Pre-emp for 50 uS is a 12K resistor in parallel with a 4n7 Cap, (4700 pF) Or 47K in Parallel with a 1 nF Cap, (1000pF) Hope that helps you out. That's all it is.

....That looks a little bit wrong - it's over 56µs.

Try two 10n in series (for 5n), with a 10k in parallel. That's very accurately 50µs.

Also, bear in mind that you need to roll off rapidly after 15kHz to prevent the "blinking stereo pilot" problem.

Hello, since I am using what it says thewoodstarr and works well.

Sietedj wrote:Hello, since I am using what it says thewoodstarr and works well.

That's good, and they will sound quite similar, but technically Albert is correct.

OK, then 10n are two capacitors in series and a 10k resistor in parallel. I do not understand it from (for5n)

Analyser wrote:

Sietedj wrote:Hello, since I am using what it says thewoodstarr and works well.

That's good, and they will sound quite similar, but technically Albert is correct.

What were the values you used? I vaguely remember 2 caps in parrallel with a 10k resistor back in the day. If I remember correctly they were 22uF (222 mylar?). It used to work fine, anyway.

I have this: 12K resistor in parallel with a Cap 4N7, (4700 pF)

Sietedj: capacitors in series calculate just like resistors in parallel:

1/CTotal = (1/C1) + (1/C2) etc...

So: two 100k resistors in parallel give 50k, and two 10n capacitors in series gives 5n.

Incidentally, there's a simple way to do the 15kHz lowpass filtering using a coil and capacitor in parallel as a lowpass "trap" - I'll put the details up here if anyone wants them.

I put all my audio processing at the studio end of the link, and the main rig actually has a de-emphasis circuit feeding it - even with stereo - since I use a pre-emphasis circuit for the whole baseband, including pilot, difference signal and even RDS!

My link receiver has a corresponding de-emphasis, which removes the 3dB/octave "tilt" that's added by the pre-emphasis. This helps to reduce link noise, and improves the signal to noise ratio of the stereo part of the composite multiplex stereo signal. It also prevents rig thieves using my gear.....

Since you should be doing your audio pre-emphasis at the studio end, you may as well spend a few pennies on the parts, and do it right. If you're processing mono, there's a simple (but very effective) circuit that I put up on the old Radionecks. If you had to buy all the parts, it'd cost less than £10 (as long as you didn't go to Maplin!), and if adjusted correctly, will completely eliminate the problem of over-enthusiastic DJs who never mind their levels, prevent the "blinking stereo pilot" problem, and sound nice on the air.

If you're doing stereo, then there's a little more to it, and if you're going to add RDS into the mix, then there's even more....

Albert H
Thanks for the explanation. Do not know much about electronics, I'm just an amateur and also I have to translate with Google because you do not know much English, so I find it more complicated sometimes.
If you were kind enough to say what I have to buy to make the pre-emphasis correctly, it would be easier.
And if you say how to make the filter to 15kHz, the transmitter will stereo and RDS encoder.
Thanks for the help !!!

How is the pre-empth worked out?

So does 5n and 10k resistor calculate to 50us, ive search and search and cant figure it out

using the same 10k resistor id like to work out wat cap i need for 75us

Id like to have the the option for both 50us and 75us on the board im drawing up.

ok so i think i worked it out, ive asked question too soon

It was right on front of me all along hehe
10 x 5 = 50 (10k x 5n)

So....say I have several modules in my chain all with pre emph jumpers included on the manufacturers boards ( my st coder , limiter, link box, my exciter etc, where should i be applying the pre emphasis ? just so I have it right ....and is juggling pirate off the mark with his circuit?

Ragga - do the maths on the network in the diagram you posted, and you'll find that the actual pre-emphasis with the values shown is 47µs. The 100Ω series resistor will make the pre-emphasis start to work at 3.3kHz....

This is close to what you want, but the 47n would be better replaced with a couple of 100n caps in series (to give 50n) - which will give you 50µs exactly, beginning at 3kHz (that's what the 100Ω series resistor is for).

Remember, you're going to have around 5.6V on the lead coming out of the collector of the transistor. If you use a high value of resistor there (100k will do), you can use the collector voltage to bias the modulation varicap. If you're going to do that, the +12V needs to be stabilised and filtered.

I've got something here and it has 10k resistor with 4n7 cap, does that work out to be 47uS then?

Albert H wrote:Ragga - do the maths on the network in the diagram you posted, and you'll find that the actual pre-emphasis with the values shown is 47µs. The 100Ω series resistor will make the pre-emphasis start to work at 3.3kHz....

This is close to what you want, but the 47n would be better replaced with a couple of 100n caps in series (to give 50n) - which will give you 50µs exactly, beginning at 3kHz (that's what the 100Ω series resistor is for).

Remember, you're going to have around 5.6V on the lead coming out of the collector of the transistor. If you use a high value of resistor there (100k will do), you can use the collector voltage to bias the modulation varicap. If you're going to do that, the +12V needs to be stabilised and filtered.

Apply pre-emphasis at the first point in the chain, ie before the audio limiter input.

Elopid wrote:I've got something here and it has 10k resistor with 4n7 cap, does that work out to be 47uS then?

Yes.

Elopid wrote:I've got something here and it has 10k resistor with 4n7 cap, does that work out to be 47uS then?

Exactly

Thanks Albert , Analyser.
Tbh Albert I hadnt given this preamp circuit too much thought I'd just gone to it because I need to add preemphasis and jugglingpirates site was one where i remembered there was a circuit described with it added, now i know different I will go for the 50us instead, after all thats the real value

Remember, you're going to have around 5.6V on the lead coming out of the collector of the transistor

Hmm that seems very high considering it is supposed to feed directly into jugglingpirates opamp gunn mod circuit below..can this be right?



Ive just had a look in my old link (ive been on a phone for a bit but its not reliable) and i'm sure ive got one of your circuits wired up to my gunn Albert! A Pair of voltage regulators and a couple of transistors plus assorted bits ....bollocks, my soldering was much better a few years ago

The 2µ2 going to the + (non-inverting) input of the op-amp will provide DC blocking, so the voltage from the transistor collector won't get through. If you use the circuit above, and add two 1n caps and a 10k in series between the - (inverting) input of the op-amp and the positive end of the 1µ capacitor. That'll give you 50µs pre-emphasis as well!

Like this:
It'll save you all the preamp stage components!

NB: The TL071 is a slightly better op-amp for this purpose. It's pin-compatible with the 081, but lower noise and slightly higher output current capability, so it'll run cold. The transistor can be either a 2N3053 or the BFY51. Either should be fitted with a small heatsink.

The 2µ2 will provide DC blocking,

duh! how did i miss that ? ...oh yeah I havent had any sleep for 36 hours .

As always, thanks Albert for your help ..and your patience