i have a mosfet amp that looks like it came from the stone age ( well you can see all the parts have been hand soldered in) but it still works well and can drive a pretty decent speaker.
it has the preamp built in - so all u have to do is hook up a cd player, speaker and it plays music.
the only problem is that the amp distorts before it reaches its power limits (i think), because the supply voltage doesn't drop too much (maybe 1 volt) and the bass doesn't thin out, and the amp doesn't even get warm
is this just how mosfet amps work or does it sound like i could get some more power out of this amp?
it has the preamp built in - so all u have to do is hook up a cd player, speaker and it plays music.
the only problem is that the amp distorts before it reaches its power limits (i think), because the supply voltage doesn't drop too much (maybe 1 volt) and the bass doesn't thin out, and the amp doesn't even get warm
is this just how mosfet amps work or does it sound like i could get some more power out of this amp?
Hi,
Mosfet amps generally perform better with a higher bias current than a BJT amp.
This usually means that it runs warmer. Odd that you say it does not warm up.
I wonder if the distortion is a crossover problem?
Can you identify how to measure the output stage bias current?
Can you estimate the heatsink capacity and temperature rise?
Can you tell us what the output stage consists of? Driver and output device type numbers and number off.
Mosfet amps generally perform better with a higher bias current than a BJT amp.
This usually means that it runs warmer. Odd that you say it does not warm up.
I wonder if the distortion is a crossover problem?
Can you identify how to measure the output stage bias current?
Can you estimate the heatsink capacity and temperature rise?
Can you tell us what the output stage consists of? Driver and output device type numbers and number off.
Dan2 [/i][B] how do you check the electrolytics??? [/B][/QUOTE] Measure them with a capacitance meter and see if they are still the same value as written on them. You can pretty much guarantee they won't be. [QUOTE][i]Originally posted by Dan2 [/i][B] and what happens to the amp when the caps dry out? 'cos it still works well said:
Maybe if you can tell us what voltage it runs on...
When the elko's got dry you can hear it.
The bass gets less*fat* .
Best would be to change all ,but most vital ones are powersupply and output.
When i look at it i agree with Elvee that its no mosfets .
To me it looks like made in the 70's.
When you want to know the age a lot of parts have year and weeknumber printed on it 7310 will be 1973 week 10.
Goodluck
The bass gets less*fat* .
Best would be to change all ,but most vital ones are powersupply and output.
When i look at it i agree with Elvee that its no mosfets .
To me it looks like made in the 70's.
When you want to know the age a lot of parts have year and weeknumber printed on it 7310 will be 1973 week 10.
Goodluck
oh yes, the voltage is 50v dc (actually looking at it now the caps are only rated 50 volts)
the bass is still pretty fat, so if its gets better when i replace the caps it will be a really nice little amp
as for volume control, just a 470k pot and 2 47k resistors to combine stereo into mono - its just for testing and buzzes when turned down. at full volume amp runs quiet
the volume control it came with was also just pots (volume, bass, treble) that hooked up straight to this circuit - it didn't buzz with those pots though
I put the transister numbers (that i could read) on this photo
the bass is still pretty fat, so if its gets better when i replace the caps it will be a really nice little amp
as for volume control, just a 470k pot and 2 47k resistors to combine stereo into mono - its just for testing and buzzes when turned down. at full volume amp runs quiet
the volume control it came with was also just pots (volume, bass, treble) that hooked up straight to this circuit - it didn't buzz with those pots though
I put the transister numbers (that i could read) on this photo
Attachments
Looking at the numbers, it is almost certainly not a MOSFET amp.
More likely, 2N3055 equivalent to give 25W output.
The volume control pot. should be in the region of 50K ohms log. which could explain the buzzing at part-volume.
The cause of the distortion is probably the input stage overloading. Input sensitivity is likely to be in the region of 750mV for full output and the CD player gives 2V.
Andy
More likely, 2N3055 equivalent to give 25W output.
The volume control pot. should be in the region of 50K ohms log. which could explain the buzzing at part-volume.
The cause of the distortion is probably the input stage overloading. Input sensitivity is likely to be in the region of 750mV for full output and the CD player gives 2V.
Andy
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