WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
I own one as well. I have no schematic, but in close examination of the preamp I have determined it to be a design based on the Marantz 7. The audio circuit uses a slight change at the front end of the phono stage and it uses parallel cathode followers at the output of the line stage. Of course it uses vastly superior parts. The power supply has three separately regulates B+ stages (each with slightly higher voltage than the Marantz 7) and two separate regulated filament stages. IMO, it is the finest Marantz 7 ever built for the consumer. The second best Marantz 7 is the VTL Ultimate. Both are far better than the original Marantz 7. I've owned all three.
I too had noticed the VTL Ultimate was a virtual direct copy of the Marantz 7 and I was always surprised nobody else seemed to have noticed. Given your interest in the Marantz circuit, I am curious whether you ever examined the Hovland preamp to see how similar it was to the Marantz. From photos I looked at, it appeared the phono stage at least was a nearly exact copy as well.
Salectric, I see you that you hail from Maryland? I grew up in Maryland - about 23 mile straight North of Baltimore. Miss it.
I have not really looked closely at the Hovland. I'll google for hi-res photos or even better, a schematic - though I doubt one is available. The PAC and VTL also differ from the Marantz in some slight (pretty much insignificant) changes in plate resistor values (the B+ voltage is a little different as I stated above, well), but the main difference is that the PAC is so fully regulated and while the VTL has no regulation on the B+, it is a true dual-mono with one power transformer for each channel and a very stiff supply of capacitance.
SiCo, the Carolinas are nice too! I have never seen a schematic for the Hovland so I doubt you will find one online. The company principals seem to have kept that a closely guarded secret, perhaps because there wasn't much new to the design. The whole matter is really just of academic curiosity for me since I haven't used 12AX7 based phono or line stages for a long time, but I was impressed with the sound of a Hovland preamp when I listened to it a long time ago in a hifi store while comparing MC cartridges.
Salectric, I find that it is all about the synergy of gear and listening room. I'm a tube guy all the way. Just more fun for me. I've done all types of phono preamps and understand why so many of us are in either one "camp" or another. The 417, the 6GK5, the 6DJ8, the 12AX7, the 6SL7, the 7025, the 5751, the 6CW4, etc., one can make a great preamp out of each one (despite what the other camp says). Self bias, fixed bias, regulated, unregulated, film and foil, metalized, cascade, transformer coupled, parrafeed, cathode follower, white follower, fet input, etc., etc., any of these can make a great preamp. All of them can also contribute to junk. I still enjoy the VTL, PAC, Paragon 12, Paragon 12A, Eroica Phoenix 70, Counterpoint SA-5.1,, SA-2, SA-9jr, Melos GK1+1. I've also owned in the past, several C-J preamps, Theta tube pre, NYAL Minuet in-A, Marantz 7, Luxman CL-35iii, HH Scott 130, HK Citation I, Eico HF-85, and many other tube models that aren't coming straight to mind. I've built a few of my own - some using old tubes like the 71a, 01A, WE 101F... I've also had the pleasure (well most of the time) to work on many other vintage types that are deemed exotic collector items... too many to mention. I used to do a lot of work for a collector who owned a collection that must have been worth a million dollars, but he had to sell quickly - everything in one sale for $250,000, about a dozen years ago, or so. Anyway, fun hobby - love the gear and enjoy the music. That's what it is about.
Very well stated SiCo. I could have used nearly the same words myself. My phono preamp is DIY and uses a D3a (in triode) with passive RC eq feeding a 56 or 27. CCS on the 56 plate and cap coupled output. Totally unregulated B+ and heater supplies. I tried regulators and preferred my CLCLCRC filters. All BG WKZ. V-Cap TFTF and CuTF couplers. I have been experimenting with this basic platform for nearly 10 years so it's quite well dialed in by now.
I know what you mean about the 27. It has a very nice clean sound. In fact, I have a nice pair of National Union 27 tubes, probably my favorite version, in my phono right now. I alternate between them and Cunningham 56's. Each sounds good but in different ways.
For many years before trying the 27/56 in the phono, I used a 5687. For my system that makes a super-quiet phono stage but the 56 and especially the 27 have a special magic.
I have this preamp as well and trying to find out whatever I can. The tubes in it are Sovtek 12AX7WC and some unbranded 12AX7 ECC83. Hand-written over in a Sharpie from the factory 92/93 is what they say, I assume they came with the unit, but I don't know. The unbranded ones are written in big white letters, so possibly from Yugoslavia. Unsure.. I am told the Telefunken Smooth Plates are the best to get, but again, unsure. Any thoughts on this from the other owners?
Sorry in advance for resurrecting an ancient post.