The Seduction Repro Amp Project

[docb]

Here's a link to the project that kind of started it all:

http://www.bottlehead.com/et/adobespc/Seduction/bottleheadtapeheadpreamp.htm

[ironbut]

It seem like just yesterday when I was bugging you about tweaks for my ampex f44. I still pull it out every once in a while but the rs1500/seduction rules the roost for now. I took my f44 and a super dynamic BC tape to a local audio dealers to hear an amp once. My f44 is the type that comes in the suitcase. It's so clunky and early '60's looking I could feel the eyebrows raising and hear mumbling as I threaded the tape. I turned it off after the first movement but the store owner made me play the rest. This time on his reference system.
BTW did you see the post I left with the specs on the different heads over on the bottlehead forum. I think you were still at CES or just gotten back.
Also, regarding the repo amp, as far as i'm concerned, I wouldn't mind if there was a way for you guys to produce it without the balanced studio level outputs because, like i said, I have no need for it and I could save some money. But, I would prefer to have it built with the premium components.

[docb]

The F44 was sort of the RS1500 of it's day, an expensive, quality, consumer grade machine. 960 and 1260 are almost identical to the F44. It's not nearly as sophisticated in the tape path and the shifting head is really only 1/4 track even in the 1/2 track position, but you can get great sound from pre recorded 7" tapes if you keep it scrupulously clean. I found that the felt pad will get loaded up from old tapes, and needs to be rotated fairly often and cleaned every once in a while. I use dry cleaning fluid. The one mod suggestion I have is to check the Delrin bearing that the bottom tip of the capstan shaft rides on. The one in my 934 (which is a fairly rare 960 variant without any electronics and a playback head only) was a little worn and we replaced it with several layers of Teflon insulating tape (heavier than pipe thread tape and adhesive backed). That made quite an audible improvement in terms of flutter reduction on my machine.

I think it would be great if you would repost the head info over here, either in this forum or Tape Tech.

The repro amp will have both -10dB single ended outs and +4dB balanced outs. We're trying to establish three levels of electronics to cover all the bases. The repro amp as shown in the TAD room is the "middle" one, intended to be a pro quality repro amp that can be adapted to a wide range of machines, from something like an F44 up to an ATR. As such it will be available in it's own rack mount case.

At the "I could save some money" level we already have the Seduction repro amp, which we may soon make available in the form of a small upgrade kit that mods a stock phono Seduction into an NAB/IEC switchable repro amp. And we will probably offer these built for folks who don't want to DIY. This amp of course has single ended RCA outs, and sonically it's no slouch. In fact it was the repro amp in the system that got applause in the Magico room at CES.

At the top end we are in the development phase of a full on custom playback machine with built in electronics. Stay tuned on that one.

[xcortes]

At the "I could save some money" level we already have the Seduction repro amp, which we may soon make available in the form of a small upgrade kit that mods a stock phono Seduction into an NAB/IEC switchable repro amp

Hey Doc, where do I signup for one? You can count me in as a beta tester.

Xavier

[john]

Hi Doc, is this still in the pipeline for production?

 

At the top end we are in the development phase of a full on custom playback machine with built in electronics. Stay tuned on that one.
[/quote]

[Ben]

I'll stay tuned, but since I have to count my pennies
all I can afford is the Seduction amp. Since I found the price
of the Reproduction amp at $4K, I don't think I will consider
it for next summer, but use the Seduction amp if I can find
a way to get the gain up a bit. The 6B4G AMP I am using
was designed for CD levels. So just what is the peak to peak
voltage levels off a typical tape head?

[docb]

With stock heads on a Technics RS1500 playing into a Seduction with the C4S upgrade (40dB of gain) we typically see about 140-180mV RMS output signal from the Seduction with a 250 nWb/m 1kHz tone. That would be about 0.4V - 0.5V pk-pk at the output of the Seduction. Working backwards that would imply about 5mV pk-pk at the tape head.

[wcb]

I to have the seduction with a gain problem. I have a fluxmagntics playback head and have to turn the volume up all the way. what can we do to fix this  problem.

[docb]

The output of the Flux Magnetics head is a little bit lower than the stock head. The Seduction was designed to operate into one of our Foreplay preamps, which currently adds an additional 10dB of gain. This in turn is intended to run into one of our amps, which come with recommendations of what level of sensitivity the speakers should be to achieve acceptable levels. We have designed around an accepted standard that has existed since the days of LP. The Seduction has been pressed into service as an economical solution to great tape sound and it's simplicity limits how much more gain we can squeeze out of it.

It may not be that case that the gain budget in other manufacturer's gear is set up the same way. Over the years manufacturers have often drifted away from the general standards that we have built our equipment around. The introduction of high output CD players really threw a curve into the whole concept of standards for output levels, falling somewhere between the standards of -10dBV and +4dBu of home audio and pro audio.  In a lot of cases manufacturers tended to reduce the gain of their control preamps and folks went more towards CD and away from LP. Their phono stage may have more gain and their preamp may have no gain. So when using different brands of gear together you may find some situations in which the volume control has to go up very high, and some cases at the other end of the spectrum in which the volume control can be "hair trigger". Our more expensive Tube Repro has more stages, more gain, and adjustable trim at the balanced XLR outputs, with the idea that it can be used in just about any system imaginable. All that stuff adds a lot to the cost of making one.

But I'm not trying to sell you our more expensive preamp as the only solution. Which AR preamp and amp are you using, Wally? If I can examine the specs I may be able to make some recommendations for a solution.

[Ben]

Well don't listen to me, I am thinking of solid state (opamp)
replacement board to be designed for my Otari 5050. It would
have some advantages as (hopefully) better components like caps
could be used and external boxes out. The phono-amp
from TNT-audio is almost what I am looking for.
http://www.tnt-audio.com/clinica/solidphono_e.html

(Note: I would try 1/2 wave rectifier from a CT transformer
and pre-regulate that and use a simple transistor regulator.
With the low current, one can afford to drop a few volts on the
front end)


What I could like to see is a Foreplay .5 out.
1/2 the size -- just 1 line in for the seduction pre-amp.
As a wish, could the seduction & a simplified foreplay amp
be combined on a single chassis?

PS. How come the 'tape project' don't have the model
posing ...  I guess you can't find 1/4" tape to wrap her in. :)

[steveidosound]

While we are visiting this subject (gain etc.),
What effect does head inductance and impedance have on gain and frequency response for the tape-modified Seduction. I have both newer machines with heads designed for solid state head preamps and older ones that were designed for use with tube head preamps. The first photo in this thread shows the Seduction being used with a machine that obviously is of the tube era head design, while the majority of (tape) users are using it with the Technics (or Otari) heads, or some similar spec. aftermarket replacement for same.

[docb]

Hi Steve,

I think the answer to your question has been addressed in the web page about modifying a Seduction for tape use.
http://www.bottlehead.com/et/adobespc/Seduction/bottleheadtapeheadpreamp.htm
Basically you need to increase the input impedancefor higher inductance/impedance heads. That's what we did for the machine in the photo. This will keep the treble response flatter up to the point where older heads just plain run out of gas. In the case of the older Ampex heads that's around 12kHz.

from the Seduction tape head preamp web page:

Some modeling yielded starting figures of 91K for R1 and 1.5K for R2. The RCA input trimpot was set to 100K. But this is only a starting point. The easiest way to accurately adjust this network is to use alignment tapes such as those provided by Magnetic Reference Lab. Once the alignment track of the tape has been used to properly adjust the head alignment for minimal phase differential one can proceed to trim the pots in the NAB EQ network for flattest response. In general R1 will determine the amount of relative bass boost and will also be useful in compensating for head bumps caused by fringing effects. It was found that R1 was about right at 75Kohms in the case of the Ampex 934. R2 will more or less determine the knee frequency and to some extent the slope of the high frequency end of the response. For the Ampex the optimum value was about 1.5K ohms. This was measured primarily with the test tones at 10kHz and below, as the Ampex head exhibited a rolloff above 12kHz that is typical of tape heads from that era. The final adjustment, of the input load resistor, will also affect high frequency response. It's value will be determined largely by the impedance of the playback head. The high impedance head of the Ampex 934 seemed to work best with a 250K load. Low impedance heads may want to see a lower impedance load.

[steveidosound]

I THINK I am beginning to get it now. I have read some of what Jay said regarding eq vs. tape/head design on the MRL website.
So part of what I hear you saying is that head as well as tape design has really marched on. And so modern tapes and head design no longer fit what was needed in the NAB curve as it was compensating for more limited frequency response in the heads and lower output tape.
So for the truly best from the TP tapes one needs state of the art heads and the CCIR eq. curve they are recorded with of course, and all that with the properly recorded high output modern tape gives extended frequency response and S/N ratio.
So, even though the seduction is a tube design that does not mean it will mate best with and give really extended response with old tube era heads no matter what kind of shape they are in or if they were state of the art in 1960.
To put it another way, they really had to work to coax reasonably flat response to 15k with Scotch 111 by use of the NAB curve on the pro recorders back in the day.

[wcb]

Hi Doc, audioresearch Sp-16 preamp, d-115 amp. I also have marsh  msd-200b preamp with bal. input,if that would help. running quicksilver mid mono. Thanks Wally
         

[Studer Fool]

Steve,
I think you've got it, but your understanding as stated may get misinterpreted.  You state:
"So, even though the seduction is a tube design that does not mean it will mate best with and give really extended response with old tube era heads no matter what kind of shape they are in or if they were state of the art in 1960."

It really has nothing to do with the seduction being "a tube design".  Indeed it really has nothing to do with the Seduction.  The seduction is what it is, one approach, and as such represents certain trade-offs, JUST LIKE EVERYTHING ELSE!  (Actually, I personally think the selection of those trade-offs in the Seduction are rather nicely and artfully made.)  

As time has moved on there have indeed been appreciable changes and improvements in head design and tape formulations.  Some of those changes may seem like one-step forward, two steps back, for anyone who has ever had to deal with sticky-shed syndrome for example.  There are always trade-offs.  The NAB standard in particular was, as you correctly sense (if I'm getting you correctly), directed to making the most of the situation in the trade-offs as they existed back then.  However, just like the QWERTY keyboard (which was designed to slow down a typist so the keys wouldn't get stuck so often), a standard can also be limiting, as time and advances move forward.  What Doc and Paul and Michael are showing us, and sharing with us, is that with the advances in materials/manufacturing techniques/audio circuit understanding, is that a new set of trade-offs can be made which are an exceedingly satisfying and genuine step forward in listening pleasure for those to whom such things delight.  (Thanks so-much you guys)  Of course they are building on top of something which a few of us fortunate to have had the experience already knew, which is just how good pro-level (15 ips & halftrack) reel-to-reel already sounds.

So while the Seduction has certain trade-offs, they really are not that directly related to the trade-offs in tape formulations/equalization/head design & manufacture.  The Seduction will mate as well with old tube era heads mostly just as much as it will with new ones.

Yours truly in tape tomfoolery,
cdw