audio-talk

Right, so for an 8 ohm driver and corner frequency of 180Hz you'd need a choke around 7mH. Should be a lot cheaper than an equivalent 60mH choke. And you'll get a "built in" high pass filter.

simon wrote: ↑Thu Dec 24, 2020 7:50 pm Right, so for an 8 ohm driver and corner frequency of 180Hz you'd need a choke around 7mH. Should be a lot cheaper than an equivalent 60mH choke. And you'll get a "built in" high pass filter.

Thanks again Simon. Any suggestions of where to look for such a choke of suitable quality?

Maybe;

https://www.hificollective.co.uk/catalo ... -disc.html

Good question Ray, I've wondered that myself. I've been thinking about a tweeter amp so a much higher f making air cores possible. Something like a Mundorf L140 might do you but they're not cheap at £40-odd each + vat. Air core should be better than ferrite, but whether that's actually audible is another matter.

I've had a quick browse of the HiFi-Collective inductor offerings - seemingly lots of choice but not much available by way of specifications. More reading required- I think I'll have a look on the DIY Audio thread next.

So, I reasoned that the normally recommended Hammond 193T inductor is specced for a max DC current of 2A and is a common mode type so I had a look at what's available on the Mouser site; less than a fiver each...

https://www.mouser.co.uk/datasheet/2/28 ... -49386.pdf

Ray P wrote: ↑Fri Dec 25, 2020 7:06 am

So, I reasoned that the normally recommended Hammond 193T inductor is specced for a max DC current of 2A and is a common mode type

Common mode ? Not as I understand things ?

https://www.hammfg.com/files/parts/pdf/193T.pdf

What current are you estimating the amp will run Ray ?

Yeah, be careful with those Ray they're not the right type. Bear in mind also the DCR of the choke needs to be small, which in turn means higher current capacity, rather than the other way round if that makes sense.

Yeah, that was a bit of a senior moment! Must engage brain when browsing....

pre65 wrote: ↑Fri Dec 25, 2020 9:09 am What current are you estimating the amp will run Ray ?

Good question Phil. Theory says I'll need less power with the bottom rolled off but not thought beyond that so far.

If you require a choke for midbass use upwards , consider the Triad C-56U . 35mH 2A . About £12 a piece at Mouser . I have an amp under construction that uses one per channel in CLC power supply and as choke load for the output stage

cheers

Nic

Looks a decent spec for the money, thanks nic.

Yes, thanks nic, that looks to be a useful suggestion.

On the topic of rolling off the bass, if I change the value of C1 to give a high pass filter and use a smaller inductor to load the MosFET I'm assuming it will create some sort of second order filter? Not sure how to model it though?

C1, C2 and L1 will all affect the bass roll off i.e. a high pass filter. But I think they'll all act as their own filter, which while the effects could superimpose over each other wouldn't add to form a higher order filter. But others may correct me. And I think you'd have to model it in spice or similar if you wanted to have a really good idea of what would happen.

I think you have just described a second order filter. Two first order filters superimposed.

Hmmm, yes, I suppose so. I'd never really thought of it in that way. Might need to read MJ again to understand how the two filters act together - I've only ever sized them in isolation.