Analog tape compression circuit

[flexagon]

hi all, been browsing this forum for awhile now, just taken the plunge.
i'm studying electronics at college, for the main reason of getting into audio design, but i'm still a bit of a beginner really.
for my first project i fancy building an analogue tape comp simulator, as i love that natural sounding saturation/compression. i've come across this design http://home3.netcarrier.com/~lxh2/tapesat.html
& have a question about it, it states that 'Any decent quality op-amps can be used'
so was wondering if anyone could enlighten me on this, as i'm not sure whether it means any op-amp or an audio specific one?
cheers

 

[unsolved]

I suppose a ordinary 741 will be good enough and a safe card. Otherwise, maybe NE5534?


//Erik

 

[jman 31]

This is a very vague application. I have been looking at a DAT 12 track recorder that I was thinking about getting to run my digital recordings through to "warm" them up. I am curious as to where in the scheme of things this would be used? Would you put it between the instrument and the board, or after the total mix in to a final wav file? I guess I just am not getting enough info. I think it would be really cool if it worked and it would save me roughly $650 usd, but me thinks it's to good to be true?

Jman

 

[unsolved]

If you will use it on the final mix, you probably will link the channels (otherwise they will sound different and make a skew stereo image... I think you may have more use of it if you insert it on the channel you are recording. Build one and test, maybe it sounds like crap, maybe it´s perfect on some kind of instrument, you´ll never know. Maybe it gives you a really fat snare... I think you shuld go that way.


Anyway, i prefere the real stuff for tape saturation, so i should use my B62 or B67...


//Erik

 

[jman 31]

I think I will!

 

[flexagon]

thanks for the replies,
i'll probably be using it between instrument & desk(to soundcard) as i recently transferred some older 8-track recordings onto p.c & was really impressed with how well the bass track sounded. whether it works or not is a different matter of course, but it looks a cheap build to mess about with!
also, if i may, is there a general rule of thumb when choosing resistors for audio, is there a best type, power rating, tolerance e.t.c? i.e. metal film/carbon comp, 0.25w/0.75w...
cheers

 

[jman 31]

Hey guys, I found this an interesting idea so I am going to try it also. I was wondering about this statement in the instructions:

"1. Power supply is a split supply of +/- 15 volts."

I am assuming that it would be a virtual ground supply, but is that +/- 15 volt supply divided into 7.5 volts, or is it a 30 volt supply divided into 15 volts?

By the way it's stated I would assume that it's the latter, but I would just be guessing. Here is the page again: http://home3.netcarrier.com/~lxh2/tapesat.html

Thanks
Jman

 

[unsolved]

that's right, 30 volts dividet to 2.. It's not critical unless you need +4dB out, if you are using a unbalanced circuit, 0,775 V, and if it's ok for the opamp, you can test the circuit with two 9V batteries..

question about resistors, take what you have. It doesn't matter... 5% will be fine,1/4 W, cheap and easy to find.

 

[jman 31]

Thanks for the quick response unsolved. I'll let you all know how this works when I get done. I will have to order the 1n34 diodes I think.

 

[flexagon]

quite by accident i stumbled across this site http://doorstopelectronics.googlepages.com/home2
there's a slight mod to the tape comp circuit on there.

hey jman, was wondering if you've built one yet & how it sounds?

 

[jman 31]

quite by accident i stumbled across this site http://doorstopelectronics.googlepages.com/home2
there's a slight mod to the tape comp circuit on there.

hey jman, was wondering if you've built one yet & how it sounds?

No, I never built it although it wouldn't take long to throw one together. In my other thread http://www.diyaudio.com/forums/showthread.php?s=&threadid=137007 Nigel said it was just a glorified fuzz box, so I decided not to put one together. Maybe I'll do one just for the fun of it. I'll let you know when I do.

Jman

 

[tron888]

sorry i know this may come across as dumb hehe but im very new and i cant figure out how to plug a power supply here ?! is there a chance anyone would explain to me or just draw from where to where the power would go?
id apreciate it a lot!
also if its possible to make a channel "B" and make it stereo?

 

[teemuk]

In my other thread DAT Simulator - diyAudio Nigel said it was just a glorified fuzz box.

It is.

Then again, even tape compression itself is nothing but a glorified way to introduce fuzz.

In case you wonder, here's how this glorified tape compression looks like:

An externally hosted image should be here but it was not working when we last tested it.

The wave on the left is an undistorted sine wave (which I used as the input signal), the wave in the middle is the same signal mildly "tape-compressed", and the wave on the right is the same signal with maximum tape compression. Some of the harshest clipping of peaks now even comes from overdriving the preamp of the recorder. The rows should be pretty self explanatory.

The outcome is actually pretty much identical to running the signal through a soft diode clipper and then filtering out some of the highest and lowest frequencies (which you can clearly observe from the way how the wave skews). No magic in this stuff, really. It's softer than brickwall clipping of digital recording media but it's definitely not anything that couldn't be achieved with very basic analog circuitry, such as the soft clipping circuit of the LXH2.

The 1Khz wave make look a bit "fuzzy" but that's due to wave plotting software of which the screen captures are taken from: At high frequencies the resolution is so small that the software begins to show the sampling points as little rectangular boxes.

The graphs are derived from recording sine wave @ 400 Hz and 1kHz to an analog tape, steadily "overdriving the tape" by turning up the gain of the recorder's preamp. At high enough levels the tape saturation will be replaced by harsher saturation of the amplifier itself. These were then recorded back to the computer and analysed with a basic wave file editor. Crude but quick and works.