Connecting line level 1v signals to 0,3v inputs teac 80-8

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Garagerock

New member
This may be a totally imbecile question but… if I take a mic pre that puts out line level ( I guess 1v to 1,3v to a reel to reel deck that wants to see -10db (0,3v 20k or more in ….without routing it all threw a mixer ) directly into the teac pre how would you go about. I think keeping the chains as short as possible is desired. I have few old pieces of gear and do not want to kill anything so I have to get the math around matching each component perfectly as I am pretty shure the pres need the 1v resistance to not fry over time. I want to connect some 70s altec stuff so … direct in threw pres and maybe bypassing or modding the pre cards and a seperate output mixer with comp and rev etc. could be desirable. It is that direct connecting that bothers me . As for finetuning specially drums the volumepot of the inputcards is pretty useful so what ways would you go ? Transformers maybe ? Then again I need to measure and do the math. It is a low tech fixed recordingsetup that way and normal people would route it all but then I would be going threw like three pres in. I want to drive things hard especially for drums on the way in and the mixerstage makes no sense to me . So I rather need 6 to 8 inputs that are line level for not always plugging things too crazy …
 
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A simple resistive attennuator of 12k Ohms in series with 3k9 will reduce the 1V line level by approximately 12dB and deliver you neg 10 signal of around 316mV. You can get more exact by using less common resistor values but it does not really matter.
Should you want to more accurately 'calibrate'the setup you can put 10k log pots in a tin and set things up with sine tones. This will allow you to keep all the meters in the system agreeing with each other. This is however often an exercise in futility because meters on different bits of kit have different 'ballistics' and even if they agree on sines (which you MUST use to line them up) they will surely waggle differently on programme!

You will not "kill" anything by using the 'wrong' input loads. Very old gear MIGHT be damaged by a total short and a blast of high level signal but not likely. Keep input Rs at 10k or higher and you will have no bother at all.

N.B. Put any attennuators at the input end of the line and use short, 2mtr ish max cables.

Dave.
 
An L Pad with R1 12k and R2 3k9 1/4 watt resistor's and that is it ?
And it would tame +4dbu level enough too ? Don‘t think I have such gear but understanding the principles is where the recording starts for me at the moment. As for fx loops …If I use old guitarpedals in that place what pad attenuation would that need for line level ?
Really I cannot thank you enough.
 
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Garagerock said:
An L Pad with R1 12k and R2 3k9 1/4 watt resistor's and that is it ?
And it would tame +4dbu level enough too ? Don‘t think I have such gear but understanding the principles is where the recording starts for me at the moment. As for fx loops …If I use old guitarpedals in that place what pad attenuation would that need for line level ?
Really I cannot thank you enough.
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Yes, 0.25W Rs are more than enough you can go wee'er if you like (buy big RCA plugs and fit them inside? )
+4dBu is only slightly above 1V rms at 1.228V so no worries there.

Dave.
 
Now the output is -10db at 0,3v also but 10k or more … am I okay assuming that both the signals are somehow instrument level tailored towards big ohm mics ? Analog is in charge here not me. I can build a fuzzbox but this is very new to me . I know I can feed this 10k signal to my good ok shitty mixer but why the heck is there half the ohm and how does it affect or better change the type of signal?
 
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Garagerock said:
Now the output is -10db at 0,3v also but 10k or more … that sounds like instrument level ??? Analog is in charge here not me. I can build a fuzzbox but this is very new to me . I know I can feed this to my shitty mixer but why the heck is there half the ohm and how does it affect or better change the type of signal? Yeah acoustic is great too .
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I don't really understand much of that? If you are confused about the loading and output resistance* of the pad then let me break it down for you...

The load resistance, i.e what the mic pre say 'sees' is about 14.8k assuming the pad is feeding a 10k input.
The output resistance of the pad is about 2.94k assuming the source driving it is close to zero, most mic pres are 100R or less. It is because the output resistance is few k that I say "keep it close to the recorder to avoid HF cable loss".
I promise you that is all you need to know.

*I use the term "resistance" here and not "impedance because neither the circuit nor the feed device have a resistance that various with frequency, at least over tht wanted audio band 20Hz to above 20kHz.

Dave.
 
Also worth pointing out that all this assumes there really is .3 or 1V most times, that's a sort of wish list level. if you have typical kit, it will cope perfectly well with too much and not enough - sometimes you run out of knob or fader travel, at the top or bottom, but most times you'll be fine. Getting it wrong just means distortion, or hiss - neither damaging.
 
Now I have my 0,3v 10k ohm signal comming from the reel to reel … should I pad the output fed it into my ol RFT mixer ( most basic wannabe broadcast console ). Sorry to be tripple checking but I had a mic pre die and learn more and more it wasn‘t a mishandling. What pad configuration could I use to bring line level equipment at 1v down to 0,3v ? Assuming the 1v unit gets it‘s needed load with the pad. Too kewl. Thanx
 
Garagerock said:
Now I have my 0,3v 10k ohm signal comming from the reel to reel … should I pad the output fed it into my ol RFT mixer ( most basic wannabe broadcast console ). Sorry to be tripple checking but I had a mic pre die and learn more and more it wasn‘t a mishandling. What pad configuration could I use to bring line level equipment at 1v down to 0,3v ? Assuming the 1v unit gets it‘s needed load with the pad. Too kewl. Thanx
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Unless the mixer uses old style 600 Ohm output transformers it will not "need " a load and will be perfectly happy to drive that 12k pad I described. It is almost impossible to damage a mixer's output circuit, most use an op amp and all of those in general use can stand an indefinite short. There might be some VERY old discrete transistor circuits that can be damaged but we have had very good op amps for well over 30 years.

Dave.
 
Buying into analogue is a hobby in itself. Buying test gear, demagnetisers, scopes, meters, alignment tapes. Learning how to do board level repairs, replacing failed parts, learning mechanics and logic. I suspect most analogue folk who use the gear to record have all these skills. For me, I have the skills, the equipment but the patience has gone. Rediscovering all the hard work required has convinced me analogue is NOT for me.

The other thing is a willingness to learn, that new folk seem not to have. In 50 years I’ve never killed anything, but tried so many crazy things. You do need to learn a bit of basic electronic theory, but it’s school science stuff really.

My old students at college grew up with modern gear and processes. Very often they were totally stumped by having to go backwards and forget stuff. The people who understand parallel compression, nested EQ and other clever techniques have to record totally differently. They’re used to easy adjustment and tweaking after and have to learn to record with signal to noise and distortion very clear in their heads. The idea you press record and don’t get a good recording is totally alien.

The other thing is they want to avoid the learning process and jump in at a high level. Watch a YouTube video and it works. Not with analogue it doesn’t!
 
Well the pre I killed or whatever was brand new and died after 5 minutes on me because I am so ugly and it hated my sound. Ace for 5 minutes. Replaced by the store. All they said cooool todays dud. It took me hours to recover. The thing is it has giant transformers … and not all pres state line level only exclamation point … that is where I get my trusty errrm 5 buck multimeter.
 
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Sure you can do it all faster in the box … all just to cut down screentime … wouldn‘t do complex composing without modern crap ;)
 
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Garagerock said:
Well the pre I killed or whatever was brand new and died after 5 minutes on me because I am so ugly and it hated my sound. Ace for 5 minutes. Replaced by the store. All they said cooool todays dud. It took me hours to recover. The thing is it has giant transformers … and not all pres state line level only exclamation point … that is where I get my trusty errrm 5 buck multimeter.
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Don't really understand that last sentence ? In any case beware the use of multimeters (digital?) for audio use. The vast majority lose accuracy above about 2kHz and some even as low as 1kHz. Even the so called "true rms" reading meters are only good at 'power' frequencies, say up to 400Hz

I have an old Fluke 83 DMM and that IS accurate past 20kHz but others I have had or used fell far short. Not only will they misread HF test signals but be very optimistic about noise!

The venerable Avo 8 was much better but even that was only good up to 10kHz or so. You can make a very decent analogue meter with a response past 50kHz easily with a VU meter movement and an op amp.

Dave.
 
I know. I tried to be sarcastic regarding the multimeter. Analogue is so cheap these days, it mainly takes space. I have the feeling that impedance matching is for audiophilliacs with expensive equipment but these guys just get someone installing their stuff with very pricey solutions. My first goal should have been just bypassing stuff in the teac. Making the teac itself line level. I am not dumping too much cash in my recordingcrap. It is not the ideal machine
 
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Garagerock said:
I know. I tried to be sarcastic regarding the multimeter. Analogue is so cheap these days, it mainly takes space. I have the feeling that impedance matching is for audiophilliacs with expensive equipment but these guys just get someone installing their stuff with very pricey solutions. My first goal should have been just bypassing stuff in the teac. Making the teac itself line level. I am not dumping too much cash in my recordingcrap. It is not the ideal machine
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Oh! OK well, don't give up the day job. Re "impedance matching" There is nothing in the audio domain than needs it. We do not even "match" speakers to valve amplifiers what is done is provide an "optimum load".

Dave.
 
I still do not trust pads in a in reamping box situation. Pluging a mic pre into a mic pre is pretty fucked up to begin with. The 80-8 is what it is.
 
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