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KiCAD: Velleman K4700 DC Offset Detection PCB - updated

Arkless Electronics said:
With the parts I will be using it will cost a lot more than the kit or the figures you give above. Chassis mounting 12VA transformer alone about £10 plus VAT and I'll probably use heavier duty relays. I may well add protection against oscillation.

I have designed the trickiest parts of an "ultimate" protection unit which uses phased mosfet and relay switching so as to provide the lowest possible resistance and distortion when connected and be able to safely break even the output from 300W++ amplifiers without relay contacts welding together etc. Other possible features include over driving protection for all drive units by averaging the power within the bandwidth handled by each driver. It was mainly a design exercise and "to prove a point" and I'm not likely to do anything with it...
Click to expand...

It certainly would be more expensive if you were to build a heavy duty protection device, oscillation protection is definitely a worthwhile addition.
 
I am thinking of getting some more PCB's made in the next week or two (maybe a batch of 10), but I am also thinking of redesigning it to make them mono as this would make it even more useful. Currently to use this design in the CS1500 amp as described I have to take the PA output for one channel across the whole amp twice which is unlikely to be a problem, just undesirable.

And I have some mono amps that need some sort of protection.
 
S-Man said:
Or you could decide not to fit a relay and use the stereo board for mono.
Click to expand...

The benefit is that it <should> be smaller - currently looking like 78 x 55mm (ish) instead of 78 x 80mm - that make a lot sense in my intended usage. Two of them in the same amp could use a single transformer linked by a simple 3 core power cable, interconnecting 'trigger' functions could be a single wire, or probably two including common ground.

The ideal solution is to get rid of the transformer(s) altogether....
 
The problem with running it from the amps rails is that you then must make sure it fails safe if a DC fault condition is CAUSED BY either rail going down...
 
There is a design study published in Doug Self's book on audio that uses the main power rails - that may be a useful place to start.

His commercial module uses a different design by the looks of it though, I wouldn't want to make a clone of that version for obvious reasons.
 
Arkless Electronics said:
The problem with running it from the amps rails is that you then must make sure it fails safe if a DC fault condition is CAUSED BY either rail going down...
Click to expand...

Very good point Jez.
I tend to use the UPC1237 based circuits. This runs off the +ive rail only, so loss of the +ive rail means the relay must open. If the -ive rail was to go, then any dc on the amp output will be interrupted by the UPC relay.
Actually, the UPC can check for loss of AC as well - which gives you belt and braces.
 
I've nearly completed a basic design for a mono DC detection PCB, these are designed to be inter-linked to use a single transformer and common fault/manual mute operation, or they can operate separately.

The benefits of making the device mono, in my case, are to simplify the PA wiring in a stereo amp, for a mono amp the benefit is a bit more obvious !
It is also quite a lot smaller - approx 57 x 78mm, this makes it easier to fit in confined spaces and the PCB itself will be cheaper to make offsetting the increased cost due to needing two and some duplicated components.

All the comments about power options for the stereo version as described above apply.

Hopefully I will be able to finish this soon.

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I will keep the conversation going on this thread as the other is kinda complete.
Not opened up one of the little blue relays to see if there is more meat inside the workings, the larger Omron that I have fitted works a treat on the testbench in pic and in one of my in-use HackerNaps, have not got round to finishing the other 5 yet.
The larger metal tabs and the fairly substantial contact areas inside the unit suggest they could take a bit more abuse.

Reading about the solid state relays, if they fail, they tend to fail short which isnt much use for our purposes.

Ramona asked if they could be made a little more sensitive 500-600mV DC rather than 1V, is this possible?

I had not looked into the UPC1237 based circuits S-Man mentioned, quite the PCB space-saver and tick quite a few boxes too. Are they available other than ebay?

If you were to run a batch of PCB`s in the future once settled on circuit, I may well invest in aleast 10 or 12pcs
As Arkless mentioned on the first page, the Capacitors supplied in the Velle kits are a bit poop!
 
juz400 said:
I will keep the conversation going on this thread as the other is kinda complete.
Not opened up one of the little blue relays to see if there is more meat inside the workings, the larger Omron that I have fitted works a treat on the testbench in pic and in one of my in-use HackerNaps, have not got round to finishing the other 5 yet.
The larger metal tabs and the fairly substantial contact areas inside the unit suggest they could take a bit more abuse.

Reading about the solid state relays, if they fail, they tend to fail short which isnt much use for our purposes.

Ramona asked if they could be made a little more sensitive 500-600mV DC rather than 1V, is this possible?

I had not looked into the UPC1237 based circuits S-Man mentioned, quite the PCB space-saver and tick quite a few boxes too. Are they available other than ebay?

If you were to run a batch of PCB`s in the future once settled on circuit, I may well invest in aleast 10 or 12pcs
As Arkless mentioned on the first page, the Capacitors supplied in the Velle kits are a bit poop!
Click to expand...

Normal relays can also do this! See my last post in your other K4700 thread.
 
Sadly NEC discontinued the 1237 years ago. The Ebay ones are all made in China and it's not clear what brand/origin they are.
I think Unisonic used to make them, not sure if they still do.

However, I have not yet found a Chinese 1237 chip that does not work correctly. The design of some of the Ebay PCBs leave room for improvement IME, but they can usually be modded.
 
juz400 said:
If you were to run a batch of PCB`s in the future once settled on circuit, I may well invest in aleast 10 or 12pcs
As Arkless mentioned on the first page, the Capacitors supplied in the Velle kits are a bit poop!
Click to expand...

I will definitely be putting in an order for a batch of the stereo version sometime soon as this has been proven to work and I am happy for others to use it, for the mono version I will also be ordering a small batch (6) for test purposes - only fair I do it this way to be sure it works !

As promised BOMs will appear over the weekend as well as posting the gerbers on github.

The caps on the two Velleman kits I can get to are all Jamicon, these are probably reasonable enough, but no use if the latest kits are some wunhunglo crap. You can always use better quality caps but you are stuck with the average quality PCB.

One of the other main benefits to making my own PCB is that the quality (from JLC or OshPark) is very good indeed - the design is double sided with a ground plane on both sides.
 
S-Man said:
Sadly NEC discontinued the 1237 years ago. The Ebay ones are all made in China and it's not clear what brand/origin they are.
I think Unisonic used to make them, not sure if they still do.

However, I have not yet found a Chinese 1237 chip that does not work correctly. The design of some of the Ebay PCBs leave room for improvement IME, but they can usually be modded.
Click to expand...
Unisonic is OK, but where to buy?
I have religious principles against buying parts from auction sites
 
As someone who is hoping to go active with mono-blocks, I'd be very interested n the outcome of your experiments.

I'm wondering how much interest there might be on the site for a GB of the mono PCBs ?
 
I would be interested the in mono setups for the 10-12 pcs, I already have 7 built and working K4700 sets which would be used as mono`s
Building a new set with better quality PCB and Caps should give peace of mind for long term use.
 
The plan is to put in an order to JLCPCB next Saturday (at the latest) for the stereo version (updated images below), and also for a small batch of the mono version for testing - my only concern is whether the interconnection between separate PCB's for fault and manual mute facility works as I <think> it should. They were pretty quick at delivering last time - less than a week.

The cost - this is very approximate.

For example: 20 boards (inc P&P) £28, add on the inevitable customs charge (is it 20% ?).

All in all not very expensive.

If your interested for either type let me know.

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An interesting KiCAD generated interactive BOM and gerbers to follow.
 
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