Good Morning
Thanks that you remind me. I know ...i miss to do more audio stuff...
I have really a bad feeling that I actually cannot go ahead.
since Dec. 2019 I change my life = I am practical teacher now in electronic, bio medicine etc..
I am actually on the university to study (pedagogy) the next 3-4 years in parallel to my job. the next 5 years I have to close my bachelor-otherwise I will lose my job.
after my first exam in December 2020 i hope that i got a better time planning for audio
cu
chris
Thanks that you remind me. I know ...i miss to do more audio stuff...
I have really a bad feeling that I actually cannot go ahead.since Dec. 2019 I change my life = I am practical teacher now in electronic, bio medicine etc..
I am actually on the university to study (pedagogy
) the next 3-4 years in parallel to my job. the next 5 years I have to close my bachelor-otherwise I will lose my job.after my first exam in December 2020 i hope that i got a better time planning for audio
cu
chris
Sorry for my reduced electronic activity.
I am still busy cleaning-up after a Covid-death in the family. Quite a lot of work.
I need to update the IC comparison chart I once made.
Before my activity drop, we managed to show how it is possible to connect more LM1875 (or similar) in parallel for increased output current and how two groups of LM1875 can be connected for BTL with 4 times the output power. The necessary OP-AMP circuit for control was published.
My 3x2 “fake” LM1875 amplifier stage gave above 100W output. Unfortunately, the LM1875 were fake and had an overall failure after one LM1875 collapsed, probably due to self-oscillation. It worked well for about one hour.
In another forum thread, I tested various chip-amps as alternative to LM1875 with low closed-loop gain. Once when the Covid work is over, I will continue constructing composite amplifiers with parallel chip-amps but rarely BTL coupled. For my use, I do not need power above what SE configuration can deliver.
I am very happy to hear that Chris is well though stuck with other obligations for the time being.
I am still busy cleaning-up after a Covid-death in the family. Quite a lot of work.
I need to update the IC comparison chart I once made.
Before my activity drop, we managed to show how it is possible to connect more LM1875 (or similar) in parallel for increased output current and how two groups of LM1875 can be connected for BTL with 4 times the output power. The necessary OP-AMP circuit for control was published.
My 3x2 “fake” LM1875 amplifier stage gave above 100W output. Unfortunately, the LM1875 were fake and had an overall failure after one LM1875 collapsed, probably due to self-oscillation. It worked well for about one hour.
In another forum thread, I tested various chip-amps as alternative to LM1875 with low closed-loop gain. Once when the Covid work is over, I will continue constructing composite amplifiers with parallel chip-amps but rarely BTL coupled. For my use, I do not need power above what SE configuration can deliver.
I am very happy to hear that Chris is well though stuck with other obligations for the time being.
Thanks guys that would be nice and i really appreciate your help !!
the latest schematic is at post 577
but it should be corrected:
R4, R6, R8, R20, R22 and R24 should be 560R if we have -3,5 gain at the power ic.
my idea was to have big "welcome caps" (33000µFeach rail)at the psu terminals and bigger caps near each power ic e.g. europe chemicon 3900/35VµF...
chris
the latest schematic is at post 577
but it should be corrected:
R4, R6, R8, R20, R22 and R24 should be 560R if we have -3,5 gain at the power ic.
my idea was to have big "welcome caps" (33000µFeach rail)at the psu terminals and bigger caps near each power ic e.g. europe chemicon 3900/35VµF...
chris
Last edited:
Hello,
I just finished redrawing schematics to KiCad. Can someone take a look and verify if I didn't missed anything before I proceed with layout?
There is one thing bothering me.
PCB going to be big, I estimate around 25x10cm. There are 10 trimmers on schematics. Because of that, project becomes really expensive, defying the idea of good performance while being dirt-cheap. I wonder if LM1875 is worth the effort. Theoretically more expensive LM3886 could possibly be better and cheaper option as it's going to be much more compact and won't require trimming resistors.
Regards,
Miłosz
I just finished redrawing schematics to KiCad. Can someone take a look and verify if I didn't missed anything before I proceed with layout?
There is one thing bothering me.
PCB going to be big, I estimate around 25x10cm. There are 10 trimmers on schematics. Because of that, project becomes really expensive, defying the idea of good performance while being dirt-cheap. I wonder if LM1875 is worth the effort. Theoretically more expensive LM3886 could possibly be better and cheaper option as it's going to be much more compact and won't require trimming resistors.
Regards,
Miłosz
Hi Milosz
thanks you for your effort.
You are right that the pcb is not small. If you look some pages back to FF prototype its not really small.Yes the LM1875(3 euro) is not as good as the 3886. no mute...less power rating, no mute pin, small package...
a UTC 2050 is still available for 1 euro at reichelt and then the power chip is not expensive anymore.
maybe if you will to a second version with nearly all SMD parts then you can shrink the pcb.
but the initial idea by FF was that every power chip could be scaled to a power amp (BTL !!) and if you understand the principal you can do this for other chips too!
chris
thanks you for your effort.
You are right that the pcb is not small. If you look some pages back to FF prototype its not really small.Yes the LM1875(3 euro) is not as good as the 3886. no mute...less power rating, no mute pin, small package...
a UTC 2050 is still available for 1 euro at reichelt and then the power chip is not expensive anymore.
maybe if you will to a second version with nearly all SMD parts then you can shrink the pcb.
but the initial idea by FF was that every power chip could be scaled to a power amp (BTL !!) and if you understand the principal you can do this for other chips too!
chris
Small update. Board probably going to measure 200mm x 75mm.
Value errors at schematic are possible, but not really an issue until component shares same package.
I tried to use universal footprints. Most resistors are metal film 0.6W type (DIN0207 like Vishay Beyshlag SMA / BCcomponents MRS25 series).
Small film capacitors can be both with 2.5mm or 5mm lead spacing. Larger 4.7uF gonna be ceramic X7R, just didn't had that 3D model.
Value errors at schematic are possible, but not really an issue until component shares same package.
I tried to use universal footprints. Most resistors are metal film 0.6W type (DIN0207 like Vishay Beyshlag SMA / BCcomponents MRS25 series).
Small film capacitors can be both with 2.5mm or 5mm lead spacing. Larger 4.7uF gonna be ceramic X7R, just didn't had that 3D model.
Attachments
May i draw your attention to miniref and myref amps that are also from this site and have received much praise? They use howland current pumps for the output ic of which arrangement is not much talked about. Im curious what their advantage would be compared to a traditional gain + attenuated input setup as seen on this thread.