Endler stepped attenuator w/Cary active preamp

I have an idea for fixing a little problem, but don't know if it makes any sense (I have no background in electronics).

I had been running a Modwright Transporter directly w/balanced outputs to a big SS power amp w/no active pre. W/o attenuation, the volume was too loud at even the lowest levels and I could hear some hiss during quiet sections in music. I solved both problems w/Endler stepped attenuators. They almost completely eliminated the hiss and yet seemed to be transparent.

I just upgraded my system by adding a Cary SLP-05 active preamp. Huge improvment in dynamics, detail, soundstage, image weight, etc. Dramatic improvement, actually.

One downside, I can hear a hiss during quiet passages. Not super bad, but loud enough to notice. I tried using the built in attenuators (input control) on the CAry. It helped but did not completely fix the problem.

Anyway, because the Endlers fixed the hiss problem before, I thought I would try using them in conjunction w/the active pre. I will just give it a try, but wanted to know if that made sense? What problems should I look out for? Is this a common set-up? Etc. Any input will be much apprefciated. Thanks.
It sounds like the problem is the Transporter.

If you plan to keep it I guess you either have to live with the hiss or give the attenuators a try, although they are only a band-aid.

My SLP-05 is dead quiet, and I agree that it's a great piece.

Good luck.
Hmmmmmmm, could it be just a bad tube in the TP?

Any downside to the attenuator even if just a band-aid?
If the hiss is constant it is in your pre-amp. If it fluctuates when you use the volume control then it is in the TP. If it is in the pre-amp using an inline attenuator, either a constant fixed value or one which can be used as a stand alone VC will reduce the hiss below audibility, but depending on your expectations and listening skills you may note some minor degredation, especially if you have to use an addition set of IC's. I would prefer a fixed value resistor (like a Rothwell, but not necessarily one).

If the hiss changes with volume it is likely because of a noisy tube(s) in the TP or you may well have a noise floor issue. If the noise is the same in both channels it is likely a noise floor issue. You might have to plug in some new low noise tubes to ascertain this unless other owners confirm the noise floor issue.

And, where do I put the attenuator? B/w TP and pre or b/w pre and power?
Oh, and the Endlers do not require another set of ics. It plugs into the ic on one end and into an input on the other.
You would put the Endlers between your pre-amp and your amps. I suspect you will discover that the noise still exists when you do.

If you are concerned that the Cary might be the source of the hiss, simply turn your source off leaving the volume control in the same position that revealed the hiss. Once again, if the hiss goes away then you know it is not being introduced by the Cary.

Topographically speaking, the pre-amp amplifying stage is always at full power. When you use the volume control all you are doing is attenuating the incoming signal from the source before it gets to the pre-amp amplifying stage.
Thanks. If the Endlers fixed the problem before (albeit w/o the pre), why don't you think it will work now (w/ the pre)?

I actually suspect the TP is the problem as the problem was present when used w/o either attenuators or a pre. If so, wouldn't I want the attenuation before the pre?

I really do ne3ed help with this.Thanks much.
It is possible that the level of hiss that you are hearing, or not hearing, in the various configurations, has something to do with impedence matching between the sources and the amps, as well as the IC's used to connect them, when using either the Cary or the Endlers. I don't know. Passive pre-amps are problematic and improperly used could easily result in a roll off of frequency extremes. which you have interperted as a reduction of hiss.

What I do feel confident about though is that the TP is the source of the hiss and reducing the hiss at the source, assuming it is not inherrent in the design, is the best, if not only, way to skin this kitty.

The Endlers placed between the TP and the Cary will only reduce the overall output of the TP - it will not just reduce the hiss level and leave the rest of the signal intact (other than perhaps introduce some impedence issues referred to above). When you crank up the volume to the same levels at which you heard the hiss before it should still be there.

But you can't hurt anything by trying both locations for the Endlers just to satisfy your curiousity if not solve your problem. And if it does 'solve your problem', used in either location, and doesn't introduce any degredation to your ears, then great.
OK. I have contacted Dan Wright at Modwright about this and he has always been very responsive.

One other factor-I am using brand new ics w/no break in (Anti-ICs to be exact). If the ics can be a factor, is it possible that the lack of break in is a factor?

Try moving your IC's if they are close to a power cord.
What tubes are in the transport?
The worst culprits evidently are not giving you any difficulty. That would be the 6SN7s in the Cary preamp gain stages. I assume you have not rolled them. It is almost always a compromise between a very low moise tube and a better sounding but with some noise tube . That is if you accept the notion that old stock tubes sound much better in many ways. However they are supremely difficult to get noise free. If you have Old tubes in there already that are silent consider youself lucky.
The transport tubes it appears have been used a fair amount of time. Even if they were new production, they are now used and prone to old tube noise. Why not switch them out?

If you are using a common tube, that is in current production it might be a cheap and quick fix. I assume they are the 9 pin preamp double triode type tubes. Once tested for just working or not. The remaining working tubes are mainly quiet right off the shelf. Even yet they are not certainly quiet- not all- not ever I have been told by some dealers of new production. Read the RAM tube site.
I would get them pre tested for matching and noise. Several dealers offer noise testing but very few compared with the simple gain match which is almost a universal service.
Noise testing service is included in the price of Jim McShane Citation amp and tubes. His site is on the het or go over on Audio Asylum Tubes. Upscale Electronics Kevin Deal, Brente Jesse at audiotubes .net do it. .
I can attest for the names I mention like Jim Sautter here on the Gon. He goes almost overboard testing and I have bought from him. Just ask for what you want. He is verr honest, meticulous and very very fair. The only question is what he would have available. He specializes in old stock tubes and only on occasion has a current production lot to work from. His prices for truly tested selected older tubes are, as I said very fair and near what you might pay anyway.

I have no vested interest in any of the tube dealers at all just a customer.