It is OPS has 1 amp idle current and drivers has 30 mA each side.
I have also read that put a pot in series with the irfp240 devices you can adjust for as clean as possible square wave, just put a square in and adjust it so the upgoing part is clean without glitches, it came from here.
http://www.ti.com/lit/an/snaa045a/snaa045a.pdf
Hi X and Banat
The CCS in my amp is not stable enough, it do run to much with temperature changes and possible we need a led with a bjt here who as I have read are temperature stable.
It go when get warm run to high idle current, or maybe a N and a P jfet will do, the DN2540 did also change to much, the amp is vert sensitive when current
in lto go walk what however is normal so we need a tem stable current source
Some ideas.
The CCS in my amp is not stable enough, it do run to much with temperature changes and possible we need a led with a bjt here who as I have read are temperature stable.
It go when get warm run to high idle current, or maybe a N and a P jfet will do, the DN2540 did also change to much, the amp is vert sensitive when current
in lto go walk what however is normal so we need a tem stable current source
Some ideas.
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The Jfet has to be adjusted in ghis TC=0 area where he is stebale with temp, and further on it switch completely and temco get reversed to positive, or negative depending of Jfet.
So I need to go calculate because in data it is not present most of the time, so I need a jfet, supply, heater, and time to get on that current a stable outcome.
This schematics I do now of, possible here is also TC=0 adjustment done, but I have a higher idle current on the jfets in ltp.
And I need other mosfets for the circlotron because these do suddenly switch on from nothing and pull full amperages, who happen when
gates do leak, these mosfets are pull out of a pcb in china and sell as such to me. I awaiting the irfp460
regards
So I need to go calculate because in data it is not present most of the time, so I need a jfet, supply, heater, and time to get on that current a stable outcome.
This schematics I do now of, possible here is also TC=0 adjustment done, but I have a higher idle current on the jfets in ltp.
And I need other mosfets for the circlotron because these do suddenly switch on from nothing and pull full amperages, who happen when
gates do leak, these mosfets are pull out of a pcb in china and sell as such to me. I awaiting the irfp460
regards
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I have used in the amp carbon resistors from china who are 0.25 watts, I did heat them with the iron and I did see that the voltage did rise 1 volts, and that was just one resistor, that is quite much, do you agree, I did it on the resistors on drain zvn4424 mosfets in LTP however also the bottom ones of 150 ohms to CCS did it, that is why I get things not stable, so I go change them for metal films where audio go not through them. Maybe these resistors are not that good, the 2sk170 Jfets need repplaced with ones with more current, that makes the amp also more stable, so I have not yet a good performing amp in stability.
'regards
'regards
I never use carbon resistors and the metal film Chinese ones seem to work fine for me. Values are accurate.
I use carbon in the signal path, because these sound much better, metalfilm can sound hars.
The problem with the unstability of the amp are the CCS and 2sk170 jfets, these need adjusted in dead zone so she do be stable.
That needs adjustment, otherwise a bjt with a led who is stable as I did read
otherwise the amp is unpredictable. I go als use caps between vas and the ltp for decoupling who I have not done.
Hi All
I have still problems with the idle current, and the strange thing is it jumps between high and low value's I can not get it stable, it go swing dc on scope also, I did see on gates irf240 is a very strange unbalance.
I think these irf240 are pulled out and maybe damaged because the other ones did let smoke the gate resistor who normally is not possible or there is a leak.
see the movie and maybe you recognise it, I say just chinese bargage from ebay, I think aliexpress is much better because that site removes the bad stuff.
https://youtu.be/gpM_wcHzPbc
Or the supply do strange, most because of HF radiation, and that is here a lot.
regards
I have still problems with the idle current, and the strange thing is it jumps between high and low value's I can not get it stable, it go swing dc on scope also, I did see on gates irf240 is a very strange unbalance.
I think these irf240 are pulled out and maybe damaged because the other ones did let smoke the gate resistor who normally is not possible or there is a leak.
see the movie and maybe you recognise it, I say just chinese bargage from ebay, I think aliexpress is much better because that site removes the bad stuff.
https://youtu.be/gpM_wcHzPbc
Or the supply do strange, most because of HF radiation, and that is here a lot.
regards
Kees,
I accidentally shorted the gate on a MOSFET with drain pin once and it kept playing but bias was high and unstable. It sounded a bit distorted too. I think damaged gates can cause this.
I accidentally shorted the gate on a MOSFET with drain pin once and it kept playing but bias was high and unstable. It sounded a bit distorted too. I think damaged gates can cause this.
I go look what happens if I do this, discard the offset feedback and give only ac through, it seems this way the amp can do better.
C12 and C11 in the schematic of feedback path, 1uF.
also this do give the possibillity to set the feedback to local without changes of the idles currents.
on 47 ohm there is some mV and other side 4,27 local and 2,38 full , first local has extra gate voltage.
regards
C12 and C11 in the schematic of feedback path, 1uF.
also this do give the possibillity to set the feedback to local without changes of the idles currents.
on 47 ohm there is some mV and other side 4,27 local and 2,38 full , first local has extra gate voltage.
regards
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I think I already have same issues with china metal film.
This resistor was 1W 10 ohm, and now it is a infinite ohm resistor 🙂
But I have to say it is 1 resistor on hundreds I used...
They also work well as fusible links. The ones used in my CRC PSU's have certainly blown and went open circuit when I shorted the outputs accidentally.
Hi Kees52,
Another way to limit the DC current through R14-R15 is to move R25 and R26 from their current positions, putting R25 in series with the U3-U5 drain connection and R26 in series with the U2-U4 drain connection. This may give a similar result without the need for C11 and C12. As R25 and R26 would then be passing a lot more current, their values would need to be reduced accordingly.
As with china capacitors 10.000 uF when I put the amp off (i use them temperaly in driver) who use 126 mA it is empty in seconds, This do tell me she are not so well, because I thing with that current it last some more seconds, so when having such stuff it is difficult to make a amp, because al this trouble is only because of the parts.
I did think ablout removing the irf610 ccs mosfets and use only the resistors in the amp making a better way to control the mosfet capacity. or the other with a extra driver in the circlotron section who give real drive to the irfp240
see schematic, has low distortion also.
I did think ablout removing the irf610 ccs mosfets and use only the resistors in the amp making a better way to control the mosfet capacity. or the other with a extra driver in the circlotron section who give real drive to the irfp240
see schematic, has low distortion also.
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Thanks Joe, I go try that out, it is a nice idea, I have also did ones put low 47 ohm resistors in series with the 150 source resistors of 2sk170 on the side of the ccs did give lower distortions.
I do now also think about removing the two ccs fron the sep drivers and replace them by resistors, also the new schematic in the previous post where I have drastically lower current in ltp and use smal mosfets as drivers for a extra source follower in the circlotron did lower HD significant, almost -120 dB by some watts, in full output on other picture it did still -100.
By yes X then we need a other pcb, but I go then make them myselfs and if succes then make more or let make.
Joe, can you tell me what schematic you did read, because of changes the destinators are also changed.
regards
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I wanna ask how you mean in series with the drains U3 U4 etc, have you a kind of drawing for me because the amp did protest on my way.
PS china caps are oke, 9850 uf.
thanks.
I have removed the irfp240 mosfets and make a photo from them, these looks for shure reprinted ones and maybe even are igbt making them useless.
second photo with a genuin on the left side as comparison. on ebay are the most troubles, I do like the aliexpress site, look better to fakers.
regards
second photo with a genuin on the left side as comparison. on ebay are the most troubles, I do like the aliexpress site, look better to fakers.
regards
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