 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
68.39.179.254
In Reply to: RE: Advent 300 for phono stage posted by Marantzguy on September 15, 2010 at 12:55:22
Not to downgrade the Advent 300 phono stage, or rob the post, but tube phono preamps are the preference to many of us. I have an Advent around, but rarely use it. By itself, the Advent can sound great. The tuner is a bit harsh sounding. Connecting an upgraded tube phono stage, like an M65 into the Aux jacks will probably convince most that tubes rule...
Shure purposely built-in a high frequency peak of +3 db at 10KHz in this Phono Conversion Preamp unit. Developed in the early '60s, Shure's M3D, M7D and M33D cartridges available at that time, were a bit reticent in the upper highs, compared to later Shure carts and many magnetics. That peaking network, with 100K across 420 pf, should have about 680-750 pf for flatter RIAA EQ. The stock M65 bass EQ is ballsy; very pleasant. The quickest fix would be simply adding 250-330 pf across the 420 pf caps inside; yielding 680-750 pf across 100K. Even better, use polystyrene caps instead of the stock ceramic EQ caps. Polystyrenes are superior to mica as well, in this circuit. Be prepared to let the new poly caps break-in for over 20 hours of listening. You might want to upgrade the four coupling caps also. Short out that ridiculous input ceramic cap with wire; as it's not needed. Upgrade the power supply capacitance to a few hundred uf, and the M65 is very hard to beat.
In my photo, there are two M65s uncovered. Note that one still has it's original coupling caps. Those of us that have the white coupling caps inside their M65s need to replace them. Also uncovered is the chrome stereo phono pre available from Japan. This little cutie needs even more phono EQ upgrading and wiring needed in it's tight quarters; but when done, I can use this with two turntables !
Follow Ups:
Hi, IT:
Much thanks for the lovely images and the very useful suggestions for upgrading the Shure Brothers M-65 two-tube phono preamplifier from the sixties.
The two examples I own were found over several years in local flea markets and I really had no idea just how good they were until I lent one to a friend ofmine one day and he was quite impressed with it.
I only replaced the coupling caps in them, but noticed that in one unit, there was some low-level hum most likely coming from the two sectional electrolytic. I was going to consider re-stuffing it, but I see that you managed to squeeze in some replacements under-chassis, which I much prefer doing.
Incidentally, I do not know what brand of tubes you selected for your units, but the smooth-plate Telefunkens which came in mine were hardly ever used and tested very well, so I left them in. I also tried some NOS Amperex 12AX7As and they just did not do it for me. I concluded that the units were somewhat fussy about which tubes you put in them, including some Mullards I had around. The Mullards worked nicely, but to me, the Teles were the trick, and some old Tungsrams were not that great sounding in the same circuit, that is.
I saw that some of thse M-65s were offered on eBay recently and that is interesting, considering that this unit was such a sleeper and got little or no attention several years after its introduction.
Tell me a little about the Japanese unit, however!
Intersting to see such an apparent knock-off. Is the circuit identical?
If so, Shure Brothers might be interested in knowing about that, but then again, these things are so old by today's standards, yet they work so splendidly.
Thanks again!
Richard Links
Berkeley, CA
...will be much less fussy about tubes after you increase the 420 pf to 680-750 pf. That is for sure, my friend. Also, upgrading power supply capacitance is needed and highly rewarding, throughout the musical spectrum.
The chrome preamps were sold by the thousands, from every distributor, way back when we were kids. Unfortunately, and very ironically, they were designed for Japanese stereo carts that were hardly ever offered stateside ! These would be copies of the GE VR carts, but stereo versions, like the GE VR22, but able to track much lighter. These carts are like unobtainium; so don't even bother. More importantly, the Japanese mono chrome preamp circuit design was literally a GE UPX-003 copy, but with unique EQ. The VR carts(GE RPX and VR-II) had highish inductance and the preamps' low input resistance(6K Ohms) enabled the required RIAA high freq. deemphasis, without any EQ networks underneath, other than the bass boost network. The sometimes switchable Tape Head EQ on these units only provided High Freq cut. Why they didn't complete the task and offer real world EQ for the popular carts then and now available, is anyone's guess.
When you find these mono or stereo chrome preamps, they were branded with many names, yet obviously they were only built at a few factories. Rewiring the tape head switch, after deciphering it, and changing phono EQ with proper values for bass boost and high cut, plus adding proper input resistances(the Tape Head input had no input R yielding nice howl when switched in), you can have a nice phono stage. It is very, very tedious wiring the stereo units, as these are real small inside. But, with careful choice of parts and meticulous wiring, you can actually fit two different phono EQ networks, or simply jump the switch for the same EQ on both sets of input jacks. Power supply cap augmentation is the tough part. I build in a similar circuit that I derived from the Shure M65 and classic preamp research, plus trial and error in choosing certain EQ parts and certain values depending on the parts choices I have on hand. For this reason, I cannot give an exact schematic. For example, if mica or ceramic caps are on hand, the high freq deemphasis cap value will be different than if using polystyrenes. Likewise, the sound character will be different with different coupling cap type and value choices.
I have to get some stuff together for my sojourn this weekend. After Sunday, ping me here, and I'll try to post a scheme that is not too confusing. In the meantime, research the classic tube preamps schemes and their RIAA EQ parts values. Comparing them will open your minds. They are not that different from one another; even comparing to modern stuff ! There is very little that is new out there, my friends. There are some unique schemes, to be sure. Plus, the movement to Passive EQ is growing. However, many of us know it's hard to beat active Feedback EQ, especially when listening to vintage discs. Later...
It was loaned to me by henrybasstardo.I like it a lot but it does hum a bit.I don't know which it is,Lafayette,Fentone,etc.I use a cheap ratshack
input selector to switch between 2 tts.
If yours is the unit Henry got more than a few years ago at the Kutztown event, then maybe it's time for some mo' better upgrades.
First, concerning hum, hummmmm should not exist, at all. These units do use parts that are not new. Some of these have the underneath augmented power supply caps added, in parallel, with the stock, original stand-up electrolytic mounted atop the chassis. That original electro is now 50 years old. It lasted this long because the unit only draws about 4 mA of DC voltage. I know Henry uses a Variac for his tube gear, keeping AC voltage from the wall at a safe level going into the tube gear; around 110-115 VAC. If you don't use a Variac, you are increasing all the working voltages and running this unit hot. Furthermore, if you run vintage tube gear originally designed for 115-117 VAC in, without lowering the 120-125 VAC in, that is available at your AC wall sockets, then you are abusing the tubes and many parts, including the power supply caps.
So, check which cap or cap section is leaking AC, by isolating the caps or electro sections, so you or Henry can replace the leaky hum causing power supply cap or caps. Then, please resume thorough enjoyment by making sure the unit is seeing 115-117VAC maximum. 110-115 VAC will work fine, by the way.
Now, if Henry bought your particular chrome unit, way back when, the phono EQ network choice and parts values have evolved since then. Also, many of these units are out there, rewired for allowing two tables to be switched at the chrome unit; a nice feature. But, first thing is first. Let's make sure the power supply is hum free and you feed the unit 117VAC or less. In 1965-1970, AC wall voltages were 115-117. Today, we are looking at 120-125 VAC available at the wall, depending on your locale and time of day. If we feed in 120-125VAC, filament voltage increases, high voltage increases, parts get abused and the parts and tubes' useful lives get shortened. Henry has my contact info and I will be glad to help you sort this stuff easily...It's all about the enjoyment factor and I want a high enjoyment factor...
Thanks for the reply.Ok,I've forgotten the details on this unit but hedid say it came from Kutztown.All I know is it looks very fresh,no dents,rust,etc.The ps cap looks recent too.I know that one input jack is loose,Henry tightened it up a while but it's obviously loose again.No,I don't have a variac but I knew tube gear requires a lower ac line voltage.
Now,I'm physically disabled so no way I could work on it.Henry's kinda busy with work these days-he & a friend of his are due to stop by in good time,methinks.He can easily tighten it up.I was at his mancave back in May,had a ball.
Yeah,I wouldn't mind changing the input selector for 2 tt switching but my budget is nearly non-existant(a long story).Btw,if it's any clue the switch is black like the one in the pic but there's no protruding tab,it's nearly flush.
I may have gotten Henry ticked off..I openly,stupidly (on the vintage forum) proposed trading 2 paintings if he'd find some speakers I'm after.
Jeesh,I shoulda called him instead.Anyhows here's my website:
robertwoltanski.com Check out my gallery of paintings.
Hi again, IT:
Nice details, much continued thanks!
I hope to get to one of these M-65's one day soon and will first try updating the electrolytics and then concentrate on installing more pf capacitance as you have suggested.
I also need to do some restorative work on the Marantz Model 1 Consolette owned by a friend of mine. That unit needs a new filter can and I have been walking circles around that project all too long!
Thanks once more for the neat information on the M-65.
Now the price of them will shoot up, eh?
Richard Links
Berkeley, CA
Completely agree about tube phono pre-amps. I have a Jolida JD-9 with GE 5751 triple mica black plate tubes in my home system. If I could afford an EAR, I'd have that. But since this was for a secondary, office system and it is being used with a Prima Luna Prologue One amp and original Advent speakers, the combination (and price) couldn't be beat. I'm liking the combo.
Catama is enjoying his stuff and that is most important.
I was just wondering if Rich upgraded his Shure M65... Perhaps, the M65 was one of the finest tube preamp bargains; just as the Advent 300 was definitely one of the finest bargains in solid state hifi...
Post a Followup:
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
