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New to tubes. Preamp question

formuladale

formuladale

Active Member
I'm new to tubes. My question is when using a solid state preamp with solid state amp I have double the volume gain as opposed to using my tube preamp with solid state amp. Also the solid state amp runs warmer with the tube preamp. But I'm getting only half the gain from it. Is this normal ? Thanks Dale
 
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The volume gain might just be a difference in output voltage. The tube preamp may not make as much as the SS amp does. Its also possible that the tube preamp can't drive an SS amp. Many were not intended to drive into the lower impedance input that a lot of solid state amps run. Typical tube amps are 470k or so, a lot of SS amps are under 100k.

The amplifier should not run warmer though. What sort of preamp are you using? Some will put some DC voltage out of the jacks, and some solid state amps are direct coupled and can't deal with that. It will end up passing DC voltage all the way through the speakers, but it makes heat in the meantime. A voltmeter measured across the preamp's output jacks would tell you the story there.

A stock Dynaco PAS for example doesn't drive low impedance very well, and if the tone controls are bypassed incorrectly it puts out some DC voltage as well.
 
Okay what kind of voltage should I be looking for and can this be read off the rca jacks. A little about the preamp. I built this from a kit the sp14 from tubes 4 hifi. I did put in larger Mundorf 1 uf output caps in. Knowing I would be using a solid state amp. You mentioned right and left gains when I turn them up all the way I'm pretty close in volume level so that's where my volume went. For now Im using the amp from my rotel 1603 receiver. I have an usher 1.5 amplifier on back order should be here in a few weeks. Never built anything before this I actually had a lot of fun putting it together. Seems to be working. Regards Dale input impedence on usher amp specs say 47k. So I'm hoping it's a good match
 
Okay what kind of voltage should I be looking for and can this be read off the rca jacks. A little about the preamp. I built this from a kit the sp14 from tubes 4 hifi. I did put in larger Mundorf 1 uf output caps in. Knowing I would be using a solid state amp. You mentioned right and left gains when I turn them up all the way I'm pretty close in volume level so that's where my volume went. For now Im using the amp from my rotel 1603 receiver. I have an usher 1.5 amplifier on back order should be here in a few weeks. Never built anything before this I actually had a lot of fun putting it together. Seems to be working. Regards Dale input impedence on usher amp specs say 47k. So I'm hoping it's a good match
 
There are two salient specifications to be aware of when considering the suitability of your amp/preamp combination: input sensitivity of the amp and the input impedance of the amp. Both these specifications are normally provided by the amp manufacturer. Input sensitivity is the input voltage that drives the amps to clipping, e.g. full output and input impedance is the load that the amp puts on the preamp. Check both specs. with the manufacturer of the amp.

If the input sensitivity is less than 1VRMS then you don't even need a preamp; a simply volume control on the amp would be sufficient to give you 6dB of headroom. The amount of gain in the preamp is only relevant in that in general the more gain it has, the more noise and distortion will be present in the signal, because there will be more stages for the signal to pass through and each gain stage adds noise and distortion, even if it is small. Here's the point: there are 2Vrms as standard output from a CD player and if your amp can be driven to full output by 1Vrms you can see that any more gain in the signal chain will be a complete waste and will be attenuated by the volume control. So if you have 2V coming from the CD player and the preamp has a gain of 10, you now have the potential 20V to be reduced by the volume control to whatever the input needs of the amp. In the example above that would be in the range of millivolts for typical listening levels. The point is that your preamp should be as simple as possible with the fewest stages possible or all the gain will be wasted in the volume control as added noise.
 
formuladale said:
Okay what kind of voltage should I be looking for and can this be read off the rca jacks
Click to expand...

Multimeter connected to the RCA output jacks on the preamp. You want to see 0 volts DC.

If it has output caps, it will probably be zero. Also taking a guess by the number of tubes, its probably got a cathode follower rig which should make for low output impedance. I don't see actual specs on the page though, but it might be in the manual.
 
Palustris said:
There are two salient specifications to be aware of when considering the suitability of your amp/preamp combination: input sensitivity of the amp and the input impedance of the amp. Both these specifications are normally provided by the amp manufacturer. Input sensitivity is the input voltage that drives the amps to clipping, e.g. full output and input impedance is the load that the amp puts on the preamp. Check both specs. with the manufacturer of the amp.

If the input sensitivity is less than 1VRMS then you don't even need a preamp; a simply volume control on the amp would be sufficient to give you 6dB of headroom. The amount of gain in the preamp is only relevant in that in general the more gain it has, the more noise and distortion will be present in the signal, because there will be more stages for the signal to pass through and each gain stage adds noise and distortion, even if it is small. Here's the point: there are 2Vrms as standard output from a CD player and if your amp can be driven to full output by 1Vrms you can see that any more gain in the signal chain will be a complete waste and will be attenuated by the volume control. So if you have 2V coming from the CD player and the preamp has a gain of 10, you now have the potential 20V to be reduced by the volume control to whatever the input needs of the amp. In the example above that would be in the range of millivolts for typical listening levels. The point is that your preamp should be as simple as possible with the fewest stages possible or all the gain will be wasted in the volume control as added noise.
Click to expand...
The specs on the usher 1.5 amp says input sensitivity is 1.6 V and input impedance 47 K. Still not sure if this is a good match with my Tube Preamp.
 
gadget73 said:
Multimeter connected to the RCA output jacks on the preamp. You want to see 0 volts DC.

If it has output caps, it will probably be zero. Also taking a guess by the number of tubes, its probably got a cathode follower rig which should make for low output impedance. I don't see actual specs on the page though, but it might be in the manual.
Click to expand...
Yes 0 volts DC. It does have output caps. Received no specs with kit. Just instructions to build it.
 
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