DHT Heater using VCCS - PCB or Kit (Possible Group buy)

jack · Post by **jack** » Sat Mar 02, 2013 6:10 pm

Hi Andrew - only just really read this thread - what approach are you using - I've been playing with something along the Tent Labs line but using high-side current sensing (instead of low) and instrumentation amps (AD8274 / AD8603) with a TIP121 at the moment - also using an ultra-low-noise reference voltage - not an expensive, though slightly exotic, design...

All probably overkill, but they are low-cost and extremely low noise, as well as being temperature stabilised.

I like the Tent Labs over-temperature safety too, but I fail to see why its needed if the design of the VCCS is right...

Andrew · Post by **Andrew** » Sat Mar 02, 2013 6:39 pm

Hi Nick,

Its a twin op amp design using a cost effective generic rail to rail twin op amp, current is sensed in the tail of the CCS.

I plan to use a TL431 as the Vref as it can be set with just two resistors, its pretty cheap and absolute accuracy isn't all that important. I'm not wedded to the TL431; it just seemed a practical solution to allow folk to run at various voltages.

The image attched is the best I've manged yet in terms of spectrum. I tried powering the op amp from its own (bench) supply, it was actually worse.

Andrew

Mike H · Post by **Mike H** » Sun Mar 03, 2013 10:24 am

This may be a spanner in the works, but I'd forgotten all about it but just remembered and found it again. First found this over a year ago. Design by Kees Soeters?

jack · Post by **jack** » Sun Mar 03, 2013 10:48 am

Mike H wrote:This may be a spanner in the works, but I'd forgotten all about it but just remembered and found it again. First found this over a year ago. Design by Kees Soeters?

Indeed - http://members.ziggo.nl/techgraphix/PDF ... Supply.pdf

Main pages for his astonishing 300B amp - http://members.ziggo.nl/techgraphix/Amplifier.html

I remember coming across this years ago (2005/2006?) and being amazed at the workmanship - a bit "blingy" for my tastes, but very impressive work ntl... e.g. having your star earth stud hallmarked (even though no-one can see it) because its made from 99.999% pure silver. Sheer lunacy

Andrew · Post by **Andrew** » Sun Mar 03, 2013 11:34 am

Mike H wrote:This may be a spanner in the works, but I'd forgotten all about it but just remembered and found it again. First found this over a year ago. Design by Kees Soeters?

Some similarities, but that just confirms we're on the right track.

Andrew

Mike H · Post by **Mike H** » Sun Mar 03, 2013 6:39 pm

Fairy nuff!

Think you were asking me about this a while ago, or somebody was, as an alternative to e.g. the Rod Coleman method insofar self Voltage stabilisation could be incorporated as well.

Andrew · Post by **Andrew** » Mon Mar 04, 2013 11:56 am

Andrew, for 2.5V out (2A3) what would be the volts in required, roughly....I have 5.5V and 7.5V options with my existing TX.

I reckon the 7.5v should be fine, I used 9v RMS for 5v out, which gives 12v smoothed DC or about 7v working overhead between Vin and Vout. I may try this out as a test case, I might be able to get the required voltage down a bit more, dunno, yet, its all work in progress.

Andrew

Clive · Post by **Clive** » Mon Mar 04, 2013 1:44 pm

Andrew wrote:
Andrew, for 2.5V out (2A3) what would be the volts in required, roughly....I have 5.5V and 7.5V options with my existing TX.

I reckon the 7.5v should be fine, I used 9v RMS for 5v out, which gives 12v smoothed DC or about 7v working overhead between Vin and Vout. I may try this out as a test case, I might be able to get the required voltage down a bit more, dunno, yet, its all work in progress.

Andrew

Thanks Andrew.

Andrew · Post by **Andrew** » Thu Mar 28, 2013 7:23 pm

First prototype layout done...I'll try out a home made PCB sometime soon.

Andrew

Paul Barker · Post by **Paul Barker** » Thu Mar 28, 2013 7:52 pm

Megastar!

Dave the bass · Post by **Dave the bass** » Fri Mar 29, 2013 12:29 pm

Shoddy!

DTB

Andrew · Post by **Andrew** » Sun May 19, 2013 7:28 pm

I finally managed to dislodge the digit and here's prototype PCB #1.

I found a few things layout-wise I want to change so its been worthwhile exercise; testing will commence this coming week.

Andrew

Andrew · Post by **Andrew** » Thu May 23, 2013 6:40 pm

Quite a shock, it worked first time

Mk2 to iron out a few layout bugs and some measurements on this one to follow.

IslandPink · Post by **IslandPink** » Thu May 23, 2013 6:46 pm

Top work young fella !
It's definitely very topical for me as I'm going to be trying 4P1L as a driver for 300B pretty soon .

Andrew · Post by **Andrew** » Thu May 23, 2013 6:52 pm

What voltage/current are those Mark?

audio-talk

DHT Heater using VCCS - PCB or Kit (Possible Group buy)

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