Roger Mayer RM57 build?

[dirty1_1garry]

i'm a sucker for a drawing!!! thanks ruud

would a 10468 type transformer be ok to use?

as input? not sure. May be in backward, like this (attached). In a such connection it works as stepdown, so you will get less level and less threshold of compression.

 

[RuudNL]

Would a 5534 be better on the output ?  At least it has some drive capability and in conjunction with a complementary pair of power transistors is quite good

Yes, a 5534 would give you more output 'power'.
But I used a TL074, because I liked the idea to have only one chip in the design.
Personally I would prefer the THAT receivers/drivers for balanced inputs and outputs.
Less iron = less distortion. (But maybe transformer distortion is what some people like...)

 

[RuudNL]

A 10K->600 ohm transformer will have a ratio of  ~16:1.
That means the level at the 600 ohm side is ~24 dB lower than at the 10 K side.

 

[dirty1_1garry]

A 10K->600 ohm transformer will have a ratio of  ~16:1.
That means the level at the 600 ohm side is ~24 dB lower than at the 10 K side.

I think you forgot square root.
10K:600 = 4:1 turn ratio. So 1V in = 0.25V output. 12dB gain loss.

 

[Spencerleehorton]

So are you now saying ideally a 1:1 or a 2:1 for input and for output it would be a 4:1 ratio?

 

[RuudNL]

I think you forgot square root.
10K:600 = 4:1 turn ratio. So 1V in = 0.25V output. 12dB gain loss.

Yes, you are right!
(Is was probably too early here!  )

 

[Spencerleehorton]

Mains hum coming from shoddy PSU i've built as i have an adjustable DC PSU which i've put on and with both channels it pulls 0.18A current at 18v.
Both channels noise wise sound more than acceptable, and this thing compresses like a beast!!!

Like you said Ruud the bottom end distorts quite badly so if there are any mods which could improve this?

I'm running unbalanced as I haven't built any TXF yet!! I think the 2018 version will be a real winner if the S/N comes down and the bottom end distortion is addressed.

Great fun compressor

could someone suggest a good PSU to build please, so i don't get any ripple, i'm using a 7818.

Ive splashed out £1.28 on a proper PSU!!!

 

[Spencerleehorton]

Typical it isn’t being delivered until Feb!!  So I’ll have to build one!!!
Pretty easy to copy from the pictures!!

 

[dasnevestheo]

link to that £1.28 PSU ?

 

[Spencerleehorton]

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F263346981532

 

[dasnevestheo]

Oh ok the PSU is single rail ?

 

[Spencerleehorton]

Yeah, ive made 3 pcbs now, will populate and test in the morning as i gotta 12 hour shift to do tonight!!!

 

[dasnevestheo]

Good luck with that !

 

[RuudNL]

This is my 'more serious' prototype.  Stereo limiter on 7 x 10 cm.
Signal to noise ratio is 81 dB ("A" weighted) re. 1 Volt.
Stereo tracking is within 0.5 dB (I found 2 'matched pairs' out of 20 FETs)
Distortion is 0.3% @ 10 dB limiting (400 Hz, fast attack, fast release).
Metering circuit is 'under construction'.
It will directly take the voltage from the gate of the FET, so no extra FET for the meter circuit.

 

[Spencerleehorton]

Great work, can’t wait to hear this version.

 

[ilfungo]

Great work, can’t wait to hear this version.

Me too!!!

 

[Spencerleehorton]

My stereo version is fully operational and sounds fantastic, top tip if you can, cut at 49hz and the distortion goes away.
If there was a way of doing this within the circuit perhaps? HPF?

 

[mjrippe]

My stereo version is fully operational and sounds fantastic, top tip if you can, cut at 49hz and the distortion goes away.
If there was a way of doing this within the circuit perhaps? HPF?

That's awfully close to the 50Hz mains.  Possibly power supply ripple?

 

[Spencerleehorton]

No I’m meaning when you input a signal into it, the distortion is reduced.
There is no mains hum now, clean as a whistle.

 

[RuudNL]

There is always a problem with low frequencies and fast release times.
In this case you get the situation that the release already sets in  during the waveform.
As a result, a sinewave will be converted in something that looks like a sawtooth.
The only solutions are: a longer release time, or less LF feeding the compressor.
(Or maybe: a high-pass filter in the side chain, but this means the lower frequencies will be less limited...)