Yeah, PIA until you gets used to them.
I reckon there would be a simple way to set the LDRs accurately up to replace both the trimmer pots and the thermistors and still get the same cct benefits - I've tried a number of different quality "gain" resistors and it's the cermet pots that seem to determine the overall sound signature, even with carbon resistors (Th1,2 have been unplugged for now).
The main Source resistors (0R47s) and the gate stopper resistors (47R) made up of the Manganin Resistance wire is a definite improvement in sound.
Interesting thing, eh!
I reckon there would be a simple way to set the LDRs accurately up to replace both the trimmer pots and the thermistors and still get the same cct benefits - I've tried a number of different quality "gain" resistors and it's the cermet pots that seem to determine the overall sound signature, even with carbon resistors (Th1,2 have been unplugged for now).
The main Source resistors (0R47s) and the gate stopper resistors (47R) made up of the Manganin Resistance wire is a definite improvement in sound.
Interesting thing, eh!
Well there's about 4 volts dc plus the signal so I think the 5volt limit is well and truly exceeded altho if you were to reduce the approx 1k0 resistance (?) down to maybe something like a 500R fixed resistor plus the balance via the LDR, possibly this would be okay - not quite sure. Might be easier to just try it altho possibility of large dc offset at spkr terminal quite possible.
Setting up the LDR to the "correct impedance" when you turn the amp on (rapid heating, zero offset, etc) is maybe too complicated/unreliable.
I reckon it would sound better tho!
off would
Setting up the LDR to the "correct impedance" when you turn the amp on (rapid heating, zero offset, etc) is maybe too complicated/unreliable.
I reckon it would sound better tho!
off would
They increase in resistance with more heat. PTC right? Thermistors can be either I think. If I recall you can buy PTC and NTC thermistors.
Down at lower resistances they are super stable. For instance at 250 you wont get them to change for anything. At 10k they start to change when you breath on them. 2k5 is still pretty stable as is 5k. These are my normal test resistances so just quoting from what I am normally working with. This is all, however, at room temperature.
The summer before last I was messing around and experimenting with them in the oven when I realized "hey, I live in Houston, its about 110 outside" and just stuck them out the door. I was trying to replace a current limiting resistor with a thermistor that would decrease in resistance at around the same rate that the LDR increased in resistance or at least at a rate that would hold the LDR still in the heat. I got bored with that and worked on the Lighter Note circuit and dont recall what thermistor actually got close to working because I did get close. No cigar, but close. This was all in regards to putting LDRs into a chipamp and having them NOT change resistance with increase in temperature. Have the board layout but have not built it yet. Its got to sound good.
So, anyway, I think you can do it and if you need a higher value to be stable then just string a few LDRs in series at lower values to equal your higher value and this is another way to get it to come closer to working. Ends up being a very expensive resistor but who cares? Its all fun anyway.
For anyone who is thinking this is off topic its really not because we are talking about replacing a resistor and a thermistor in the F5 with LDRs and whether it would be possible.
Uriah
Down at lower resistances they are super stable. For instance at 250 you wont get them to change for anything. At 10k they start to change when you breath on them. 2k5 is still pretty stable as is 5k. These are my normal test resistances so just quoting from what I am normally working with. This is all, however, at room temperature.
The summer before last I was messing around and experimenting with them in the oven when I realized "hey, I live in Houston, its about 110 outside" and just stuck them out the door. I was trying to replace a current limiting resistor with a thermistor that would decrease in resistance at around the same rate that the LDR increased in resistance or at least at a rate that would hold the LDR still in the heat. I got bored with that and worked on the Lighter Note circuit and dont recall what thermistor actually got close to working because I did get close. No cigar, but close. This was all in regards to putting LDRs into a chipamp and having them NOT change resistance with increase in temperature. Have the board layout but have not built it yet. Its got to sound good.
So, anyway, I think you can do it and if you need a higher value to be stable then just string a few LDRs in series at lower values to equal your higher value and this is another way to get it to come closer to working. Ends up being a very expensive resistor but who cares? Its all fun anyway.
For anyone who is thinking this is off topic its really not because we are talking about replacing a resistor and a thermistor in the F5 with LDRs and whether it would be possible.
Uriah
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Thanks for the info - will try a few of those non-match LDRs and see what happens - series, eh - never thought about that - could be interesing, partic with heating one on the o/p transistor inself.
Yes, I think also that could be significant improvement in the sound of the amp.
Cost? - Not as much as some of the exotic resistors.
Yes, I think also that could be significant improvement in the sound of the amp.
Cost? - Not as much as some of the exotic resistors.
Adding a little Blowtorchianism to this thread Andrew
?Right you are, a little colour in this thread certainly makes things interesting.
Relays are not much of a concern to me; there are really high quality ones, I don't see anything wrong with them.
And they remove startup noise, a really nice feat.
...currently having some trouble sizing the Thermite charge on an F5 prototype. seem to be having some difficulties with the effect upon the chassis and the listening room... NP, need advice!!
Maybe I am getting the wrong type, wrong brand of Thermite...
_-_-bear
PS. the sound is much more, ummmm... , explosive!
Maybe I am getting the wrong type, wrong brand of Thermite...
_-_-bear
PS. the sound is much more, ummmm... , explosive!
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F5 All in One
Hello all ...
I'm here cause I thought of an F5 all in a board, and I wanted to ask if someone has already thought about it...
Some advice?
Pics....
PCB
Cabinet
Cabinet without front panel
Hello all ...
I'm here cause I thought of an F5 all in a board, and I wanted to ask if someone has already thought about it...
Some advice?
Pics....
PCB
An externally hosted image should be here but it was not working when we last tested it.
Cabinet
An externally hosted image should be here but it was not working when we last tested it.
Cabinet without front panel
An externally hosted image should be here but it was not working when we last tested it.
I had a friend help me match jfets for my F5 project. He made a circuit similar to the F5 on a test board and powered it from a 24V supply. We spent many hours registrering current thru the different jfets. We had them powered up for the same amount of time (about 4 minutes) and then reading off the voltage drop over a resistor. Ended up with two pairs of sk170bl/sj74. One pair was 6.11mA/ 6.08mA, the other 6,25mA/ 6,29mA. It was the best pair we could get from about 40 jfets total.
Is this methd ok and are my pairs a nice match for F5 now?
Is this methd ok and are my pairs a nice match for F5 now?
Attachments
...currently having some trouble sizing the Thermite charge on an F5 prototype. seem to be having some difficulties with the effect upon the chassis and the listening room... NP, need advice!!
Maybe I am getting the wrong type, wrong brand of Thermite...
_-_-bear
PS. the sound is much more, ummmm... , explosive!
The new nano thermite gets even hotter!!!!
Your JFETs are well matched
There is a guy here who successfully sells F5 kits with k170 belonging to BL grade and j74 from GR grade with Idss difference greater than 120% between them and yet no one complains...
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I cannot see them
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
For more information about matching the Transconductance of the jfets, rather than just concentrating on their Idss, see Patricks post #8689 - requires an extra resistor.
And would suggest considering the effects of even a good Thermistor in parallel with the voltage gain resistors, plus the effect of a typical cermet pot on that same gain resistor.
... just 2 cents.
And would suggest considering the effects of even a good Thermistor in parallel with the voltage gain resistors, plus the effect of a typical cermet pot on that same gain resistor.
... just 2 cents.
I'm sure you have nice matches on your Jfets, but then you
will need exact matches on your P vs N channel Mosfets -
not probable.
This is why we have pots off the Drains of the Jfets and why
we also have a balance pot across the Sources of the Jfets.
in F5 , indeed ;
you forgot to write - usually/generally . and not in F5 - at least according to sch and allowed
pictures ;this way you are risking avalanche of panic - "did we really missed to see that trimpot in sources
- in F5 ? "