i'm building my own simplified newby version of Sy's heretical unity gain line stage. mine will not have the b+ or heater regulation. i've also dispensed with the relay dethumper and will leave the output coupling cap in. all this is subject to change as hopefully i will learn! this is my first attempt at using cathode ccs and have some questions.
ive built my own single "test" ccs on a fixture per sy's schematic. just ccs and a little PS.in sy's instructions for calibrating it he says to load the ccs with 1k directly from ccs b+ to collector of first transistor.(b+ is taken from highly filtered supply with 24v tranny. b+ adjusted to provide @ 25v for very small current requirment as i'm not running heaters off the string and dont plan to)
i did this and every thing seemed fine- got 10ma in circuit reading from the trim pot to the negative rail after some adjusting. and when pot was measured afterward it was 103ohm. OK so far so good i think. top of red led reads 2v and is lit. i used 1.7 red led so i'm assuming this is good. emitter of first transistor reads about 7v and the second @1v.
per sys instructions he say there should be a 10v drop across afore mentioned 1k loading resistor. i get 13-14v. my meter is accurate. should i be alarmed? i'm attempting to learn more about ccs so please bear with me!
here is sy's thread with schematic(scroll down a little to second schematic.)
http://www.diyaudio.com/forums/showthread.php?s=&threadid=59244&highlight=
also another concern is after i have this ccs on tubes cathode where should i measure for bias? at cathode as traditionally done in cathode bias since tubes grid is grounded? and is there anyway to predict what the bias will be before i hook this thing to a tube?
your help is appreciated! thanks!
ive built my own single "test" ccs on a fixture per sy's schematic. just ccs and a little PS.in sy's instructions for calibrating it he says to load the ccs with 1k directly from ccs b+ to collector of first transistor.(b+ is taken from highly filtered supply with 24v tranny. b+ adjusted to provide @ 25v for very small current requirment as i'm not running heaters off the string and dont plan to)
i did this and every thing seemed fine- got 10ma in circuit reading from the trim pot to the negative rail after some adjusting. and when pot was measured afterward it was 103ohm. OK so far so good i think. top of red led reads 2v and is lit. i used 1.7 red led so i'm assuming this is good. emitter of first transistor reads about 7v and the second @1v.
per sys instructions he say there should be a 10v drop across afore mentioned 1k loading resistor. i get 13-14v. my meter is accurate. should i be alarmed? i'm attempting to learn more about ccs so please bear with me!
here is sy's thread with schematic(scroll down a little to second schematic.)
http://www.diyaudio.com/forums/showthread.php?s=&threadid=59244&highlight=
also another concern is after i have this ccs on tubes cathode where should i measure for bias? at cathode as traditionally done in cathode bias since tubes grid is grounded? and is there anyway to predict what the bias will be before i hook this thing to a tube?
your help is appreciated! thanks!
The voltage across the 1k test resistor is what you use to set the current. 13V across it means that your CCS is running a little rich. Increase the emitter resistor a skootch and all will be well. If I wasn't clear about it, the test resistor gets disconnected before the CCS is installed into the preamp circuit.
Starting simple is an excellent idea. Everything you removed is gingerbread and frosting; your approach will work fine.
Starting simple is an excellent idea. Everything you removed is gingerbread and frosting; your approach will work fine.
thanks much SY. i really liked your idea-no gain-just a volume pot switching and cable driver. all with good isolation and low noise-
i figured i would use it also as a learning tool-i have been reading about followers trying to learn- the way you presented it was really good, i thought! i'm just trying to find out the hows and whys. building(copying from schematics gets kind of old after a while!
those transistors i used are npnbipolars radio shack guys ceo=40v beta 100-300
running rich? to much current through input resistors?
do i adjust emitter by the input divider resistors? the ones connected to the bases of transistors? i thought i adjusted the current by just adjusting the pot? i will admit this is my first project with transistors and after this i will hit the books and try to learn some more about them!
i appreciate your response, thanks
i figured i would use it also as a learning tool-i have been reading about followers trying to learn- the way you presented it was really good, i thought! i'm just trying to find out the hows and whys. building(copying from schematics gets kind of old after a while!
those transistors i used are npnbipolars radio shack guys ceo=40v beta 100-300
running rich? to much current through input resistors?
do i adjust emitter by the input divider resistors? the ones connected to the bases of transistors? i thought i adjusted the current by just adjusting the pot? i will admit this is my first project with transistors and after this i will hit the books and try to learn some more about them!
i appreciate your response, thanks
That's what the 1k test resistor is for, measuring the current. Once it's set (10V drop across 1k), you can put the CCS into the circuit and don't have to worry about it any further. If a sketch will help, let me know and I'll try to draw something (won't happen tonight, I'm heading out to demonstrate diy cooking for some visiting dignitaries).
The trimpot IS the emitter resistor, sorry for being unclear.
The trimpot IS the emitter resistor, sorry for being unclear.
One other thing- either boost the voltage you're using to test the CCS (the preamp power supply will work fine) or temporarily reduce the feed resistor to the LED string to get a few milliamps through the LED. That will ensure that the LED reference voltage is the roughly the same in and out of circuit.
i didn't try the boosted voltage, i went back to work on it and missed your second post. here is what happened. my b+ is at 24v under load for the following....
i placed the meter reading ma in circuit in between the 1k and collector. the lowest i can get that current is 12ma-( trimpot is a 1k)- actual voltage reading across 1k resistor is 12v. turning trimpot almost all the way back down i can get 15ma. probably more .i didn't bother going there
i swapped the led and it is at 1.9 volts-
so, i got brave ... so i hooked it up to a tested 6dj8 follower i had ready- i placed the current meter in between cathode and collector, yes i removed the 1k resistor
fired it up and it settled in and stayed a very stable 16ma .the plate vol @100v.. bias voltage at 2.3v. i didn't listen to it yet. i'm done for tonite.
i'll try to lower the resistor tomorrow.
i placed the meter reading ma in circuit in between the 1k and collector. the lowest i can get that current is 12ma-( trimpot is a 1k)- actual voltage reading across 1k resistor is 12v. turning trimpot almost all the way back down i can get 15ma. probably more .i didn't bother going there
i swapped the led and it is at 1.9 volts-
so, i got brave ... so i hooked it up to a tested 6dj8 follower i had ready- i placed the current meter in between cathode and collector, yes i removed the 1k resistor
fired it up and it settled in and stayed a very stable 16ma .the plate vol @100v.. bias voltage at 2.3v. i didn't listen to it yet. i'm done for tonite.i'll try to lower the resistor tomorrow.
i attach + meter lead to cathode of tube, and attach - lead to collector on top transistor in schematic. the meter being the actual connection in circuit-varying the pot did vary the current- so i think it's working ok?
with your calibration setup(the 1k resistor patched in) ,i took the reading from the collector to the 1k. again the meter was the connection. did i do right?
i'm going to mess about with it some more shortly..
thanks for bearing with me- i often stumble before i learn anything!
with your calibration setup(the 1k resistor patched in) ,i took the reading from the collector to the 1k. again the meter was the connection. did i do right?
i'm going to mess about with it some more shortly..
thanks for bearing with me- i often stumble before i learn anything!
Scratch anything I said about a higher voltage supply. The version you referenced (now that I had a few minutes to look it up) was indeed set for a 24V supply. In the words of Emily Litella, "Never mind!"
If I read you right, you're trying to measure the current directly with a milliameter? That's OK, but the purpose of the 1k test resistor is to allow you to measure the current by putting a voltmeter across the test resistor and setting the trimmer for a 10V drop.
If I read you right, you're trying to measure the current directly with a milliameter? That's OK, but the purpose of the 1k test resistor is to allow you to measure the current by putting a voltmeter across the test resistor and setting the trimmer for a 10V drop.
i understand the point of it, but i cannot get this drop to 10v. even turning pot all the way up max setting-just wondering why this would be.i wonder if bipolars i chose were wrong? ( just a uneudcated newby guess?:0) could you make a educated guess? somewhere i could start to look or try?
i'm not adverse to running the tube a little hot, for now, if thats what it will be. bias at 2.3 seemed ok-dissapation is under data limit.
concerning all my actual current readings-i'm just anal! like to see cause and effect to back up math and vice versa...
thanks again
i'm not adverse to running the tube a little hot, for now, if thats what it will be. bias at 2.3 seemed ok-dissapation is under data limit.
concerning all my actual current readings-i'm just anal! like to see cause and effect to back up math and vice versa...
thanks again
success so far! construction was good, BUT i look very closely with a mag glass and notice that both transistors are not labeled the same.one is 8099 and one is 2489 i think. i bought one of those really cheap RS blisters with 15 or whatever pcs, supposed to be the same- i take them all out and all but 2 are the same.-i swapped out one, matched the other, NOW it's behaving exactly as you outlined-
i suppose by chance the one i replaced was defective, but.....i doubt it.
moral- do not blindly assume all are the same in radio shack bulk packs!
i'm gonna go back build the other ccs-for other channel-test and hook it up hopefully it will sing songs.-thats the plan anyway!
can i share a ccs for both? or is this verboten?
i suppose by chance the one i replaced was defective, but.....i doubt it.
moral- do not blindly assume all are the same in radio shack bulk packs!
i'm gonna go back build the other ccs-for other channel-test and hook it up hopefully it will sing songs.-thats the plan anyway!
can i share a ccs for both? or is this verboten?
yeah, the second i read your response on shared ccs i got it ,duh!
success project, my first working ccs!sounds very good, and very quiet also! considering my "proto" is more test lead than preamp. right now. they are adjusted to 15ma with 100v plate-some like it hot
i DID perform the "cable capacitance drive test-"my work space is a room over from main system, and i lent my bench amp out. so i ran 6meter cables from cd to preamp back to amp. i there was no sonic degradation i could tell-
for increased simplification i ditched the separate 12-0-12 PS(i used for test supply) and took the 5ma feed off b+ . simplified everything considering i'm not brave enough to tackle any sort of regulation yet, and to these old ears i'm not sure there is much lacking!
this is a keeper, and i'm now planning a six channel unity gain. for those rare 5.1 movie evenings-with seperate power off/on for the primary 2 channels-remote control master volume(welborne labs, has anyone tried these??) , and levels to match center and the rest. maybe by that time i get everything together-i'll try a regulator scheme on it.
this concept fills my needs prefectly for now-thanks sy-i'll be watching for anything more you do with this project!
success project, my first working ccs!sounds very good, and very quiet also! considering my "proto" is more test lead than preamp. right now. they are adjusted to 15ma with 100v plate-some like it hot
i DID perform the "cable capacitance drive test-"my work space is a room over from main system, and i lent my bench amp out. so i ran 6meter cables from cd to preamp back to amp. i there was no sonic degradation i could tell-
for increased simplification i ditched the separate 12-0-12 PS(i used for test supply) and took the 5ma feed off b+ . simplified everything considering i'm not brave enough to tackle any sort of regulation yet, and to these old ears i'm not sure there is much lacking!
this is a keeper, and i'm now planning a six channel unity gain. for those rare 5.1 movie evenings-with seperate power off/on for the primary 2 channels-remote control master volume(welborne labs, has anyone tried these??) , and levels to match center and the rest. maybe by that time i get everything together-i'll try a regulator scheme on it.
this concept fills my needs prefectly for now-thanks sy-i'll be watching for anything more you do with this project!
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