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Author Topic: IEC Equalization  (Read 6199 times)

Offline AZ_Gary

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IEC Equalization
« on: January 15, 2007, 06:15:02 PM »
I have two R2R machines, a Technics RS-1506 and a Otari MX5050-BII2. My preference is to use the Otari for Tape Project tapes. Should I proceed getting a Bottlehead Seduction and modify it for IEC or maybe sit back and wait a bit for "further developments"?

Gary Marklund
Sun City, AZ - USA

Offline docb

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Re: IEC Equalization
« Reply #1 on: January 15, 2007, 06:38:08 PM »
Hey Gary,

Welcome to the forum. The MX-5050BII should have a switch on the back for IEC EQ. If it's a 7.5 ips/15ips model you should be good to go with the stock solid state repro (studio talk for playback) electronics. If the 5050 is a 3.75 ips/7.5ips model you can convert it to 7.5/15 by getting a service manual and finding the instructions for moving some jumpers or a switch - I can't remember which.

For the Technics, if it's a US model you will need to add IEC EQ in the repro electronics, which you can do with a Seduction modified for IEC EQ and a very simple rewire of the cables coming off the head selector switch. I don't have the specific scoop, but I have heard from a customer who has a 1520 with switchable NAB/IEC EQ, and it may be that the non-US versions of the 1500/1700 machines have IEC EQ. If anyone can confirm this, please let us know.

Regardless of which machine you use, make sure it is in top notch shape mechanically - fresh belts, good pinch wheels, good bearings and good heads.

As for further developments, we do have a more advanced NAB/IEC repro amp design that we demoed in the TAD room at CES with. It's not quite ready for prime time but it will be soon, and it should be able to integrate with a wide range of tape decks by tapping directly off the repro head.

We're also laying plans for an all out assault on a home playback machine, based on the Technics isoloop tape path and our own electronics, repackaged in a more modern looking chassis and with some extra features like IR remote, built in scope, etc.
« Last Edit: January 15, 2007, 07:17:33 PM by docb »
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline stellavox

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Technics 1500 series suggestions
« Reply #2 on: January 17, 2007, 10:30:43 AM »
Not to denigrate Doc B's tubed Seduction NAB tape preamp efforts in any way; but I did a 1500 mod for a customer that worked out REALLY well.

Added a new set of high quality RCA's on the back next to one pair of the existing (cheap) paralled line output jacks. Wired a shielded cable from it directly to the output of the tape preamp section in parallel with R197 just before the monitor select switch. When this switch is in the "source" position, the tape preamp output is "unloaded" i.e. disconnected from the rest of the circuitry. Also changed C151 to a high quality mylar and C's 159 and 193 to Elna Cerafine's. Tape preamp is a decent simple design.

Sounds REALLY nice, although the gain is down about 15 dB from the main output jacks - about the same as from a Seduction. Don't have a way to compare them but bet it would be close. So you do need to feed the signal into a preamp with 15dB or more of gain and an input impedance of at least 10K ohms.

"Tweaked" 15ips response is within 2dB from 35 hz to 20kHz (upper limit of my Sound Technology 1500A). 7 1/2 response within 3dB from 35hz to around 18 Khz. NOT shabby! Record sounds VERY good also - with better line input jacks and better caps. Record/playback response tweaked to same as above. Power supply voltages to the electronics are regulated.

Regarding IEC equalization - in the playback amp, this appears to be switched in via transistor TR128. and it appears that the components to add this equalization are built it to all the 1500 series "Main Amplifier" PC boards - but this function is only enabled on the "higher order" models (1520). I don't have enough of the schematics to fully analyze this however, so I can't suggest if/how it can be turned on or off.

Keep your heads clean and your tails out!

Charles King


Offline heideana

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Re: IEC Equalization
« Reply #3 on: January 17, 2007, 05:44:27 PM »
FYI...I'm pretty sure the Technics RS-1520US was a US unit aimed at pseudo-studio crowd.  It has balanced I/O, NAB/IEC EQ switch and built-in tone oscillator to fine-tune bias....I bought it primarily for the balanced I/O and seems I lucked out with the IEC EQ switch...best, Hopkins
Studer A810 and Otari MTR-15...Klipsch CWIII's, KG2's & RF7's

Truth is a kind of error, so vaporize it to find your way to heaven, or at least to a smile...