Going back to Vinyl

Hi group,are there any specific changes/upgrades, that "need" to be done to Dynaco pre-amps to get a good phono result. I just bought a Marantz 6100 and I want to know what type of cartridge to settle into and or what changes to make to my Pas, if any

much apreciated

Interesting question! Difficult to answer, though.

The following will probably not be of much help, but hope it does make a difference to what you should be looking out for...

I currently have a "hybrid" system - a mix of solid state and tube equipment: Preamp is a NAD 114 driving a VTA-equipped ST-70. Using either a Hagerman Bugle phono pre-amplifier, as well as the built-in phono preamp on the NAD, I find that moving magnet cartridges (Audio Technika, Ortofon etc) sounds overly bright, whereas moving coil cartridges (I have only two in my "stash", both Denons - a DL 160 and a DL 103) gives a far more neutral (and detailed) sound.

(For what it is worth, the pickup cartridges are mounted on a Thorens TD 160).

I think the overly "brightness" of the MM cartridges may be a fault of the solid-state nature of my preamplification, perhaps. I would have blamed preloading / cable capacitance etc but the MM designs sound bright, no matter if I run it through the Hagerman phono preamp or the NAD preamp, so...

I have a suspicion that the brighness on MM cartridges will dissappear once I can lay my hands on a tube-based phono preamp.

-- JunkyJan

The PAS needs some changes anyway, to get RIAA equalization closer to standard. Best way is to move all the RIAA network parts to the phono board, using precision resistors and capacitors (preferably individually screened) and taking them off the selector switch. That gets a set of switch contacts out of the feedback loop and if done correctly, will give you THREE phono inputs. That may sound like overkill but there are many phono enthusiasts who have turntables with multiple arms, one for stereo LPs and one for mono LPs with a dedicated cartridge having a slightly larger stylus tip.

The Van Alstine Super PAS rebuild, which unfortunately is no longer available for DIY use on the Web, also revised the RIAA feedback loop to eliminate any possibility of overloading the first 12AX7 stage; and dropped the feedforward link between stages. There were some parts value changes, greatly increased coupling capacitors, and a unique method of setting the cathode voltage in the second gain stage. That rebuild transforms the PAS phono stage while still using the original board. If you can find a way to get that DIY article from Van Alstine's "Audio Basics", it's worth looking into.

One thing EVERY PAS should get, if it has not already, is replacement (or at least bypassing) of the original selenium rectifier with silicon diodes. By now, most of the old selenium rectifiers have developed high series resistance, so that the filaments are running way below rated voltage. Low filament voltage guarantees soggy, slow bass and lack of "focus" in the sound because the tubes would be running way below their normal gain, and the feedback loops would be working very hard to compensate. More capacitance in the filament supply is also an easy addition; modern capacitors are much smaller than those available when the PAS was originally built.

Much appreciated responses. I will start with precision resistor upgrades [hand picked] I don't think I will ever graduate to the "spare tone arm box" but sticking with stereo Vinyl should keep my costs and listening assesments down to simple....
you guys are great...thnx again

GP49 wrote:...The Van Alstine Super PAS rebuild, which unfortunately is no longer available for DIY use on the Web, also revised the RIAA feedback loop to eliminate any possibility of overloading the first 12AX7 stage; and dropped the feedforward link between stages. There were some parts value changes, greatly increased coupling capacitors, and a unique method of setting the cathode voltage in the second gain stage. That rebuild transforms the PAS phono stage while still using the original board. If you can find a way to get that DIY article from Van Alstine's "Audio Basics", it's worth looking into. ...

I would second this recommendation. I doubt that you will find the original article, as it has been deleted from the Audio Basics archives. You could do as I did, purchase the assembly manual for the Super PAS Three and build it on a stock board from the schematic diagram.

Another option that I have built in a second PAS and would also recommend is Joe Curcio's upgrade, found here:
http://tinyurl.com/bedhrz

Perhaps most importantly, the biggest problem with the PAS phono stage IMHO is the line stage that follows it. Again, VanAlstine's Super PAS Three circuitry gives good results if you wish to go that route. If not, at least delete the tone controls. Hope this helps.

Best regards,
Mike