[xTr3Me.aka.Chris]

Hey,

today Ive finished my Jisbos Buffers.. some hours ago I started to adjust the right bias but then I noticed that I do not have the right voltages on the main soha-pcb.
for example at the 60V testpoint I have above 100V after some time

Same problem goes with the two 40V points. since the voltages of the 60V testpoint is much too high I cant adjust the 40V voltage. I cant adjust it below 50V and 55V on the other control point

The voltage is growing per time.. now I turned the Soha off because also the tube is getting more and more hot..

Does anyone of you have an idea?

I havent adjusted the DC offset on the jisbos boards yet, because I havent found out where to messure. Might that be that reason?

greetings,
xTr3Me

 

[Pars]

Can you take it back to the opamp configuration? If so, does it still do it in this configuration? What CCS configuration did you use?

Sorry, I haven't actually built one, but did put the JISBOS buffers in another users SOHA for them so do have some experience.

As for the JISBOS boards, the bias is adjusted across the resistors (a couple of test points, adjust + or - side and that is good for both of them), then DC offset at the amp output must be adjusted on the JISBOS boards (1 per channel).

 

[xTr3Me.aka.Chris]

Hi Pars,

i can take it back. I soldered all wires on an OP-Amp-Socket so that I can change it. But the ground ist soldered to the PCB board.

Can I leave the ground - connection between the jisbos and the soha and just switch the wired-socket with the old op-amp?

I used this CCS-configuration:
http://www.mb3k.com/pics/SOHA/LND150.gif

I cant put them into another soha.. would take a lot of time to reach some1.. this could be tested at last. but Im quite sure that they are ok.

I adjusted the bias once to 40mv but then it increased more and more so I turned the trimpot to minimum voltage (clock-countervise).

 

[Pars]

The bias will climb when you first adjust it, but should settle. Keep backing it off until you get it stable where you want it. I would think the gnd would be fine to leave, as long as you are sure it is actually connected to gnd at both ends (check it to be sure).

If you have replaced the VR1 and VR2 regulators for 15V, make sure your opamp can handle +/-15V. I assume the SOHA worked fine with no issues before you decided to do the JISBOS (highly recommended, BTW).

 

[xTr3Me.aka.Chris]

Yes the Soha worked perfectly!

I havent replaced vr1 and vr2, should i? i bought a kit from glassjar audio and there werent any 15v included :O

The problem atm isnt the climbing bias, i know that it grows when the parts heat up but the problem is that on the soha pcb the 60v control point goes over 100v and the heat of the tube is at 18v insteand auf 12,6v...
the 60v point already had about 70v before but i read this is no problem at all.. the tube heat was at 12,59 .. nearly perfect

maybe its also because of the jj tube i use? hmm



EDIT:

I changed back to the opamp.. now the voltages are STILL GROWING.. at start they are right but then they increase more and more.. OMG

 

[Pars]

I would doubt it is the tube. If you unplug the JISBOS, does it still climb at the 60V point? When you say tube heat, you mean the heater for the tube? That is regulated (VR3) and climbing to 18V is a big problem. I suppose if you have another tube, you could try it, but first I would unplug the JISBOS boards and see where you are at that way. Step thru it.

The JISBOS boards will work at 12V, but the VR1 and VR2 regulators will get quite hot and probably require heatsinking. If you switch them to 15V (7815 and 7915 IIRC), there is less voltage dropped across the regulators and less heat therefore, so recommended for JISBOS. And no, GlassJar doesn't include those.

 

[xTr3Me.aka.Chris]

i willchange to 15v later on..

but i edited above:
I changed back to the opamp.. now the voltages are STILL GROWING.. at start they are right but then they increase more and more.. OMG

and yes i mean the tube heater

edit: now the voltages are corret..... without jisbos

 

[Pars]

Not sure what to tell you on that. The heater and the +/- 12V are regulated, so they should stay where they are supposed to be...

The 60V is unregulated, but past the CCS the 40V points I would think should not rise (but maybe I'm not thinking?).

At this point given that it had worked fine, I would look for any solder bridges or perhaps traces that aren't connected. Did you previously have the opamp socketed or did you remove the opamp and install a socket? One place to look. Basically go over the schematic and with a meter verify connectivity.

 

[xTr3Me.aka.Chris]

now its working... u said that the voltage is regulated by vr3.. so I put the pcb out of the enclosure and now it is working.. maybe the heatsink of vr3 touched the case..

I will try so adjust bias now.. thank you for your help (so far )

 

[Pars]

Quote:

Originally Posted by xTr3Me.aka.Chris /img/forum/go_quote.gif now its working... u said that the voltage is regulated by vr3.. so I put the pcb out of the enclosure and now it is working.. maybe the heatsink of vr3 touched the case.. I will try so adjust bias now.. thank you for your help (so far )

VR3 regulates the tube heater. Yeah, if you don't have the regs insulated from the heatsink, the tab is live and could present a short to the case or whatever. Use a TO-220 mounting kit, or heatsink grease and a fiber or nylon step washer on the screw/nut for the reg to heatsink.

 

[xTr3Me.aka.Chris]

Well now it doesnt work again....

I even have the Problem with unplugged and plugged Jisbos..

Ground is still connected so there must be a problem with the ground channel?!

maybe the groundchannel cable is touching another cable from the jisbos where it is attached to the jisbos pcb...

i can also messure a dc offset with unconnected jisbos...

i will check if there is a bridge or sth

____________

i checked for bridges but i couldnt find any..

so i disconnected the jisbos ground from the sohas.. now the voltage is still rising. i have 22v on tube heater...

mb my multimeter needs a new battery? it shows battery symbol but it messures.. i will buy new ones tomorrow .. but i dont think its because of the battery... its very strange

the voltage is rising slowly everywhere on the soha board

 

[amb]

I think your meter is lying to you.

 

[Pars]

Quote:

Originally Posted by amb /img/forum/go_quote.gif I think your meter is lying to you.

Yes, I would agree (and was waiting for the new batteries).

 

[xTr3Me.aka.Chris]

new batteries are in use... now its working so far :X

this is rly strange..

well now im trying to adjust bias.. which resistors are the output resistors? i need to know to adjust right bias.. i want to go for 20ma

greetings

 

[Ferrari]

Quote:

Originally Posted by xTr3Me.aka.Chris /img/forum/go_quote.gif well now im trying to adjust bias.. which resistors are the output resistors? greetings

What do you think about about R11 and R12, the big ones

!