Menu

Show posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Show posts Menu

Messages - J M Fahey

#1
Schematics and Layouts / Re: FAL Super 100 4 channel PA
February 15, 2025, 09:46:22 AM
Quote from: Bandito on February 14, 2025, 04:41:04 PMExcellent! I am East Devon, UK. Done the cleaning. The Amp works but sounds weak and different on channels 1/2 compared to 3/4.
It should.
Channels 3-4 are Instrument (Guitar/Bass) level so  more sensitive, 1-2 are high impedance Line level, think a Grammophone with a crystal/ceramic pickup, a radio tuner or tape recorder output, etc.
Any modern pedalboard would work fine there.

If you want to convert 1-2 to 3-4 specs, replace current 1M pots and 1M mixing resistors with 50k pots and 47k rtesistors, look at inputs in the schematic kindly provided by G1

QuoteHas 3 sockets for speakers.  1 and 2 (straight parallel connection) work, but the slave (3) does not.
1 and 2 are regular speaker outs, 8 ohm impedance *total* so 16 ohm each if using both.



The 3rd one, clearly marked Slave, is NOT a speaker out but a Line out, meant to drive an extra power amp with its own speakers.

Old school design, not surprising in an early 70s amp.

QuoteIs this a "good" amp, worthy of investment?

You should ask your Financial Manager for that.

In my book, for a Musician, Amps (and Instruments and any Musical stuff) are either useful, good sounding, etc. or not.

I reserve the word "investment" for Tesla stock, gold, Bitcoin and similar stuff.

FWIW that amp is quite old style but very well made, working fine (except for some "cleaning" issues, of course) for 50 years now.
#2
Schematics and Layouts / Re: FAL Super 100 4 channel PA
February 14, 2025, 06:25:49 AM
Thanks G1

Looks VERY much like an unauthorized Traynor clone, which also made a similar 4-passive-input mixer PA, YVM something.  YVM4?

Doubt anybody will "repair it for fun" though.

But maybe all it needs is some love and care: clean all pots and jacks with Deoxit or similar good quality product, (NOT WD40), check all wires are intact, etc.
Schematic apparently hints at a plug-in board.
If so, pull it, clean socket with compressed air, squirt Deoxit on contacts and wipe them with clean paper towels, etc.

It "should" work.

Do NOT start pulling parts at random "justt check them", you will needlessly damage the PCB.

A gut picture could help
#3
Amplifier Discussion / Re: Ruby amp from LM386M-1 module
February 14, 2025, 06:11:00 AM
That FET takes 25V with no problem, LM386 does not.

Your first video had better sound, it used a different speaker.

To my ears your amp now is unstable and jumps into oscillation, giving an ugly buzzy sound.

IF you have a scope, check that.

If not, pull board from new one and mount it in the old multimeter one and check.
#4
You trust our divination skills too much  8|

WHICH Amp? Brand and model?

Post a picture of headphone out.

Is it a Guitar or a Hi Fi amplifier?

Show the speaker output jacks/terminals too.

Any speaker selector switch on the front panel?

LOTS of questions.
#5
Amplifier Discussion / Re: Ruby amp from LM386M-1 module
February 11, 2025, 01:06:02 PM
Good!!! :dbtu:

No need go get *exact* cap values if not available, +/-20% is always close enough.
At least it was close enough for Leo Fender ;)

We are pampered by modern parts availability and precision; but way back then ... not that much ... yet they made killer amps.

Please continue posting your experiments  :tu:
#6
Thanks for posting, this one looks much cleaner.

There is an error at the power supply: the -12V rail is shown feeding 4558 Op Amp pin 8, it should go to pin 4

Maybe there are others, will check the full schematic later.
#7
Schematics and Layouts / Re: FAL Super 100 4 channel PA
February 10, 2025, 12:30:08 PM
You place too much trust in our divination skills ;)

We don´t even know what *Country* you are in, let alone state or province :o 
#8
Amplifier Discussion / Re: Ruby amp from LM386M-1 module
February 10, 2025, 12:26:15 PM
Just checked your YT video: killer sound  :tu:

Congratulations :)
#9
Interesting data, thanks.

I see a blast furnace as a tube, one end open, one end closed, with high pressure air injected at the closed end: an organ pipe (or a flute)





the analogy is evident.

It will definitely produce sound, at an easy to calculate frequency.

A 20 meter )(60 something feet) long pipe will produce very high power 4.29Hz, go figure.

Chest pounding indeed.

I was *smashed* by the power involved: an Austrian blast furnace used 8.4 MEGA watt blowers, an old 1919 US one used eight 2000kW steam powered ones.

At the same time, the very low frequency/long wavelength (40 meters) makes it very hard for human ears , separated by mere 30 cm/1 ft or so, to pinpoint source. 
#10
Being popular means nothing.
people copy each other ... the blind leading the blind.

5532 will have a *somewhat* lower noise floor, but pull twice as much current, have lower in put impedance (bipolar vs FET), in all not much advantage, if at all.

Not sure about your "desolder rather than pull."

In my book both go together.
#11
HAPPY to see Mouser now has them in stock, in large amounts.

It was not so for *years* , where they did not straight say "forget it" but gave ridiculous lead times for restocking.

Oh well, all is well that ends well.

In this case, it becomes again an option for a Guitar amp.

Personally much prefer the metal tab version

A slice of mica or a laminated silpad or even Mylar insulator will *always* be thinner (so better heat conducting) that some Epoxy or any other plastic that has to be *injected* into a die, and flow to fill it.

The OP can use that KT something board or any other tried and proven one.

There is a guy at DIY Audio called "Brian GT" who has been supplying high quality LM3886 boards for years now, hundreds have been built by Forum Members with success.
#12
I love LM3886 but they are out of production for years now.

Only non original ones freely available.

Most are straight junk; *maybe* a honest chip factory (in Asia of course) cloned one or makes something which reasonably works, who knows?, but that is still betting on unknown horses, how would you know who is who? :(

For "just one" not worth the risk.

The real ones are made by TI; they are not "officially" discontinued but typically on heavy backorder because they have WAY more profitable products to make, think car, solar energy, electric vehicles, etc. stuff.

A hobby type (commercial factories have switched to Class D) market is not even a drop in a bucket.

There is a specific tread on LM3886 unavailability on DIY Audio.
Currently 29 pages long, maybe that means something :o

https://www.diyaudio.com/community/threads/whats-going-on-with-lm3886-availability.386577/

Now and then a few appear at Mouser or Digikey or Farnell, they are swept out within hours.

*Maybe* you get lucky, I commercially make amplifiers and can not work with that uncertainty.
 
#13
Quote from: Tassieviking on December 28, 2024, 04:12:32 AMI think that PCB is not well designed, you will need a good heatsink on the power transistors but the transistors are right in the middle of the PCB, right behind the transistors where you should mount the heatsink bracket are 2 small footprints for 7 watt resistors.
Have I been asleep for centuries and 7 watt resistors have now shrunk right down in size ?
I would throw that PCB in the bin, I would never try to build that amp since it will undoubtedly lead to heartache.
You can buy a 100 watt class D amp for less then the cost of the components you need to complete it, and the transformer will be expensive as well. There are so many better and cheaper options out there.
Fully agree.

Checked KM Tech site out of curiosity, thinking it might be a Chinese site, it reeks of it.

To my surprise, it IS UK based, but otherwise the description fits .

There is a Business Model based on ordering stuff in China , wholesale, and reselling it.
PCBs can be ordered from fabricators such as PCB Way and others for peanuts, think 10 boards for $5 or so.
https://www.pcbway.com/
https://www.pcbway.com/orderonline.aspx?x=100&y=100&num=10&Layersquote=2&Thicknessquote=1.6

KM seems to be a hardworking PCB design office, churning out tons of PCBs.
Their catalog shows over 200 different designs, they have sold over 20000 empty boards, so the Business model is working.

Most are for the Retro Gaming market, think Amiga, Playstation, Atari, Amstrad, etc. but they also offer some Audio boards.

Most look reasonable, but when being so broad banded sometimes a lemon sneaks in.

Their LM3886 power amp looks fine, the Chipamp is "heat sink mountable" along an edge, they show a populated picture, proof it is "buildable":





Now the "150W Darlington Amp" looks like it was hastily thrown together.
It may meet the "electrical" connections but layout is ludicrous, the thing is unbuildable; so much so that they show a *simulation* where to boot Power Transistors are NOT inserted  :duh
Because they can´t.



Bonus points:
* as noted above, real 7W resistors will NOT fit there, no way.
* speaker ground return track is impossibly thin, it will explode on the first drum roll or something.

Funny notice: LM 3886 board has the "Use heat sink" warning printed on the silkscreen side ; "150W" one does not even mention them.  :lmao:

That said, IF you already bought it and have no option, it *may* be built, sort of (assuming design is fine, of which I am not sure) by mounting TIPs on a heatsink proper, and running wires to PCB holes.
Same with 7W resistors.
But why bother to correct a botched board design which to boot is also poor electrically?

If you want the hands on build challenge, fine with me, just get the Velleman board, either as a kit or on its own, use your own heatsink and transformer.

If you find another kit that looks suitable, feel free to post/link it here so we can have a look.


#14
You are lucky: exactly that same basic amp but properly made (not much more added, yet ...)is offered in kit form with an *excellent* 20 page assembly manual.

Enter the Velleman k8060.

Proper biasing, short protection, very flat assembly (board,  supply,  power transistors at the ends) make it easy to mount inside a Guitar amp chassis or a powered speaker back aluminum plate.

Circuit:  (eerily similar to the crude one):



Full  manual :  https://cdn.velleman.eu/downloads/0/illustrated/illustrated_assembly_manual_k8060.pdf

from:  https://www.velleman.eu/products/view/?id=360242

They even offer a heatsink, custom drilled or not, and a suitable power transformer.

Of course you can buy only the PCB and parts kit and mount it on your own heatsink or aluminum chassis and get a cheaper and maybe closer to home ANTEK toroid.

Anything from 26+26 to 30+30 VAC, 2.5 or 3A will do fine.

Amp marketing is "optimistic" as usual, forget the meaningless "200W peak power", it has honest 70-80W RMS into 8 ohms, which is perfect for live use.

#15
Use it as is, crude but does its job.

Later you can build a better one but it´s fine for experimenting.

It´s somewhat on the edge, use +/-40V rails or so (30+30VAC PT, 2,5A), 8 ohm load, beware it has NO short protection.

No big deal in a Combo or powered cabinet, somewhat dangerous on heads because someday you WILL meet a bad cable.

Power output is similar to a Bandit, VS8080, Crate or Laney 60, etc. , enough for playing around with a good speaker, say an Eminence or Celestion or modern Jensen

Not HiFi, Car, Home Theater class speakers.

Use good heatsinks.