I'm nearly finished with a pair of Welborne Labs / Borbely Audio Linestages; EB-1190/123
http://www.welbornelabs.com/classa.htm
Question is:
1) I have some trouble sourcing "BL" version of some of the j-fets. I have however some "GR"'s. Can the circuit be adjusted to these?
2) I would like two separate, adjustable outputs, how do I implement attenuators(Goldpiont) after the circuit? (What type atten. would work best?) Or do I need to use two separate linestages?
3) Can this circuit drive headphones? (32 ohm).
Arne K
http://www.welbornelabs.com/classa.htm
Question is:
1) I have some trouble sourcing "BL" version of some of the j-fets. I have however some "GR"'s. Can the circuit be adjusted to these?
2) I would like two separate, adjustable outputs, how do I implement attenuators(Goldpiont) after the circuit? (What type atten. would work best?) Or do I need to use two separate linestages?
3) Can this circuit drive headphones? (32 ohm).
Arne K
My Problem Now With 1190/123
And I bought them from you ! Mounted 4 new double transistors and have finished them using Teddy Pardo Supplys. I only need to adjust the pots. Anybody can tell how to adjust the pots ?
😱🙁😕
And I bought them from you ! Mounted 4 new double transistors and have finished them using Teddy Pardo Supplys. I only need to adjust the pots. Anybody can tell how to adjust the pots ?
😱🙁😕
One of the pots is near the input fets, that is the DC offset for the output.
The other pot is the bias for the output stage.
_-_-bear
The other pot is the bias for the output stage.
_-_-bear
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Thank You ! Your schematic looks A little bit like mine ! 🙂 I have the schematic for the 1190/123 but no explanation where to place the measurement pins and what to measure. 🙁
I have written to the Welborne labs. Hope they come up with an answer.
I have written to the Welborne labs. Hope they come up with an answer.
Do not plug in the servo opamp until the end of all this. Hopefully your input devices are IDSS matched within 10 % and their IDSS is between 7.5 and 8.2 (if it's higher you need to add resistance in series with P1 - try 22 ohms on each end if the input pair IDSS is closer to 9ma).
Before applying power set P1 200 ohm to mid point ( measure 100 R from either end to wiper). Set P2 to 0 ohms.
Apply power. Measure voltage across R4 it should be around 3 volts - if the input stage devices are in the correct IDSS range (if the input pair's IDSS is higher than 8.2 add something like 22 in series with the pot and you'll have to experiment with the value for one in parrallel with the Pot if the input pair's idss is lower than 7.5 IdSS).
Once you have verified 3 volts across R4 short the input and set P1 at turn on by monitoring the output for DC offset -set it as close to 0 as you can achieve. Increase P2 slowly to a board current draw of maybe 70 ma - monitor the heat sink temperature of the ouput devices. Retest the dc output and reset P1 for offset. Watch for 15 minutes and reset both P2 and P1 if needed - you want the output heatsinks as warm as possible so you can touch them for 10 seconds without letting go. (assuming you have an adequate power supply and regulator)
The second stage jfets Q6 and Q9 have to be matched IDSS above 9 ma within 10 % - it's worth replacing Q7 with 2sj74 and Q8 with 2sj170 both with iDSS above 9ma - no need to match Q7and Q8 - watch out thier pinout is different than the 2SK982 /2SJ148 if you do it.
Once offset and temperature are stable for half an hour , power down, insert servo opamp and recheck that the offset stays with in a couple of mv of 0 and very slowly moves around 1 or 2 mv with time. Burn it in for 100 hours with music signal - check off set and bias once more and enjoy.
Before applying power set P1 200 ohm to mid point ( measure 100 R from either end to wiper). Set P2 to 0 ohms.
Apply power. Measure voltage across R4 it should be around 3 volts - if the input stage devices are in the correct IDSS range (if the input pair's IDSS is higher than 8.2 add something like 22 in series with the pot and you'll have to experiment with the value for one in parrallel with the Pot if the input pair's idss is lower than 7.5 IdSS).
Once you have verified 3 volts across R4 short the input and set P1 at turn on by monitoring the output for DC offset -set it as close to 0 as you can achieve. Increase P2 slowly to a board current draw of maybe 70 ma - monitor the heat sink temperature of the ouput devices. Retest the dc output and reset P1 for offset. Watch for 15 minutes and reset both P2 and P1 if needed - you want the output heatsinks as warm as possible so you can touch them for 10 seconds without letting go. (assuming you have an adequate power supply and regulator)
The second stage jfets Q6 and Q9 have to be matched IDSS above 9 ma within 10 % - it's worth replacing Q7 with 2sj74 and Q8 with 2sj170 both with iDSS above 9ma - no need to match Q7and Q8 - watch out thier pinout is different than the 2SK982 /2SJ148 if you do it.
Once offset and temperature are stable for half an hour , power down, insert servo opamp and recheck that the offset stays with in a couple of mv of 0 and very slowly moves around 1 or 2 mv with time. Burn it in for 100 hours with music signal - check off set and bias once more and enjoy.
Mixed Designs ?
Thank you so much but are you sure we are talking about the same PRE ? There is no Opamp in this design. Voltage across R 4 is almost nothing it is just a 100 ohm stop resistor in series with input. Also all Transistors are double i same house !
This is EB-1190/123. I just got a profil on facebook and sent an email to Mr. Borberly
Thank you so much but are you sure we are talking about the same PRE ? There is no Opamp in this design. Voltage across R 4 is almost nothing it is just a 100 ohm stop resistor in series with input. Also all Transistors are double i same house !
This is EB-1190/123. I just got a profil on facebook and sent an email to Mr. Borberly
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The 1190 would have been in 1990 IF the numbering system he used is consistent.
If you post the schematic it can be figured out.
It seems that Mr. Borbely has not been active on Facebook for a while now. So, that may not work.
Most of these early designs were described in articles in Audio Amateur magazine, including how to set them up. I'd look there for starters, unless someone comes along with that information here.
_-_-bear
If you post the schematic it can be figured out.
It seems that Mr. Borbely has not been active on Facebook for a while now. So, that may not work.
Most of these early designs were described in articles in Audio Amateur magazine, including how to set them up. I'd look there for starters, unless someone comes along with that information here.
_-_-bear
The Board Including Supply draws aprox 554/6,6 = 80 ma and the ouputs is aprox 45 c . So maybee its fino. 🙂 I will show the schematic to a friend by Thrane & Thrane tomorrow !
Hi,
there may be two ways to search for the info you are looking for:
- Have a look at Zen Mod's mirror of the Borbely website:
http://www.diyaudio.com/forums/pass-labs/185003-borbely-site-mirror.html
- Search at Internet Archive: Digital Library of Free Books, Movies, Music & Wayback Machine for old versions of the Borbely website.
Hope this helps & good luck
there may be two ways to search for the info you are looking for:
- Have a look at Zen Mod's mirror of the Borbely website:
http://www.diyaudio.com/forums/pass-labs/185003-borbely-site-mirror.html
- Search at Internet Archive: Digital Library of Free Books, Movies, Music & Wayback Machine for old versions of the Borbely website.
Hope this helps & good luck
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