The ultimate DIY? A Stax SRM-T2!

[Kerry]

You can use the RK50 50K A taper pot.

Model number is RK50114A0001.

[Craig Sawyers]

That is an expensive pot for sure. Mouser are expecting 8 of them in September for UKP729 (so about $1k)

I think I ended up using a DACT switched attenuator. The RK50 was just too hot for my pocket.

Edited July 3, 2021 by Craig Sawyers

[Kerry]

Here's a new twist on my T2 build.  I've added both the HE-90 jack as well as a custom built Teflon HE-60 jack with appropriate voltages/resistances. 

This one is in black chrome

That's the back of the power supply... 

[judo]

Gorgeous! I would have the urgency to put the amp to the top of the power supply but how can somebody do this with these shiny things?

[Lord_Rexter]

9 hours ago, Kerry said:

Here's a new twist on my T2 build.  I've added both the HE-90 jack as well as a custom built Teflon HE-60 jack with appropriate voltages/resistances. 

This one is in black chrome

That's the back of the power supply... 

Hearty congratulations Kerry, What a beauty to behold am quite sure it would be sounding absolutely A M A Z I N G 💥👏✌️

[johnwmclean]

That is fucking BEAUTIFUL! Congrats Kerry!

[swt61]

What he said!!!

[Voltron]

Wow. Tasty!

[morphsci]

Absolutely gorgeous Kerry!

[Torpedo]

2 hours ago, morphsci said:

Absolutely gorgeous Kerry!

This. Congratulations for your build.

[Rinat]

About using 2sa1413 as a substitution of 2sa1486. Am I wrong that they looks pretty similar? 

I am waiting them from bdent, they are in TO-251 cases. I've found only one datasheet with this type of case for 1413: 

1413 datasheet jp to-251

1413 datasheet en

2sa1486 en

[starcat]

On 7/9/2021 at 2:01 AM, Kerry said:

Here's a new twist on my T2 build.  I've added both the HE-90 jack as well as a custom built Teflon HE-60 jack with appropriate voltages/resistances. 

This one is in black chrome

Congrats, Kerry. That one looks gorgeous! 

Are you using all original transistors or modified boards with substitutes? 
Digital attenuator or analog pot in there? 

On 7/3/2021 at 12:02 PM, Craig Sawyers said:

That is an expensive pot for sure. Mouser are expecting 8 of them in September for UKP729 (so about $1k)

I think I ended up using a DACT switched attenuator. The RK50 was just too hot for my pocket.

Indeed, way overpriced by now. In fact the almost only reason I decided to go with the RK50 is that it is still available in quad 50 ohm and 50 ohm is what the T2 was designed for. 

810€ at Mouser plus 20 VAT, makes up for stunning 972€ for a pot. 

Edited July 10, 2021 by starcat

[johnwmclean]

 

2 hours ago, starcat said:

Indeed, way overpriced by now. In fact the almost only reason I decided to go with the RK50 is that it is still available in quad 50 ohm and 50 ohm is what the T2 was designed for.

50k not 50ohm

The Goldpoint V47 is an incredible attenuator, I prefer way more than DACT or RK50.

 

[starcat]

Yeah, sure kOhm (still in sailing mode, returning home tomorrow and back to amp building :-) 

I have a T2 PCB that accepts only the DACT or the RK50 with a pre-drilled front panel as well. So, "has" to be one of the two. 

John, what do you like on the Goldpoint V47 better? 

[johnwmclean]

I see 

2 hours ago, starcat said:

Yeah, sure kOhm (still in sailing mode, returning home tomorrow and back to amp building 🙂

I have a T2 PCB that accepts only the DACT or the RK50 with a pre-drilled front panel as well. So, "has" to be one of the two. 

John, what do you like on the Goldpoint V47 better? 

 

Ok gotcha, DACT or RK50 only then.

The Goldpoint V47 is 47 steps vs DACT 24 steps. I also prefer the wafers with PCBs vs DACTs pinouts (not an issue with your T2 pcb though). Then channel matching on either DACT or Goldpoint would be better than the RK50 as well as a lot less money. The Goldpoint feels incredibly good quality not RK50 quality, but a lot better than the DACT from my experience. I’ve also had Kozmo’s as well and was not a fan, maybe quality has improved but not willing to gamble.

[Kerry]

19 hours ago, starcat said:

Are you using all original transistors or modified boards with substitutes? 
Digital attenuator or analog pot in there? 

I've redesigned my own boards and using the RK50 typically.

I'm currently using C3675 (4x for the active batteries), KSA1156, C4685A (output CCS), FJPF2145, STN9360, J79, K216.

[JoaMat]

Thanks Kerry, for internal picture of and info about your T2. It’s always very inspiring see your work.

I assume the four small boards, one at each big tube, are CCS for the two LEDs on main board at respective output CCS. They must differ (schematically) from the original design, mustn’t they?  Do you mind tell us what the small boards look like?

Edited July 12, 2021 by JoaMat

[starcat]

What resistor values are you guys using for load testing the T2 PSU? 

[Kerry]

On 7/12/2021 at 6:57 AM, JoaMat said:

Thanks Kerry, for internal picture of and info about your T2. It’s always very inspiring see your work.

I assume the four small boards, one at each big tube, are CCS for the two LEDs on main board at respective output CCS. They must differ (schematically) from the original design, mustn’t they?  Do you mind tell us what the small boards look like?

Yes.  It's the CCS for the LEDs that feed the the output CCS.  It's a simple cascaded DMOS with a cap on board.

[JoaMat]

Nice, Kerry! 

Now I get it - and the three pins (-, +, o) and all vias visible on the other side make sense even to me.

[starcat]

I have put the 2SC3675 with the highest breakdown voltage (above 1120) into the batteries. Any particular places of importance for the remaining 3675? I have 1060 to 1105. 

[Kerry]

You really want the highest Hfe for the batteries. I shoot for around 60

[Kerry]

The maximum potential voltage there is only about 810v, so the 900v rating is perfectly fine. 

[starcat]

On 9/13/2011 at 11:44 PM, kevin gilmore said:

For the K216

Make an adapter that ties the gate pin to the source pin
which goes to the emitter pin in the socket, and the drain goes to the collector.

Then test as a NPN. The real ones test at 230 volts, The fakes test much less.

Kevin, does the same connection and testing procedure apply for the J79 as well?
Then testing as PNP of course. Thanks! @kevin gilmore

Edited July 18, 2021 by starcat

[Craig Sawyers]

Then there is this http://www.tkd-corp.com/products/att/pdf/p65cs-e.pdf which is what Curl used in the Blowtorch. He used a stereo one, not four channel, because Blowtorch was not inherently a balanced preamp.

It is available in four channel, I have no idea of the price, but expect it to be substantial.

Then there is the Seiden 74005, 58 position 4 channel switch. You need to add resistors of course. That switch is Y47,000 direct from Seiden ($430, shipping, taxes etc on top). Depending on the resistor choice you could be back in RK50 territory or beyond.

Although the Seiden price list is 2012, that is the one that Seiden sent me in Feb 2020.

I have not tried either the TKD nor the Seiden, but at least considered the Seiden for another project (pending) that needs a really weird attenuation law.

SEIDEN.pdf PRICE_LIST_2012.10.pdf