My 4Mhz amplitude modulated audio sstc / Projects / Forums

Forums

4hv.org :: Forums :: Projects

« Previous topic | Next topic »

My 4Mhz amplitude modulated audio sstc

first previous 2 3 4 5 next last

Move Thread

LAN_403

uzzors2k

Sun Jun 15 2008, 06:56PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Wonderful. Is the sound quality really crystal clear, and is there much/any noise from the streamers? My PLL class E coil is useless for audio modulating because the streamers hiss so loudly. I'm not sure if it's the PLL, my PSU or the low frequency that does it.

Reaching

Sun Jun 15 2008, 07:06PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

the streamers are almost silent, and around 2cm long. there is no hiss from the flame itself
sound is wonderful, crystalclear, yes. :)

Firefox

Mon Jun 16 2008, 02:02AM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

That is a beautiful thing *starts scrounging for parts*.

Arcstarter

Mon Jun 16 2008, 02:49AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Firefox wrote ...

That is a beautiful thing *starts scrounging for parts*.

Haha i do the same thing every time i see someone else's projects.

teslacoolguy

Mon Jun 16 2008, 03:56AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

Can you post the pcb files for this thing?

GeordieBoy

Mon Jun 16 2008, 10:01AM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Reaching - What material are the two toroids? I assume the RF drive transformer is Mn:Zn ferrite, and it looks like your RF choke is using the same material? A closed ferrite toroid is not really the best choice for the PA's drain choke, because it can saturate due to the DC current component. You might see better performance (better efficiency and cooler PA MOSFET) using a Type-2 iron powder toroid, or a gapped ferrite or stick inductor here. These generally work better as RFCs than ferrite with no air-gap.

Just a comment. Cool project and a nice PCB too!

-Richie,

Marko

Mon Jun 16 2008, 12:48PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi guys,

Yes, for drain chokes, best to use are the yellow-white iron powder toroids from SMPS output chokes. The choke only sees DC so there is no need to be worried about dissipation on it.

One thing I was personally wondering about from time to time - what *assures* that volt-seconds on the link choke remain constant in class E amplifier? While device is the choke sees full bus voltage for full time, but during off-time wouldn't it see sinusoidal voltage slope?
Why doesn't this disbalance the Vs on the choke?

Marko

GeordieBoy

Mon Jun 16 2008, 02:24PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

No don't use yellow/white iron powder (type-26) for Radio Frequency chokes (or green/blue type-52 for that matter! These materials are very lossy above a few hundred kHz and will turn a nice crispy brown colour quite quickly when exposed to rapid large flux excursions. You ideally want carbonyl iron powder like the red/clear type-2 toroids commonly used by radio hams. I forget the other type, maybe 6 or 8? Gapped ferrite is okay though.

The drain choke sees a voltage equal to the supply voltage minus the drain voltage of the MOSFET. The time-averaged value of the applied voltage is zero. Energy that is pumped into the magnetic field when the switch is closed, is released to the resonant tank circuit when the switch opens. It is similar to a boost or flyback converter in that respect.

-Richie,

Marko

Mon Jun 16 2008, 02:30PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

No don't use yellow/white iron powder (type-26) for Radio Frequency chokes (or green/blue type-52 for that matter! These materials are very lossy above a few hundred kHz and will turn a nice crispy brown colour quite quickly when exposed to rapid large flux excursions. You ideally want carbonyl iron powder like the red/clear type-2 toroids commonly used by radio hams. I forget the other type, maybe 6 or 8? Gapped ferrite is okay though.

I don't see what is the problem, how you mean this? Since DC link choke carries only DC current with very small ripple, although it sees AC voltage. I always use them on royer oscillators without any problems.

Matt Bingham has used them a lot for class E amplifiers at very high frequencies without any problems too.

I thought you used them as well Richie, for class E amps. Why aren't all our chokes frying then?

Long ago I was also afraid of using the powder toroids for link chokes thinking they are 'lossy' but everyone assured me against that.
And indeed they work rather well, once enough inductance is used to keep ripple small... (??)
High frequency actually seemed to be beneficial by allowing to use less inductance.

GeordieBoy

Mon Jun 16 2008, 03:09PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

It depends on the power level you are running at Marko. Type-26 is the cheapest crapiest grade of iron-powder for use in very high-volume low-cost SMPSUs operating the tens or low hundreds of kHz. If it suffices for any other particular application then great, because it is dirt cheap, but there are many better materials for RFCs.

My point was that at high power levels and high frequencies where only the right materials will survive, type-2 Fe powder is best for minimal heating as the drain choke.

first previous 2 3 4 5 next last

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob