olds1959special
Senior Member
I may order a cheap passive volume control that I'm going to try in between my dac and power amps. Will it sound better than my tube pre amp?
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is a passive pre amp better than a tube pre amp?
- Thread starter olds1959special
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JayGilb
Major Contributor
Depending on the design quality, it should have less distortion than your tube preamp.
There are Pros and Cons:-
A passive pre-amp has no gain and can only attenuate. This may be a good thing if your source voltage is adequate to fully load the power amp, as it avoids the issue of excessive gain that means the volume control all works at the bottom
A passive pre-amp has a variable and quite high output impedance that limits the length of cable that can be used before the higher frequencies are attenuated. In practice, this may not be much of a limitation, as using decent low capacity cable like RG59 or RG6, 5m or more can be used without affecting audio frequencies.
A tube pre-amp may also have a high output impedance, as it depends on whether the output comes from a cathode follower, which can be acceptably low, or from the final tube anode, where it will be several kohms, and therefore not a lot less than a passive pot.
A passive pre-amp generates no noise or distortion (other than thermal noise) whereas a tube pre-amp will have higher levels of both. Nevertheless, a decent tube pre-amp will be acceptably low on both with the possible exception of a MC phono input, although usually transformers are used for this reason.
I've used passive pre-amps a lot, as they are very easy to make, tube pre-amps just seem to me to be rather pointless. If they are well designed, then they won't sound any better (or worse) than a passive or SS active, and if they aren't well designed and do sound different, (it won't be better!) why would one want to use one?
S.
A passive pre-amp has no gain and can only attenuate. This may be a good thing if your source voltage is adequate to fully load the power amp, as it avoids the issue of excessive gain that means the volume control all works at the bottom
A passive pre-amp has a variable and quite high output impedance that limits the length of cable that can be used before the higher frequencies are attenuated. In practice, this may not be much of a limitation, as using decent low capacity cable like RG59 or RG6, 5m or more can be used without affecting audio frequencies.
A tube pre-amp may also have a high output impedance, as it depends on whether the output comes from a cathode follower, which can be acceptably low, or from the final tube anode, where it will be several kohms, and therefore not a lot less than a passive pot.
A passive pre-amp generates no noise or distortion (other than thermal noise) whereas a tube pre-amp will have higher levels of both. Nevertheless, a decent tube pre-amp will be acceptably low on both with the possible exception of a MC phono input, although usually transformers are used for this reason.
I've used passive pre-amps a lot, as they are very easy to make, tube pre-amps just seem to me to be rather pointless. If they are well designed, then they won't sound any better (or worse) than a passive or SS active, and if they aren't well designed and do sound different, (it won't be better!) why would one want to use one?
S.
I would say in your case with an AI tube preamp, probably not. A lot of distortion from a preamp like that, which will most likely "sound better".
Your query is diffuse and impossible to really answer.
OP
olds1959special
Senior Member
- Thread Starter
- #5
I can try a cheap volume knob and see, but I assume the tubes are fine for now, even with the slight hum/noise and the distortion.
A "passive preamp" will have less hum, noise, distortion, and gain. (Relative to your AI preamp, way less gain.) 
Whether that will "sound better" or not.....who knows.
If there is no requirement for phono, I would have set that preamp aside a long time ago. The AI preamps have horrible usability characteristics.
Whether that will "sound better" or not.....who knows.
If there is no requirement for phono, I would have set that preamp aside a long time ago. The AI preamps have horrible usability characteristics.
I have several tube preamps, and none of them are noisy. Make sure the cable routing and where you place your tube pre is not the cause of the noise. 90% of the time NIOSE is poor cable routing, and one of the best reasons to use compliant XLT cabling and equipment if you can.
I'm using an inexpensive 69.00 usd tube headphone preamp (it has tone control) on my laptop with a 59.00 class D 50X2/100X1 power amp into 95% + efficient 8-ohm speakers, and powering a small passive 10" sub. ZERO noise. It's all RCA cabling too. PS cable can't touch, and all the cabling is at least 1/2 apart. All the RCAs came from the Parts Express discount. They are copper with SS terminal ends. The speaker cable is # 12 copper zip cord with poly/vinyl insulation. It's routed to stay away from any PC, IC, or PS.
Nothing fancy, but they are routed carefully.
Regards
A suggestion @olds1959special . Try a good solid state pre amp like Fosi Audio P4 vs your tube pre amp.
But on the other hand if your tube pre amp is well constructed it should not audibly color the sound/signal. Then it is a rather pointless exercise, listening comparison to make. Why listen for something that you can't hear?
Fosi Audio P4 has tone controls and a remote control if those features appeal to you?
audiosciencereview.com
But on the other hand if your tube pre amp is well constructed it should not audibly color the sound/signal. Then it is a rather pointless exercise, listening comparison to make. Why listen for something that you can't hear?
Fosi Audio P4 has tone controls and a remote control if those features appeal to you?
Fosi Audio P4 Preamplifier Review
This is a review and detailed measurements of the Fosi Audio P4 budget RCA preamp. It was sent to me by the company and as of this writing, is on sale for US $80. The look is attractive enough for the class. A momentary switch turns on the unit and cycles through inputs, with a reassuring...
audiosciencereview.com
Of course a passive attenuator is better than almost any amplifier. But it is necessary to consider the DAC output impedance and the amplifer input impedance as well any capacitance from the cable(s). So some technical knowledge is nessesary. If it is a high qualtiy potentiometer like ALPS or switched resistors with good reliable contacts the sound shoud be very OK. One of the best way would be resistors switched by relais. Such a scheme can also provide constant input and output resistance which is also used in professional measurement and signalgenerator instruments. Of course not really cheap.
Passive attenuator with a 10 kOhm potentiometer would be fine for the Kenwood Trio L-05M with 50 kOhm input resistance. For this the low pass limit frequency would be around 30 kHz (- 3 dB) when a RCA cable with 10 meter length would be used. So for 1 m the limit is 10x which is enough not to dim the highs.
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The issue(s) for passive attenuation will be (can be) insertion loss and/or variable impedance as a function of level of attenuation. A constant impedance attenuator. Cheap probably isn't a value-add for a passive attenuator.
EDIT: @SSS makes some good points in their earlier posts. A good switched resistor ladder attenuator or - ahem - a tapped transformer or autoformer (yeah, I can hear the ASR-ites gasping and clutching their metaphorical pearls
) is probably well worthy of consideration. Better than an active gain stage (vacuum tube or solid state)? Possibly, especially if the gain/drive or impedance matching (buffering) of an active "preamp" stage is not needed.
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FWIW, I used a passive attenuator (Dave Slagle/Intact Audio tapped transformer) and source selector for many years, but have switched to an active preamp.
This being said, my case is way out of the norm for ASR denizens: a very simple single-ended vacuum tube preamp that benefits from the additional drive provided by the active preamp. Thanks to an ASR benefactor (who'll remain nameless, although I think I've ratted him out in other posts at ASR) and a bit of bartering (or is that quid pro quo?)
there's a very capable active preamp here now that I am very pleased with.
This being said, my case is way out of the norm for ASR denizens: a very simple single-ended vacuum tube preamp that benefits from the additional drive provided by the active preamp. Thanks to an ASR benefactor (who'll remain nameless, although I think I've ratted him out in other posts at ASR
) and a bit of bartering (or is that quid pro quo?) there's a very capable active preamp here now that I am very pleased with.
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The best option would be to get a DAC with a volume control and get rid of the preamp.
OP
olds1959special
Senior Member
OP
olds1959special
Senior Member
Except for maybe a bit of HF rolloff if driving a capacitive load, a passive preamp, which is just a volume control pot or stepped resistive attenuator and input switching facilities, cannot introduce any distortion. It takes an active device to do that. You could get a bit of hiss, likely inaudible, from the intrinsic noise that resistors generate. Best practice is to use as low a resistance as is practical in the circuit to minimize that small amount of noise.
OP
olds1959special
Senior Member
- Thread Starter
- #20
using the tube pre instead of a passive volume control seems to fix my DAC left channel ground loop buzz.
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