A basic Limiter

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LeeCavanagh
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Re: A basic Limiter

Post by LeeCavanagh » Tue Dec 22, 2020 9:03 pm

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?
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Albert H
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Re: A basic Limiter

Post by Albert H » Wed Dec 23, 2020 11:32 pm

Lee
Your eyes are getting old. I'll label everything for you later today
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

LeeCavanagh
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Re: A basic Limiter

Post by LeeCavanagh » Thu Dec 24, 2020 2:52 pm

Albert H wrote:
Wed Dec 23, 2020 11:32 pm
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
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Re: A basic Limiter

Post by Albert H » Sun Dec 27, 2020 2:34 am

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
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LeeCavanagh
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Re: A basic Limiter

Post by LeeCavanagh » Mon Dec 28, 2020 11:39 pm

Thanks Albert.
Where would you link the stereo signal from two devices?
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Albert H
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Re: A basic Limiter

Post by Albert H » Tue Dec 29, 2020 2:36 am

LeeCavanagh wrote:
Mon Dec 28, 2020 11:39 pm
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.
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Re: A basic Limiter

Post by EFIALTISFM » Tue Sep 07, 2021 5:09 pm

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

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Re: A basic Limiter

Post by reverend » Wed Sep 08, 2021 9:01 am

Albert H wrote:
Tue Dec 29, 2020 2:36 am
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
if it ain't broke, keep tweaking

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Re: A basic Limiter

Post by rigmo » Wed Sep 08, 2021 6:23 pm

why you not use 062 thy have lover noise flour

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Re: A basic Limiter

Post by Albert H » Mon Sep 13, 2021 3:09 pm

The '062 is lower supply current, not lower distortion. They're also noisier than the '072.
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Re: A basic Limiter

Post by Albert H » Mon Sep 13, 2021 3:17 pm

reverend wrote:
Wed Sep 08, 2021 9:01 am
Albert H wrote:
Tue Dec 29, 2020 2:36 am
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!)
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Re: A basic Limiter

Post by EFIALTISFM » Tue Sep 14, 2021 8:16 pm

Albert H wrote:
Sun Dec 27, 2020 2:34 am
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
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Re: A basic Limiter

Post by Albert H » Wed Sep 15, 2021 4:04 am

The FET was originally a 2n5457 and the transistor should be a 2N3707, 2SC1815 or a BC183L. I really should get some sleep!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Re: A basic Limiter

Post by EFIALTISFM » Wed Sep 15, 2021 6:23 pm

Albert H wrote:
Wed Sep 15, 2021 4:04 am
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

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