Thanks,
I found a simple diagram the uses a 9 volt battery. Wonder what difference a volt makes? Most of the parts showed up from Digikey today. Hopefully I'll have some time tonight to start populating the boards. I have barely started this project, now I'm think of either a BA-1 or F3 as next one as I want hear S.E. amp. I think this hobby might be a disease.
Chad
I found a simple diagram the uses a 9 volt battery. Wonder what difference a volt makes? Most of the parts showed up from Digikey today. Hopefully I'll have some time tonight to start populating the boards. I have barely started this project, now I'm think of either a BA-1 or F3 as next one as I want hear S.E. amp. I think this hobby might be a disease.
Chad
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Not much. I have compared results from 9V battery and 10V on lab power supply.
If there were any differences they were no more than 1%.
.... I can confirm that!
and I matched this way today two sets of four J74 for Babelfish 2. It worked good!
Tomorrow I will hear one channel! And in two days two channels, heaven is open!
long live ZM!!!
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JFET IDSS matching
Attached a sketch of the methode we used to match 2SK170 GR types (N-cahannel) for the ONO phono pre amp.
To measure P-channel types as 2SJ74 reverse DC-polarity and mill volt meter.
But please be aware, JFET's are very temperature sensitive. A temp. variation of +- 2°C can have a significant influence on the results.
I use a Textronic curve tracer with a temp. controlled measuring chamber.
Attached a sketch of the methode we used to match 2SK170 GR types (N-cahannel) for the ONO phono pre amp.
To measure P-channel types as 2SJ74 reverse DC-polarity and mill volt meter.
But please be aware, JFET's are very temperature sensitive. A temp. variation of +- 2°C can have a significant influence on the results.
I use a Textronic curve tracer with a temp. controlled measuring chamber.
AndrewT
Don't compare with MOSFET'S where we use a similare method to measure VGS.
But we are measuring JFET's.
This method was published by NP - to whom I trust- for the IDSS matching of the FET's for the ONO.
I have compared the results with those of my curvetracer and came to the same results, if you divide through the 22Ohm.
Gerd
Don't compare with MOSFET'S where we use a similare method to measure VGS.
But we are measuring JFET's.
This method was published by NP - to whom I trust- for the IDSS matching of the FET's for the ONO.
I have compared the results with those of my curvetracer and came to the same results, if you divide through the 22Ohm.
Gerd
http://www.passdiy.com/pdf/diyopamp.pdf
I have found the Pass circuit you used.
It is on page11.
This circuit is for finding Jfets that pass an Id=2mA. This is not for measuring Idss.
I have found the Pass circuit you used.
It is on page11.
This circuit is for finding Jfets that pass an Id=2mA. This is not for measuring Idss.
Erno Borbely describes a method for measuring Idss, gm, etc in these papers:
http://www.borbelyaudio.com/adobe/ae599bor.pdf
http://www.borbelyaudio.com/adobe/ae699bor.pdf
I am attempting to build the BA-2 amp but I'm feeling my way very slowly. One question I need to answer is the power supply bridge rectifier rated at 35A, 200V. Now if I was to build this from separate diodes, would each diode in the bridge have to be rated at 35A, 200V? Also are those power supply resistors rated at 1ohm, it is not clear from the diagram? Incidentally, why this design for the power supply and not a 'Pi' filter?
Thanks in advance,
Chris
Thanks in advance,
Chris
Hi,
as the values are a bit oversized anyway imho, you could also take half as much. But remember that bigger diodes will get less hot compared to smaller ones...
If you mean the 4 paralleled Rs in the Filter, they're all 1R at 3W
I thought this was a CRC thus Pi-Filter, isn't:
Code:
-o-R-o-
| |
C C
| |
Thanks to you both.
So for each phase of the AC current the total current flow is being split between two of the diodes, which is what I wasn't sure about. I had my eyes on some 30A Vishay (30EPF02) diodes which are called QuietIR series, designed to keep RF to a minimum. Anyone know whether they sound good?
Best wishes,
Chris
So for each phase of the AC current the total current flow is being split between two of the diodes, which is what I wasn't sure about. I had my eyes on some 30A Vishay (30EPF02) diodes which are called QuietIR series, designed to keep RF to a minimum. Anyone know whether they sound good?
Best wishes,
Chris
There's no big issue about the value, but I would try to
keep Idss in the range of 8 to 10 ma. If you have seen the
version with the potentiometer on the Sources of the Jfets,
this is used to trim the performance, with regard to Jfet
and Mosfet mismatch. Unfortunately, you need a distortion
analyzer to do the trim.
Thank you Nelson.
This site is great where else can you get an awesome design from a legendary amp builder and he answers amateur questions on how build it the best.
I haven't finished the BA-2 yet but I'm trying to decide what Pass single ended design to build next. BA-1 looks good, plus already have the input built minus a cap. But a few of the First Watt j-fets SE's look so good too.
Chad
P.S.- Maybe some day I'll show up on your door step with bottle of Vino to bribe you for some distortion analyzer time. Will be a while since I live Florida though. Hell I'll just be happy to make it to BAF someday.
This site is great where else can you get an awesome design from a legendary amp builder and he answers amateur questions on how build it the best.
I haven't finished the BA-2 yet but I'm trying to decide what Pass single ended design to build next. BA-1 looks good, plus already have the input built minus a cap. But a few of the First Watt j-fets SE's look so good too.
Chad
P.S.- Maybe some day I'll show up on your door step with bottle of Vino to bribe you for some distortion analyzer time. Will be a while since I live Florida though. Hell I'll just be happy to make it to BAF someday.