hi everybody!
my F5 mono's are working fine, so I thought I have to build a suitable preamp for them.
I use jumas layout for it.
http://www.diyaudio.com/forums/pass-labs/125893-preamp-ideas-f5-6.html#post1690625
This time I'm building it dual-mono, both preamps in one enclosure with own r-core-transformers, supplys, relays, etc...
Controlled by an Atmega16 with 16x2 lines display. The menus are controlled by an alps encoder with switch.
Relays (and everything else like the supplys, etc...) will be switched by the controller, too... The software is ready and tested, now it's time to get all the parts together.
The controller gets his own power supply, which also supports the relais, the leds, etc... (31 relais, about 40 orange led's)
It will have 5 inputs and 2 outputs.
enclosure-dimensions: 430x280x50mm
bottom 3mm aluminium, top 6mm security-glass brown tinted
sides and front/back 10mm aluminium with all the holes for needed parts (display, volume + preamp control)
Here a few pics from the parts and first measurements on a demo-pcb:
more pics will follow, forgot to make some of the display and the black laquered PCB's...
regards,
matthias
my F5 mono's are working fine, so I thought I have to build a suitable preamp for them.
I use jumas layout for it.
http://www.diyaudio.com/forums/pass-labs/125893-preamp-ideas-f5-6.html#post1690625
This time I'm building it dual-mono, both preamps in one enclosure with own r-core-transformers, supplys, relays, etc...
Controlled by an Atmega16 with 16x2 lines display. The menus are controlled by an alps encoder with switch.
Relays (and everything else like the supplys, etc...) will be switched by the controller, too... The software is ready and tested, now it's time to get all the parts together.
The controller gets his own power supply, which also supports the relais, the leds, etc... (31 relais, about 40 orange led's)
It will have 5 inputs and 2 outputs.
enclosure-dimensions: 430x280x50mm
bottom 3mm aluminium, top 6mm security-glass brown tinted
sides and front/back 10mm aluminium with all the holes for needed parts (display, volume + preamp control)
Here a few pics from the parts and first measurements on a demo-pcb:
more pics will follow, forgot to make some of the display and the black laquered PCB's...
regards,
matthias
hi everybody!
long time since the last update, not much time to work on it.
small progress with a big problem:
I build the power supplys the last 2 days:
12V AC r-core transformer with 12000µF and bridge rectifier, gives about 16V DC.
I use 7812 for +12V, and 7912 for the negative (-12V) lines.
I bought 10 devices of every type, and ALL of them have about 400mV difference in ouput voltage?!
the 7812 types always have about 11.88V while the 7912 have -12,35V.
Are there any ideas of getting the correct voltage?
best regards,
matthias
long time since the last update, not much time to work on it.
small progress with a big problem:
I build the power supplys the last 2 days:
12V AC r-core transformer with 12000µF and bridge rectifier, gives about 16V DC.
I use 7812 for +12V, and 7912 for the negative (-12V) lines.
I bought 10 devices of every type, and ALL of them have about 400mV difference in ouput voltage?!
the 7812 types always have about 11.88V while the 7912 have -12,35V.
Are there any ideas of getting the correct voltage?
best regards,
matthias
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Not a problem at all. It won't influence your preamp except for slight asymmetry in clipping behavior which is absolutely unimportant...
Idss is Id at Vgs=0V (Vds=10V)
Please read this (figure 5):
http://ken-gilbert.com/images/pdf/erno_borbely_on_jfets.pdf
Please read this (figure 5):
http://ken-gilbert.com/images/pdf/erno_borbely_on_jfets.pdf
Of course it's possible but I wouldn't do it before we know what are we dealing with. So, what's the Idss of JFETs that you have ?
you are suggesting to measure across a 100R drain resistor for both k170 and j74 ?
Not without changing some resistors.
There is no use in watering the subject down before you do the measurements...
yes.
I don't understand why the question. Do you see a problem that I have missed?
hi!
measuring (maybe correct) done:
my "high quality" chinese devices have following values for Idss:
2SJ74 BL : from 4.7 to 6.2mA (3 pcs.)
2SJ74 GR: 6.2mA (1 pc.)
2SK170 BL: from 13.8 to 13.9mA (5 pcs.)
the N-types are from china (3pcs.) and from a german distributor called "reichelt" (2pcs.)
their values are very close together (if measuring was correct, then they would be higher then BL specification, I think?)
three P-types (guess which ones- the chinese) have 4.7 to 4.85mA and should be "BL", the reichelt one has got 6.2mA and is a "GR" graded one.
changing one of the chinese devices gave me an DC-offset of 160mV, much better than before, but not really changeable if I turn the pot?
so, where can I get GOOD jfets for this preamp?
best regards- and as always- THANK YOU for helping!
matthias
measuring (maybe correct
) done:my "high quality" chinese devices have following values for Idss:
2SJ74 BL : from 4.7 to 6.2mA (3 pcs.)
2SJ74 GR: 6.2mA (1 pc.)
2SK170 BL: from 13.8 to 13.9mA (5 pcs.)
the N-types are from china (3pcs.) and from a german distributor called "reichelt" (2pcs.)
their values are very close together (if measuring was correct, then they would be higher then BL specification, I think?)
three P-types (guess which ones- the chinese
) have 4.7 to 4.85mA and should be "BL", the reichelt one has got 6.2mA and is a "GR" graded one.changing one of the chinese devices gave me an DC-offset of 160mV, much better than before, but not really changeable if I turn the pot?
so, where can I get GOOD jfets for this preamp?
best regards- and as always- THANK YOU for helping!
matthias
Last edited:
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