Tape Preamp Variable EQ

[stellavox]

Guys  (and Doc),

I continue to see posts regarding NAB / IEC equalization and using or "converting" other (non IEC) machines to that EQ.  Let me expand a bit.

May have mentioned this before but my own "playing" with the electronics of many machines AND listening to hundreds of pre-records has convinced me that having the ability to vary the high frequency response can be of great benefit - especially when listening to early 2 tracks when the standard playback curve didn't exist or wasn't adhered to.  In many cases, just making the resistor variable in the RC circuit that determines the HF EQ can allow for, say a boost or cut of 6dB at 10Khz.  This can make all the difference in the world when "taming" the bright high end on certain tapes OR boosting/compensating for too much treble rolloff in others.  The variable control need only have it's "center position" indicated - which "exactly" follows the NAB curve. Understand too that this is NOT a tone control  per se, in that it is part of the EQ circuit.

I have added this type of control to the front panel of Revox G36 and A77's and it's a fairly simple mod - hardest part is mounting it.  This control also allows "tweaking" of the HF response to match the IEC curve

Doc - I strongly suggest you consider adding something like this to your preamps - could be implemented with a screwdriver adjust pot. I would hope that folks who buy your equipment won't JUST listen to Tape Project tapes - or maybe not.

Charles

DDoc you might         

[ironbut]

No way Charles! I just sent off a lengthy email to Jeff/beefman regarding a very similar topic. I've just begun to toy with the idea so I won't go into details right now. I'd love to bend you and Doc's ear about it at VSAC though.
Some of my earlier acetate tapes have seemed a little bright(1/2 track as you mentioned). Considering your experience with these, which ones have you found to be recorded with alternate eq curves?
I just saw a presentation at the ARSC conference where Gary Galo has made an exhaustive study of the Columbia lp curve which has been a bugger to eq correctly. Real interesting (in an uber geek sort of way) stuff.

[docb]

As a manufacturer I wonder about the number of users who would really use this feature. In fact the first couple prototypes have trimmers, including ironbut's. We have gone to tight tolerance fixed resistors that give very consistent results on the current production units. I suspect this kind of thing might be best implemented as a DIY mod for those who are among the hardest core, because I fear it would add greatly to the already considerable price of the Tube Repro and really jack up our tech support issues. If you want to get crazy with adjustability there are many layers where it can be employed, like current trimmers on each stage to adjust for various tube brands, etc. But man, would all those trimmers make the thing tweaky to build and to adjust.

[TonyB]

Hi Doc,

IF (did you notice the capital IF) one can tolerate an additional switch, one could switch between the exact, high precision resistor and a pot.

Regards,

TonyB

[astrotoy]

My experience with LP's may be of interest. I recently bought a Graham Slee Revelation and Elevator phono preamp. The Revelation (the upscale version of the Jazz Club) has variable equalization for vinyl. It has three switches with three positions each to recreate RIAA and several other EQ's including the old ffrr Decca and Columbia and various 78 rpm. I reported on the Oistrakh (TP-006), that the vinyl matches the tape in tone quality only with the ffrr Decca EQ. There is a hugh difference in playing back old EMI and Decca recordings with the proper EQ. I am getting a lot of enjoyment, particularly with the early EMI's which had previously been not pleasant to listen to. The Decca's are also much improved. I'm not sure where the EQ issue occurs. It seems from the Oistrakh tape that the masters are fine, but that in cutting the vinyl, the EQ is put in. I'm not sure when the standardization to RIAA occurred for each of the companies, but later (late 60's and 70's) issues seem fine with RIAA and late 50's and early 60's need the different EQ. For those with regular and low output MC cartridges, the Graham Slee Elevator boosts the gain by 20db and also has adjustable loading which feeds into the Revelation. The total package is aboiut $2500, less than many high end phono preamps. HiFi+ January 2008 issue talks about this.

Larry