[replytoken]

Quote:

Originally Posted by profsbg Are the problems cited above that there was not enough low end control in preamp gain , or that at even at low end of preamp gain still had noise floor, or both? I would think if preamp gain could be reduced to unity or few db then well-designed tube preamp would not induce noise floor ( like a tube buffer, which is then used with passive attenuators and high gain amp).

I am not an engineer, but I'll take a stab at an explanation. While the problems can vary in each instance, a common one is that the volume control on a tube preamp comes before the tube output. Thus, the volume control regulates the source signal, but not the output. If the design is not quiet, then all of that noise from the output section makes it way into the power amp, regardless of gain or volume control (i.e. a high noise floor). There are many threads on Audio Asylum that describe this type of problem as well as others (search for "hiss" and "hum"). The typical solution is to use attenuators to raise the S/N ratio. Some say this is effective, and other say there is a loss in the sound quality. There are good reviews of Rothwell and Endler Attenuators that can give you an idea of how they impact the sound. I hope this has been helpful.

 

[sacd lover]

Quote:

Originally Posted by drarthurwells The Woo 3 has great tone body textural resolution, magical tonal quality, with a smooth and sweet sound in a tube headphone/preamp - a SET OTL design that some say beats any Singlepower of twice its price. 3D imaging (a must for me) with a tone focused clearly in precise spatial location surrounded by air, is a deficit - tones are soft edged and tend to blur together. Most people don't mind this. Have never used it as a preamp however.

Who is that some Art? You always make these vague unsubstantiated claims.

I owned the Woo 3 and the $799 SLAM ppx3 is well worth the higher price IMO; no contest. As a headamp the Woo hummmed and as a preamp the Woo was noisy, and like every other tube preamp I have tried, has to much gain. In fact, I cant think of a Chinese headamp or dac I have tried that doesnt have a high noise floor .... and thats based on personal experience not hearsay.

The best headamp/ preamp combination I have tried is the Headamp GS-1. The GS-1 has a nice musical and full bodied sound, excellent dimensionality for a SS unit, very good resolution without any etch or grain, superior dynamics, superior bass response .... and its dead quiet. Furthermore, the units has a gain switch thats extremely effective at providing a lower gain that mates with amps that require little drive for full output .... which is most amps these days. I have used the Woo 3, Eddie Current HD300, Singlepower ppx3/mpx3 and all of them had way to much gain to use as a preamp with my power amp.

The recommendation for the Portal Panache from Steve M324 is another good choice IMO and covers all the bases ...... offering preamp, amp and headamp duties.

 

[profsbg]

While the problems can vary in each instance, a common one is that the volume control on a tube preamp comes before the tube output. Thus, the volume control regulates the source signal, but not the output. If the design is not quiet, then all of that noise from the output section makes it way into the power amp, regardless of gain or volume control (i.e. a high noise floor). ...The typical solution is to use attenuators to raise the S/N ratio. Some say this is effective, and other say there is a loss in the sound quality.

So if I understand you, the preamp gain needs to be increased to increase SNR, and then attenuated to deal with sensitivity. I wonder if the SNR at unity gain is typically specified for these preamps, and also what SNR corresponds to low/acceptable noise floor. This would be part of preamp/amp matching I guess to go along with impedance and sensitivity, neither of which refer directly to the noise level. Tube preamps seem to be widely used with the tripath and gainclone variety amps, some new models are even coming out with tube preamp and amp on same chassis. Whether preamp is seperate or onboard, I would think the attenuation would use a lumped network with these amps, usually a pot or stepped attenuator for flexability and to keep the cost down. Anyway that is what I am going to try with the charlize/mpx3.

By the way, is this an issue more related to tube preamps in general with high gain (current, solid-state) amps, or more specific to tube headphone amps with preamp outs? sacd lover mentioned a number of headphone amps with too much gain, so I was wondering

 

[mojorisin676]

Mapletree Audio Ear++III....

 

[Jahn]

Quote:

Originally Posted by jcn3 but i'm lucky enough to not have the amp and speakers to constrain me at this point. anyone out there using a headphone amp and pre-amp as the same device. i know the melos sha owners could be doing that . . thanks, jim

that's what i'm doing, and the SHA-Gold works like a charm in both capacities - plus being a preamp for my electrostatic setup as well.

 

[gpalmer]

Another vote for the GS-1. It's a truly excellant preamp with the gain of 1... I use mine with a set of powered monitors and the sound is fantastic for the price.

 

[replytoken]

Quote:

Originally Posted by replytoken By the way, is this an issue more related to tube preamps in general with high gain (current, solid-state) amps, or more specific to tube headphone amps with preamp outs? sacd lover mentioned a number of headphone amps with too much gain, so I was wondering

I cannot really say. I know that somebody on AA was having a problem with a VTL preamp, and I have heard of stories here about tube units that can do both (preamp and headphone amp). I am guessing it is more design dependent than use specific. It would be great if somebody who has some knowledge of tube amp designs could fill in the gaps. Inquiring minds want to know!

 

[Ferbose]

PreSonus Central Station is a reference quality pre-amp in the pro-audio market. It uses microchip-controlled mechanical realys and a network of fixed value resistors to acheive passive attenuation. To my knowledge, this is probably the most optimal way to build a passive preamp. More than a half dozen of pro-auio magazine reviews all say it sounds totally transparent, and I agree with that.

It also has a very nice headphone amp section, about as good as Hornet. The sound is pretty warm and relaxed for an SS amp. It is powerful enough to drive even K1000, a combination I listen to a lot nowadays. Its DAC section is also suprisingly good.

Read more of my impressions here: http://www6.head-fi.org/forums/showthread.php?t=155336