[ginetto61]

Hi ! maybe i am wrong but usually headphone amps have a voltage gain going from 4-5 times to 10 and more.
I wonder if there is a way to take the voltage gain of an headphone amp down to 2 or 3 times without degrading its sound quality.
Because sometimes it happened to me to listen to an amp that i like a lot and i am thinking to use it to drive a power amp for speakers.
Advice are very welcome and appreciated.
Thanks a lot
KInd regards,
gino

 

[tomb]

You need the circuit diagram to locate the gain setting. With solid state amps, it's often a pair of resistors around an opamp. The ratio of those resistors sets the gain. They can be easily replaced for a different gain, or even wired with another pair and a switch to change the gain on the fly. You need to be careful, though, because some opamps or other circuitry may not be stable below a certain gain.

If you're using a tube amp, it usually requires a tube change, because the "amplification factor" of the tube sets the overall gain. The circuit may be such that the gain is not equal to the tube's amplification factor, but the tube still sets the range.

Bottom line, with all the possibilities, you need to know the circuit. If you can obtain an image of the schematic, you can post it here. There will be many who can point out how to change the gain, if the circuit allows it.

 

[ginetto61]

You need the circuit diagram to locate the gain setting. With solid state amps, it's often a pair of resistors around an opamp. The ratio of those resistors sets the gain. They can be easily replaced for a different gain, or even wired with another pair and a switch to change the gain on the fly. You need to be careful, though, because some opamps or other circuitry may not be stable below a certain gain.
If you're using a tube amp, it usually requires a tube change, because the "amplification factor" of the tube sets the overall gain. The circuit may be such that the gain is not equal to the tube's amplification factor, but the tube still sets the range.
Bottom line, with all the possibilities, you need to know the circuit. If you can obtain an image of the schematic, you can post it here. There will be many who can point out how to change the gain, if the circuit allows it

Hi ! thanks a lot for the very kind and valuable reply.
Actually i was thinking to some kind of combination of high quality passive resistors ,,, in order to have not to mess with the internals.
This could be the best way to preserve the sound i can hear from the headphones.
To elaborate a little my rationale ... imhe often the speakers used to test a rig are not very transparent so i could blame the preamp while instead are the speakers to blame.
With a high quality headphone everything is usually much more clear and evident. It is a very transparent transducer.
Not only ... if i hear really great sound from my headphones i can be sure that everything upstream (source and amplification) is very very good.
I see heapdhones as a formidable evaluation tool ... and headphone amps as possibly formidable line preamps. If they can driver properly HP they will not have the least issues with power amps.

 

[tomb]

Hi ! thanks a lot for the very kind and valuable reply.
Actually i was thinking to some kind of combination of high quality passive resistors ,,, in order to have not to mess with the internals.
This could be the best way to preserve the sound i can hear from the headphones.
To elaborate a little my rationale ... imhe often the speakers used to test a rig are not very transparent so i could blame the preamp while instead are the speakers to blame.
With a high quality headphone everything is usually much more clear and evident. It is a very transparent transducer.
Not only ... if i hear really great sound from my headphones i can be sure that everything upstream (source and amplification) is very very good.
I see heapdhones as a formidable evaluation tool ... and headphone amps as possibly formidable line preamps. If they can driver properly HP they will not have the least issues with power amps.

Actually, there are faults in this kind of reasoning, both with your idea of using "high quality passive resistors" and your comparison between headphones and speakers. The answer is the same for both: load impedance.

Speaker amps have circuitry designed to deliver optimum power at around 8 ohms (or 4 or 16 ohms, depending on design - even 2 ohms if it's in a car). Headphones typically vary between 32 and 300 ohms, with outliers at 16 and 600. If you apply resistors on the output of an amp, they need to be significant in comparison to the headphone load impedance, to have any noticeable affect in gain. When you do that, you are altering the output impedance of the amplifier and its corresponding damping factor. The result is that you have altered the frequency response of the headphone.

You can use input resistors. We recommended that on the Starving Student, for instance, because of the high inherent amplification factor of the tubes used. That simply throws the usable volume control range into a higher position on the pot. It doesn't really alter gain. Taken to extreme, it means less control range of the volume as well.

Do a bit of research around here where questions are asked about the best receivers to use for headphones, and you'll find that the worst simply apply a dropping resistor between the receiver circuitry and the headphone connection, resulting in altered frequency response of the headphone. The best receivers include separate circuitry altogether for the headphone connection.

Similarly, and as cause for the above, the circuit used for speaker amplification is optimized for a different load impedance and power goals. Usually - most things being equal - the best headphone listening is with an amplifier designed specifically for headphone loads, not speakers. Yes, you can have some crossover where speaker amps are used on headphones and headphone amps are used on speakers, but the systems are far from optimum. Headphone circuits are also designed for much more intricate detail response because power demands are not that great; speaker amps are usually more power focused, but again, the impedance mismatch causes all sorts of issues with headphones.

 

[ginetto61]

Actually, there are faults in this kind of reasoning, both with your idea of using "high quality passive resistors" and your comparison between headphones and speakers.
The answer is the same for both: load impedance.
Speaker amps have circuitry designed to deliver optimum power at around 8 ohms (or 4 or 16 ohms, depending on design - even 2 ohms if it's in a car).
Headphones typically vary between 32 and 300 ohms, with outliers at 16 and 600.
If you apply resistors on the output of an amp, they need to be significant in comparison to the headphone load impedance, to have any noticeable affect in gain.
When you do that, you are altering the output impedance of the amplifier and its corresponding damping factor. The result is that you have altered the frequency response of the headphone.
You can use input resistors. We recommended that on the Starving Student, for instance, because of the high inherent amplification factor of the tubes used. That simply throws the usable volume control range into a higher position on the pot. It doesn't really alter gain. Taken to extreme, it means less control range of the volume as well.
Do a bit of research around here where questions are asked about the best receivers to use for headphones, and you'll find that the worst simply apply a dropping resistor between the receiver circuitry and the headphone connection, resulting in altered frequency response of the headphone. The best receivers include separate circuitry altogether for the headphone connection.
Similarly, and as cause for the above, the circuit used for speaker amplification is optimized for a different load impedance and power goals. Usually - most things being equal - the best headphone listening is with an amplifier designed specifically for headphone loads, not speakers. Yes, you can have some crossover where speaker amps are used on headphones and headphone amps are used on speakers, but the systems are far from optimum. Headphone circuits are also designed for much more intricate detail response because power demands are not that great; speaker amps are usually more power focused, but again, the impedance mismatch causes all sorts of issues with headphones

maybe i have expressed myself badly ... i was thinking to use the HP amp as a line preamp to drive a power amp ...
Or maybe i should look instead at lowering the gain in the power amp ? ( last time i tried in a cheap Rotel ra 930ax i fried it badly ... and burnt my palm ... )
i understand the impedance issue. But if i realize a voltage divider with very good quality low value resistor ?
Usually power amps have input Z from 5K (the lowest i have had) up ...a little like putting a passive preamp in this way

headphone amp > passive preamp > power amp ... could it work ?

maybe modifying it and putting two rcas on the back ... could it work ?
as i said through HPs differences between amp are more evident than through speakers ... they act like a doctor's stethoscope
a very revealing tool indeed and i would like to take profit of this
If an amp sounds very good through HPs it must sound very good when asked to drive a power amp