Hello,
I have a Rotel RA-930AX integrated that I have completed a lot of modifications to.
My question is: Would a seperate power supply for the pre-amp section improve the sound?
The pre-amp section is using OPA627 op-amps.
I could get another transformer and bridge and some caps and have an unregulated supply or I could throw in a voltage regulator for good measure.
The current pre-amp power supply section is using a zener to achieve the needed + & - 18v.
Would anything be gained by using the existing transformer in the amp and adding a new bridge/caps & regulator?
Any input or experiences would be appreciated.
Thanks
KevinLee
I have a Rotel RA-930AX integrated that I have completed a lot of modifications to.
My question is: Would a seperate power supply for the pre-amp section improve the sound?
The pre-amp section is using OPA627 op-amps.
I could get another transformer and bridge and some caps and have an unregulated supply or I could throw in a voltage regulator for good measure.
The current pre-amp power supply section is using a zener to achieve the needed + & - 18v.
Would anything be gained by using the existing transformer in the amp and adding a new bridge/caps & regulator?
Any input or experiences would be appreciated.
Thanks
KevinLee
Thanks for the info analog_sa!
The secondary voltage of the amps transformer is 28 volts, once I go through the bridge it is like 39 volts.
The pre-amp section currently is supplied with + & - 18 volts.
Most regulators will not accept this kind of input voltage.
Maybe I would be best to but a transformer of say 20 volts and then build a bridge, add caps & 18v regs & more caps & call it a day.
Or would I be better to use an unregulated supply using a 12v secondary transformer and bridge & caps and supply my pre-amp section with 16-17 volts unregulated.
What will change by supplying the pre-amp section with 16volts instead of 18volts? Will I need to change some resistors values?
As always, any input is appreciated.
Cheers
KevinLee
The secondary voltage of the amps transformer is 28 volts, once I go through the bridge it is like 39 volts.
The pre-amp section currently is supplied with + & - 18 volts.
Most regulators will not accept this kind of input voltage.
Maybe I would be best to but a transformer of say 20 volts and then build a bridge, add caps & 18v regs & more caps & call it a day.
Or would I be better to use an unregulated supply using a 12v secondary transformer and bridge & caps and supply my pre-amp section with 16-17 volts unregulated.
What will change by supplying the pre-amp section with 16volts instead of 18volts? Will I need to change some resistors values?
As always, any input is appreciated.
Cheers
KevinLee
Nothing much changes at 16v - no need to change any resistors. You will severely limit your choices with a low voltage transformer though, good regulators sound better than no regulation at all and some experimenting is a must. I just don't see how you can decide everything in advance and 'call it a day' without critically listening to all changes. After all you want your amp to sound better, right?
You are 100% right!, I do want my amp to sound better.
From what you are saying, I understand I should have a regulated supply.
I will source a couple different voltage regs and get to work.
The reason I was thinking of supplying the pre-amp section with a lower voltage than 18v is that the OPA627 have a limit of 18volts and I would rather not work any electronic part at its extreme.
Thanks
KevinLee
From what you are saying, I understand I should have a regulated supply.
I will source a couple different voltage regs and get to work.
The reason I was thinking of supplying the pre-amp section with a lower voltage than 18v is that the OPA627 have a limit of 18volts and I would rather not work any electronic part at its extreme.
Thanks
KevinLee
If you get anywhere between 20-25v raw dc you should have ample voltage to drop accross the regulators; 18v is a bit marginal if you aim for 16 regulated. In my experience you may get better audible results using a simple emitter follower with a zener in the base than any 3-terminal but the opposite opinion is also popular It's largely a question of taste: if you value air and dynamics more than control and bass solidity the emitter follower is likely the winner.
It's largely a question of taste: if you value air and dynamics more than control and bass solidity the emitter follower is likely the winner.
If it's like the RA-931AX (which i have a service manual showing PCB layout and schematic for), the regulators are basic transistor zener followers.
Simply replace the zeners with a slightly higher voltage zener, for example BZX85C24, then use LM317/337 to regulate down to 18V (or whatever) before the opamp.
Cheap, easy, good
The only issue here is that it may involve cutting the track. Again i'm going by the RA-931AX service manual. Another issue might be the dissipation in the pass transistors (they are only TO-92 devices !) - I would probably replace them with TO-126 packaged devices (the pinouts match). BD139/140 would do.
Simply replace the zeners with a slightly higher voltage zener, for example BZX85C24, then use LM317/337 to regulate down to 18V (or whatever) before the opamp.
Cheap, easy, good
The only issue here is that it may involve cutting the track. Again i'm going by the RA-931AX service manual. Another issue might be the dissipation in the pass transistors (they are only TO-92 devices !) - I would probably replace them with TO-126 packaged devices (the pinouts match). BD139/140 would do.
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