The SOHA II Tube Thread
Nov 15, 2009 at 3:30 PM Post #46 of 99

TimJo

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Well, I see I need to find some 6680's. Thanks for the tip.
smile.gif


I've never been a fan of Grados (other than their phono carts) but maybe I need to try out the RS2's being that I'm a guitar freak as well. You never know...
 
Nov 17, 2009 at 12:18 AM Post #48 of 99

wolf18t

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Quote:

Originally Posted by regal /img/forum/go_quote.gif
On another note this SOHA II is the first tube amp that has me completely impressed by Grados, never liked them till now, the Senns and AKG's are gathering dust after building this amp.


Finally I'm not alone using Grados with the SOHA II! In fact I prefer my SOHA II over my B22 with both RS-1 and PS-1000.

Try to get some Holland made 6DJ8 Orange Globes. Soundwise similar to 8416 but a bit smoother, they are less focused but they have larger images (intruments and singer voice is larger) and offer a more enveloping sound. I prefer them with the RS-1 than 8416. And yes, mids are as good as 8416 if not slightly better.
 
Nov 17, 2009 at 4:37 AM Post #49 of 99

regal

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Quote:

Originally Posted by wolf18t /img/forum/go_quote.gif
Finally I'm not alone using Grados with the SOHA II! In fact I prefer my SOHA II over my B22 with both RS-1 and PS-1000.

Try to get some Holland made 6DJ8 Orange Globes. Soundwise similar to 8416 but a bit smoother, they are less focused but they have larger images (intruments and singer voice is larger) and offer a more enveloping sound. I prefer them with the RS-1 than 8416. And yes, mids are as good as 8416 if not slightly better.



I think I have a pair of amperex orange globes 6DJ8, will give this a try.
 
Nov 20, 2009 at 5:20 AM Post #50 of 99

regal

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Here's how to get the most of your tubes on the SOHA II. The issue I was hearing on some of the 12AU7s and 6DJ8's was a slight weakness or thinness. So here is how you can safely get more current thru the tube:

1. Set B+ to 85V
2. Add another 18k ohm resistor on top (parallel) of R4L&R (makes it 9k ohm)
3. Add another 200 ohm resistor on top (parallel) of R6L&R (makes it 100 ohm)

Adjust P1L&R to give .550 V across R6L&R

Check to make sure you have at least a 19V drop across the top CCS (adjust P1 until you do)

This gives 2.75 mA thru each tube section.

Now the Mullard 12AU7's has pulled ahead of the 8416's. All the tubes I have been working with are sounding better.

I think the original design of 1 mA per tube section is too low and a remnant of the old (pre TL783) PS design. The amp is competing with what I breifly remember my Stacker II sounding like. The biggest improvement is in bass definition (i.e. telling the difference between the bass drum and the bass guitar.)

.
 
Nov 20, 2009 at 7:40 PM Post #51 of 99

tacitapproval

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I tried this mod and it does sound good. I will have to do more extensive listening to pick out the changes.

Is there a downside to this? Am I stressing the tubes or other parts? I do have almost a 30v drop, is this too much?
 
Nov 20, 2009 at 7:57 PM Post #52 of 99

holland

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I run @ 5mA per triode. There are no downsides that I can see. The only thing you need to worry about is the voltage drop across the cap multiplier. It is relative to current (the more current, the larger the drop). If you have the proto board with 3 cap multipliers on the B+ rail you may have to remove some.

The higher current then led to a higher voltage B+ mod.
smily_headphones1.gif
 
Nov 21, 2009 at 12:21 AM Post #53 of 99

regal

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Quote:

Originally Posted by tacitapproval /img/forum/go_quote.gif
I tried this mod and it does sound good. I will have to do more extensive listening to pick out the changes.

Is there a downside to this? Am I stressing the tubes or other parts? I do have almost a 30v drop, is this too much?




5ma is still on the low side, so you aren't stressing the tube at all. If you raise B+ and change R4 to 9k you shouldn't get a 30V voltage drop across the CCS but it shouldn't hurt.
 
Nov 21, 2009 at 1:13 AM Post #54 of 99

tacitapproval

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Quote:

Originally Posted by regal /img/forum/go_quote.gif
5ma is still on the low side, so you aren't stressing the tube at all. If you raise B+ and change R4 to 9k you shouldn't get a 30V voltage drop across the CCS but it shouldn't hurt.


I did both of those steps and r6 is 100--not sure why I get that much of a voltage drop.
 
Nov 21, 2009 at 4:13 AM Post #56 of 99

bmwpowere36m3

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Quote:

Originally Posted by holland /img/forum/go_quote.gif
I run @ 5mA per triode. There are no downsides that I can see. The only thing you need to worry about is the voltage drop across the cap multiplier. It is relative to current (the more current, the larger the drop). If you have the proto board with 3 cap multipliers on the B+ rail you may have to remove some.

The higher current then led to a higher voltage B+ mod.
smily_headphones1.gif



So a 10 mA tail current, correct? That would require a ~3.6k R4, correct? Along with ~ 66R for R6 & P1, so you could just jump R6 with a lead and just use the 200R trimpot.
 
Nov 21, 2009 at 6:21 AM Post #58 of 99

regal

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Quote:

Originally Posted by holland /img/forum/go_quote.gif

The higher current then led to a higher voltage B+ mod.
smily_headphones1.gif



You just have to rub that in
regular_smile .gif



You just wait till my Stacker II works with OCTAL tubes
ph34r.gif
 
Nov 21, 2009 at 3:31 PM Post #59 of 99

tacitapproval

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This sounds really good. I am listening to Bitches Brew now and wow, the bass is thumping.
dt880smile.png


With the 6n23, I get 84v at B+ and 53v at TP. With 5814, I get 84v and 56v, respecitvely. I did use a 22k resistor at r4 (I didn't have 18k), so I get 9.8k--I think I have some 16k's, so I could switch to that if it would be better. R6 is 110ohms (I only had 220s), with 550mV across it.

By the way, this is the production board, not the proto, so I believe the HV changes were already made?

edit: 6211 gives a 20v drop--83v and 63v. Interesting.
 
Nov 21, 2009 at 4:34 PM Post #60 of 99

regal

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Quote:

Originally Posted by tacitapproval /img/forum/go_quote.gif
This sounds really good. I am listening to Bitches Brew now and wow, the bass is thumping.
dt880smile.png


.





Yea it really helps the bass.
 

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