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SOHA II Builders Thread - Page 91

post #1351 of 1686


Seems like 90% of the SOHAII issues are heatsink, heatsink, heatsink.

 

Before you take on this project understand the how,what, where, and why's of heatsink isolation.

 


 

Quote:
Originally Posted by Jaivan View Post

Just finished my build but I'm having problems.

My R3P resistor gets really hot and starts to smoke, I've tried looking for shorts but I do not see any.

I orginally had LV- and H switched around and it was working okay there, but after I corrected it this happened.

 

EDIT: Fixed it forgot to put the plastic washer back onto the H reg I guess I should get some rest haha..

post #1352 of 1686

hey guys so i am running through the initial setup of the soha II but I am only getting 24 volts for tb+ .  what would cause this low reading?  every other test point for the power supply checks out..  thanks!

 

editr: ok nm I believe I wired the trafo wrong:(:(  voltages are cool!  proceeding to the next steps of setup..


Edited by particleman14 - 6/11/10 at 3:54pm
post #1353 of 1686

Hi all,

 

After a few problems my Soha is finally up and running, but unfortunately I'm not completely happy with it...

 

At high volumes the e12 trips (I can't go beyond 3/4 of the pot), this is not a problem with low impedance cans such as grados, but makes the amp unusable with a pair of HD650 or with a pair of K1000.

 

I've tried regal's current mod, but I still get tripping and distorsion with my K1000's (not with my sr325i, though). I'm assuming this is not normal, since other head-fiers have reported good results with k1000 and HD650.

 

I suspect this could be related to the fact that I can't adjust the idle current of the buffers beyond 94 mA. I reach the end of P2L and P2R at about 205 mV of voldage drop across R10. At first I thought that it was not that important, but now I realise that I should have a wider adjustment range. I've already replaced P2L and P2R pots with same results. I was about to replace Q6 and Q7, but thought that maybe was a good idea to ask before.

 

Any idea???

 

Thanks!!!!  

post #1354 of 1686

Hey i am getting the same results as you alcaudon.  I have done regals current mod using 6DJ8s.  However, when I set the hv to 80v, the dropout is far above 19v(I am getting about 55V on my tpl.  what does this mean?  otherwise the soha works at low volumes.  but I am still unsure about the current settings..

post #1355 of 1686



 

Quote:
Originally Posted by particleman14 View Post

Hey i am getting the same results as you alcaudon.  I have done regals current mod using 6DJ8s.  However, when I set the hv to 80v, the dropout is far above 19v(I am getting about 55V on my tpl.  what does this mean?  otherwise the soha works at low volumes.  but I am still unsure about the current settings..



Did you change R4?

post #1356 of 1686

yes my r4s both read 9kohms. 

post #1357 of 1686



BC560's are 35V devices,  so yours must be toast if they are droping 55V's,  how old are your tubes?

Quote:
Originally Posted by particleman14 View Post

yes my r4s both read 9kohms. 

post #1358 of 1686


With K1000's you are pushing the limits of the SOHAII high current,  you can try lowering B+ to see if it helps with the tripping.
 

Quote:
Originally Posted by Alcaudon View Post

Hi all,

 

After a few problems my Soha is finally up and running, but unfortunately I'm not completely happy with it...

 

At high volumes the e12 trips (I can't go beyond 3/4 of the pot), this is not a problem with low impedance cans such as grados, but makes the amp unusable with a pair of HD650 or with a pair of K1000.

 

I've tried regal's current mod, but I still get tripping and distorsion with my K1000's (not with my sr325i, though). I'm assuming this is not normal, since other head-fiers have reported good results with k1000 and HD650.

 

I suspect this could be related to the fact that I can't adjust the idle current of the buffers beyond 94 mA. I reach the end of P2L and P2R at about 205 mV of voldage drop across R10. At first I thought that it was not that important, but now I realise that I should have a wider adjustment range. I've already replaced P2L and P2R pots with same results. I was about to replace Q6 and Q7, but thought that maybe was a good idea to ask before.

 

Any idea???

 

Thanks!!!!

post #1359 of 1686

 

Quote:
With K1000's you are pushing the limits of the SOHAII high current,  you can try lowering B+ to see if it helps with the tripping.

 

Even lowering B+ down to 70V, I still get tripping. I guess that the best that I can do now is to un-mod the amp, make sure that even then I have tripping (right now I'm not sure but as far as I can remember the tripping was there before the mod ) and see if I can drive k1000's 

 

At least I can always use it with grados, but that would be a shame because I put a lot of time and effort into this amp thinking that It was going to behave better than my other amps with the k1000's .

 

Anyway, many thanks for your help regal, much appreciated

post #1360 of 1686

tubes are brand new matched..  the BD's arent dropping 55v more like 25V.  my B+ is set to 78V  and I get 52V at the tpr and 45V and the tpl and so about 26 V and 33V drop drop.. is this too much?  how can it be reduced?  when I turn down the B+ i still get the same differences.  blown BDs?


Edited by particleman14 - 6/17/10 at 1:56pm
post #1361 of 1686

This is a little high for the mod,  especially the -33V.   Measure both plates of that tube and see if there is a big bismatch. 

 

Quote:
Originally Posted by particleman14 View Post

tubes are brand new matched..  the BD's arent dropping 55v more like 25V.  my B+ is set to 78V  and I get 52V at the tpr and 45V and the tpl and so about 26 V and 33V drop drop.. is this too much?  how can it be reduced?  when I turn down the B+ i still get the same differences.  blown BDs?

post #1362 of 1686

Sorry but I couldnt find your mod via search Regal. Could you please send me the link?

I couldnt find it on the Soha II website either.

ta

post #1363 of 1686

ok swapped out one tube that was giving plate voltages of 53 and 45.. now both tubes get about 55V with my left tube there is a 1.5V (54.5v pin1 56v pin 6) difference between plates, is this significant? 

otherwise my tpl now measures 56V and my tpr is 54.5V  with a B+ of 80V.  is this within range? 

the switch still goes off when i turn the volume pot almost towards the top.. however if I move the volume pot very slooowly up then I it doesnt trip the relay.  when i turn it up or down too fast it seems to trip. 

aside from this, the amp is singing, I just want to make sure it will be sustained.. also this thing puts off a ton of heat and I only have the small heatsinks.. should i upgrade?  also heatsink HV as well?

 

cheers

 

particleman14

post #1364 of 1686



Yes and turning up B+ will cause trips.  Use the heatsinks mouser in the excell BOM

Quote:
Originally Posted by particleman14 View Post

ok swapped out one tube that was giving plate voltages of 53 and 45.. now both tubes get about 55V with my left tube there is a 1.5V (54.5v pin1 56v pin 6) difference between plates, is this significant? 

otherwise my tpl now measures 56V and my tpr is 54.5V  with a B+ of 80V.  is this within range? 

the switch still goes off when i turn the volume pot almost towards the top.. however if I move the volume pot very slooowly up then I it doesnt trip the relay.  when i turn it up or down too fast it seems to trip. 

aside from this, the amp is singing, I just want to make sure it will be sustained.. also this thing puts off a ton of heat and I only have the small heatsinks.. should i upgrade?  also heatsink HV as well?

 

cheers

 

particleman14

post #1365 of 1686
Quote:
Originally Posted by tamu View Post

Sorry but I couldnt find your mod via search Regal. Could you please send me the link?

I couldnt find it on the Soha II website either.

ta



Its in the SOHAII tube thread

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