The Stax Thread III

[Metalboyy]

Check out the Used/Special Amplifiers page at Mjolnir Audio. Those are refurbished Stax amps that have sometimes been upgraded to higher power. For under $2000, the CCS-modded T1 and 006t amps are quite good, and those are between $900 and $1300. If you can stretch your budget a bit beyond $2000, there are the modified SRM-727, 007t, and 717 amps between $1900 and $2400 which are a step above the T1/006t amps.

There's also the used market. I recall that there's a Mjolnir KGSSHV mini being sold for 1700 GBP right now in the classifieds. That is a full KGSSHV build, a step beyond the modified SRM-727/717, and that's just a bit over 2000 Euros right now.

Thanks for the tips Very appreciated. I wonder how a Bottlehead stat would stack upp against these.

 

[Svperstar]

I listened for about two hours after doing the mod and the difference in sound, particularly with percussive notes, was noticeable. Snare drums and kick drums have a tighter impact with more kick vs the looser and bloomier bass of the unmodded 727. It's now very much like the 717 that I heard earlier this month. I'm quite satisfied with the mod. It's a notable improvement in dynamics and impact for the X9000 and it emphasizes the innate snappiness of the Shang Jr well.

Was fun swapping back and forth between the 717/727. Like I said when you were here, at a meetup they needed a balanced amp to run a Mjolnir 3 off of so we used my RME ADI-2. There is a button that switches the Mjolnir 3 from Feedback/No Feedback. The no feedback option to me just made everything sound a little darker. It was noticeable but not a massive difference. Now how that compares to local feedback vs global on a Stax amp I'm not exactly sure.

 

[mulveling]

My assumption is based on the fact that with the current Kingsound M03 amplifier I am completely disappointed in the sound of 009, and I hope that Carbon will solve the situation SIGNIFICANTLY.

So you assume that for my genres even Carbon in addition to 009 will not change the situation CARDINALLY?

Make no mistake, any Carbon is going to be a world of difference over an M03. The legitimate question, and your challenge, is determining whether the 009 + Carbon (or whatever) is going to be optimal for your preferences, versus investing that same $ in a great planar. I was seriously impressed by og Susvara when I had them on loan some years ago - and that was right next to 007 and 009 on my DIY T2, with the Susvara driven by "just" a Head-amp GS-X mini (it has enough power). Susvara was far and away superior to the Stellia, Utopia, Empyrean, and HE1000 I also tried around that time. Honestly - sometimes I want to just go fetch myself a pair, but either the used prices seem too high, or I start worrying about their reliability without full warranty support.

You might also have been better off starting with an L700 - they have bit more of a "fun" sound while retaining some of the 009's qualities. They also perform better on lesser amps. The O-series Stax are always a bad time on cheap amps.

At this point, nobody can accurately predict the subsequent outcome for you - further enlightenment will come only from 1st hand listening

 

[SolarCetacean]

No how that compares to local feedback vs global on a Stax amp I'm not exactly sure.

It's basically the difference between the stock 727 and the 717. Whatever differences you heard between my 727 and your 717 is the difference that the mod makes. I've read that the 727 is technically a bit better after the mod since it uses better parts (CCS in the voltage gain stage) and the output stage runs at a slightly higher power, but I think those would be minor differences vs the change in feedback.

I recall that KG and spritzer developed another mod for the 727 that rebuilds the output stage, replacing the transistors and such, so that it has more power and is more similar to the KGSSHV. The 727s that spritzer sells on his site have that output stage mod performed on them in addition to the feedback mod. I have not seen any schematic for that output stage mod and I've heard that it's much more complicated, so I have no real interest in doing it.

Thanks for the tips Very appreciated. I wonder how a Bottlehead stat would stack upp against these.

The Bottlehead Stat has less power, at least based on its spec sheet. 200Vrms vs the 300Vrms on an unmodded 006t/T1. The modded 006t/T1 has even higher voltage output, just a bit less than the solid state Stax amps. The Stat is nice if you want to tube-roll, as tube-rolling Stax amps is difficult due to the lack of self-biasing for the tubes and the single-turn potentiometers used for biasing them. The Stat also doesn't use global feedback, so it might sound a bit boomier or looser, if my experience with the 727 is any indication. It's sort of hard to recommend the Stat due to the output power limitation, but some people like it.

 

[Metalboyy]

The Bottlehead Stat has less power, at least based on its spec sheet. 200Vrms vs the 300Vrms on an unmodded 006t/T1. The modded 006t/T1 has even higher voltage output, just a bit less than the solid state Stax amps. The Stat is nice if you want to tube-roll, as tube-rolling Stax amps is difficult due to the lack of self-biasing for the tubes and the single-turn potentiometers used for biasing them. The Stat also doesn't use global feedback, so it might sound a bit boomier or looser, if my experience with the 727 is any indication. It's sort of hard to recommend the Stat due to the output power limitation, but some people like it.

Okey I will probably skip that one then thanks I just found a crazy cheap 727ii I might take that one.

 

[Svperstar]

Okey I will probably skip that one then thanks I just found a crazy cheap 727ii I might take that one.

I recommend the 727. It sounds similar to the 717. Great estat amps if you don't want to go higher up the food chain.

 

[etc6849]

I finally built the bias board @aokman designed. Only one small change: I added an inline switch off a jumper that's downstream of the fuse as I wanted to ensure the switch was included in the fused circuit.

I really like the board design. Measuring less than 100mV ripple at 580VDC. Running it off a 9V power adapter, and the regulator works great. I didn't test it's very large input range as the LED circuit is designed for 12VDC, so I can't exceed that.

If anyone builds this, just be sure to buy a bunch of 5.1V zener diodes, and measure the reverse bias voltage. As aokman says in his video, you are looking for one that is very close to or around 5V. If you install one with too low of a Vr (as measured in the pic below), it will switch the thyristor on, which will pull down the input voltage going into the DC-DC converter as it's trying to "protect" the circuit from the over voltage (set by Vr of the zener). My voltage at test point 2 was around 4.78V for 580V out. All 10 of my zener diodes measured 4.3-4.4V, so they weren't going to work. Luckily I found one in an old kit with a higher Vr, around 5.1V.

 

[etc6849]

Just got the last faceplate in the mail and installed trim strips to tie everything together and to hide the screws.

 

[bobkatz]

This is true. However, given Enco/XP Power has an actual spec sheet in english and a design guide, and UHV Power couldn't be bothered to have an English spec sheet, I'm willing to bet the Enco/XP Power Q06-5 measures better and doesn't fail in a way that has runaway voltage. If I'm going to plug $6000 headphones into something, I'd feel a lot more comfortable with the XP Power. It's really only $120 more, and only $100 more if you factor international shipping versus mouser's reasonable shipping.

I agree that UHV has no experience dealing with English-speaking clients. But I've been down that road before and at least they give an output voltage and current. Personally I'd prefer a regulated supply to keep the ripple down. An unregulated DC-DC converter can be rather noisy. I'll let you know the ripple of the UHV once I have breadboarde the ciruit. And keep in mind that putting an overvoltage circuit on the INPUT of the Enco does not protect its output from over voltage!!! You still need protection on its output. Dr. Gilbert suggested a 10K R in series with a nominal 600 V string of Zeners across the 5M buildout resistor. I would do that whichever route you choose, the Enco or the UHV.

 

[etc6849]

Would the XP Power/Emco HRC05 solve the voltage regulation concerns?

https://www.xppower.com/product/HRC05-Series

They also list some neat features such as short circuit, arc and overload protection.

1)
the bias supply on all my desktop headphone amplifiers is a voltage doubler from the + regulated supply which makes 700v-800v. don't care what the voltage is because it is followed by a 10m90s and a 580v string of 1% zener diodes. then 2 stage filter. this produces a regulated 580v +/- 5v that is not adjustable. over time and temperature and long term the measurements drift less than 1%

the 600v of the uhv power is too low to do the 10m90s, but 2 resistors bring it down to 580v easily and sure looks to be extremely stable, less than 1%
(have it on a long term measuring rig right now)

you could use the emco module and set it for about 700v and then do the same thing with the ixys and zener diodes.

the one problem i know of for sure is that as the bias current changes mainly due to humidity, the emco module output voltage will drift even with a fixed input voltage.

alternatively you can wrap the emco module in a fully regulated differential discrete amplifier similar to the grhv.

2) personal opinion is that the stax headphones will not be damaged with 600v as long as you use the 5Meg resistor

3) correctly measuring the bias voltage is easy with any standard 10M input resistance dvm. just have to do it before the 5Meg resistor.
(or get one of the 1Gohm input impedance voltmeters, which is much more expensive)
(new versions of these are hard to find, have to go vintage vtvm)

If the headphones are new, the inital charging current is 50 micro amps which drops very quickly to under 10 microamps (5 minutes)
using 1gohm input impedance voltmeter measuring voltage accross the 5M resistor. i have seen really trashed headphones continuously draw over 100 microamps which does not decrease with time.

doing a fully regulated everything with feedback directly after the 5M resistor is probably a bad idea because it will try to force the headphones to charge faster.

doing a quad esl63 charging circuit which includes a neon light in series with a 47k resistor across the 5M might be a way to charge headphones safely and much quicker.
since it works reliably for 20+ years on my quads, it must work.

I agree that UHV has no experience dealing with English-speaking clients. But I've been down that road before and at least they give an output voltage and current. Personally I'd prefer a regulated supply to keep the ripple down. An unregulated DC-DC converter can be rather noisy. I'll let you know the ripple of the UHV once I have breadboarde the ciruit. And keep in mind that putting an overvoltage circuit on the INPUT of the Enco does not protect its output from over voltage!!! You still need protection on its output. Dr. Gilbert suggested a 10K R in series with a nominal 600 V string of Zeners across the 5M buildout resistor. I would do that whichever route you choose, the Enco or the UHV.

 

[kevin gilmore]

sure, great. $400 each, none in stock.

 

[bearFNF]

sure, great. $400 each, none in stock.

Yep, none at mouser or digikey (says 14 week lead time).
Newark says they have them in stock ($457 each).

 

[VandyMan]

@bobkatz Do you know if you will be doing an EQ for the Audeze CRBN² ? I really like EQ for the original CRBN.

 

[etc6849]

Maybe I'm looking at the wrong version? I was looking for the 600V model that's $255 everywhere: HRC0524S600P. The 600 means 600V and the P means positive (needed to avoid dust build up). I would presume HRC05 is the series and 24 means it takes 24VDC in.

The only drawback I was seeing was this: "N/A – Input ground is internally connected to output ground." I'm not sure if this could allow for higher noise at the output or not. I would have liked the option of not having the input and output grounds internally connected.

Mouser has them in stock now, not sure about other places. No site has it for $400+ so it could be you're looking at the much higher kV versions?

https://www.newark.com/xp-power/hrc0524s600p/dc-dc-conv-adj-600v-8-33a-dip/dp/12AM7719?cfm=true

https://www.mouser.com/ProductDetail/209-HRC0524S600P

sure, great. $400 each, none in stock.

Yep, none at mouser or digikey (says 14 week lead time).
Newark says they have them in stock ($457 each).

 

[bearFNF]

Maybe I'm looking at the wrong version? I was looking for the 600V model that's $255 everywhere: HRC0524S600P. The 600 means 600V and the P means positive (needed to avoid dust build up). I would presume HRC05 is the series and 24 means it takes 24VDC in.

The only drawback I was seeing was this: "N/A – Input ground is internally connected to output ground." I'm not sure if this could allow for higher noise at the output or not. I would have liked the option of not having the input and output grounds internally connected.

Mouser has them in stock now, not sure about other places. No site has it for $400+ so it could be you're looking at the much higher kV versions?

https://www.newark.com/xp-power/hrc0524s600p/dc-dc-conv-adj-600v-8-33a-dip/dp/12AM7719?cfm=true

https://www.mouser.com/ProductDetail/209-HRC0524S600P

I just looked up the one in the link you had posted which showed a picture of the -6KV version (HRC0524S6K0N). so YMMV... I R ME