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January 22, 2019, 09:20:44 pm

Author Topic: Repro tape preamp head compliance  (Read 295 times)

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Offline nikaudio

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Repro tape preamp head compliance
« on: January 04, 2019, 01:48:55 am »
Hello there,
I'm new on this forum and have a question regarding Repro.
 
According to Bottlehead website “works well with medium to high inductance playback heads“.

I have Tascam BR-20 retrofitted by JFR with FluxMagentics Extended Response head.

This is very low impedance head 8mHy. I have read that Repro is 50dB gain only, and for Flux heads I will need 60dB tape preamp like King cello. Kara from deHavilland told me that 222 will not work with Flux head.

Hence it is confusing for me “ It has been developed from the start as the perfect match to Flux Magnetics Extended Response playback heads”.

If this pre is designed for medium to high inductance playheads it is not designed to work with Flux heads which are low impedance.

Simple question will it work in my application ?

Have anybody used it with such low impedance head ?

Regards

Offline Paul Birkeland

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Re: Repro tape preamp head compliance
« Reply #1 on: January 04, 2019, 04:55:37 am »
The Repro has an extra 10dB of gain available on the balanced output (which we can build for you with unbalanced jacks if you prefer).

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Doc B.

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Re: Repro tape preamp head compliance
« Reply #2 on: January 04, 2019, 05:12:40 am »
It's actually 11.79 dB hotter (-10dBv at the RCAs vs. +4dBu at the XLRs), so about 62dB gain from the balanced outputs.

Did Greg Orton or John French rate the inductance of the head you had installed as 8mH, or is that just what the stock head is spec'd at? The reason I ask is that Greg can make extended response heads with a higher inductance for use with external tube repro amps. We specify a 200mH head for our own machines. FWIW ATRs have pretty low inductance heads and they work well with the Tube Repro. It might require head damping trimpots to be installed in the Repro, which is not too big a deal.
Dan "Doc B." Schmalle
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Bottlehead Corp.

Offline nikaudio

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Re: Repro tape preamp head compliance
« Reply #3 on: January 06, 2019, 03:46:06 am »
Hello again,
Thank you for replays.

Yes John French actually specified that my head is 8myH, and I was was told that I will need 60dB amplification for it to work.
I wish I knew, that I could have asked for 200myH Flux head, that would make my life much easier.

My understanding was that, the only tape preamp suitable for such combination is King/Cello (60dB).

My preamp Supratek Cortese has only unbalanced inputs.

So stock Repro will not work with such head, but custom Repro can be make to order.
Such Repro could provide 62dB on unbalanced outputs ?

I'm curious how King/Cello would compare to Repro.
I have once heard Repro with Technics RS 1500 on tape project tape and it was fabulous, very close to UHA-Tascam I heard on different occasion.

Just do not know which way to go, solid state King/Cello or tubed Repro.



Offline Paul Birkeland

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Re: Repro tape preamp head compliance
« Reply #4 on: January 07, 2019, 08:00:16 am »
So stock Repro will not work with such head, but custom Repro can be make to order.
Such Repro could provide 62dB on unbalanced outputs ?
Yes, it's absolutely no problem to provide the unbalanced outputs in place of the balanced outputs. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Doc B.

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Re: Repro tape preamp head compliance
« Reply #5 on: January 07, 2019, 08:26:10 am »
Do you know what the nominal mV output of the head is with a 250nWb/M tape at 1kHz and 0dB? This will give a more useful reference point for what gain you need from a repro amp than the inductance alone. Typically one would like to see at least 2mV, with 3mV or more being even better.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline Paul Joppa

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Re: Repro tape preamp head compliance
« Reply #6 on: January 07, 2019, 01:49:40 pm »
Head voltage is proportional to the square root of inductance.

For 2-track 1/4" tape at 7.5ips, I found a 1975 Nortronics publication with specs for three otherwise-identical heads as follows:

8mH 0.3mV

120mH 1.2mV

650mH 3.5mV

The reference flux was not specified, but these numbers are probably a good ballpark estimate. The 8mH is not really enough for a tube preamp.
Paul Joppa

Offline Doc B.

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Re: Repro tape preamp head compliance
« Reply #7 on: January 07, 2019, 02:08:02 pm »
Well, then even 60dB of gain is not really going to cut it.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline nikaudio

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Re: Repro tape preamp head compliance
« Reply #8 on: January 08, 2019, 04:05:53 am »
Since I did not know the answer about value of the output, I have shoot email to John French, he promptly replied:

" I checked through the Nortronics data base and the typical output

from their 10mHy playback head is .4mV.  The King/Cello preamps like between 100 and 200mHy which is typically 2-3mV.  8mHy

is too low to work with any external preamp that I am aware of.  It might be time to decide if you want to change over to a high inductance

playback head and wire it directly out to your preamp of choice."
So output is really low, but with my internal repro it is working just fine, so why external one cannot have enough gain ?
How much gain do I need?
So how to understand this:  "It has been developed from the start as the perfect match to Flux Magnetics Extended Response playback heads".

Offline nikaudio

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Re: Repro tape preamp head compliance
« Reply #9 on: January 08, 2019, 04:21:30 am »
So output is as low as from MC cartridge.
And there are many phono preamps working with such low output cartridges.
Just a thought...

Offline Doc B.

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Re: Repro tape preamp head compliance
« Reply #10 on: January 08, 2019, 06:04:01 am »
The head most likely feeds a FET that gives the extra gain in the stock internal repro. And the phono preamps you mention use the same approach. I have not heard a FET input repro that really knocked me out. Tim de Paravicini has probably gotten the closest, but with all due respect to Tim, I prefer a slightly different sound than he does. My preference is to stick with tubes, and getting the noise floor low enough for .4mV is not really possible with an all tube stepup. We have tried very hard and we have gotten pretty close. Other than the noise floor intruding a bit an all tube high gain repro or phono preamp sounds amazingly open and fast. It might be possible to use a step up transformer, but my experiments with this on tape heads of higher inductance have not yielded great results. Perhaps a low inductance head could work better with a transformer, I don't know.

Note that Charlie actually specs the same type of head as we do and his (well, his and Mark Levinson's) preamp has roughly the same gain structure. I also note that you are now talking about a Nortronics head rather than Flux Magnetics head. That is confusing. Also, Greg can make virtually any head known to man. So one Flux head may not be built to the same spec as another. John's response to you was, IMO, exactly the right thing to say. Pick a head that works with the repro you want to use.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline nikaudio

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Re: Repro tape preamp head compliance
« Reply #11 on: January 09, 2019, 04:11:03 am »
So in summary Flux head cannot be used with really good quality repro because of low output 0.4mV.
For testing purposes I have tried Tascam direct head out output with my tubed preamp Supratek Cortese (as you have stated it is using FET input and E180F,6922 tubes for amplification).
Supratek  is very fast and open with my MC cartridge.
With Flux head there was more than enough gain, it was quit fast and open but strange, lacking bottom end. I guess because of RIAA curve.
Maybe all tube design would be even better.
> . We have tried very hard and we have gotten pretty close.
What does it mean close ? Enough gain for 8myH but slight noise floor ? Too much noise to make it commercial ?
> Pick a head that works with the repro you want to use.

I wish I knew, I have actually done opposite way, I have wanted to pick up repro which works best with my Flux head which I heard is best.

Offline Doc B.

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Re: Repro tape preamp head compliance
« Reply #12 on: January 09, 2019, 05:10:29 am »
To clarify, the 8mHy Flux head you have would not work well with our Repro because of the low output. But Greg makes more than one head under the Flux Magnetics Extended Response name, and thus there are other higher inductance Flux heads that will work extremely well.

Yes it is likely that a phono preamp will sound rather bright with NAB or IEC eq tape because of the differences in the equalization curve. IEC, which I think is perhaps the best eq to use with modern tape formulations, makes the situation even more complex than NAB because of the bottom end response curve not having a knee at 50Hz requiring much more headroom than NAB (or RIAA).

The prototype tube stepup preamp we designed is large, complex (it uses 4 6C45pi tubes per channel), expensive, and yes, the noise of the tubes intrudes a bit with very low output transducers. We spent a lot of time working with this design to try to understand what the limitations were but we were not able to make it a silent as we felt it needed to be for a commercial product. A step up transformer might be worth experimenting with as an alternative, but I don't have any experience using one with a low inductance repro head.

I'll just add that the term "best" is pretty vague when it comes to rating audio components. The trick is to combine components in such a way as to get the sound that is the most pleasant to you. That is to say one person's "best" phono cartridge may sound terrible with another person's "best" phono preamp. The head you bought may be the best one to use with the internal repro in your deck, but it is not necessarily the best head for all applications.

I am always happy to talk to anyone about a tape setup before they buy anything.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline nikaudio

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Re: Repro tape preamp head compliance
« Reply #13 on: January 12, 2019, 05:45:01 am »
Thank you for all very informative answers. Original Tascam Head is 8myH too, unfortunately  internal stock Tascam tape preamp is not that great. Does not have neither dynamics nor button end nor openness of Repro or UHA Tascam decks I have heard, not even close.
Hence I have figured out that I will it  first get best possible head and later better external repro.

Changing Tascam head to Flux head, has given me much better low and (big difference) a slightly better dynamics, but only 20-30% of the way to what I have heard  from Technics 1506 with Repro.

Base on  responses I git from you, I have two choices , change to less linear but higher inductance head head  (>200mHy), or find external  preamp with >70dB gain.

My Supratek Cortese is FET, E180F/6922 design and works like a charm with 0.3mV phono cartridges.

I curious if it is  a big change to change it from RIAA pre to IEC pre.
Supratek is really fast open and  very dynamic with my SME  20/2 Kiseki cartridge.

Just do not know how big difference is between phono pream and tape preamp if this is not like comparing apples to oranges.


Regards

Offline Doc B.

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Re: Repro tape preamp head compliance
« Reply #14 on: January 12, 2019, 06:29:47 am »
There are issues of matching with any head in order to get the best response, so linearity is more complex than just the head itself.

RIAA and IEC are quite different eq curves. You might get away with substituting RIAA for NAB just to get the general feel for the sound, but the treble turnover (different by about an octave) and bass contour (50Hz rolloff vs very low bass rolloff) are very different between RIAA and IEC, and RIAA also has a shelf in the midband that is not present in tape eq curves. Going to all this trouble of new head and outboard repro amp just to end up using the wrong eq is counterproductive.

Changing the eq in a phono preamp from RIAA to NAB is possible. Changing to IEC is rather more difficult because of the extra 20 or so dB of headroom needed to accommodate the bass curve. A different gain structure is often necessary in the preamp for IEC eq because of this.

What I am getting at here is that we're talking about a system. You have to take into account the head when considering a repro amp, and you have to take into account the repro amp when considering a head. It's a bit more complex than phono cartridge/preamp matching.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.