ChrioN
Well-known member
...and the new URL is http://mnats.net/JE-990.html
DIY JE-990 DOA
- Thread starter mnats
- Start date
Help Support GroupDIY Audio Forum:
seavote
Well-known member
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
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
Ptownkid
Well-known member
It's on the first page of this thread.
Cheers
Cheers
seavote
Well-known member
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
saint gillis
Well-known member
Hey guys!
Is it normal that the 2 big transistors are getting quite hot ( and one more than the other) ?
Otherwise is works...
Is it normal that the 2 big transistors are getting quite hot ( and one more than the other) ?
Otherwise is works...
sbranco said:
Soeren_DK said:
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
Are CR9/10 (diodes) thermally bonded to Q8/9 on your DOAs?
Check also for oscillation.
Oh, and in which cirquit do you use the 990?
In a API312-ish circuit they're tend to blow.
Check also for oscillation.
Oh, and in which cirquit do you use the 990?
In a API312-ish circuit they're tend to blow.
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.
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.
TillM
Well-known member
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.
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.
saint gillis
Well-known member
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 :
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.
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.
TillM
Well-known member
saint gillis said:
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.
saint gillis
Well-known member
I think it was basically VK200 inductors that I rewired as in the diagram above...
TillM
Well-known member
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
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
saint gillis
Well-known member
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..
So you have to test and measure, but I'm not sure the value is critical, others might correct me..
TillM
Well-known member
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?
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?
saint gillis
Well-known member
saint gillis said:
Maybe not critical but important, read again Samuel's post in page 2,
and read this to understand why http://www.technicalaudio.com/pdf/Jensen_Transformers/Jensen_OpAmps_990_and_related/Jensen_JE-990_opamp_JAES_reprint_1980.pdf
Beatpeat
Member
- Joined
- Mar 5, 2019
- Messages
- 24
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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