Giving Magnepan another try

[JoeE SP9]

The 750 may be Adcom's best but I'd be surprised if you found it better than the SP9.

I've been told that in passive mode the Adcom is up there with the best. I've got a chance to get one cheap. The only replacement for my SP-9 would be a better ARC Maybe an SP-10 or 11.

[E-Stat]

I've been told that in passive mode the Adcom is up there with the best. I've got a chance to get one cheap. The only replacement for my SP-9 would be a better ARC Maybe an SP-10 or 11.

For high level sources, ever tried a set of attenuators instead? Don't get me wrong, I really like my SP-9MKIII - but its not perfect. For the CD source, I don't use it at all. My DIY attenuator box has higher resolution and better separation (see the Stereophile test) resulting in a wider soundstage. I stumbled upon that discovery years ago when I built an inexpensive attenuator box for the office system. Just for grins, I put it in the main system. I was floored when I heard the $18 Radio Shack attenuator box (at half the price of one ARC knob) easily better the SP-9 for the CD source. On the other hand, the 9 works great for vinyl where the gain is needed and the separation issue is largely limited by the cartridge anyway. I later built a higher quality unit using DACT stepped attenuators, JPS Labs wire and Cardas connectors in a Par-Metal aluminum case that looks like a Levinson JC-2. It means I have to change cables when switching sources, but I think that is well worth the effort.

Similarly, I don't use a line stage in the vintage garage system either. The Pioneer tuner, Bellari phono preamp and Manley DAC each have gain controls and drive the amp directly.

rw

[JoeE SP9]

For high level sources, ever tried a set of attenuators instead? Don't get me wrong, I really like my SP-9MKIII - but its not perfect. For the CD source, I don't use it at all. My DIY attenuator box has higher resolution and better separation (see the Stereophile test) resulting in a wider soundstage. I stumbled upon that discovery years ago when I built an inexpensive attenuator box for the office system. Just for grins, I put it in the main system. I was floored when I heard the $18 Radio Shack attenuator box (at half the price of one ARC knob) easily better the SP-9 for the CD source. On the other hand, the 9 works great for vinyl where the gain is needed and the separation issue is largely limited by the cartridge anyway. I later built a higher quality unit using DACT stepped attenuators, JPS Labs wire and Cardas connectors in a Par-Metal aluminum case that looks like a Levinson JC-2. It means I have to change cables when switching sources, but I think that is well worth the effort.

Similarly, I don't use a line stage in the vintage garage system either. The Pioneer tuner, Bellari phono preamp and Manley DAC each have gain controls and drive the amp directly.

rw

From time to time I've thought about building a passive attenuator using a Shallcross ladder attenuator. What has stopped me is that I use long cables (20Ft) from my preamp to my power amps. Spending close to $500 for a something only to find that it's unusable is something I'd rather not do. Does anyone have any input on long cables and passive attenuators? How about long cables and transformer attenuators? I hear some think transformer attenuators are better than switched.
However, I'm open to almost anything. The Par-Metal case sounds interesting. I checked the web site. My interest is piqued. Where can I get some really nice knobs? I would need some holes drilled. Does Par-Metal do that?
Maybe it's time to build my own ultimate passive preamp. My financial situation is loosening up and I'll shortly have a great deal more discretionary income than I've had recently. I'm a vinyl junkie. What funding I've had went to new vinyl. A few CD's managed to sneak in there also.
No! I'll not be going to Goodwins for the Apogee Mini Grands they have right now. I will be on the lookout for a pair of Studio Grands.

[E-Stat]

What has stopped me is that I use long cables (20Ft) from my preamp to my power amps. Spending close to $500 for a something only to find that it's unusable is something I'd rather not do.

Agreed. If you have basic soldering skills, you can make one for under twenty bucks. I can even provide detailed instructions since an inmate over at AA had asked me to do that years ago. Here's what it looks like:

Does anyone have any input on long cables and passive attenuators? How about long cables and transformer attenuators? I hear some think transformer attenuators are better than switched.

Total capacitance is the rub with attenuators which requires short and/or very low cap cables. I use 2 meter runs of JPS Labs Superconductor+ which has a total of 160uF. Twenty feet of Bluejeans Cable LC-1 only runs 244 uF. Using a DACT supplied spreadsheet calculator, there shouldn't be any audible HF rolloff with that.

The Par-Metal case sounds interesting. I checked the web site. My interest is piqued. Where can I get some really nice knobs? I would need some holes drilled. Does Par-Metal do that?

I used some ARC knobs. I'm sure Par-Metals would drill the holes for you, but it really wasn't a big deal. Here is the updated version:



rw

[JoeE SP9]

Thanks for the info E-Stat. I don't think there will be any problem with soldering. I applied the POOGE treatment to my Haflers years ago and my MK-III's have only the transformers in common with their namesakes. All the work was done by yours truly.

Do you have any experience with using transformers as attenuators?

[hermanv]

Some generic opinions:

Passive pre amps are very impedance sensitive, mine is driven by a Mark Levinson 360S. Mark Levinson claims an output impedance of 6 Ohms, so I designed my passive to average 3 KOhms instead of the usual 10K.

I also audition only low capacitance cables (currently running Cardas Golden Presence).

According to a very long discussion on the John Curl blowtorch DIY thread, a switched passive is much better than variable POT attenuator until you spend hundred$ for POTS.

The Placette gets good reviews, uses first class parts and with the remote allows the pre to power amp cable to be arbitrarily short.

I've never heard them, but transformer passives should do well with long cables. They have other issues making it all but impossible to make them inexpensive.

Maggies and other planar speakers seem to do best with very low amplifier source impedance (no built in dynamic damping in the driver cones?) So, either very high power tube or reasonable power solid state. Most solid state switching amps have high damping factors, maybe even higher than equivalent power conventional transistor amps. So planar bass will sound quite good with a competent switcher