Mix Bus Compressor from scratch

[Analog_Fan]

With the transistor you still burn the power up. Why do you think the transistor gets hot. Hint "transistor" is short for "transfer resistor". As others have siad you get a filtering effect with the resistor anyway.

Sure, but now are guessing somewhat.
The LA-2A sidechain and others circuits is designed for 270/275 V, when i see their circuits that's a long way from 323 V rectified.'
Add/subtract +/-10 % variations of the daily grid, the properties of the power resistor, etc.
Sure it works, but if you're a nitty ...

A, i would flick a mosfet to down grade 323 V (rectified) or
B, flick some H bridge from 9 V to 275 V or
C, have a company roll me a dedicated transformer or do it yourself.

The 12ax7 datasheet talks about a few milli amp.



I'm always stunned that they can get like 500 mA from a thing that's as big as your thumb.

 

[Rob Flinn]

Sure, but now are guessing somewhat.
The LA-2A sidechain and others circuits is designed for 270/275 V, when i see their circuits that's a long way from 323 V rectified.'
Add/subtract +/-10 % variations of the daily grid, the properties of the power resistor, etc.
Sure it works, but if you're a nitty ...

A, i would flick a mosfet to down grade 323 V (rectified) or
B, flick some H bridge from 9 V to 275 V or
C, have a company roll me a dedicated transformer or do it yourself.

The 12ax7 datasheet talks about a few milli amp.



I'm always stunned that they can get like 500 mA from a thing that's as big as your thumb.

I work for quite a few studios that have real La2a's, Pultecs, Gates, V72's etc. I've never see anyone replace the PSU with a transistor regulated one in any of these units because they deemed the unit to be unusable without one. In fact nobody has ever complained to me about the unregulated PSU's or even mentioned them. Maybe you're overthinking things......

 

[Analog_Fan]

I work for quite a few studios that have real La2a's, Pultecs, Gates, V72's etc. I've never see anyone replace the PSU with a transistor regulated one in any of these units because they deemed the unit to be unusable without one. In fact nobody has ever complained to me about the unregulated PSU's or even mentioned them. Maybe you're overthinking things......

Well, many folks also like nostalgia.
These things where designed in the 60ties, fully mathological correct, but they didn't know better back than.

https://www.youtube.com/@HyperspacePirate
This guy, uses ferrite cores, you can buy at mouser and co and creates voltages like 500.000 V from 12 V with it.
it is possible to achieve these 275 V or any voltage with some tricks, using ferrite cores and 555 timers.
He shows the schematics and results.

The new official La-2a is the size of a pedal.

 

[emrr]

Propensity for reinventing the wheel retroactively in electronics DIY. Question should mostly be a consideration of number of potential failure points and longevity, with a historical overview of what has and hasn’t worked well in the past. Work in a repair shop a bit, you’ll rearrange your perspective.

Analog_Fan should stop trolling this thread and start a new one, if so certain. The hubris feels significant.

It’s safe to say “they didn’t know any better back then” is an ignorant wildly out of context statement.

 

[Analog_Fan]

I work for quite a few studios that have real La2a's, Pultecs, Gates, V72's etc. I've never see anyone replace the PSU with a transistor regulated one in any of these units because they deemed the unit to be unusable without one. In fact nobody has ever complained to me about the unregulated PSU's or even mentioned them. Maybe you're overthinking things......

the only problem is finding the right inductor ... and later some low pass filters.
the correct psu to start from.

Propensity for reinventing the wheel retroactively in electronics DIY. Question should mostly be a consideration of number of potential failure points and longevity, with a historical overview of what has and hasn’t worked well in the past. Work in a repair shop a bit, you’ll rearrange your perspective.

Analog_Fan should stop trolling this thread and start a new one, if so certain. The hubris feels significant.

It’s safe to say “they didn’t know any better back then” is an ignorant statement.

I'm not trolling, i would do what the circuit says, 275 V.
That's it, you just can't buy those transformer on specs made back than in 99% of the cases, unless you wanna buy 1000, i asked in Germany.

You can buy the metal E and I, these plastic cores.

 

[JohnRoberts]

It’s safe to say “they didn’t know any better back then” is an ignorant statement.

A little bit true, but based on personal ASSumptions about what "better" means.
===
Let's play nice and stop trying to veer this thread away from Dave's project design.

JR

 

[Analog_Fan]

Well, the tubes just uses max 5 milli amp but at 300 V.
says 12ax7.

than you can conserve the original resistor values.
how it's intended. back than.

i did spend some time on finding metal cores for ring cores.
accept for the regulator E and I stuf.

 

[slipperyflax]

Well I believe Dave has finished this one but I'm looking forward to Analog_Fans new thread about his version.

I've really enjoyed your build Dave! Thanks!

 

[DaveP]

This project is not quite finished.............
I was preparing to measure the signal:noise ratio when I found that my scope probe had a 162kHz sine wave on it, especially when I touch the chassis case of the mix bus when it's on, its much less when the EIC plug is out...........
I have turned off lights (LEDs) to no effect

The signal is being amplified by the circuit making it difficult to measure noise etc.

Any ideas? Maybe it's Analog_Fan's Switch Mode Power Supply coming down the line?
best
DaveP

 

[[email protected]]

With the transistor you still burn the power up. Why do you think the transistor gets hot. Hint "transistor" is short for "transfer resistor". As others have siad you get a filtering effect with the resistor anyway.

Hi rob

Hope you are well

 

[ruffrecords]

But you got advantage, you can aim pretty exact for the 270 (volts) and not need to burn it.

Class A tube preamp circuits are very tolerant of HT voltage. There really is no advantage in a specific HT voltage.

Cheers

Ian

 

[Rob Flinn]

Hi rob

Hope you are well

Yes, thanks Ian. Hope you and family are well too.

 

[DaveP]

I just searched google for 162kHz interference and it came up with the French long wave transmitter at Allouis. This is 200km away from me but is strong enough to give me 5mVp-p on my scope! Any ideas?
best
DaveP

 

[[email protected]]

Yes, thanks Ian. Hope you and family are well too.

Like your profile picture

 

[thomasdf]

I just searched google for 162kHz interference and it came up with the French long wave transmitter at Allouis. This is 200km away from me but is strong enough to give me 5mVp-p on my scope! Any ideas?
best
DaveP

Using ferrite beads or small inductor on the input ? Or does it get in the audio at some other point of the path. ? Are you concerned the bats might hear it, or does it mess with the audio / functionning of the comp ?

 

[DaveP]

or does it mess with the audio / functionning of the comp ?

I am trying to measure the signal to noise ratio because my DMM will not respond to noise frequencies. Normally I can measure noise on the scope but the signal is swamped by the 162kHz .
best
DaveP

 

[Stevie342000]

I am trying to measure the signal to noise ratio because my DMM will not respond to noise frequencies. Normally I can measure noise on the scope but the signal is swamped by the 162kHz .
best
DaveP

Hello Dave another excellent job looking forward to the final set of schematics and I am old school if worked then it will work now and with judicious usage of modernisms where applicable (better tolerance passives whilst we still have them) but as Ian said Class A does not care in this and simple is often the best solution.

We have been here before with my comment a Notch Filter at 162Khz with some variability until that signal interference is gone? Yes the Fairchild equaliser. Just a thought?

Do I recall correctly that you said this will be your last project?

 

[13engrsapper]

I am trying to measure the signal to noise ratio because my DMM will not respond to noise frequencies. Normally I can measure noise on the scope but the signal is swamped by the 162kHz .
best
DaveP

Maybe it is tIme for a Faraday cage, lol.

I am eager to see how this works out Dave.

-Tony

 

[DaveP]

Do I recall correctly that you said this will be your last project?

Yes, when I started the project I was in remission, now it has come back and I start a course of immunotherapy next week. In addition I have arthritis in both hands and some carpal tunnel problems in my right, probably caused by a lifetime of DIY!!!

I still have to get this mix bus to the finish line though
best
DaveP

 

[DaveP]

We have been here before with my comment a Notch Filter at 162Khz with some variability until that signal interference is gone? Yes the Fairchild equaliser. Just a thought?

Thanks for this, I need ideas like that.
best
DaveP