Hi
My (RCA only) tube preamp has a lot of gain.
When using the 25dB RCA input of the V3M it's too loud.
Is there an easy way to reduce the V3M gain even more?
Op amp change/bridge?
The op amp in position 1 converts the unbalanced signal from RCA into a balanced signal. The op amps in positions 2 and 3 are responsible for adjusting the tone. If you're looking to change only one op amp, it's recommended to replace the one in position 2. However, if you replace both op amps, the effect will be more noticeable. Positions 2 and 3 can be replaced with different chips. You can personally experiment with changing different op amps and their positions to experience the changes in sound.
My (RCA only) tube preamp has a lot of gain.
When using the 25dB RCA input of the V3M it's too loud.
Is there an easy way to reduce the V3M gain even more?
Op amp change/bridge?
The op amp in position 1 converts the unbalanced signal from RCA into a balanced signal. The op amps in positions 2 and 3 are responsible for adjusting the tone. If you're looking to change only one op amp, it's recommended to replace the one in position 2. However, if you replace both op amps, the effect will be more noticeable. Positions 2 and 3 can be replaced with different chips. You can personally experiment with changing different op amps and their positions to experience the changes in sound.
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No easy way, unless you have schematic and find surface mount soldering easy. What source are you driving it with? The problem is there, not the amp. It's putting out too hot of a signal and likely easier to correct there. If not, an inline or passive attenuator may be in order.
Changing opamps will certainly not affect gain. I have dialed down the volume knobs of my ZA3s to 1:10th of max. And I don’t have gain in my pre. But I have sensitive speakers.
Planning the gain chain is an important part of the total experience
Planning the gain chain is an important part of the total experience
Just the nature of the beast. This is a power amp, and must be mated with a pre-amp that has volume control. Right- changing op-amps will not decrease gain.
My noob guess is that 2 pins of the opamp are the source signal and 2 are the output.
Jumper in to out = zero gain?
Jumper in to out = zero gain?
Well two 5 cents resistors would have solved that but whatever makes your boat float 🙂
Why are you posting the 5532 pinout diagram?
Why are you posting the 5532 pinout diagram?
The gain switch wires should be traced back to that OPAmp. There are two ways to control the gain (below), so once the circuit is traced / back-engineered, it will be easy to adjust the appropriate resistors to reduce the gain.
My hope is that I can reduce the gain without soldering.
By removing/bypassing one of the NE5532 (position 2 or 3).
I assume they are amps or buffers in the signal way. Maybe do balancing or unbalancing. Remove and see. If they are in the signal way your amps will go quiet
Or just read the original post, which includes a diagram indicating what function each op-amp performs.
By the way, this amp uses Post Filter Feed Back (PFFB) so by mucking with the op-amp gains you are probably going to cause yourself problems. The first op-amp is likely a differential amp, converting the balanced input to single ended likely at unity gain, so nothing you can do there. The other two op-amps indicate they are responsible for "adjusting the tone", which is dubious because there is no tone adjustment, but they may be doing some filtering and implementing the post-filter feedback, which I highly recommend you don't mess with. The op-amps, likely being inside the global feedback network, may not actually effect the global gain of the amp so much as just the open loop gain, meaning you may not achieve the effect you are trying for by modifying the op-amp gain. Without a schematic, we might as well just start shorting out things with a screwdriver and see what effect we can achieve.
Because far more difficult and impractical ridiculous solutions are being considered over the obvious "buy a pre-amp", I could suggest you knock down a wall of your living room, extend the room by a good 30 feet or so, and place your speakers at the far end so they don't sound so loud. Or put cotton in your ears, or pillows against your speakers. If you don't want to buy a pre-amp, perhaps buy an inline attenuator/volume control and NOT destroy your nice amp?
By the way, this amp uses Post Filter Feed Back (PFFB) so by mucking with the op-amp gains you are probably going to cause yourself problems. The first op-amp is likely a differential amp, converting the balanced input to single ended likely at unity gain, so nothing you can do there. The other two op-amps indicate they are responsible for "adjusting the tone", which is dubious because there is no tone adjustment, but they may be doing some filtering and implementing the post-filter feedback, which I highly recommend you don't mess with. The op-amps, likely being inside the global feedback network, may not actually effect the global gain of the amp so much as just the open loop gain, meaning you may not achieve the effect you are trying for by modifying the op-amp gain. Without a schematic, we might as well just start shorting out things with a screwdriver and see what effect we can achieve.
Because far more difficult and impractical ridiculous solutions are being considered over the obvious "buy a pre-amp", I could suggest you knock down a wall of your living room, extend the room by a good 30 feet or so, and place your speakers at the far end so they don't sound so loud. Or put cotton in your ears, or pillows against your speakers. If you don't want to buy a pre-amp, perhaps buy an inline attenuator/volume control and NOT destroy your nice amp?
Switching opamps brands/models is Fosi's idea of "adjusting the tone" 😉
Good point about PFFB, I think I'll give up removing opamps.
In AVS forum someone just posted a conversation with the maker.
I'll try to find out what they changed in the recent revision.
BTW, I was temp. using the XLR input (20dB) with a simple RCA to XLR cable.
This worked quite well, so I guess the TPA3255 also accepts non-balanced input.
I switched back to RCA because the XLR input is 4V and has much lower input impedance.
Good point about PFFB, I think I'll give up removing opamps.
In AVS forum someone just posted a conversation with the maker.
I'll try to find out what they changed in the recent revision.
BTW, I was temp. using the XLR input (20dB) with a simple RCA to XLR cable.
This worked quite well, so I guess the TPA3255 also accepts non-balanced input.
I switched back to RCA because the XLR input is 4V and has much lower input impedance.
The same Monacor line attenuator as I used before.
To get -10 dB, I switched to four Vishay dale resistors ( two for each channel ) 10K in series and 2K in parallell ( to earth ), soldered the resistors inside the amplifier at the RCA:s and the sound became much clearer , better than using Monacor.
Doing this you both get better sound and dont have to mess with the op amps. I would personally switch opamp 2 and 3 to opa1612 or opa1642 , I think those are better sounding than ne5532 .
Audiophonics is a good seller.
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Maybe just maybe that tube preamp of unknown brand/origin without any given specifications (why be specific in a specific area?) has way too high output level as tube stuff even today often has massive amounts of GAIN. GAIN that no one needs in 2025 but folks keep adding tube preamps with GAIN to power amplifiers that silently cry that they don't want to be overdriven. The audio variant of self cutting. Endorsed by YouTube audio specialists or influencers?!
Let's be specific to solve your specific issue:
What are the signal levels of your sources and what is the input sensitivity of that Fosi? Does the Fosi work with correct volume when connected to a normal (younger than 20 years) source with built in volume control? If the answer is yes it is a fools decision to change the Fosi. You then need a preamp that has less or even no gain. A buffer, signor! Possibly you only want source selection and volume control. Choose a nice relay based version and possibly an output buffer and it is solved. You married 2 incompatible devices and now the marriage is over. Finito, there were no winners in this marriage. Let's hope there are no children.
A way better marriage is to switch over to XLR/balanced pre/buffer/source selection/volume.
Let's be specific to solve your specific issue:
What are the signal levels of your sources and what is the input sensitivity of that Fosi? Does the Fosi work with correct volume when connected to a normal (younger than 20 years) source with built in volume control? If the answer is yes it is a fools decision to change the Fosi. You then need a preamp that has less or even no gain. A buffer, signor! Possibly you only want source selection and volume control. Choose a nice relay based version and possibly an output buffer and it is solved. You married 2 incompatible devices and now the marriage is over. Finito, there were no winners in this marriage. Let's hope there are no children.
A way better marriage is to switch over to XLR/balanced pre/buffer/source selection/volume.
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Well, that's the problem- We have no indication of =what= the source is, and why a volume control is not in the picture? (or why a pre-amp is not desired?)
Is this phono, CD, or other? I'm not sure anything was ever said about a tube amp or pre-amp.
Rotel75- can you enlighten us?
Is this phono, CD, or other? I'm not sure anything was ever said about a tube amp or pre-amp.
Rotel75- can you enlighten us?