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free advice thats worth every cent you paid

128.231.88.2

Posted by rodney on December 29, 2003 at 15:22:22

In Reply to: advice for vintage preamp w/phono section. posted by nigelbetts on December 29, 2003 at 14:35:47:

Hey,

Well there are allot of options out there. Many have piped in with their comments. Most of these would not fit into a high resolution system. (I infer this is the type of system you are running.) Here are a few suggestions:

(1) Dynaco PAS. This is a good, decent unit. Updating parts and redoing the power supply will result in a very good performer for little money. The phon stage of this unit is not the end all, but it is a rather good standard from which to measure. Lots of inputs (and you can rig some more). The problem here is the low output impedence that will not match well with all amps.

It is worth noting that the Conrad Johnson preamps are very similiar in design to the PAS. Some of these add a cathode follower on the output. This would make the preamp capable of matching amps with lower input impedences. Given your solid state amps, it may be worth looking at the CJ's.

A cheaper solution would be a Eico HF-85. I am not sure of the output impedence on this one, but there is an extra tube compared to the PAS. The preamp is also point to point wiring. No crappy circuit boards. This would allow you to do some mods such as taking out the tone controls and installing a cathode follower output. The problem is that once you do all this you are going to wish you had nicer sounding tubes than the 12AX7's and, unfortainately, the power transformer will not allow it.

(2) Bottlehead Phono and Line preamps. Lots of info on the Bottlehead board about these. The drawback here is that is that these definately look DIY without any "modern" style chasis. This means you probably will want to get a aftermarket cabinet (see Bottlehead site). However, this set up would allow you to play around with phono stages.

I personally have an Eico HF-85 sitting (in parts) on my bench. I am considering putting in a new power transformer and installing the Bottlehead Foreplay circuit in place of the stock circuit. (I have a modded Foreplay and like it much). Some problems exist such as the need for new potentiators of the right value and shaft length.

It is also worth noting that several other companies sell preamp kit. However, I have no experience with these.

(3) Well Known Vintage Preamps. Well there are lots of them. Most suck compared to modern components. There have been a number of DIY driven improvements to tube preamps, including active loading, better power supplies, and parallel feed outputs. My best recomendation here would be the Fisher 400C. It has several shortcomings, but a very sweet midrange which mates well with dryer sounding amps. This pre is sort of a pain to work on but... it does sound good. I personally sold mine, but I still run the 80C (a very similiar mono preamp) as part of a mono system. I doubt I will ever part with it as both the line and phono stages are very nice. Yet I would say that my modded PAS phono stage is better.

(4) Total DIY. Venture over to Tube DIY and ask around. There are lots of possibilities and many tested circuits out there.

Take care,

Rodney

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