DIY JE-990 DOA

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p town
  i got some kits quite a while ago but im ready to tackle them now. could you repost the photo of the transistor /diode coupling?
still not sure how that works. thanks
 
thanks .saw that but thought phot you posted was different. i get it now. if the transistor in your kit has a heatsink i'll couple to that rather than the lead of the component  ala mnats
 
sbranco said:
Built two doa's from the parts list posted before. Though I used 62K resistors for R10 and R11 which are supposed to be for 24V, I supplied 18V and it appears to work fine. If you plan on 18V use 42.2K resistors, for 15V - 33.2K and 12V - 28K.

One doa worked and one did not. Fried R7 on the one that did not work.

Soeren_DK said:
I have some problems with the 990 DOA.
The R7 resistor on the DOA started to burn and I turned it off. I can't see any problems on the PCB but maybe you out there have an idéa what to look after.
Cheers
Soeren

Hello I have two diy JE-990 Opamps,
one works perfectly an the other one is burning R7.

It seems that is quite common to have problems in burning R7 as there was more people with the same problem.
Anyone knows what might me causing this?

I''m supplying + and - 18V and I have 43K resistors installed for R10 and R11 on both Opamps.

The Opamp that keeps burning R7 resistors worked well before, suddently started to burned R7 each time I turn the unit on, it takes 10-20 seconds to start burning.

Thanks for your help
 
Sredna said:
Are CR9/10  (diodes) thermally bonded to Q8/9 on your DOAs?

Check also for occilation.

Oh, and in which cirquit do you use the 990?
In a API312-ish circuit they're tend to blow. ;)

Hi Sredna,
I will check the diodes, thanks.

How do I check for oscillation?

Yes, I'm using them in and API 312 type circuit,  I know the 990 is supposed to be used with a lower ration input transformer, although I'm waiting for 2x 2520 type opamps I decided to try these in the meanwhile as I had them for a long time in a drawer and never got a chance to try them. They sounded really good (even with a 1:10 input transformer).
The strangest thing is why it's only the same one that burns R7? The other one is completely fine, if the problem is from the 312 circuit shouldn't both of them blow? An why only and always R7?

thanks
 
Whoops said:
Sredna said:
Are CR9/10  (diodes) thermally bonded to Q8/9 on your DOAs?

Check also for occilation.

Oh, and in which cirquit do you use the 990?
In a API312-ish circuit they're tend to blow. ;)

Hi Sredna,
I will check the diodes, thanks.

How do I check for oscillation?

Yes, I'm using them in and API 312 type circuit,  I know the 990 is supposed to be used with a lower ration input transformer, although I'm waiting for 2x 2520 type opamps I decided to try these in the meanwhile as I had them for a long time in a drawer and never got a chance to try them. They sounded really good (even with a 1:10 input transformer).
The strangest thing is why it's only the same one that burns R7? The other one is completely fine, if the problem is from the 312 circuit shouldn't both of them blow? An why only and always R7?

thanks

Please, anyone could help on this?

thank you so much
 
I solved the problem with my Opamp,
R7 was burning because Q5 transistor was shot, it had a short between Collector and Emitter.
Replaced the transistor and the burned resistor and all if fine now.

 
I know Mike sells the DOA at his page, but I've laying around 10 pcbs from the Gerber files from Mnats.
After years of laying around I get some LM394 for cheap from a friend of mine who don't need them anymore.
Now I want to finish some DOAs.
The only thing I need to know is whether I can use some other 20uH inductors?
In the thead someone linked inductors from Würth.
Can I use any 20uH inductor or did I've to pay attention on something?
I hope anybody can help me.
 
I bought on ebay some axial inductors using the same kind of ferrite as in the 990 20µH, and rewired them radially as in the 990C :
inductors-wiring.gif


I measured them and obtained successfully something very close to 20µH.

Otherwise I think you could use any kind of inductor but others might add deeper considerations on the subject, like importance of the ferrite core, etc.
 
saint gillis said:
I bought on ebay some axial inductors using the same kind of ferrite as in the 990 20µH, and rewired them radially as in the 990C :

Otherwise I think you could use any kind of inductor but others might add deeper considerations on the subject, like importance of the ferrite core, etc.

Thats what I also thought.
Buy some 20uH or 22uH inductors and take them inside, what could happen? Nothing, maybe I get no sound, but when I can resolder it and then I will see what I can do.
Thanks for your answer and your  experience with inductors.
 
thanks for that !
so maybe this will work with 28 copper tinned gauge wire ?
https://www.mouser.de/search/refine.aspx?Ntk=P_MarCom&Ntt=118477892

I've just to choose the right one ;)
 
The exact coil inductance math calculations are quite complicated, I'm not the one who really knows them, but here : https://www.eeweb.com/tools/coil-inductance  if we consider we have 3 turns, an approximate 7mm loop diameter and a 0.321 wire diameter, with a relative permeability of the core between 100 and 600µR, we get an inductance between 12.5 and 75µH...
So you have to test and measure, but I'm not sure the value is critical, others might correct me..
 
I now build four of them.
Three work like a charm.
At one I’ve a problem.
He passed audio but had permanently a high frequency noise.
My thought is, that it is the cheap lm394 from China.
Anyone of you had the same issue? What  could be the problem?
 
Hi, has anybody tried to build this with MPSA06 and MPSA56 instead of PN4250A and PN2484? and BD180/179 instead of MJE 181/171? AND AS194H instead of LM394. Original parts are impossible to get, so will give these Parts a try. Any doubts or recommendations?
 
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