[jmf]

Hi,

I just launched the amp. I must say that I found the amp too lean with the provided Sylvania 5369. I was a bit dispointed.

I had found in an old electronic lab a pair of RCA 6922 (golden pin). Just changed the jumpers on the board and tried those lamps.

=> a completely different amp : more warm, more full, more flesh (but maybe the piano is still not OK...). Maybe less speed and not as good on strings.

Is a so big difference between Sylvania 5363 and RCA 6922 normal ?

Are my "feelings" in line with what one could normally wait from those lamps ?

(I use SOHA II with K701 + Monica DAC (DIYParadise))

Regards.

JM.

 

[regal]

Quote:

Originally Posted by jmf /img/forum/go_quote.gif Hi, I just launched the amp. I must say that I found the amp too lean with the provided Sylvania 5369. I was a bit dispointed. I had found in an old electronic lab a pair of RCA 6922 (golden pin). Just changed the jumpers on the board and tried those lamps. => a completely different amp : more warm, more full, more flesh (but maybe the piano is still not OK...). Maybe less speed and not as good on strings. Is a so big difference between Sylvania 5363 and RCA 6922 normal ? Are my "feelings" in line with what one could normally wait from those lamps ? (I use SOHA II with K701 + Monica DAC (DIYParadise)) Regards. JM.

Try it with a real Amperex 6Dj8/6922 and the tail current mod I posted and it is a huge step up from the stock 5963 setup, talking a completely different amp.

 

[jmf]

I'll try to find Amperex tubes...

In a fist time, I would have prefered not tomod the amp (aka add resistors...), but if it makes the difference .

I also do not understand if it needs mods to try the 6FQ7 tubes...

Regards.

JM

 

[jmf]

Hi,

One more question : what can be the max B+, tail current possible to experiment in a "plain vanilla" SOHA II : without resistor / heatsink / transfo mods ?

I see that this "setpoint" is an important point, but I won't have time to source new components, get the board out of the box...

Definitly, with 6922 and K701, I'm happy with voices, but not the Piano.

Thank's a lot for all infos.

Cheers.

JM.

 

[regal]

Quote:

Originally Posted by jmf /img/forum/go_quote.gif I'll try to find Amperex tubes... In a fist time, I would have prefered not tomod the amp (aka add resistors...), but if it makes the difference . I also do not understand if it needs mods to try the 6FQ7 tubes... Regards. JM

Yes 6FQ7 needs the heater mod. The piano will come alive with Holland 6922/6DJ8's.

 

[darkhoek]

I got a tip to try out the TESLA E88CC goldpin. They sound really magnificent. The Phillips SQ tubes sounded a bit lean IMO, but very smooth. The Teslas however has a poweful yet very defined and detailed low end, beautiful mids and a crystal high. At any price they are good, at their asking price they are an absolute steal. My Denon AH-D5000 Markl modded cans with the Jena ultrawire/Furutech upgrade sound abolutely etherical with the SOHA II w/Mundorf Supreme silver/oli caps and these wonderful Teslas.

BTW, Tesla had two plants where these E88CCs were made, and the 32 plant is said to have by far the best quality.

 

[regal]

Quote:

Originally Posted by darkhoek /img/forum/go_quote.gif I got a tip to try out the TESLA E88CC goldpin. They sound really magnificent. The Phillips SQ tubes sounded a bit lean IMO, but very smooth. The Teslas however has a poweful yet very defined and detailed low end, beautiful mids and a crystal high. At any price they are good, at their asking price they are an absolute steal. My Denon AH-D5000 Markl modded cans with the Jena ultrawire/Furutech upgrade sound abolutely etherical with the SOHA II w/Mundorf Supreme silver/oli caps and these wonderful Teslas. BTW, Tesla had two plants where these E88CCs were made, and the 32 plant is said to have by far the best quality.

I like the 1970's Tesla 6922's they do have good bass and are underrated, tubemonger.com is a good source for them. I didn't like my Phillips SQ 6922's and sold them they were deffinately lean, my favorite now is the 8416 Amperex tied with the Mullard 12AU7.

Were you able to fit the Mundorf SIO caps in the standard Hammond enclosure?

 

[darkhoek]

Quote:

Originally Posted by regal /img/forum/go_quote.gif I like the 1970's Tesla 6922's they do have good bass and are underrated, tubemonger.com is a good source for them. I didn't like my Phillips SQ 6922's and sold them they were deffinately lean, my favorite now is the 8416 Amperex tied with the Mullard 12AU7. Were you able to fit the Mundorf SIO caps in the standard Hammond enclosure?

Well, kinda. To get proper cooling, I made a new lid from perforated aluminium, and raised the hight a tad towards the sides of the cabinet while I were at it, almost like fitting a turbo under the hood of a smallish car

BTW I am planning to do your high current MOD to the SOHA to see if even more good can be squeezed out of this little marvel of a head amp.

 

[regal]

Quote:

Originally Posted by darkhoek /img/forum/go_quote.gif Well, kinda. To get proper cooling, I made a new lid from perforated aluminium, and raised the hight a tad towards the sides of the cabinet while I were at it, almost like fitting a turbo under the hood of a smallish car BTW I am planning to do your high current MOD to the SOHA to see if even more good can be squeezed out of this little marvel of a head amp.

Thanks, I have KY40s under my PCB in the standard enclosure but know that the Mundorf SIO would sound much better. I have a perforated top but can you share a picture? I think this is a super mod you have done.

 

[darkhoek]

Quote:

Originally Posted by regal /img/forum/go_quote.gif Thanks, I have KY40s under my PCB in the standard enclosure but know that the Mundorf SIO would sound much better. I have a perforated top but can you share a picture? I think this is a super mod you have done.

Here are some pictures. I have installed a switch on the back to be able to flip the heater voltage w/o opening the amp when rolling tubes. I have done the 600mA heater mod to be able to experiment with some of the russian tubes (6N1P). I also found out that when using my media player, a SONY NWZ-829, bypassing the Alps pot by installing a "direct-in" as you can see just to the left of the volume knob on the front, would do the sound more dynamic and airy. No use passing the signal through two attenuators.

The lid is made from an old PC tower cabinet side panel. The metal is somewhat thinner than the original lid, and by adding the small ridge along the edge, I gain about 5mm inside, which is just enough to host the Mundorf barrels. The real problem is that the cap leads are to fat for the holes in the PCB, so I have silver soldered the cap directly to the tube socket and R15.

I am really intrigued by the SOHA II design, and I am thinking about buying a couple of blank SOHA II boards to build different versions. One all botique with tantalum/Holco resistors, Nichicon/ cerafine or other caps, silver wiring the signal path, teflon tube sockets, ladder type 24 step volume regulator with Holco/tantalum resistors, larger cabinet or alternatively separate power supply plus your tail current mod, and one standard "very safe" version with an inbuilt USB DAC for my work place.

Attachment 28081

Attachment 28082

Attachment 28083

Attachment 28084

Attachment 28085

 

[regal]

Thats amazing, how did you get that beautiful bend in the perforated aluminum? I need to try this.

 

[darkhoek]

Quote:

Originally Posted by regal /img/forum/go_quote.gif Thats amazing, how did you get that beautiful bend in the perforated aluminum? I need to try this.

Well, the 90 degree bend towards the front panel was already a bend in the PC cabinet panel,so I started from that and cut out a piece that was about 0,2" wider than the original top of the hammond case. Then I made a jig from two pieces of stiff plywood and mounted them together with a piece of the panel material inbetween them so that I got something like a vice. See cross section to the left. Then I could place the perforated metal sheet in the slot and by pressing as close to the vice as possible I got a nice controlled bend. By bending along the perforations I didn't have to use much force either, and got naturally straight bends.

Attachment 28086

 

[regal]

Fantastic job. May be beyond my skillset as chassis work isn't my forte' but I got to try with my other hybrid upgrading the coupling caps from Ky40s made a huge improvement.


Has anyone tried rolling the output transistors? I've had real good luck with the 2SC 3421's from Beezar.com in other amps, think I might try them in the SOHAII.

 

[TimJo]

You really built a nice amp darkhoek. Nice work on the enclosure too. Very creative problem solving...

I hope you get the chance to build the other custom version, and if you do, be sure to take more pictures...

 

[darkhoek]

Thanks guys. I'll make sure to take pictures of the eventual SOHA II tour de Force, cost no object, hot shot sundance version build... or what ever...