Yeah, I definitely cooked R1 and R2. Will replace the IRFs and .47 ohm resistors. What worries me though is why I cooked them. DC offset had drifted a little high. Oscillation in the right channel (but not the left) with inputs open. So I shorted the inputs, oscillation went away and I successfully adjusted the left channel. Disaster during biasing of the right channel. I was getting close to .59 V across R11 when R12 somehow went over .8 V and I smelled something cooking. Shut it all down but it was too late.
Thoughts?
Also, I'm pretty sure I posted my question in the long F5 thread, but I think the admins moved it here. Or I could have posted it in the wrong thread too; it was a very late night.
Thanks,
C
Thoughts?
Also, I'm pretty sure I posted my question in the long F5 thread, but I think the admins moved it here. Or I could have posted it in the wrong thread too; it was a very late night.
Thanks,
C
Could yon have biased it too quickly?
Second: I had a similar problem in mine - turns out there was a metal filing caught in the insulating pad and it was shorting the irf when hot. The other thing is that I believe that the irf are very tough so its kinda unlikely that they are damaged - most likely casualties are the 0.47r resistor.
Are your 0.47r high enough wattage?
Fran
Second: I had a similar problem in mine - turns out there was a metal filing caught in the insulating pad and it was shorting the irf when hot. The other thing is that I believe that the irf are very tough so its kinda unlikely that they are damaged - most likely casualties are the 0.47r resistor.
Are your 0.47r high enough wattage?
Fran
I have shorted a Mosfet before. The resistors started smoking, really glowing on that get, then it moved to the others..Not pretty.
You can test the mosfet by putting over 4 volts across it, with a larger source resistor. Look for some links on testing mosfets.
As far as shorting with the heatsink filings, that is more common, or at least shorting the Fets to the heatsink in the first place. What I do is not connect the Common grounds when first mounted to the chassis. If the metal tab on the Fet gets continuity to ground, don't power it up. Good Luck. Although this problem really should go to the primary F5 thread...
You can test the mosfet by putting over 4 volts across it, with a larger source resistor. Look for some links on testing mosfets.
As far as shorting with the heatsink filings, that is more common, or at least shorting the Fets to the heatsink in the first place. What I do is not connect the Common grounds when first mounted to the chassis. If the metal tab on the Fet gets continuity to ground, don't power it up. Good Luck. Although this problem really should go to the primary F5 thread...
I bulged/blistered and smoked a .47R Panasonic 3W monkeying around with the bias.
I shut it down, measured resistances and powered up again, all apparently with no damage to anything.
I'm using Toshiba 2SK1529/2SJ200 MOSFETs.
Excellent quality and just the right quantity of low frequency info. Clear, smooth highs, not bright or in your face. For example, there is great stick definition on ride cymbals with the corresponding wash sounding tonally perfect. I can almost tell whether or not the sticks have nylon or wooden tips.
I shut it down, measured resistances and powered up again, all apparently with no damage to anything.
I'm using Toshiba 2SK1529/2SJ200 MOSFETs.
Excellent quality and just the right quantity of low frequency info. Clear, smooth highs, not bright or in your face. For example, there is great stick definition on ride cymbals with the corresponding wash sounding tonally perfect. I can almost tell whether or not the sticks have nylon or wooden tips.
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Lost in too many posts & threads
Hey guys, Sorry to ask this here but it is relevant to the sonic output of the F5.
I have searched, and read, and read, and read, but I'm not finding what I was hoping for.,
Which resistors values were changed to "upgrade" the sound? I think Papa wrote about it but for the life of me I can't find it!
When speaking of changing R5&8 to 100 Ohms is that 2 / 100Ohms in ?? or 100 ohms in total?
Thanks for the help.
Ron
Hey guys, Sorry to ask this here but it is relevant to the sonic output of the F5.
I have searched, and read, and read, and read, but I'm not finding what I was hoping for.,
Which resistors values were changed to "upgrade" the sound? I think Papa wrote about it but for the life of me I can't find it!
When speaking of changing R5&8 to 100 Ohms is that 2 / 100Ohms in ?? or 100 ohms in total?
Thanks for the help.
Ron
Hi Ron,
R5&R8 are feedback resistors. Standard configuration is 50ohm for R5&R8 (leaving out R6&R7). Changing the values to say 100R will certainly change the sound. Can't say "upgrade" as it becomes a matter of personal taste. If you do change it, try to keep the ratio of R5:R1 approximately 5:1 (i.e. if R5=100R then R1=20R).
Alazira,
Right, Modification not upgrade.........too much time on the inside of the computer lately. 🙂
thanks, that's exactly what I wanted to know!
I'm running a 50R 5W wire wound in R5 & R8 so 1:5 ratio is 10R for R1 & R2.
thanks very much.
Ron
Right, Modification not upgrade.........too much time on the inside of the computer lately. 🙂
thanks, that's exactly what I wanted to know!
I'm running a 50R 5W wire wound in R5 & R8 so 1:5 ratio is 10R for R1 & R2.
thanks very much.
Ron
Ron, these may help, from my notes............
Post #3731
Originally posted by JC951t
I know I'll get shot for this. If sound is too clinical or clean, stay away from metal film resistors.
=================================================
NP > Alternatively, you can increase the value of the Source resistors to 1 ohms,
and increase the value of the feedback resistors from 2 X 100 ohms and 10
ohms to 1 X 100 ohms and 22 ohms.
The lower amount of feedback will warm the sound up, and you can keep
increasing proportional values in the feedback loop if you wish.
=================================================
rob lenk f5 feedback mod per NP Post #3843
Just thought I'd post my initial impressions of having modified the feedback network relative to Nelson's suggestion( R11 & 12 to 1 ohm/
R5 & R8 to 100 ohms and R1 & R2 to 22ohms-pass site)
Yep,Yep amp runs a little cooler(perhaps 8-10 degree farenheit) and the "tight fist" now has a velvet glove!
I found the original spec a bit dry and etched in sound relative to my dynaco st70- accurate and detailed but lacking a bit of body or warmth. The new feedback seems to be a definite step in the right direction.
=================================================
Pillendreher post#4215 page 141
Hello there,
i also tried the alternative feedback a´la:
Alternatively, you can increase the value of the Source resistors to 1 ohms, and increase the value of the feedback resistors from 2 X 100 ohms and 10 ohms to 1 X 100 ohms and 22 ohms.
But now i cannot set the bias to more than 1.1A! If i set the dc offset to 0 the bias levels at 0.9A.
Is it correct to increase the value of P1/P2 to 10k?
bobodioulasso
It should be simpler to increase R3 and R4 to 2K7 or 3k3
Pillendreher
You are right....Thank you!
f5 problem with amp draw Post #4218
Pill
I had a similar problem at one point in the mod process(ie could not bring the bias up on one channel) and found a cold solder on a ground lead to be the problem.
I am currently(no pun intended) running my f5 with the revised feedback and no current limiting or thermister and have no problems setting bias- I did make sure to set the bias around .4vdc until the amp had warmed up for about an hour then reset to .59vdc and watched and micro tweaked for the next hour.
with my heatsinks and fan arraingment my usual ambient temp directly above the mosfets is about 20 degree ferinheit above room temp.
Hope this helps
rob
Pillendreher [Find more posts by Pillendreher]
diyAudio Member
Registered: Jan 2007Location: RTGermany Post #4219
Rob, do you mean you run it with 1R source resistors and set the voltage to 0.59V?
=================================================
Regarding the 10 ohm resistors that sit between the input jfets.
I have observed that if the the source resistor of 2sk170 is slightly higher than the drain resistor of 2sj74 (eg 10.2ohms and 9.8ohms respectively) then the 2nd harmonic content increases.
If the source resistor of 2sk170 is slightly lower than the drain resistor of 2sj74 then the 3rd harnonic content increases (eg 9.8ohms and 10.2ohms respectively).
=================================================
Another option is to change the limiter resistors R21 and R22 - 22K instead of 10K. At least the version proposed by Papa. I did it. I can not compare the sound with 10K because i stayed at 22K from beginning.
RE: post 328
The post#'s referrenced are to thread
http://www.diyaudio.com/forums/pass-labs/121228-f5-power-amplifier.html
the F5 power amplifier thread
The post#'s referrenced are to thread
http://www.diyaudio.com/forums/pass-labs/121228-f5-power-amplifier.html
the F5 power amplifier thread
Alazera, Ichiban, Osscar,
Ichiban, nice collection of information. How do the "Thors" sound with the F5?
I am slightly concerned that with my Thors the F5 may be too much of a good thing. Clarity and revealing all the poor recordings I own. 😕
Thanks for the input(s) Pun intended!
..........
.......
.....🙂...........🙂......
..🙂..................🙂..
.....🙂...........🙂......
.................
Group Hug 😉
Ron
Ichiban, nice collection of information. How do the "Thors" sound with the F5?
I am slightly concerned that with my Thors the F5 may be too much of a good thing. Clarity and revealing all the poor recordings I own. 😕
Thanks for the input(s) Pun intended!
..........
............🙂...........🙂......
..🙂..................🙂..
.....🙂...........🙂......
..........
.......Group Hug 😉
Ron
"Thors" sound
I like it/them. Really jealous of your build, they look very nice.
Some day I hope to try the redesign and use an active crossover.
I find the F5 has enough power to play quite loud. Soon I hope to
try a balanced version.
I have found that some recordings that I thought were poor turn out to sound
good. Revealing more nuance to the sound. This I believe is due to the
Twisted Pair Sabre32 and F5. A good TT/phono would probably blow
digital away on the F5/Thors.
How is your F5, did you get it back from repairs?
I like it/them. Really jealous of your build, they look very nice.
Some day I hope to try the redesign and use an active crossover.
I find the F5 has enough power to play quite loud. Soon I hope to
try a balanced version.
I have found that some recordings that I thought were poor turn out to sound
good. Revealing more nuance to the sound. This I believe is due to the
Twisted Pair Sabre32 and F5. A good TT/phono would probably blow
digital away on the F5/Thors.
How is your F5, did you get it back from repairs?
I was afraid you'd ask that! 😱
Yeah, I got it back..........and proceeded to burn up one channel while adjusting the pots. I have to laugh at myself and the # of errors I've made while learning how to build a SS amp. One side is working perfectly. (Thanks Steve)
Parts are being ordered today and I got Christian's (Cviller) last old stock board. I suppose I could always hacksaw off the ends on new ones ....😉 if I had to. LOL
I really appreciate the information on which Rs to use and how they effect the sound of the amp. Man, those Thors are so clinical. Mine are anyway. New design XO. Agreed an active XO would be nice!
I've built an Aikido 6SN7 preamp that works smooth like buttermilk.
After reading the MODs again, I think I'll use 1R for the source R11&12
100R for the feedback R5&8 (1 each not //)
22R for R1&2......................any opinions?
Ron
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Not really. I've built the F5 as per original, still need to increase R21/22 from 10k to 22k as suggested. That should allow more current for the 4Ohm Thors.
I've been itching to do an Aikido.
Sounds like you need a varistat (I think that's the correct name?) to slowly bring up the voltage, on a new/mod'd circuit, so you can check the current before damage is done. It saved my butt many a time. There's a trick with a light bulb wired in series with the AC hot line that's supposed to work also. Have never used that method, tho. A search on the forums should have good info on that. I remember my first Borbley B60 build, 1985, using pc boards from Old Colony. So excited to get a listen, Plugged the thing in and instantly two resistors on the board at the input diff pair lit-up like an incandesent bulb for about two seconds. As they say, I let the smoke out.
I had mis-read the pin outs on the differential transistors 🙁
I wish you better luck going foreward. Experience is a hard mistress, she tests first and teaches after.
Ichiban,
You can't cure stupidity..........I use a Varistat!
I'm a very "hands-on" learner. I'm OK with mistakes when I learn from them.
I kinda like harsh mistresses........🙄
Tea-Bag; yeah, that was directed at you. 😉
Thanks for the tips.
Ron
You can't cure stupidity..........I use a Varistat!
I'm a very "hands-on" learner. I'm OK with mistakes when I learn from them.
I kinda like harsh mistresses........🙄
Tea-Bag; yeah, that was directed at you. 😉
Thanks for the tips.
Ron
So... has anyone heard a difference when
that's my question de jour.
has anyone heard a difference when switching to Toshiba from Fairchild??
_-_-bear
that's my question de jour.
has anyone heard a difference when switching to Toshiba from Fairchild??
_-_-bear
Hi guys, before burning anymore of those F5's, I think you should read this guide by AndrewT, it is quite good:
http://www.diyaudio.com/forums/pass-labs/121228-f5-power-amplifier-713.html#post2094545
Also you might want to think about how aggressively you turn the pots:
http://www.diyaudio.com/forums/pass-labs/121228-f5-power-amplifier-714.html#post2094841
You also have to not only focus at one pot at a time, because you'll end up turning one fully on and then as soon as you touch the other one you'll release the dogs and fry up your power resistors.
http://www.diyaudio.com/forums/pass-labs/121228-f5-power-amplifier-713.html#post2094545
Also you might want to think about how aggressively you turn the pots:
http://www.diyaudio.com/forums/pass-labs/121228-f5-power-amplifier-714.html#post2094841
You also have to not only focus at one pot at a time, because you'll end up turning one fully on and then as soon as you touch the other one you'll release the dogs and fry up your power resistors.
