If the supply voltage is really 30 volts (check that please) then the amplifier may
able to produce 50 watts, but while using 4 ohms loads... the power transistors will be working into the maximum dissipation limit.
I do not think they are using more bias, despite this makes a lot of sense too, and i think that because the heatsink area exposed to the air is too much small to operate this way.
The heatsink, evaluating it just watching, can work with two amplifiers producing 30 watts of sinusoidal power, a continuous steady tone, a non clipping power, or at the threshold.
This heatsink will not be good to continuous full power (around 50 watts) over 4 ohms, only musical power, average power, not continuous, because too small for that.
Maybe was used this way, owner said was very hot..a miracle that have survived, maybe Toshiba has underpowered his transistors into the datasheet, maybe they have informed less than the transistor can really face related power dissipation, maybe the informed maximum dissipation power is the guaranteed power, it is possible the unit can outstand, at least, 20 percent more.
It is more safe to Toshiba doing this way..imagine if the transistor is really maximum 30 watts (for example), and someone decide to use exaclty 30 watts of dissipation..and then the transistor burns...bad for Toshiba this way...more clever to them to say the transistor is 30 watts when in the reality it may be able to face more than that..for safety reasons..and then no surprises, no one will complain if the transistor could face more power than the datasheet informed.... no one complains when have advantage...but the opposite...........
The opposite is terrible, someone may say:
- " I have bougth Toshiba because reliable, good products, BUT, the unit was 30 watts in the datasheet, i made it dissipate exaclty 30 watts and the unit burned"
The same way happens with electrolitic condensers, imagine if a 35 volts explode with 35.001 volts..when the mains voltage use to float 20 percent...this would be electrolitic factory suicide...the 35 volts condensers accept, at least 42 volts...i have tested several with 55 volts without problems, i never had a single one burned, with leakage or exploded.
I have lost condenser because i have inverted them, never because excess of voltage.
regards,
Carlos
able to produce 50 watts, but while using 4 ohms loads... the power transistors will be working into the maximum dissipation limit.
I do not think they are using more bias, despite this makes a lot of sense too, and i think that because the heatsink area exposed to the air is too much small to operate this way.
The heatsink, evaluating it just watching, can work with two amplifiers producing 30 watts of sinusoidal power, a continuous steady tone, a non clipping power, or at the threshold.
This heatsink will not be good to continuous full power (around 50 watts) over 4 ohms, only musical power, average power, not continuous, because too small for that.
Maybe was used this way, owner said was very hot..a miracle that have survived, maybe Toshiba has underpowered his transistors into the datasheet, maybe they have informed less than the transistor can really face related power dissipation, maybe the informed maximum dissipation power is the guaranteed power, it is possible the unit can outstand, at least, 20 percent more.
It is more safe to Toshiba doing this way..imagine if the transistor is really maximum 30 watts (for example), and someone decide to use exaclty 30 watts of dissipation..and then the transistor burns...bad for Toshiba this way...more clever to them to say the transistor is 30 watts when in the reality it may be able to face more than that..for safety reasons..and then no surprises, no one will complain if the transistor could face more power than the datasheet informed.... no one complains when have advantage...but the opposite...........
The opposite is terrible, someone may say:
- " I have bougth Toshiba because reliable, good products, BUT, the unit was 30 watts in the datasheet, i made it dissipate exaclty 30 watts and the unit burned"
The same way happens with electrolitic condensers, imagine if a 35 volts explode with 35.001 volts..when the mains voltage use to float 20 percent...this would be electrolitic factory suicide...the 35 volts condensers accept, at least 42 volts...i have tested several with 55 volts without problems, i never had a single one burned, with leakage or exploded.
I have lost condenser because i have inverted them, never because excess of voltage.
regards,
Carlos
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Sakis is right, i have increase the stand by current to 500mA
And them i simulate, distortion increased to 0.2%, fourier was not so good anymore, and the transistors would melt.
So, the advanced bias point, to make it work in class A into the first watts, would not work fine for this amplifier.
Working with 4 ohms the amplifier was able (simulator) to put out 45 watts RMS, distortion was 0.05%... stand by bias around 50 mA (this is standard)...power consumption was 90 watts, and this is the consumption informed in the power amplifier back panel, so, 45 watts per channel, 4 ohms makes sense with normal bias.
It can go to 68 watts, but distortion increases too much, and power consumption goes to 120 watts, and this is too much, back panel said 200 (both channels) and not 340 watts.
I have advanced the stand by bias to 350 mA, but this does not result better in distortion, the maximum consumption remains the same as the amplifier leaves the class A very soon and start to work class AB
regards,
Carlos
And them i simulate, distortion increased to 0.2%, fourier was not so good anymore, and the transistors would melt.
So, the advanced bias point, to make it work in class A into the first watts, would not work fine for this amplifier.
Working with 4 ohms the amplifier was able (simulator) to put out 45 watts RMS, distortion was 0.05%... stand by bias around 50 mA (this is standard)...power consumption was 90 watts, and this is the consumption informed in the power amplifier back panel, so, 45 watts per channel, 4 ohms makes sense with normal bias.
It can go to 68 watts, but distortion increases too much, and power consumption goes to 120 watts, and this is too much, back panel said 200 (both channels) and not 340 watts.
I have advanced the stand by bias to 350 mA, but this does not result better in distortion, the maximum consumption remains the same as the amplifier leaves the class A very soon and start to work class AB
regards,
Carlos
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Hello sakis, perhaps I missed something in the chain here, but I thought that nad stated it was a 25wpc amp, thus 50 watts total out. At 50% eff, then it would consume 100w. If this is consuming 200w, they are running it with a high bias. Of course some power will be consumed by the preamp stage, this being an integrated amp, but no where near 100w will be consumed by the preamp stage.
Peace,
Dave
Here's a link to the service manual.
Kapcsolási rajz, szervizkód, eeprom keresés eredménye | ElektroTanya | Service manuals and repair tips for electronics experts
Kapcsolási rajz, szervizkód, eeprom keresés eredménye | ElektroTanya | Service manuals and repair tips for electronics experts
Hello 'stainless', as I mentioned in a previous post, the amp is an RA-412 and not a 314 as my first post reads, sorry for the confusion.
I have a Rotel RX550 from about 1980, with a very similar story. It's been mine all along, but I wasn't nice to it in college- yes, it too will heat up like that if pushed and not fail. It also sat in a very smoky environment for years and years. I used it in my garage for 5 years where it saw temps over 110F and below 0F for extended periods of time.
A few months ago I finished my Thor speakers- 86db at 4 ohms. This old Rotel pushes those with no problems at all, despite being rated for 40WPC at 8 ohms. The pots were a bit scratchy but some electronics cleaner took care of that. It works just like it did the first day I got it.
A few months ago I finished my Thor speakers- 86db at 4 ohms. This old Rotel pushes those with no problems at all, despite being rated for 40WPC at 8 ohms. The pots were a bit scratchy but some electronics cleaner took care of that. It works just like it did the first day I got it.
I have a ROTEL RX-402 .. Amazing amp receiver and the design looks almost exactly the same as this RA-314, with the same SanKen 2sc1444 Bipolar transistors
I replaced the power supply caps with same capacitance but higher v rating to allow for a higher ripple current. It does seem more dynamic. A bit edgy at the start but after warmed up and worn in after 100 hours or so, it really is an amazing amp. In the process of replacing all of the caps.
I also have a RA-820BX and the 402 certainly wins on all grounds.
ROTEL really knew how to make these BJTs perform.
I recommend replacing the fuses on the speaker protection, strange suggestion.. i know.. i was just in an electronics shop and saw some 6.3A quick blow fuses just for £2 so i bought some and there is a significant difference in detail!
I replaced the power supply caps with same capacitance but higher v rating to allow for a higher ripple current. It does seem more dynamic. A bit edgy at the start but after warmed up and worn in after 100 hours or so, it really is an amazing amp. In the process of replacing all of the caps.
I also have a RA-820BX and the 402 certainly wins on all grounds.
ROTEL really knew how to make these BJTs perform.
I recommend replacing the fuses on the speaker protection, strange suggestion.. i know.. i was just in an electronics shop and saw some 6.3A quick blow fuses just for £2 so i bought some and there is a significant difference in detail!
The sm for rotel ra412 is now available at:
Kapcsolási rajz, szervizkód, eeprom keresés eredménye | ElektroTanya | Service manuals and repair tips for electronics experts
Kapcsolási rajz, szervizkód, eeprom keresés eredménye | ElektroTanya | Service manuals and repair tips for electronics experts
Hi to All!!!
My friend owns Ra-314 and the problem is at high gain of the amplifier.On 9 clock on potentiometer it's to loud for normal listening specially on quietly night lis.
My question is where to reduce the gain of amp?
Pot is 100kohm,input impedance of preamp is 220khom(R506,505).
Thanks for Help!!!
http://speedy.sh/G3sVH/RA-314-TM.pdf
My friend owns Ra-314 and the problem is at high gain of the amplifier.On 9 clock on potentiometer it's to loud for normal listening specially on quietly night lis.
My question is where to reduce the gain of amp?
Pot is 100kohm,input impedance of preamp is 220khom(R506,505).
Thanks for Help!!!
http://speedy.sh/G3sVH/RA-314-TM.pdf
That must be one of the funniest questions I have read in a long time.
But, if you do want to be able to turn the amplifier up to 9 o'clock and for it to be a bit quieter you simply need to attenuate the input signal. The simplest way to do that is to wire a resistor in series with the input.
If you assume that the input resistance of the amplifier is 47K, then wiring a 47K resistor in series with the input will attenuate the signal by 3dB.
Why you can't just turn the volume down beats me !!!!
Leave the amplifier alone so that you can use the volume when its appropriate to do so.
But, if you do want to be able to turn the amplifier up to 9 o'clock and for it to be a bit quieter you simply need to attenuate the input signal. The simplest way to do that is to wire a resistor in series with the input.
If you assume that the input resistance of the amplifier is 47K, then wiring a 47K resistor in series with the input will attenuate the signal by 3dB.
Why you can't just turn the volume down beats me !!!!
Leave the amplifier alone so that you can use the volume when its appropriate to do so.
Maybe i was not so clear with my question,maybe is because i never learnd English language so i can't express my self in the way i want. 😀
My friend said that he never listen this amp more then 9 o'clock at normal daily listnening so we want to move this at least to 12 o'clock by reducing gain if you know what i mean.
WHY ? Just use it at the volume setting that you need. It wont sound any different just because you can set the volume to MAX.
I think the point Basi is making is that at the 9 o'clock point the output is at the max ever required, so it is difficult to set the volume for quiet listening because the volume control only works over a range of less than 1/4 turn.
Basi, I got round this on a 'vintage' preamp of mine by installing a voltage divider on the input of the amp to attenuate the signal a bit. While this isn't regarded as the best for sound quality, I couldn't notice a clear difference and it did extend the range of the volume pot to better enable fine adjustments at low listening levels.
Basi, I got round this on a 'vintage' preamp of mine by installing a voltage divider on the input of the amp to attenuate the signal a bit. While this isn't regarded as the best for sound quality, I couldn't notice a clear difference and it did extend the range of the volume pot to better enable fine adjustments at low listening levels.
If a reasonable rotation either way from the 'usual listening position' can give you the volume range you want , your system is fine. This is dependent on the level of the input signal and the 'taper' of your pot. The 'clock' position of the pot on different amps are NOT important at all as long as you get the 'comfortable' range you want.
I've just checked on the Service manual and the input impedance on the AUX input is near to 47K.
Fitting a 47K in series with the input lead will attenuate the signal by 3dB allowing you to turn the volume control up higher to achieve the same volume.
If 47K isn't enough you can try increasing it to say 100K. You will need one in each L&R lead.
Fitting a 47K in series with the input lead will attenuate the signal by 3dB allowing you to turn the volume control up higher to achieve the same volume.
If 47K isn't enough you can try increasing it to say 100K. You will need one in each L&R lead.
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