Your Bryston 4b has 30 db. of gain and your PV10 has 80 db. of total gain when you factor in the 48.5 db. of the phono stage. The amp/preamp gain interface is out of whack. Mismatches of preamp/amp gain are common, but this one is pretty extreme. Your phono cartridge also has very high output. The easiest way to deal with it is to use a set of the Rothmann 10 db. attenuators. I hear absolutely no sonic compromise using them. You could also have the preamp modified, at a much greater cost. If you carefully selected a lower voltage output cartridge, you could use more of the volume control. It probably would not require so drastic a gain reduction as going to a low output moving coil. Are you content with the volume control's range when using your cd player? |
If you are looking for consensus, I agree with Photon46.
I think the Rothwells are an elegant solution for the money involved and that most folks with ordinary 'high fi' systems and are mere mortals here will will not detect their presence. If you have a highly resolved, synergistic system, properly set up, and you have a well trained ear, you could probably 'hear' them and anything else in the chain as well, but I think for most folks not so involved, these easy to use, cheap and reversable solution can't be beat.
BTW, be careful with the thought about changing the cartridge to a low output MC. You would in all likelyhood be posting thereafter about the low level hiss coming from your phono stage - and need to find the lowest low noise tubes to make it quiet again.
And, if we are wrong, you've only spent $70. There are other ways including the lowering of the phono stage gain or the pre-amp output gain, or even going to a medium output cartridge but the possibilities of Rothwell solving your problem without surgery is quite high. |
Find out what the 'taper' of the pot IS.
Not all provide the same attenuation for the same amount of rotation.
The 2 types are 'linear' and 'logrithmic'(sp). Both start and end at the same place....say 10Kaohms to effectively 0, but have different ways of getting there.
You may get more resolution by going from a linear taper to log taper. |
Magfan...All volume control pots these days are log taper. Linear would give ridiculous results. Actually, Log taper is a poor substitute for Audio taper which was used in the good old days. Evidently the low demand for Audio taper pots caused manufacturers to discontinue them. |
Ouch! 80db of gain in the preamp, with a 6.5mv cartridge. I wonder if 10db attenuators will be enough to get the volume control into the optimal part of its range, where resolution is good, and perhaps even into the part of its range over which it can maintain channel balance accurately as volume is changed.
80db means a voltage gain of 10,000, so that if the cartridge is putting out 6.5mv (at 5cm/sec@1kHz, if I remember correctly what the conditions are at which cartridge outputs are normally specified), the preamp output with the volume control at max would be 65 volts!
Maybe 20db attenuation would be more appropriate. And I'd also suggest checking the specs on the preamp, particularly its maximum rated output voltage, to be sure it is really suitable for such a high output cartridge. My concern would be that with the volume control set say in the middle of its range, at 12 o'clock, that high amplitude signals would get clipped before they even reach the attenuators.
Regards,
-- Al |
Thanks you all for your input. It looks like the consensus is to try the attenuators, for under $100- it is reasonable.
everything sounds great but I can't help but think it will sound that much better if I can get into the sweet spot of the preamp rather than playing around at the bottom of the gain control.
Photon46- what would be an ideal amp/preamp gain be? Are you saying that they should be more closely matched?
The gain thru the digital front end is the same as thru the analog
Newbee- I will certainly wait on the new cartridge.
Al- Ill start with the 10db attenuators and go from there.
Again,
Thank you all |
Photon46- what would be an ideal amp/preamp gain be? Are you saying that they should be more closely matched? I think he's just saying that the overall system gain of 110db in phono mode is simply too high, particularly for a high output cartridge such as you have. What is meant by a better match is that a very high gain preamp should be mated with a relatively low gain power amp, or vice versa, so that the overall gain doesn't become too high in relation to the cartridge output. Hopefully the attenuators will accomplish that, although as I said it is conceivable to me that 10db will not be enough attenuation to be satisfactory. And it is conceivable to me that you will still be limited in how far you can turn up the volume control by how much voltage the output stage of the preamp can swing, which would not be helped by the attenuators because the attenuators would be connected "after" that point (further downstream, so to speak). I'm not familiar with that preamp, but the spec on output voltage range might give some feel for that. Regards, -- Al |
I looked at the specs at the CJ site, and output voltage range is not specified. Oh, well. But it's interesting to note that in the PV10A they reduced the overall gain by 13.5db, relative to the PV10.
Regards,
-- Al |
Of course the real problem is too much gain in the phono preamp stage. Attenuation should be done there, not at the output. Some preamps can have their gain easily adjusted with a jumper. If your preamp does not have jumper provision for gain adjustment it can probably be accomplished with a resistor change in the circuitry. Contact CJ. |
If the problem is too much gain, the solution is removing excess gain, not attenuation. Fix the problem, don't try to hide it.
dave |
But it's interesting to note that in the PV10A they reduced the overall gain by 13.5db, relative to the PV10. The 10A is linestage only, could that be why? Fix the problem, don't try to hide it. Any easy suggestions on how to accomplish this? I take it that changing tubes is not a solution? Thanks again z |
The 10A is linestage only, could that be why?/ According to what I read at their site, the 10AL is linestage only, while the 10A includes a phono stage. Although it was in the line stage of the 10A that the gain reduction was made; apparently an identical phono stage was used on both the 10 and 10A. I take it that changing tubes is not a solution? I don't think so. A good circuit design is designed to be as independent as possible of variations in tube characteristics, within the range of variation that can be expected for the specified tube type. Although in a no-feedback design such as this there will probably be somewhat more variability as a function of tube characteristics than with a design that uses a lot of feedback. But I still don't think that is the way to approach the problem. Regards, -- Al |
I wanted to add the following sentence at the end of my previous post, but we don't seem to have an edit function on this forum (someone please let me know if there is a way of editing one's own posts):
A tube set for a preamp that would result in a 10 or 20db reduction in gain from the design's specifications is probably defective. |
The only thing I can suggest is to get a good feel for the proper gain structure you need and make system changes accordingly. From your last post you seem to be using something else for Phono, is this the case? Right now it seems you are adding about 30dB of gain with your pre only to attenuate around 50dB.
dave |
From your last post you seem to be using something else for Phono, is this the case? I am using the phono stage of the CJpv10 Gain: phono stage 48.5dB Gain: Line stage 31.5dB Line stage 84 dB below 2.5 volt output |
can you use the phono stage without using the linestage? If so, you could get rid of 31dB of gain right there.
dave |
