SRX-Plus Build Thread

[JimL]

Doh! (slaps forehead)  Thanks for the reminder.

[johnwmclean]

8 minutes ago, JimL said:

Doh! (slaps forehead)  Thanks for the reminder.

Been there.

[Arthrimus]

On 5/24/2016 at 9:39 PM, JimL said:

This modification does not need to be done for those of you who built the SRX Plus circuit using a Gilmore regulated PS, as that supplies the -15 volts that can be used for the input current sources.

 

Ok, so I think I know the answer to this, but because I'm a little slow (and fire averse) I'll ask just to be sure. If for some reason someone decided not to populate the 15v supply in the KGBH board, could they perform the modification you described to the amp board and only use the +/-325 from the KGBH supply?

Edited July 18, 2016 by Arthrimus

[kevin gilmore]

yes you can modify any of the power supplies to do that.

[JimL]

18 hours ago, Arthrimus said:

Ok, so I think I know the answer to this, but because I'm a little slow (and fire averse) I'll ask just to be sure. If for some reason someone decided not to populate the 15v supply in the KGBH board, could they perform the modification you described to the amp board and only use the +/-325 from the KGBH supply?

Yup, that's fine.

[Arthrimus]

Thanks fellas.

[JimL]

On May 1, 2016 at 10:59 AM, JimL said:

 

 

On April 30, 2016 at 6:52 PM, JimL said:

Jose, aka Strawhat, noticed another error on the shunt power supply board.  There is a missing connection between the input ground terminal and the output terminal ground terminal.  The easiest way to fix this is to run a wire from the center tap of the HV transformer to both the input ground terminal and the output ground terminal.  Thanks to Jose for catching this.

Well, that didn't work!  Strawhat blew up his regulator by connecting the input and output ground terminals.  Sorry about that, I was going by my original point-to-point wired PS rather than KG's PCB rendering.

[Arthrimus]

I'm on the home stretch as far as parts acquisition for this build, but I do have a question. For the 10m90S heatsink isolation, is rubberized silicone sufficient, or should I be using ceramic insulators?

Edited September 4, 2016 by Arthrimus

[kevin gilmore]

ceramic insulators with white thermal grease and the appropriate bushing and screw

[JimL]

Yup. Here's a pic.  Note that this is for my point-to-point wired unit.  For the KG board, the heatsinks are spaced so that there is enough space for the ceramic insulators to fit between the 10M90S TO2220 and the heatsink.

Edited September 5, 2016 by JimL

[jose]

Is there any progress?

[JimL]

20 hours ago, jose said:

Is there any progress?

On what?

[jose]

Your PSU for example...

I only know two amps that are still working and I would like to know if other guys are working on his srx´s.

Probably I will start my SRX for christmas.

[JimL]

Haven't done anything with my PS as I am out of town this weekend.  AFAIK, three people have completed an SRX Plus, Congo5, mwl168 and Straw Hat recently wrote me that he completed his.  I believe Congo5 used the original KGBH PS, mwl168 used a KGSSHV PSU and Straw Hat used my PSU design.  So far, nobody has written me any e-mails complaining I wasted their time and money. 

Edited November 1, 2016 by JimL

[MLA]

I built one as well; I had some boards made when JimL and KG presented the design and board. Powered it with a KGST psu as that's what I had boards laying around for at the time.

Very nice amplifier with just a slightly different sound characteristic than others, can very much recommend a build!

Dialling it in is interesting as everything is connected to everyhing else. Takes a while to figure out if one of your input tubes is underperforming, which happened to me

Also, I have all windings on the same trafo including the filament supplies, and I had to elevate the latter to avoid hum.    

[jose]

Thanks guys. I have boards (amp+ psu) too but I will use a BH PSU.

When I finish the PSU, I´ll start with the amp board but before I would like to know if the amp have problems or if I need to change resistors values for example...

[JimL]

Haven't heard of any problems with the amp.  One change I made is to feed the input tail CCS with separate resistors from B- for each channel.  This eliminates the need for a -15-20 volt PS.

[jose]

Thanks Jim

[jose]

Guys I'm finishing the amp and I want to do the last update that Jim mentioned on the "SRX Revisited" thread; change the top MOSFET in that current source from a DN2540 to a 10M90S. Can I change them directly on our PCB? I was seeing the schematic/ PCB layout and I think that it´s OK so I don´t need change or move the10M90S pins, but I would like are sure before.

Another stupid question, Are the quality of the 0.22/1kvolt critical? I have wimas (MKP) now but I don´t rule out changing them for Mundorf or other "audio grade" caps if this is necessary. I remenber that Jim used a kind of "audio grade" cap in her SRX.

Thanks

 

 

[mwl168]

Those .22uf/1000VDC caps are coupling caps between stages and directly on the signal path. Quality of the capacitor does matter in that position IMO. I started out with some Wima MKP and later changed to Teflon caps that I happen to have on hand.

Good luck and looking forward to seeing pics of your build and your impression of its sound.

Edited November 18, 2016 by mwl168

[jose]

Thanks, I finished my amp and I used Wima caps. Dr. Gilmore said on other thread:  "...evidently no amp is complete without some wima's."  

Now I ´m waiting the trafos and I need decide if I use the DN2540 or 10M90S in the CS. While I can´t do nothing.

 

 

[JimL]

The board layout uses all TO220 MOSFETs for both the DN2540 and 10M90S, so the 10M90S should be a direct drop in for the top DN2540.

[jose]

1 hour ago, JimL said:

The board layout uses all TO220 MOSFETs for both the DN2540 and 10M90S, so the 10M90S should be a direct drop in for the top DN2540.

 Thanks Jim

[JimL]

I've posted a revised power supply schematic and explanation on the SRX revised thread.  This comes as a result of trying to make the supply quieter.  Most of my attempts seemed to make it noisier, but after frying a few 431 chips, including getting some hundred plus volt oscillations, this is both quieter and more stable.

[jose]

Today my amp passed all checkpoints so I think that this weekend I can listen music.

I had problems with my first ECC81 quad (JJ´s new stock  ) and I couldn´t have a good balance between plates (50~120 volt). I was crazy looking some problem (bad solder or wrong values) but everything was OK and I had good values on the rest of checkpoints

Today I changed this quad for a new quad matched (NOS CV4024) and I read 0~4 volt (drift a bit) between plates without moving trimpot of mid-point  

Thanks to JimL and mwl168 for his patience.