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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
Out of interest, why not a PNP Darlington? (obviously the others and the capacitors etc would have to be changed too)

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Wed Aug 02, 2017 7:42 am
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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
Sangoma wrote:
Out of interest, why not a PNP Darlington? (obviously the others and the capacitors etc would have to be changed too)



Just using what I have and I just don't think it would be necessary for what I'm playing with at the moment. I have a BD675 from the first amp, but I'll need two for this. The only other Darlingtons I have are TIP137s and as they use body diodes... probably will end in tears :)

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Thu Aug 03, 2017 6:58 am
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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
Time for an update:

Ok.. totally abandoned the class A design. Too power hungry.... problems with parasitic oscillations... impossible to control bias properly... it was a mess.

I've gone for class B, but with careful consideration of biasing to minimise crossover distortion.

Designed this amp from the ground up. I've simulated it in LTSpice, and it looks good. THD of 0.04 at 6 watts into 8 Ohms. Total power RMS should be around 7 watts.

Built on breadboard. Works well!

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Designed a new board for it.

Because the design reminds me of the old amps you used to get in 70s audio equipment, TVs, Radios etc, I thought I'd give it an appropriate name :)

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I need to change the driver transistors named on the board. They are now BD139/BD140s.

The design is working really well. Doing around 7 watts RMS with 24v feeding it.

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I love it when you design something from the ground up and it works. Great feeling.

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Fri Aug 11, 2017 11:10 pm
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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
OK. Some updates finally. (Been busy)

The above board was revised once more. Not due to any flaws, but because I've been tinkering and made the amplifier more powerful. Basically, I've reconfigured and adjusted it for 30V, so now it's a full fat, 10 watts RMS. As a result I thought it prudent to move the finals off the board (with their small heatsinks) and mounted them on a separate, larger heatsink.

I've been soak testing it... and abusing it, all morning, and it hasn't put a foot wrong.... utterly flawless, and sounds fantastic!

Amplifier on test....

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Here's a shot of the finished amplifier board. Very pleased with it. It sounds utterly fantastic. I started out just wanting a reasonably powerful amplifier adequete for communications use, but this redesign in a properly hi-fi capable amp.. albeit at 10 watts, but that 10 watts is RMS, so it's punchier than you would imagine.

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One final job remains before starting on the enclosure building, is a new PSU needs to be built. Not a big deal as PSUs are easy, but now it's a beefier amplifier, the original PSU is getting very warm. If it gets warm in open air, it will get hot in a sealed box. I'm redesigning it with a LM338 instead of a LM317, so should run cool.

I'll update the thread as progress on the rest of the build as it happens, but the electronic part is pretty much done. I'll upload pics of the new PSU, but after that, it's carpentry time.

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Thu Aug 17, 2017 12:59 pm
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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
Nice work Dave, maybe if you get time a short video of the amp in action?

I spent a reasonable length of time sourcing a suitable internal speaker for my SSB transceiver project and settled on a 2.5" driver from RS Components, was not cheap and came in at £12 but is very good build quality and has a decent frequency response.
I have yet to design the AF Power amplifier but will probably settle on a TDA2030 or similar for the small footprint, I will be driving this with a low noise NE5534 pre-amp after the product detector.

You should publish this design in PW and RADCOM, nice size project for most HAM's to tackle.

Rob.


Thu Aug 17, 2017 1:06 pm
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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
I've stripped it all down now Rob, as that was just temporary wiring. I'll do a video when it's finished, as it will sound much nicer when the drivers are in the enclosure.

Thanks :)

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Thu Aug 17, 2017 1:39 pm
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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
2E1IIP wrote:
I spent a reasonable length of time sourcing a suitable internal speaker for my SSB transceiver project and settled on a 2.5" driver from RS Components, was not cheap and came in at £12 but is very good build quality and has a decent frequency response.
I have yet to design the AF Power amplifier but will probably settle on a TDA2030 or similar for the small footprint, I will be driving this with a low noise NE5534 pre-amp after the product detector.


Yep.. the TDA2030 is a robust little thing. Makes more sense than building a discreet component amp. I just wanted to do so as a project. In your case, it makes much more sense to use an on-chip solution.


David

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Thu Aug 17, 2017 1:58 pm
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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
G0SLV wrote:
2E1IIP wrote:
I spent a reasonable length of time sourcing a suitable internal speaker for my SSB transceiver project and settled on a 2.5" driver from RS Components, was not cheap and came in at £12 but is very good build quality and has a decent frequency response.
I have yet to design the AF Power amplifier but will probably settle on a TDA2030 or similar for the small footprint, I will be driving this with a low noise NE5534 pre-amp after the product detector.


Yep.. the TDA2030 is a robust little thing. Makes more sense than building a discreet component amp. I just wanted to do so as a project. In your case, it makes much more sense to use an on-chip solution.


David

My issue is space Dave, I am constrained by the dimensions of the equipment enclosure I have bought (gonna be close)
I want to magnetically shield the speaker, do you know of an easy way to achieve this?


Thu Aug 17, 2017 2:04 pm
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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
I've never needed to do this Rob, so I'm not sure. Some speakers are supplied already shielded though. I'm sure there'll be tons of stuff on t'internet though :)

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Thu Aug 17, 2017 3:00 pm
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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
Just finished testing the new PSU. Works perfectly, from 3v to 30v and can deliver 3 amps before the LM338 gets too warm. With a bigger sink, it will do 5 amps easy, but it only needs to provide just over 1 amp, so will remain cool, even when inside the speaker enclosure. A 33v Zener is used in conjunction with the SCR, so it crowbars at that voltage.

It's less than half the size of the first one.

Forgive the rat's nest of wires - they're just for testing. The LED will be removed when fitted too, as the speaker's power LED will be linked directly to the transformer secondary winding via a diode. Reason being, using the board's LED means it stays on a while after switch off due to the smoothing cap discharging.

Nice little build.

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Fri Aug 18, 2017 8:44 pm
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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
A work of art and very well built.

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Fri Aug 18, 2017 9:09 pm
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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
Now it's tested, shaken down... abused, and generally soak tested.. If anyone wants to have a go at building this amplifier as a project, here's the finalised schematic.

Being based on a "quasi" amp design, it's very forgiving to input voltage (but wouldn't go past 35V with parts used), but the values on the schematic are all tested by me for for 30V input. If you don't have a scope, set the series value of R2 and R3 to 75K.. or preset R3 to 60K before installing and you'll be very close to, but below clipping.

Q5 and Q6 will need to be on a heatsink.

C4, C6 (Miller compensator) and C7 values are important.... they have a massive effect on sound quality.

I did another design that doesn't use the Miller comp cap, and uses global phase lead compensation instead, as it's a more modern way of doing things, but as "quasi" amps are a vintage topology any way... keep it real :) It sounds lovely. The revised version seemed sterile in the mid range - probably better for true hi-fi music applications, but for radio reception, this sounds so much nicer. You'd probably not build a quasi for true hi-fi use any way these days.


If you need a volume control, insert it just after the input decoupling cap C0.

It's ideal for line level input type voltages.... so if inputting a radio's ext speaker output, you'll need a 100K pot to trim it down to acceptable levels.


Attachment:
schematic-small.jpg
schematic-small.jpg [ 123.44 KiB | Viewed 128 times ]

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Sat Aug 19, 2017 7:21 am
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Post Re: Sick of over priced extention speakers from the big thre
PSU schematic.

As designed, it will crowbar at 33V. Chose a different value zener diode (D3) if you want to limit voltage to a lower level.

With a small heat sink, it's good for 3 amps. With a larger heat sink it will easily do the full 5 amps of the 338's rating.

Soft start speeds can be experimented with by playing with C2 and R4... but preferably C2. (1 second as designed here).

The GBU10 rectifier (10 amp) was chosen so it needs no heatsink at rated output. You can use a smaller one if you sink it appropriately.

It's important to set the trimmer R5 to the middle (around 2K) when building, or it may just crowbar when powered up. If it does blow the fuse.... check this.

Fuse MUST be a fast blow design, and must be chosen to match your intended current limit. The LM338 has current limiting built in, but it is 5 amps. If you need a lower level, chose a matching fuse value.

Transformer should be chosen for a potential 5 amp draw from the PSU.

Be aware that transformer output voltages are AC. So a transformer with a 24V secondary, once rectified, will show over 30V. This is because AC is measured in RMS values and DC is not. DC value = AC value x 1.41. Bear this in mind when choosing a transformer. I used a 24v secondary transformer. That will be good for 35v without stressing the regulator.

Cap rating should exceed used voltages. Use 50v devices for reliability

Resistors are 500mw rated.


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PSU Schematic.jpg
PSU Schematic.jpg [ 130.18 KiB | Viewed 126 times ]

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Sat Aug 19, 2017 7:41 am
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 Sick of over priced extention speakers from the big three. 
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Post Re: Sick of over priced extention speakers from the big thre
Spotted a mistake on PSU schematic.

R3 should be 120 Ohms. The 220 was a hang over from the LM317 version. I'll attach a new one in a min. Ignore above diagram.

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Sat Aug 19, 2017 8:28 am
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Post Re: Sick of over priced extention speakers from the big thre
New diagram attached.... ignore the first PSU diagram.


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Sat Aug 19, 2017 9:23 am
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