50 uS Pre-Emp

[Albert H]

Ragga - if you use the circuit I've put above your last post, you'll see that you don't actually need the pre-amplifier stage at all. The pre-emphasis can be easily achieved using the modulator op-amp, and if you need more audio gain (though you probably shouldn't), just increase the value of the 100kΩ resistor between the 10k preset and pin 2 of the op-amp. If you increase it to 470k, you'll have the same gain as the original pre-amplifier and modulator combination, but this is probably going to be too much (you'd have to turn the 5k pot right down!).

[Shedbuilt]

A

[Shedbuilt]

Sorry. I made a nonsense post; tried to edit it; ended up quoting myself and posting twice.
I used to use a very similar modulator circuit (op amp with an emitter follower), and implemented pre-emphasis in much the same way. I did the voltage control slightly differently, but otherwise very similar.

[rigmo]

I needs active preemphasis..with op amp.. do you have for share
i found this two...
https://www.circuitlib.com/index.php/sc ... pathway-32
http://www.radanpro.com/Radan2400/Radio ... phasis.htm

[Krakatoa]

The first one on circuitlib looks correct. The second has too much amplification and the flatness after de-emphasis is not good (I tried a long time ago).

[Albert H]

The second circuit is fine - if built as described. The HF clipper can be useful with some types of programme material, but should be used gently, so that you don't get the grating harshness of a clipper. Mark Weiss (the designer of the circuit) is an old friend of mine, and his little radio station was the best sounding thing on the dial! He took great pains to get the shape of his filters correct - so that his M (sum) signal was >70dB down by the 19 kHz pilot. He also did some tweaks to the S (difference) signal to enhance the sound stage, and he ended up with a wonderful stereo signal, with low noise and distortion. He used quite aggressive compression and limiting, but this wasn't obvious to the listener as he took care to get the time constants of his compressors and limiters just right, and used a number of psychoacoustic tricks to make it sound really good!

Audio processing is a black art - I've spent as much time designing and building audio processors as I have on the RF side of broadcasting. My current FM stereo design is commercially available (in a 2U 19" rack case) for around $7400, and provides a stereo (balanced) audio in to MPX out one-box solution. Secondhand (earlier) versions sometimes come up on Ebay for around $3000, and still destroy stations using Orban rubbish!

[Albert H]

Rigmo - why do you need active pre-emphasis? I'll happily put up details of various pre-emphasis approaches I've used over the years (both active and passive). If you want some suggested circuit, just ask!

[rigmo]

Rigmo - why do you need active pre-emphasis? I'll happily put up details of various pre-emphasis approaches I've used over the years (both active and passive). If you want some suggested circuit, just ask!

Saint Albert
for this moment i'm looking for side of PLL exciter... "..simple preemphasis circuits attenuated a lot the audio input" right?
and also i draw new pira limiter clipper compressor... ill share here...

[rigmo]

Audio processing is a black art - I've spent as much time designing and building audio processors as I have on the RF side of broadcasting. My current FM stereo design is commercially available (in a 2U 19" rack case) for around $7400, and provides a stereo (balanced) audio in to MPX out one-box solution. Secondhand (earlier) versions sometimes come up on Ebay for around $3000, and still destroy stations using Orban rubbish!

Today stereo tool with proper audio card beat ORBAN (proper sound card who can process exact instruction like marian trace8 )
Omnia 9 is based on stereo tool to..

[mikroman]

Nope. Omnia 9 is a work of Leif Claesson. Previous work on BAO was transferred to Omnia9 with additional advanced options. There is a part of the technology incorporated from S.Tool (declipper, umpx). In terms of loudness, S.Tool has an advantage, but from the previous practice with BAO, a more natural sound can be produced. Also the stability of the application itself is on the side of BAO. I say all this from experience so far and based on personal impression.

PS I’ve tested quite a number of more expensive sound cards to create MPX, you can’t believe what wonders a cheap integrated card in the ancient Dell 755 series can do. The 3.0g core 2 duo is still capable of spinning software of this kind. If you have it somewhere this old machine (mid tower) wipe the dust and try it. The SFF version can go crazy near RF sources.

[rigmo]

PS I’ve tested quite a number of more expensive sound cards to create MPX, you can’t believe what wonders a cheap integrated card in the ancient Dell 755 series can do. The 3.0g core 2 duo is still capable of spinning software of this kind. If you have it somewhere this old machine (mid tower) wipe the dust and try it. The SFF version can go crazy near RF sources.

First Of all thank you for sharing ..
and you mean for this machine?
https://www.overstock.com/Electronics/D ... oduct.html

[mikroman]

that is the small form factor -sff version. although it is the same chipset, this version has a bad shield, so it goes crazy combined with RF equipment. The minitower works properly. I bought two pieces for 50 euros;). With the original power supply the sound card is extremely quiet, the phase and amplitude characteristic is very good. Here is an illustration: https://sakoonsay.com/product/dell-opti ... 4gb-250gb/

Tonight I was in a workshop, here’s what a combination of dell and exciter looks like:
https://ibb.co/FH7W6DZ

https://ibb.co/3fzGmyg

[ronald001]

Dell Optiplex 755 / 760 / 780 / 790 ( and others Core2Duo's ) will work fine.
Just make sure that the onboard soundcard is 192Khz capable..

When using Asio4All - even low latency processing is possible with the onboard soundcard.

Rigmo, please don't pay 200 USD for a 780!

755 is around 25/35 Euro
760 35/45 euro
780 45/55 euro
790 50/60 euro

[rigmo]

Rigmo - why do you need active pre-emphasis? I'll happily put up details of various pre-emphasis approaches I've used over the years (both active and passive). If you want some suggested circuit, just ask!

on our hand made exciters we haven't preemphasis . for example if we use on the input of the pira a non active preemphasis we must drive the audio to twice the level. active preemphasis with op amp solve the problem and to have the same level on the input.
I notices PCS electronics exciter have the same problem audio level input ...

[mikroman]

in the 3000, 6000 and 2015+ series the 50us is not accurate. If you have a reference tuner with correct deemphasis, connect it to some ppm dB meter. Modulate the transmitter with 400Hz 1KHz 10KHz and 15KHz. You will have a noticeable rolloff at the end of the band. Also with a 50us jumper on the PCS, there is no chance of achieving 100% modulation without distortion. But considering how much it all costs, it's OK.
You’ll also have + 3dB in the band below 100Hz with nasty phase distortion in the first 3000, 6000 and 7000 series. Whether this was corrected later as in the 2015+ version, I don’t know.

[rigmo]

in the 3000, 6000 and 2015+ series the 50us is not accurate. If you have a reference tuner with correct deemphasis, connect it to some ppm dB meter. Modulate the transmitter with 400Hz 1KHz 10KHz and 15KHz. You will have a noticeable rolloff at the end of the band. Also with a 50us jumper on the PCS, there is no chance of achieving 100% modulation without distortion. But considering how much it all costs, it's OK.
You’ll also have + 3dB in the band below 100Hz with nasty phase distortion in the first 3000, 6000 and 7000 series. Whether this was corrected later as in the 2015+ version, I don’t know.

Now is 100 clear about pcs... i do not make expertise but i notice problem with volume level with 2015+ now i see they have v2
with MAXPRO8015 i believe is all good...

[mikroman]

The PCS owner has good ideas, but skips thoroughly working on the beta phase of the prototype before mass production. So something always needs a tweak, and some things unfortunately can't even be done without a schematic and smd accessories. I already wrote somewhere that 2015+ V2 has a fixed audio lacks (MPX). So this old model and the 3. generations of the 3000 series (older one) are devices with good audio response. But there is also common a pll loop problem (audio rumbling is heard on part of the VHF II spectrum) in series 2015+. So in that case the 10uf electrolyte on qsonic should be replaced with a smaller value. It also lacks a trimmer for precise frequency tuning that can deviate from 1 to 5 KHZ. It further has a spur in the airband that is low (about cca -55dBc). But if this exciter were to be connected to a PA 500W + it would not meet legal norms. That is why later series were made with metal cans on the oscillator / pll. Hundreds more pages of analysis could be written about this manufactory, but I repeat for that money enthusiasts cannot find a better product (2015+ cca 80e).

[rigmo]

Microman, PCS ,I find out thy fix problems in new models..

[mikroman]

It is good to hear firsthand information. soon i will probably order module for testing. It would be good to hear a review of new products (50 / 100w from the 8000 series). The older series (50w/6000 - single board module) had problems with overheating and spurious. I hope that is also resolved.

[Albert H]

We had a few PCS units for evaluation (we had a customer who was thinking of using them for local "filler" sites). The 1 Watt unit was good enough on the RF part, but the stereo coder was poor, and the pre-emphasis sounded weird. A few component changes later, we got reasonable results, and used a couple of them through attenuators for 300mW drive-in cinema applications.

The higher power units had too many problems to consider them to be viable products. Their PAs had lots of spurious outputs, and were very unstable into unfavourable loads. We tried isolating their exciters and seeing if the exciters were clean, and we found that they were reasonably good. Unfortunately, there were a few layout issues, heat dissipation problems, and the spurs and harmonics from the PAs made them unusable.

I tried attenuating the input to one of the PAs - to see if it was being overdriven - and the harmonics reduced, but the spurs remained, and actually worsened in one case. I was not impressed. I tried improving the supply rail RF bypassing, and this reduced the spurious a little, but not enough to allow connection to an antenna in a commercial installation.

In the event, the rigs were sold on to a Greek company (at a loss) for export to Africa, and we went with rather more expensive but much better performing Bext units.