A basic Limiter

[LeeCavanagh]

It’s hard to read those values of the components for the veroboard layout, those that do have labels, and those resistors color bands are not clear either. Maybe just me, or has anyone else had the same issue?

[Albert H]

Lee
Your eyes are getting old. I'll label everything for you later today

[LeeCavanagh]

Lee
Your eyes are getting old. I'll label everything for you later today

They are indeed getting old
Any help is most appreciated, i will build this as I’m curious how it sounds compared to stuff ive used in the past, thanks Albert

[Albert H]

OK. The components are labelled. I've also repositioned a couple of parts for an easier build. Please be sure to find the dots on the (blue) wire jumpers - the ground (in particular) connects a lot of tracks together. There's a green jumper wire for one pair of the clipper diodes - you can increase or reduce the clipping threshold.

I usually feed the audio in through a 100k log pot. (You can use 47k or 50k as well).

Mono Broadcast Processor.png

[LeeCavanagh]

Thanks Albert.
Where would you link the stereo signal from two devices?

[Albert H]

Thanks Albert.
Where would you link the stereo signal from two devices?

Stereo with this circuit is slightly tricky - you'd have to select two FETs with exactly the same pinch-off voltage. You'd join track "S" on the two boards, so that the stereo image stays in the same place....

I'll put up a different circuit for a stereo processor. It uses the same audio filtering (though it's good to add an extra stage of filtering to prevent "birdies" from HF audio beating with the 19 kHz pilot). The problem of matching FETs is eliminated by using two FETs in the same IC. It's another really simple design, but it works well. I'll also add an "oversampled" stereo coder that's easy to build

If you want to build a combined processor / coder, the Inovonics "David III" is easy enough to build. I was thinking of getting some PCBs made for these. The David III knocks the socks off the competition, and costs about a tenth of the price of the Orban / Bext combination so beloved of broadcasters in the USA.

One other thing - I've recently started using the MAX297CPA lowpass filter. If you clock it at 152kHz (from your 4060 crystal oscillator / divider and your 4864kHz crystal). the turnover frequency is just perfect for stereo broadcasting.

[EFIALTISFM]

Hi guys,

Can someone shed some light on the following...

1. Is the board labeling for the 2n3904 correct? Its labeled as BCE. Should it be CBE?
2. What part number can I use for the second transistor labeled only with its "DGS" pinouts

Thanks is advance

[reverend]

One other thing - I've recently started using the MAX297CPA lowpass filter. If you clock it at 152kHz (from your 4060 crystal oscillator / divider and your 4864kHz crystal). the turnover frequency is just perfect for stereo broadcasting.

In the words of Johnny Rotten, "I could be wrong (I could be right)", however the ratio of the filter turn-over frequency versus the clock frequency for a MAX297 is 50:1, so a clock frequency of 152 kHz would lead to a filter with a cut-off frequency of 3 kHz (or thereabouts). A clock frequency of 750 kHz is what's needed for a 15 kHz filter.

Rev

[rigmo]

why you not use 062 thy have lover noise flour

[Albert H]

The '062 is lower supply current, not lower distortion. They're also noisier than the '072.

[Albert H]

One other thing - I've recently started using the MAX297CPA lowpass filter. If you clock it at 152kHz (from your 4060 crystal oscillator / divider and your 4864kHz crystal). the turnover frequency is just perfect for stereo broadcasting.

In the words of Johnny Rotten, "I could be wrong (I could be right)", however the ratio of the filter turn-over frequency versus the clock frequency for a MAX297 is 50:1, so a clock frequency of 152 kHz would lead to a filter with a cut-off frequency of 3 kHz (or thereabouts). A clock frequency of 750 kHz is what's needed for a 15 kHz filter.

Rev

Whoops - brainfart! We use the 4864kHz clock and a two-chip CMOS PLL to give 760kHz for the LPF clock. It works really well. The Maxim chip is available from all the usual suspects for between £4 and £9 each (shop around!)

[EFIALTISFM]

OK. The components are labelled. I've also repositioned a couple of parts for an easier build. Please be sure to find the dots on the (blue) wire jumpers - the ground (in particular) connects a lot of tracks together. There's a green jumper wire for one pair of the clipper diodes - you can increase or reduce the clipping threshold.

I usually feed the audio in through a 100k log pot. (You can use 47k or 50k as well).

Mono Broadcast Processor.png

Hi Albert,

I would like to build this limiter but need some clarification on the board labeling.

1) What part number is the transistor labeled only with its DGS legs?
2) For the 2n3904, the board is labeled as BCE but the transistor is a CBD. Is the board labeling wrong?

Thank you.

[Albert H]

The FET was originally a 2n5457 and the transistor should be a 2N3707, 2SC1815 or a BC183L. I really should get some sleep!

[EFIALTISFM]

The FET was originally a 2n5457 and the transistor should be a 2N3707, 2SC1815 or a BC183L. I really should get some sleep!

so if the FET is a 2n5457 the board should be labeled DSG (and not DGS).

Albert... you are top notch

[rigmo]

I want to build the mono version.
Does it work on +/-12V also?
Because all my PS are 12v (13v max).

I could make +-12v from this module with a standard 12v DC power supply?

eBay item number:252049612127

https://www.aliexpress.com/item/33034420410

[Albert H]

The quick and simple way to build a dual rail supply is the approach that I used on the NRG Pro IV stereo coder. You feed AC to the board, and half-wave rectify with two diodes, and a couple of equal smoothing capacitors:

Dual Rail supply.png

The AC adaptor we used was rated at 300mA 12V AC out. It could be replaced with a small 12V transformer inside the box with the rest of the circuitry, but we decided that it was best to use a sealed commercial mains supply for the novice constructor market!

[EFIALTISFM]

The FET was originally a 2n5457 and the transistor should be a 2N3707, 2SC1815 or a BC183L. I really should get some sleep!

Hi Albert,

Can a J112 be used instead of the 2n5457? Could you recommend a few replacements?

Ta

[Albert H]

You could try the J112, but the pinch-off would be different.... I'll try one and let you know. Another option is the venerable 2N3819, with a slight tweak to the biasing.

[EFIALTISFM]

The AC adaptor we used was rated at 300mA 12V AC out. It could be replaced with a small 12V transformer inside the box with the rest of the circuitry, but we decided that it was best to use a sealed commercial mains supply for the novice constructor market!

Hi Albert,

Would a 14V AC out adaptor work as well as the 12V without "pushing it" or damaging something.
I know that 14V is not excessively high for many 12V devices but I thought I'd ask.
Ta

[Albert H]

A 14V AC adaptor would be OK. The regulators will stand up to 30V in (absolute maximum), but you really don't want to drop too much voltage, because they'll get warm!