Uh oh, my reel to reel line in too low?

[JL Sargent]

Well I finally got my RTR hooked up today and tried to record with it. I've not got something right. I suspect it might be the cables I'm using. When I monitor the line level input at the RTR machine is too low. I can hear the signal with my headphones on but its just too low. For input I'm using XLR to RCA cables without transformers. Now I know some of these XLR to RCA cables have transformers in them. I suspect I need the transformers due to an impedance mismatch maybe?

When I switch from "line" to "mic" the volume goes much higher but the music doesn't sound too good as expected. Any ideas?

The manual says that Line in is 100K unbalanced impedance

Mic in is 600 Ohm balanced.

[JL Sargent]

My goodness. I found this on the net. Not sure what to do at this point.

"Alternatively, a dedicated line level input was sometimes provided,
with an impedance of about 100k. Now a different problem reared its
ugly head, for audio cable can easily have a shunt capacitance of 100pF
per metre. A standard 1.5m length cable would have a shunt capacitance
that would cause more than a 6dB drop at 15kHz relative to low
frequencies, which is not a good thing for a hi-fi interconnecting
system."

Read more: http://hifi-stereo.suite101.com/article.cfm/din_hifi_vintage_audio_interface_matching#ixzz0TrdnERRN

[WMcD]

I'm quite sure you do need a transformer to make this work out right. Or, let me suggest you find a regular RCA type output to feed an RCA type input (high impedance).

It is long story: the 600 ohm system used for professional microphones and line feeds inherently creates relatively lower voltage than a customary unbalanced RCA connector type circuit.

Also, except for long runs of unbalanced lines and the phonograph type feeds, the capacitance of the cable itself is too low to worry about. So take care in interpreting such information.

You can search www.radioshack.com for microphone transformers and see two returns. It looks both use 1/4 inch on the high impedance side (in contrast to the XLR balanced on the other end of the transformer) but one transformer is a male and one a female -- at least from what I can see.. The applications of these are actually not limited to microphones.

There will likely be issues of males and females and sizes. I.e. you'll have to find a 1/4 inch phone plug (it is like the old big headphone jacks) to RCA adaptor on the high impedance side to wire into your R2R..

Further: Even assuming you have a consistent XLR 600 ohm system, it is somewhat dangerous to use a line level output (which is relatively high in signal level in the 600 ohm system, or any system) to feed a microphone level input (which is expecting a very low signal level). It might work if you can very much turn down the level of the output but I think that is not your situation. I expect you are finding that the microphone input gain has to be set very low.

Wm McD

[JL Sargent]

Hey, thanks for the help. To be clear this reel to reel machine has switches for the inputs. Line and MIC are my two choices. When switched to line its a 100K ohm impedance and when on MIC its a 600 ohm. The preamp I'm using has tape out which is 500ohm if that helps any.

Looking at the transformer offerings, none I have found will handle the 100K ohm side of the problem.

When I switch the RTRs input switches to "MIC" the gain is very high but also the sound is muffled and not right. When I switch to "Line" it sounds like good quality but the gain is too low for any use. Weird.

[Rhadamanthus]

You might give these guys a call and see if they can help you out.

I use a set of Hosa unbalanced XLR to RCA to connect my DAT deck.

http://www.sweetwater.com/c861--Unbalanced_Cables__RCA_to_XLR

[JL Sargent]

It appears the high impedance problem is usually associated with the RCA type connections. In my case the RTR machine has only XLR connections for audio. Thats where I have the high impedance at 100K ohms. There are no RCA connections on this machine.

I guess I will have to try reverse engineering a pair of those MIC transformers.

[djk]

"Line' input means different things in audio.

On consumer tape decks 0vu usually produces about 280mV, on pro the standard is 775mV.

For a transformer that would require about a 1K primary and a 10K secondary.

I would buy this unit:

http://www.edcorusa.com/Products/ShowProduct.aspx?ID=50

The 10K transformer will be fine driving the 100K tape input, it takes too long to explain why.

[JL Sargent]

Thanks Dennis, I appreciate it!

[JL Sargent]

For a followup on this:

I checked on that one Dennis linked to and they won't sell just one.[] Thats what I really want.

So I have XLR line inputs on my reel to reel tape deck that are 100K ohm impedance and my preamp out is only 500ohms. They wouldn't talk too good so:

I picked up a cheap lot of barrel transformers off Ebay (6 assorted ones) and tried a pair of those. It did help but not enough so I stacked em 2 transformers on each channel. Eureka, it lives! Now this is weird, the transformers are connected back to back. For Low Zs on the outside connections and the high Zs back to back. I thought they would cancel each other out but no thats how it works the best! How can that be?

I tried connecting the high Z end of the barrel transformer to the high Z input on each channel of the tape deck and no sound at all. Flipped it and it worked but not quite loud enough.

So the tape machine is a high Z XLR connector and its connected with adapters to the Low Z on the first transformer. Then the other end (the high Z on that trans) is connected to the next high Z on transformer #2. Then the low Z connection on trans #2 is connected to the TAPE out on my preamp which is supposedly only 500ohm impedance. Amazingly this setup works without noticeable noise. How is this even working? Looks like I put the whole thing together from a midnight autoparts store but it does work.

Anybody know how/why this crazy setup works? Interesting to me that if I used only one transformer per channel it would work but only backwards to the impedance logic! If I connected the high Z on tape machine to the recommended high Z side of one trans it was a no go.