♫♪ My little cheap Circlophone© ♫♪

From ears to loaf.

Well it has been a pleasure but what a journey. :smash:

  • Read +3000 posts, understand what you read
  • Redraw the PCB twice in KiCad First pcb no good, second better. Yes all files attached.
  • Create pcb gerber files and route the board on the mill (twice!)
  • Purchase all components and assembly
  • Put everything on hold 6 months because my lab power supply was broken:headbash:. So build a new one on top of this..
  • Test assembly, all working :up:
  • Purchase enclosure and the parts needed. Drill holes in enclosure and do final assembly with everything.
All in all around 24 months. Need to step up somewhat, if I shall continue with this. Still need to build my second GainCore and the Q17

Well final figures when everything fitted.
1. Rail Voltage - 25V
2. Offset Voltage - between 0.55mV (Both Channels)
3. Quiescent Current - ~160ma (input short)

Sound. Astonishing, just do it

Would I do it again = Yes
Price wise it is a cheap amplifier compared to other more exotic alternatives here at DIY audio. For the sound. Well read all other posts.
Others. Well from what I can see there is many flavors available. The challenge when attempting this undertaking for unexpired is to decide bjt or mosfet, Decide what power output What type of circuit pcb to select. There is many options in the this thread.
Or just make your own. For a head start, attached my stuff KiCad files. disclaimer, I think everything is OK the amp is playing so probably correct

And please if you’re doing a PCB or other stuff, please share your stuff with source files, and do not just post pictures on your design. Well frankly do not post at all. No one is interested in your property IP pictures. Sharing is caring. Always remember this.

Thanks for all help. And hat off for Elveedesign.

Brgds / Sander
FInally you finshed it heartiest congratulations.
I am yet to put my amp in a box. It is still Lying in my project cupboard assmebled like a assembly ie pbc transitors heatsink in that order ( sandwich).
I ahve managed to get 1.3mv offset on one and the other is 3.2mv, I have used the CCS with transistor and zener circuit instead of resistor. Planned to run it at 28volts with a 40VCT @ 250VA. just not decided on the transistor - my present assembly is TIP 3055 ( RSComponent purchase) but looking for the M/NJW's 21194.
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Mr. Katyar,

Well i have absolutely no idea why the offset voltage is so low? Yes Matched transistors the original NOS stock.
I have the Circlo Amp powered up. let it stabilize for an hour or so.
Short the input, and measure the voltage, I have a Fluke DVM and it is calibrated with a certificate with traceability to the national metrologi. so the instrument is ok. 100%. Maybe, your instrument is out of order., have you checked the integrity of your DVM. It can be so that you have better result than your instrument.
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The topology is very versatile, and could probably accommodate SiC or GaN, with suitable adaptations.
Versions have been built with inverted polarity, MOSfets, Ge transistors, etc. There is no reason preventing the use of alternative semiconductor materials.
Would there be a benefit? That's a different question, and to answer it, the only reliable method is to build a prototype
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I need an amplifier with special constraints. I want to power monitoring speakers in a broadcast van. In use, I have access to power outlets from the dock. But any appliance that heats must be neutralized by air conditioning with limits. I don't want Class D amplifiers. I prefer a Class A amp but with minimal heat dissipation. Could this topology be the solution especially since I have all the components in stock ;)
hi Elvee, glad to ear ftom you.

Class A without the drawbacks. I love it!

I saw that danielwritesbac had done a compilation job... Perhaps more accessible than 130 pages of posts. ;)

The proximity speaker models are given for 30W so I size the amplifier for 60W. But for this use a few watts are enough!!!
I'll check the components I have.
BD140-10 or -16, no problem, and there is no particular advantage in using the higher Hfe type, you can save them for application where it matters.
2N3440 is a slow, high-voltage type, definitely unsuitable; 2SC5171 is much better, but its Cob is marginally too large; will likely work though
Q12 and 13 are completely non-critical, you can opt for any of the types
BC550 are a good choice
BDY58 belongs to the list of OP's I have personally tested, thus no problem in sight
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The 2N1893 should work, but some datasheets publish a lowish Ft (50MHz) and a highish Cob (15pF). Such a device would be marginal, but the "good" types have 200MHz and 5pF, which is excellent.
Thus it depends on the origin of yours, but you run no risk trying: when instabilities do occur, they tend to be benign and harmless
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Thank you for taking the time to test a 2N1893.
2N3440, 2N1613, 2N1893 was widely used a few decennies ago. I kept also 2N3773 and BDY58 (first used for supply and second for amp). I try to reuse old stock because I have to reach a minimum order amount. :(

This is perhaps the opportunity to order some classic references for VAS, CCS... With 60 euros what would you buy in addition to the KSC3503 ?
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The KSC3503 might be "too good": it has a Cob under 5pF, and depending on other components, it could result in instability.
This has already been observed with other BFxyz video transistors, but the remedy is very straightforward: a small additional capacitor, like 3p3 or 4p7.
It is always possible to add capacitance, but if a transistor has an excessive Cob, there is no way to remove it.
MJW21194 is a good choice for output. NJW3281 too.
TTA004B or 2SA1507 as driver.
TTC004B as VAS.
2N5401/2N5551 for the small transistors seeing a voltage incompatible with the BC550/560
The main C thread shows some designs, including TO247 and similar, and the building thread has many more, by @minek and other members.
On the net you can also find kits and implementations by Indian, Philipino and other suppliers.
These are not unauthorized, since the C is completely free and open to everyone for any purpose, but they are unregistered here. Some have asked me for permission, which I gladly gave them, and others simply went on, and that's OK for me.
This means that you can probably buy a kit using CDIL semiconductors for example, for a modest amount yet providing all the benefits of any other C
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