what can put my amp in oscillation?
zeno: I have no scope, and no light bulb
but I used an Ampmeter on the supply rails, and it draws 0.3A at iddle, bot not always
sometimes it's not, and a little input signal during 1/2 second then stop, then it's 0.3A 🙁
zeno: I have no scope, and no light bulb
but I used an Ampmeter on the supply rails, and it draws 0.3A at iddle, bot not always
sometimes it's not, and a little input signal during 1/2 second then stop, then it's 0.3A 🙁
Well it shouldn't get hot at all with no input and no output.99% it's oscillation accordind to the tradition here.Check all your connections then since it seems you don't have the input pot tie a 50k or so from the inverting input to ground.
If I am right, you don't have a pot on the input? (Hence the earpads 
)
Did you use the original shematic (National datasheet or the 'inverted gainclone') or the reduced Peter D's schematic?
Leaving out components might make the circuit more sensitive to osccillation and instability.
Is it better when you shield the circuit? (You should be able to measure the temp of course)
Marc
)Did you use the original shematic (National datasheet or the 'inverted gainclone') or the reduced Peter D's schematic?
Leaving out components might make the circuit more sensitive to osccillation and instability.
Is it better when you shield the circuit? (You should be able to measure the temp of course)
Marc
protos said:
I'm using a 10K pot now (I can put the earpads out of my ears now 🙂)
I'm using peter's minimised gainclone shematic (but with no input cap for the momment)
Bricolo,
Check post 294 in this thread.
http://www.diyaudio.com/forums/newreply.php?threadid=9112
Actually the thread we are in now
Marc
Check post 294 in this thread.
http://www.diyaudio.com/forums/newreply.php?threadid=9112
Actually the thread we are in now
Marc
Here you can find that post from Mr. K. Wang...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=9112&perpage=15&pagenumber=20
Fedde
http://www.diyaudio.com/forums/showthread.php?s=&threadid=9112&perpage=15&pagenumber=20
Fedde
fedde said:
since I use a pot now, my -in is connected to ground with the 10K resistor, and the 10K pot
+in is directly to ground
I've tested the amp deeper this afternoon:
It still gets hot even at low volume, and even with no input signal
but when I change the load from a speaker to a 10R resistor, the chip runs cooler
can this be an oscillation problem? how can I fiw it?
I wish I had a scope
It still gets hot even at low volume, and even with no input signal
but when I change the load from a speaker to a 10R resistor, the chip runs cooler
can this be an oscillation problem? how can I fiw it?
I wish I had a scope
oscilation!!
Hi bricolo!
It only gets hot with the speaker conected!
As you are using shielded speaker cable....bingo!...oscilation!
A nother question...have you a zobel at the output?
Cheers
Jorge
Hi bricolo!
It only gets hot with the speaker conected!
As you are using shielded speaker cable....bingo!...oscilation!
A nother question...have you a zobel at the output?
Cheers
Jorge
Re: oscilation!!
I'm using classical cable on my test design, this isn't the problem
no I don't have a zobel, according to it's datasheet, the 7294 don't need any
Tube_Dude said:
I'm using classical cable on my test design, this isn't the problem
no I don't have a zobel, according to it's datasheet, the 7294 don't need any
Jam, Steve, Todd,
I rewired the clone and it is now stable. Each ground point now comes back to my star ground and I wound the rails together as well. Im not sure who owes who lunch?
I cant say the sound is good at all in the upper range but better than the 3886 I built using roughly the factory recomended circuit.
Perhaps I need to try better components but some of the vocal passages are so harsh and artificial sounding Its hard to give the amp a second thought. I do notice that I can discern a big difference between recordings so it does, in a way, do a good job of exposing the recording in the high end.
Any ideas on which components might be most critical to the sound?
Im using the variable out on my cd player in place of a high quality pot and I wonder if I need some impedance at the input?
I rewired the clone and it is now stable. Each ground point now comes back to my star ground and I wound the rails together as well. Im not sure who owes who lunch?
I cant say the sound is good at all in the upper range but better than the 3886 I built using roughly the factory recomended circuit.
Perhaps I need to try better components but some of the vocal passages are so harsh and artificial sounding Its hard to give the amp a second thought. I do notice that I can discern a big difference between recordings so it does, in a way, do a good job of exposing the recording in the high end.
Any ideas on which components might be most critical to the sound?
Im using the variable out on my cd player in place of a high quality pot and I wonder if I need some impedance at the input?
Quick question. I have searched the forums and found no good answer to this question. I'm using an ESP project 88 preamp w/ my gainclones...and I'm using Peter's minimized clone schematic...only 2.2uF on inverting input etc. Ok, so I'm using this thing w/ a preamp...heresy I know...I obviously don't need the input pot. Do I just add a resistor 100k to ground and keep the 10k in series (like peters schematic)....OR!! can I just put a 10k to ground instead and then not have any resistor in serieson the inverting input? I like that idea best but I don't want to see smoke. Thanks!
-Matthew K. Olson
-Matthew K. Olson
The input resistor!
Hi Mattyo5
You need the 10k resistor in series with signal....if you put the 10 K resistor to ground ...the serial resistor will became the intrinsec
output impedance of your preamp.
Let's see if the output impedance of the pre is 1k...and if you have a 220k feedback resistor you will end up with a gain of 220 X...but even more if the output impedance of the preamp is lower...the input impedance must be defined for the gain also be defined!
resuming: not recomended! 😉
Regards
Jorge
Hi Mattyo5
You need the 10k resistor in series with signal....if you put the 10 K resistor to ground ...the serial resistor will became the intrinsec
output impedance of your preamp.
Let's see if the output impedance of the pre is 1k...and if you have a 220k feedback resistor you will end up with a gain of 220 X...but even more if the output impedance of the preamp is lower...the input impedance must be defined for the gain also be defined!
resuming: not recomended! 😉
Regards
Jorge
ok....so I need a 10k in series...so what do I use w/ that going to ground? 50k? 100k? (before or after?) Thanks
-Matthew K. Olson
-Matthew K. Olson
The apm with 3785 is very good, realy. I use the most minimized circuit possible. 10k in the (-) input, and 220k feedback resistor. That's all. No resistors to ground, no pots, etc. I use the digital volume control of the CD player.
The amp is very sensitive to parts, cables, electrolytic caps... I use 220uF Elna x5 per rail, but I'll try Panasonic FC too.
The amp replaced a 10W JLHood SE amp - 3Ohms version with Toshiba transistors (very good amp for the heavy load of my ODINs).
The GC sounds OK in comparison. Better highs and mids. The bass is not so powerful but is very special, light end defined.
In short - GC is a very, very special amp. (I was skeptical at the beginning - I'm too conservative for such kind of PSUs, chips, so little chips, etc.)
BTW it still is not in a box, but there are no oscillations. The heatsink is absolutely cold, there's no hum.
The amp is very sensitive to parts, cables, electrolytic caps... I use 220uF Elna x5 per rail, but I'll try Panasonic FC too.
The amp replaced a 10W JLHood SE amp - 3Ohms version with Toshiba transistors (very good amp for the heavy load of my ODINs).
The GC sounds OK in comparison. Better highs and mids. The bass is not so powerful but is very special, light end defined.
In short - GC is a very, very special amp. (I was skeptical at the beginning - I'm too conservative for such kind of PSUs, chips, so little chips, etc.)
BTW it still is not in a box, but there are no oscillations. The heatsink is absolutely cold, there's no hum.
I forgot the PCU...
I use 2 transformers (not toroids), 150VA each, 2 X 17 VAC. After that there is double bridge, made of BVY 133/45 - 20 A schottkey diodes (200 A picks) 40V. Since the bridges are double I don’t think the voltage is dangerous.
The cables I use in the amp are CAT 5, and a very HQ aircraft cable.
I use 2 transformers (not toroids), 150VA each, 2 X 17 VAC. After that there is double bridge, made of BVY 133/45 - 20 A schottkey diodes (200 A picks) 40V. Since the bridges are double I don’t think the voltage is dangerous.
The cables I use in the amp are CAT 5, and a very HQ aircraft cable.
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