Adding VU meters to Seduction/modified Technics?

[Teeg]

  I have a Seduction on order and plan on modding my RS1506 for direct-head output to the rear. Not so much a TP playback machine but just trying to better the playback of my pre-recorded collection. Only concern is that with the head mod, I lose the VU meters, which are often helpful when dealing with older or unknown tapes. At least they show whats coming off of each track regardless of what you think should be there.
  Has anyone done the head mod and still kept the meters, or added an outboard set?

Regards,
Tj

[docb]

Make a Y cable that comes off the Seduction outputs. Run one output leg of the cable to your preamp and run the other output leg to the line input of the Technics. Put the Technics monitor switches in the Source position. You can use your TP alignment tape to adjust the Line In Level controls to some arbitrary setting, like 0dB for the 1kHz tone.

The only potential downside to this is that driving both the preamp and the line input of the Technics might cut down the output level of the Seduction a bit. With Tube Repro's balanced output - low output impedance, higher gain and higher output level - this is not an issue, and I use a Y cable with my Nagra T-Audio in just this way.

Once you go to this trouble, you can say "OK, the meters work. Of course in playback the meters are pretty much just for looks." If you are wanting to use the meters for alignment, I would suggest instead to go right to getting an oscilloscope so that you can easily set the azimuth.

[Teeg]

  Thanks for the suggestion; when I build my Seduction, maybe it would be wise add a second pair of output jacks controlled by a switch, so the meters can be used just for a quick check.

 Watching the meters bounce back and forth does nothing for me except give a visual confirmation that there is information coming off of the tape, and which track is doing what.

Thanks,
tj

[bobschneider]

What's the problem with having the tape head outputs in parallel with the internal electronics of the deck?  That's the way I added playback head outs to my MX5050 - I just tapped into the audio PCB where the playback head is connected, but left the head also connected to the internal electronics.  I haven't used the head outs yet, since I don't yet have a suitable preamp, but the internal electronics (including the meters) still work fine.

[docb]

That's going to load the heads down, in other words, the output level of the head will be too low when both preamps are connected. The head only wants to see one preamp at a time. If you must retain the internal connection, install a switch to allow switching between the internal connection and the external one. We don't do this because it seems pointless to put the energy into putting in a switch that will be thrown just once. ;^)>

I'd also be concerned about the possibility of ground potential differences between the two switch settings. If there is a differential you might get a pop when you throw the switch, and that could magnetize the head.

[bobschneider]

Thanks, Doc.  I'll be sure to add a switch before I start using the head outputs.

[jcmusic]

That's going to load the heads down, in other words, the output level of the head will be too low when both preamps are connected. The head only wants to see one preamp at a time. If you must retain the internal connection, install a switch to allow switching between the internal connection and the external one. We don't do this because it seems pointless to put the energy into putting in a switch that will be thrown just once. ;^)>

I'd also be concerned about the possibility of ground potential differences between the two switch settings. If there is a differential you might get a pop when you throw the switch, and that could magnetize the head.

Doc,
What I did just to try it was to connect two sets of y connecters, and had no problems.

Jay

[stellavox]

Lack of VU meters can be a problem - let's talk about them a bit.

Most original tube machines used the big old Simpson (not Homer) VU meters which were effectively low impedance devices designed to be driven from 600 ohm source.  They will significantly load down a higher impedance source, like any unbalanced output - not to mention that their internal diodes (to rectify the AC to DC) can be a source of potential distortion.

To be safe, you want a "more modern" type of meter/circuit that typically uses an op amp on the front end to isolate it from the source and provide any necessary additional gain to drive the output device which can be an analog meter or multiple? LED's.  Then there is - what meter characteristic do you want - like "peak" or "average responding", peak hold - look them up.  There have been hundreds of construction articles about "add-on" meters.  Velleman and others have offered kits.  Maybe someone could do a literature survey, see what's out there and if any kits are available.  If you have the knowhow, a good way to get the parts is to scrounge the meter/LED's and driver from a trashed cassette (god knows NOT reel to reel) deck and reuse them.  With a lot of multiple LED designs, the driver circuitry is on the same PC board as the display and you only have to figure out/hook up maybe 5 wires; ground, (typical) 5 or 12V power, and L/R signal input.

Have fun

Charles   

[ironbut]

Hi Charles,
I've been thinking about buying one of the mic preamps from these guys. They always use quality components and have a pro/audiophile bent to their designs. They have a kit for LED VU meters which can be run off of batteries so you wouldn't have to worry about connecting to an existing power supply. I've got an email off to the designer to find out what the draw is but I would guess that a pair of 9v or whatever would last a long long time. $20 per channel. Take a look and see what you think.
http://www.fivefish.net/diy/ffstore.asp

[docb]

We priced "real" VU meters when we started looking into repro amp. You're talking around $800 for legitimate analog meters with the proper ballistics.

I suggest constructing a y cable that comes out of the Seduction and run the extra output from the cable cable back to the line input of the tape machine. The line input should have a pretty high impedance so it doesn't load the Seduction down too much. Just switch the monitor switch from tape to source. That's what I do with my Nagra T and a Tube repro.

[stellavox]

Steve,

The fivefish products look interesting and the prices seem very reasonable.

After looking at their VU meter kit and then searching for others on the net, I realized that there can be a problem using the "digital" approach (multiple display LED's for differing "VU's or dB's).  Most of the products/kits are actually for a "wide range" VU meter, and are built around the LM3915 chip whose "resolution" is (only) 3dB per LED. I'd opine that for calibration checking, you need a "meter" with a minimum resolution of 1db, (so 10 LED's could display a total of 10dB) and 0.5dB might be even better (display a total range of 5dB).  Remember that you'd like the frequency response of your deck to be within say 2 or 3db across the audio spectrum (good luck).

National also makes a LM3914 chip who's resolution is actually programmable - down to 200mv for 10 LED's which should fill the bill - but don't know if anyone makes a kit using this.  A quick look uncovered one analog kit: http://www.quasarelectronics.com/smart-kit/1039-analogue-stereo-vu-meter.htm.

Charles