Being a Ampex fan,of course it would be nice if it had the same signature of a 351 Ampex. Now if by some chance it sounded like a 350, that I think would be a acheivement. The 350's have all octal tubes including a 6sn7 on the master unit,outboard power supplies, and point to point wiring. These 350 Ampex units are true dual mono preamps and when grounded correctly produce a stunning sound. I'll post my thoughts when I get mine completed with the Mundorf film caps.
Being a Ampex fan,of course it would be nice if it had the same signature of a 351 Ampex. Now if by some chance it sounded like a 350, that I think would be a acheivement. The 350's have all octal tubes including a 6sn7 on the master unit,outboard power supplies, and point to point wiring. These 350 Ampex units are true dual mono preamps and when grounded correctly produce a stunning sound. I'll post my thoughts when I get mine completed with the Mundorf film caps.
Ok Roger,
I was just going by what I have read and what I heard. I did say I was led to believe that she copied or designed hers like the Ampex, no pun intended.
FYI, the phono section in the McIntosh MX-110 is identical to the Ampex 351 playback circuit, with the exception of the difference in eq. components. If you're going to copy(steal), you might as well copy from the best
Why re-invent the wheel?
Seems that I recall Dave Dintenfass telling me that the repro circuit in the consumer Ampex decks like the 960, 1260 and F44 was pretty much the same circuit as the 351 repro too. I'd have to go back and dig through my schemo files to verify that. Since the move to the new office those files are a trainwreck - a big pile on the basement floor.
To Roger -
Paul's mastering deck is an ATR 102 converted by Mike Spitz to 1" 2 track, and it uses Tim's custom tube record and repro electronics. That is the machine our running masters are made on.
The master for the duplicating line is an MM1200 that was converted by Spitz to 1" 2 track. That is the machine with dPV modded MR70 electronics.
The slaves use a slightly modified ATR record electronics chain. Repro electronics in these machines is unchanged, since we don't really use the repros except to monitor during duplication, If I ever get the time I plan to experiment with some tube record electronics of our own design.
Doc, as they say the "proof of the pudding is in its eating ". In this case all of here who subscribe to your Tape Project can vouch for how good they sound which is IMO a result of how they are mastered.
So what's the latest on Kara's new tape/pre??? Has anyone heard it since RMAF??? I know she was going to send out a demo unit anyone heard any more on that???
Kara is headed to the Bay area this weekend for a Bay Area Audio Society meeting to demonstrate her preamp, along with her 50A triode Mono amps and Sonist speakers. She is going up to Seattle for a NW Pacific Tape Group meeting in the near future(December or January). She just delivered the first Tape/Phono version to the Tri-Cities area last weekend.
Here is my latest concoction- an Audio Research SP-3 tube preamp converted from RIAA to NAB. The video was shot earlier this evening. The tape deck was my old reVox C270 with Nortronics play head directly wired to the SP-3 tape(ex-phono) section. The test tape is a 15 ips NAB MRL tape and the results are shown on a Hewlett-Packard Spectrum Analyzer. Sorry about he fan noise- it is coming from the HP.
Inquiring mind wants to know, any details of the RIAA to NAB circuit conversion on the phono preamp you can share would be interesting to me. I've been thinking - there are so many good tube based and transistor phono preamps that might be perfect candidates for such mods to be used as a tape head preamp. Even old mic preamps with no EQ would be even more appropriate to mod for tape head preamp if some one who's qualified would do the work.
Other than few machines with very low head inductance that would require huge gain (with signal transformer), most of the modern heads are in the 200mH and 150 ohm DCR range that are well suited for ~50dB gain of MC phono preamps I believe.
On the other hand, DocB and Charles King had done the hard work already for us lazy type to take advantage of...
As I mentioned a LONG time ago, most every manufacturer of "golden age" (dawn of stereo) tubed preamps had tape head inputs. Yours appears to be the FIRST posting where someone actually tried it - although it took a modification to accomplish.
BTW, I understand that your ARC exhibits "much lower noise" than the Bottlehead. Care to comment?
Judging from what Rich had said, I thought he had "converted" RIAA into NAB in a similary fashion as what you did to the Cello phono. I didn't realize it was a straight use of an exsiting tape head inputs as Rich had mentioned in one of our phone conversatiosn in regards to his experiment of using the McIntosh MX110 for the same application. If so, the SP-3 seems to have two tape inputs (assuming tape head inputs) from the photo. Could it support two different heads with two different characteristics or be modified to have one input as NAB and the second one as IEC having the different EQ selection done at the switch?
I did convert the SP-3 from RIAA to NAB eq.. I removed the complete RIAA network and installed a new board with the appropriate NAB network with two 15 turn trim pots at the 3150 hertz turnover(+/- 3 db). I will likely get an IEC and RIAA board made up and possibly an AME board. These will be installed on a pair of 4 pin sockets. The only series of ARC preamps to have NAB playback eq. are the SP-2 series, which I believe was sold up to about 1974.
Last month I had a stock MX-110 McIntosh preamp that had NAB eq. built in. It was very lovely sounding but a bit too noisy for my taste. The SP-3 is considerably quieter with my 200 mH Nortronics play head, but is lacking in 'punch' and 'slam'. It certainly is much quieter than my Bottlehead Seduction and about the same noise level as the Tape Repro, which I have to admit had WAY more slam. I'm listening to it right now with the Chopin first piano concerto with Graffman/Munch/BSO now and it is very nice. I really miss the King/Cello preamp, which I think has slam/punch in spades as well as a super lush 'tube' sound with an awesome soundstage and SUPER QUIET. CK- please get going on serial number 14
Next move on the vintage preamp/tape lash-up front will be trying some 1:15 step up transformers or some high impedance heads, a la Ampex 350/351, which were almost 1 Henry! This will certainly supercharge any old preamp. My old Presto 825 is getting restored in Seattle now and my restorer has some 351 transports, so that might be my next move.
To sum up my findings so far- 43db gain in tape is not enough for good results with modern 100-250 mH heads. I have found that around 50db is right for the modern heads. Kara has gotten around this problem by having a solid state 'step-up' stage before her tube gain stages. Ampex (MR-70) and Studer(some A-80s) used transformers to step up the level. I used an MR-70 in the 80s/early 90s and it was a gem. Will be trying the peanut Beyers and some UTC LS in experiments later this year.
To Ki and the rest of the Seattle Tape Club- I'll bring along the ARC on my next trip up for you to hear.
HI Tom
I'll leave the technical discussion of distortion to Ki or Charlie. Using the HP spectrum analyzer was a bit of technical overkill for the simple frequency response measurement of the deck.
Hi Ki
Using any tube phono stage which is passive CR type RIAA filter convert to NAB head pre amp is much easier than the other type (active filter) just change the filter to two R and one C and a pot for hi frequency adjusting or one more for gain control .because NAB curve is simple than the RIAA. the MM in put will have enough gain for a repro head
tony ma
Hi Tony
I respectfully disagree about MM Phono gain having enough juice for a typical low impedance head(ReVox, Technics, etc..). Most MM phono stages are around 43 db of gain. I have found this a bit low for these types of heads and MC gain of 60 db is a bit much. 50 to 55 db of gain seems to be the sweet spot for these heads IMO.
