Bob Cordell’s BC-1 audio power amp

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#102
Forgive me if I have missed a trick; trying to get to grips with which is the latest, definitive schematic. With reference to the SW links that came with the PCB's, under the main directory are two LTP Spice schematics one labelled 'BC-1 Schematic' dated 08/01/2022 and the other labelled 'BC1 Schematic - Rick' also dated 08/01/22. Are there any differences between these two documents so far as component values are concerned? Which of these documents should be considered to be the 'Master' with reference to PCB assembly?

If you then delve down into sub directories, for example, 'BC-1 (AFE)' amplifier front end there you will find a further two schematics 'BC-1(AFE)-BO-14-SCH' dated 12/09/22 and 'BC-1(AFE)M-BO-5-SCH' dated 07/09/22. Both these latter drawings have different nomenclature in relation to both the book and previously mentioned LTP Spice schematics (see above). There is very likely a completely logical reason for this (perhaps in aggregating a total component count) but at the moment, I am foxed.

In the book (2nd edition, page 88), you state that C2 & C4 should be bypassed with 1uF, 63V polypropylene caps - is this still current thinking? If required then I can manually add these to the PCB.

I am bound to have further questions as deeper investigation follows and am keen to point out that I am in no way trying to trip you up or cause hassle - please provide private email addresses if you would prefer communication in that way or tell me to go where the sun doesn't shine if the answers to all these questions are obvious.

All the best

Neil
 
#103
The Ltspice schematics and the schematics in the book ch4 are for reference only, the component reference designators and some values are not exactly the same.
Use the pcb design information only to build the amp.
'BC1 Schematic - Rick' is the updated Ltspice schematic that reflects the component values and any other minor ckt changes, used on the final design and tested pcbs.
The reference designators used on the pcbs do not match the book nor the Ltspice schematics because the component references on the pcbs were re-numbered for easier component location and identification rather than being scattered about after placement and routing.
 
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#110
von Ah said:
What’s a reasonable range of lower power supply voltages for the BC-1? Can the same overall performance (at lower max output power) be achieved with lower voltages than standard (e.g., +/-40 to 50 VDC)?
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The BC-1 can actually operate to fairly low power supply rail voltages and operate at lower maximum power output levels. This is because most of the biasing of the circuitry is done with constant current sources. This means that most of the circuits operate pretty much normally unless they run out of voltage headroom. If I recall correctly, I designed the protection circuit to open the speaker relay if the rail voltages fall below about 35 V, so that any thump resulting from circuit operation collapse would not be passed on to the loudspeaker. I hope this helps answer your question.

Cheers,
Bob
 
#112
Well on the way to completing this. As was candidly pointed out earlier, apparently this is not the place to come for support so would appreciate being told where I go to for questions on assembly/support. In the meantime, when considering drilling the heatsinks for output transistors and PCB mounting holes, I note upon checking that a couple of the holes (eg: LHS heatsink hole shown at 225.4mm from right hand side and that shown at 156.1mm from right hand side) if drilled through cut into the fins of the heatsink. Since I do not think that this is what was intended, you must have drilled blind holes and tapped with a plug tap? Since I cannot find any reference to whether the holes are drilled right through ( I think they are given the McMaster Carr tap quoted) or are part drilled I wondered whether you could clarify this and if part drilled the depth of holes drilled.

Whilst writing I hope you do not mind (and if I am not mistaken) that I point out a discrepancy between the parts list for the AC board whereby the parts lists shows C1-C4 being 4700pF 440V but that the schematic shows these as being 10nF 250V.

Thanks for a great project - both design and documentation.

Regards

Neil
 
#113
Hi Neil,

Since I am selling the pcb’s then official support would be using my email address, delta9electronics @gmail.com. Iirc this is provided in the documentation.
But to answer your ?’s
1) drill a pilot hole first through the meat of the heatsink and a bit into the heatsink fins and follow through with the chipping tap.
2) on the AC pcb use the parts in the BOM and Mouser shopping cart. C1-C4 being 4700pF 440V
 
#115
rsavas said:
Hello members,

We have completed the 73 page document for BC-1. Design, Build, Testing of two prototypes, Documentation, everything is complete enough to say we are happy and ready for a beta release. The document is a big update for chapter 4 in the 2nd edition of the power amp design book, detailing the building of this reference design I call it.
There are 8 pcbs in total, 7 different types in the design, 2xAFE,2xOPS,2xProtect,1xPS,1xAC
Building BC-1 is far from low cost. I have calculated parts costing in the $800 range, the chassis, transformer, PS make up a good half of that.
It's a lot of $ but worth it as it is a mini battle tank imo.
Let's be serious here, it is not a beginners project by any means. You should have a few builds under your belt to take on this big project.
You will be required to order and machine the Dissipante 3Ux300mm chassis HS's and back panel unless you want to pay for it to be done by HiFi2000, just more costs. You have to order parts from the Mouser shopping carts, solder pcbs, wire, test. There is a cloud link for pics and documents as well.

We are looking for a beta tester, if anyone is interested. I will supply a set of pcb's for the beta tester, in appreciation, for taking on this big task. Getting all the parts is a challenge these days but I see improvement in deliveries. Everyday it changes.
As a beta tester, you will be going over all the documents, reviewing, ordering parts, perform the build and finally testing it out. Of course myself and Bob are your mentors for a beta build. It should be a fun project. We've been at it for a while now so its no rush, a really nice fall/winter project, if all goes well, you might have it under the tree for xmas.

To answer the previous question "Also, when was the start of project BC-1?"
Bob's been at the BC-1 design while preparing and writing the 2nd edition of the book, I've been at it since I've had the 2nd edition book, so its been a while.


Rick
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@rsavas Is the 73 page BC-1 document available for download? I did purchase rev 1 and 2 of Bob's book but I am
curious to see this document and details of the final build.
 
#116
No it’s not available for general download, nor will it be. It details the construction of the amplifier in the chosen chassis, so it’s of no use unless you plan to build the amp using the pcb’s that we designed.
The circuit descriptions, schematics of BC-1 are in the 2nd edition chapter 4 as you are aware.
 
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