Hey all, this one has got me good.
I've never had an amplifer that hissed like this before!
I took the guts out of an old sanyo amp that had a crappy front end and EQ and really lousy wiring. I put just the power tranny and the amp block onto a board and use them wired with my own setup. The sound is far superior to the original setup it was in except for the fact that now it hisses very badly.
Is there anything I can do to make this thing quiet down some, maybe even be silent when there's no input???
I know amps can be quiet from experience with my HK A402 which is completely inaudible without signal input!
I know the sanyo has a crazy amount of gain, but it still should be capable of quieting down don't you think????
I've never had an amplifer that hissed like this before!
I took the guts out of an old sanyo amp that had a crappy front end and EQ and really lousy wiring. I put just the power tranny and the amp block onto a board and use them wired with my own setup. The sound is far superior to the original setup it was in except for the fact that now it hisses very badly.
Is there anything I can do to make this thing quiet down some, maybe even be silent when there's no input???
I know amps can be quiet from experience with my HK A402 which is completely inaudible without signal input!
I know the sanyo has a crazy amount of gain, but it still should be capable of quieting down don't you think????
Where is Sherlock Holmes - these days?
We surely can assume that not all parts produce the hissing sound.
I would guess somewhere at the input.
But how can we determine what component/components
is/are the hiss producer/producers? 😕
Once this is done, there will be a remedy.
To change components, one by one, and measure the noise
for every exchange would be too timeconsuming.
We surely can assume that not all parts produce the hissing sound.
I would guess somewhere at the input.
But how can we determine what component/components
is/are the hiss producer/producers? 😕
Once this is done, there will be a remedy.
To change components, one by one, and measure the noise
for every exchange would be too timeconsuming.
Hiss etc
Most probably the hiss is caused because the power amp part now is operating differently then before with the front end. These types of amps are really systems and you cannot always cut off one part without affecting the other part.
Maybe there is now a large (relatively) series input resistor, that was driven differently before. You say it has a "crazy gain", this could be because you inadvertently cut a feedback loop. That would lead to very high gain + high noise (=hiss).
If you short the input and it still hisses, there is definitely a problem with the topology. Measuring/replacing each component will not solve it.
Jan Didden
Most probably the hiss is caused because the power amp part now is operating differently then before with the front end. These types of amps are really systems and you cannot always cut off one part without affecting the other part.
Maybe there is now a large (relatively) series input resistor, that was driven differently before. You say it has a "crazy gain", this could be because you inadvertently cut a feedback loop. That would lead to very high gain + high noise (=hiss).
If you short the input and it still hisses, there is definitely a problem with the topology. Measuring/replacing each component will not solve it.
Jan Didden
large overall gain
Sometimes additional gain
is added to overcome the losses in Bass/Treble controls.
At the same time some filter in these controls
can be used to remove noise.
So I think janneman is right.
Sometimes additional gain
is added to overcome the losses in Bass/Treble controls.
At the same time some filter in these controls
can be used to remove noise.
So I think janneman is right.
I guess there could've been a FB loop in there somewhere... There were a couple of ribbon cables going from the eq computer board into the amp board. I figured these were just for power since most of the power supply is right on the amp. I'll check to see if there might have been more functions there....
I know that when I turned the volume of the original amp all the way up it would hiss like mad like it does now.. Perhaps the volume control is right on the amp and I just have to close it up a bit. I guess that if you have no control voltage the volume opens wide since that's how it's working right now....
Anymore ideas anyone??? I'm not putting this monster back together again, it sounds way way better on its own!
EDIT: Just to mention, I have attempted to shot the input to ground and the thing sounds no different at all!
I know that when I turned the volume of the original amp all the way up it would hiss like mad like it does now.. Perhaps the volume control is right on the amp and I just have to close it up a bit. I guess that if you have no control voltage the volume opens wide since that's how it's working right now....
Anymore ideas anyone??? I'm not putting this monster back together again, it sounds way way better on its own!
EDIT: Just to mention, I have attempted to shot the input to ground and the thing sounds no different at all!
By the way, I have another question about this weird amp...
I measured the bias ont the output devices and it's only .3 volts per device B-E voltage😱 I hear no apparent distortion but I was wondering if it might sound a bit further into class AB if I were to push it into .7 volts per device. Do you guys think that's okay???
I measured the bias ont the output devices and it's only .3 volts per device B-E voltage😱 I hear no apparent distortion but I was wondering if it might sound a bit further into class AB if I were to push it into .7 volts per device. Do you guys think that's okay???
0.3 volt. Can there be any current flowing? Very little i suppose.
They aren't Germanium?
Anyway you need some resistor to measure the current.
Put in a temporary resistor in supply line.
Try to figure out how to set the idle to 50-100mA.
They aren't Germanium?
Anyway you need some resistor to measure the current.
Put in a temporary resistor in supply line.
Try to figure out how to set the idle to 50-100mA.
Yeah, this is very weird. The transistors are silicon...
The amp runs very cold at idle, I mean, it generates no heat at all.
This design uses thermistors to regulate the bias when the amp heats up, I suppose these could've gone off a ways, but I doubt it... There are bias adjustments and I tried to bring it up at bit but the pot stops at about .5 volts in the B-E junctions. I can't even push it to .7 volts unless I alter the circuit a bit.
The amp runs very cold at idle, I mean, it generates no heat at all.
This design uses thermistors to regulate the bias when the amp heats up, I suppose these could've gone off a ways, but I doubt it... There are bias adjustments and I tried to bring it up at bit but the pot stops at about .5 volts in the B-E junctions. I can't even push it to .7 volts unless I alter the circuit a bit.
Suppose the EQ was a part of the Feedback.
Then the compensation filtering is gone now
and that is why it oscillates.
could be the case
I think this also can effect the Output stage bias
Then the compensation filtering is gone now
and that is why it oscillates.
could be the case
I think this also can effect the Output stage bias
Good points...
Mr. Pass always has the right idea!
I'll try disconnecting the inputs from my front end and see if I can make the bias proper then. I know that the inputs are direct coupled so maybe that's a good possibility that the input affects the bias. Perhaps I'll have to put in a cap or some active circuitry to fix it.
I guess it could be oscillating but I find that at idle the amp runs very cold, I'll check with a scope to see if there actually is anything there except for the white noise I hear. The amp seems to have the typical LR output networks with coils and 10 ohm resistors... There are also 0.56ohm resistors and caps in series from each output to ground. I'll try introducing some negative feedback to see what I can get. Perhaps the eq just varied the feedback to set the volume. I'll see if there is any sort of audio coming out of that ribbon connector that might be used for FB...
Mr. Pass always has the right idea!
I'll try disconnecting the inputs from my front end and see if I can make the bias proper then. I know that the inputs are direct coupled so maybe that's a good possibility that the input affects the bias. Perhaps I'll have to put in a cap or some active circuitry to fix it.
I guess it could be oscillating but I find that at idle the amp runs very cold, I'll check with a scope to see if there actually is anything there except for the white noise I hear. The amp seems to have the typical LR output networks with coils and 10 ohm resistors... There are also 0.56ohm resistors and caps in series from each output to ground. I'll try introducing some negative feedback to see what I can get. Perhaps the eq just varied the feedback to set the volume. I'll see if there is any sort of audio coming out of that ribbon connector that might be used for FB...
Well, I actually managed to stop the hiss.
All I had to do was disconnect the inputs from my front end and all was quiet. I thought I already tried that but apparently I didn't.
I'm going to make a nice little attenutation and loading network for the inputs anyway cause the gain is way to much anyhow.
The amp even sounds like the inputs aren't loaded enough, so maybe that's the cure-all solution. I find that there is no oscillation, just noise because of high gain.
All I had to do was disconnect the inputs from my front end and all was quiet. I thought I already tried that but apparently I didn't.
I'm going to make a nice little attenutation and loading network for the inputs anyway cause the gain is way to much anyhow.
The amp even sounds like the inputs aren't loaded enough, so maybe that's the cure-all solution. I find that there is no oscillation, just noise because of high gain.
CD output rules - for the moment.
had more voltage gain.
The input should be able to handle so low input voltages
as 0.150-0.300 Vrms.
Sources was mainly tapeheads and phono pickups.
The output from their preamps was not so high.
so that extra gain was often provided by the power amp.
So if it works in this case, I would reduce the feedback resistor
instead of putting in an extra attenuator.
It does NOT make sense to me, to first lower a signal,
then put more gain to compensate.
To lower the feedback resistor, will of course
increase the feedback.
So an added amount of feedback capacitance can be needed.
The relatively high input impedances (47-100kohm) of those amps,
comes out of the often low drive capacity
of those tape/pickup amps used.
For CD-players of today and the preamps we use now
a lower input impedance can easily be used for the power amp..
The development for coming years will probably
set a standard that sends more current through the interconnects.
Amps made before the CD output era,Duo said:
had more voltage gain.
The input should be able to handle so low input voltages
as 0.150-0.300 Vrms.
Sources was mainly tapeheads and phono pickups.
The output from their preamps was not so high.
so that extra gain was often provided by the power amp.
So if it works in this case, I would reduce the feedback resistor
instead of putting in an extra attenuator.
It does NOT make sense to me, to first lower a signal,
then put more gain to compensate.
To lower the feedback resistor, will of course
increase the feedback.
So an added amount of feedback capacitance can be needed.
The relatively high input impedances (47-100kohm) of those amps,
comes out of the often low drive capacity
of those tape/pickup amps used.
For CD-players of today and the preamps we use now
a lower input impedance can easily be used for the power amp..
The development for coming years will probably
set a standard that sends more current through the interconnects.
This amp was made in the early 90's and has a specific CD input.
It even had remote control and digital volume control, but the front end and the abd wiring in there made it sound much worse than it could.
I'll try reducing the neghative feedback resistance anyway and see what I can do...
It even had remote control and digital volume control, but the front end and the abd wiring in there made it sound much worse than it could.
I'll try reducing the neghative feedback resistance anyway and see what I can do...
No don't add any loops
if it is built without feedback, it is the way
it should be
I thought it was a more conventional design
if it is built without feedback, it is the way
it should be
I thought it was a more conventional design
Sorry, I just edited my comment too late.
I just checked the design a little closer and there is a traditional
NGFB loop in there, just the resistors were hidden so I couln't figure out where things were going.
I just checked the design a little closer and there is a traditional
NGFB loop in there, just the resistors were hidden so I couln't figure out where things were going.
Sanyo japanese with feedback, sounds more probable
I agree that unnessesary feedback, especially global
over many stages is not to be prefered.
But to be consekvent, a "non feedback fundamentalists"
should not use any opamp,
or a device containing an opamp.
Or any amplifier/preamplifier
dependant of such feedback.
And that limits their choice with over 90%.
It is not logical to me, to avoid feedback at one point
and then use a massive amount over many stages
in another place.
And that is exactly what OP amps do.
I agree that unnessesary feedback, especially global
over many stages is not to be prefered.
But to be consekvent, a "non feedback fundamentalists"
should not use any opamp,
or a device containing an opamp.
Or any amplifier/preamplifier
dependant of such feedback.
And that limits their choice with over 90%.
It is not logical to me, to avoid feedback at one point
and then use a massive amount over many stages
in another place.
And that is exactly what OP amps do.
True. I don't like the sound of opamps very much indeed.
Fortunately this amp has no ic's even in it at all. That's part of the reason I got rid of all the other crap in there. It was just coloring the sound.
I tried reducing the feedback resistance but it doesn't have much effect on noise reduction.
Fortunately this amp has no ic's even in it at all. That's part of the reason I got rid of all the other crap in there. It was just coloring the sound.
I tried reducing the feedback resistance but it doesn't have much effect on noise reduction.
With device I mean not only power amps
CD-players, phono RIAA amps, DACs, microphone amps
computer sound cards
any front end or source of sound
Mixers and recording equipement.
Samplers, you name it.
They can all be built without negative feedback.
But not without some "little" effort. 😀
CD-players, phono RIAA amps, DACs, microphone amps
computer sound cards
any front end or source of sound
Mixers and recording equipement.
Samplers, you name it.
They can all be built without negative feedback.
But not without some "little" effort. 😀
Well, go out and find me a non feedback soundcard
Or for that matter, complete computer without any feedback!
I see what you mean though...
Or for that matter, complete computer without any feedback!
I see what you mean though...
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