been built using the stock boards we couldn't be sure what was going on. Now fast forward to this weekend and Kevin finishes a bone stock amp exactly like the BOM on the stock boards and exactly the same results. Throw the circuit in a sym and the SRM-212 circuit absolutely thrashes the Exstata let alone the more advanced versions of the same circuit. Now KG gets tinkering and modifies the Exstata circuit so it is far, far better. Alex will then supposedly make those changes to the next board run. In other news, we are also working on quite a few things right now, including a +/-500V capable SS amp which isn't quite as insane as the KGSSHV. Cheap to build too...