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

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James
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#16

Post by James »

Hi Andrew,

Put me down for 6 please.

Thanks,

James
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#17

Post by Andrew »

Ok chaps, this is the rough and ready prototype measurement attempt #1.

I will repeat this as all good 'metrologists' should.

The scale is 200mV.

The 50hz is set as the fundamental, that's over 81db down so 17uV (perhaps a bit lower if you look at the graph) you need to add in the THD+N - that is -72dbFS that's all the stuff that isn't 50Hz) that's 44uV, so all in all a safe bet to say (assuming I am correct) we're at less than 200uV total niose, my other true RMS AC meter reckons its about 180uV noise with a 30khz low pass filter this is pretty much down in the noise floor of this meter as it reads 160uV with a shroted input.

I'll have a think about my measurement strategy and repeat later.

Andrew
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IslandPink
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#18

Post by IslandPink »

OK, so 200mV at 0db, that looks very nice - Something down in the 10's of uV is where we want to be !

So I see this is 5V AC in, what's the DC-out on this one ?
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#19

Post by Andrew »

IslandPink wrote: So I see this is 5V AC in, what's the DC-out on this one ?
That's just my rubbish labelling scheme this is 5v DC out, 9v AC in.

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#20

Post by Andrew »

OK, I grounded everything at the other end next to the meter and I get <110uV total AC noise on the output of the reg. Meter just grounded is 30uV, so this appears genuine.

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#21

Post by Andrew »

Gratuitous breadboard shot - including clip leads.....phwaoor :!:

Sounds OK, actually, more than OK, at least as good as the bench PSU, perhaps slightly more bass, if anything and more 'air'. So no worse, and perhaps slightly better. And I still have a working pair of 300B phew!

I need two of 'em now.
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#22

Post by IslandPink »

Nice work !
Ok, do you have a more accurate idea ( from Sim or hardware ) what the minimum AC-in would be to give a clean 5V out ...

( Same sort of question as per the IHT supplies we have ) .
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#23

Post by Andrew »

Very minimum AC in for 5v DC out is something like 7.5v-8.0v AC RMS, you won't get away with 6.3v, sorry, not enough headroom to regulate.

Here's the full breadboard shot.


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#24

Post by IslandPink »

Andrew wrote:Very minimum AC in for 5v DC out is something like 7.5v-8.0v AC RMS, you won't get away with 6.3v, sorry, not enough headroom to regulate.
Andrew
OK, I'll use my Guido ones for 300B's then :wink:
But that suggests I could probably run 4P1L's (at 4.2V) from a 6V toroid , which usually give about 7V around here, if not loaded too hard. Sounds good.
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#25

Post by thomas »

Hi, I'd be up for at least two of these please Andrew.
Likely suspects for use would be 801 and 4p1l (Filament Voltage: 2.1/4.2 volts @ 650mA/325mA respectively)
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#26

Post by Clive »

Hi Andrew,

I would be interested in 2, maybe 4. If you want something commercial to compare with I could send you a couple of diyhifsupply modules I have spare. I believe they aren't as good as the Rod Coleman circuit in terms of sound.

Cheers,

Clive
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#27

Post by Andrew »

Thanks Clive.

Ok so I had a module running all day and it doesn't seem to get hot, so that's a good start. I hope the final dsign will rn as cool. I still want to see if there's any value in getting the noise spectrum a bit cleaner, without chucking too much voltage and extra heat at it.

Andrew
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#28

Post by Clive »

Hi Andrew, I'm interested to know your view on how your heater circuit would compare with Rob Coleman's it terms of performance. I seem to recall he goes on about feedback used in most other modules and how this effects DHTs. I'm looking for better heaters for my 2A3 preamp than the diyhifisupply ones. Rod's are a bit of a bitch to fit as thery need a separate ps board.
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#29

Post by Andrew »

Hi Andrew, I'm interested to know your view on how your heater circuit would compare with Rob Coleman's it terms of performance. I seem to recall he goes on about feedback used in most other modules and how this effects DHTs.
I've not heard Rod's modules, not even studied his circuit - this is deliberate.

I'm using a "current source" so there should be no feedback into the signal on the cathode.

I'm looking for better heaters for my 2A3 preamp than the diyhifisupply ones. Rod's are a bit of a bitch to fit as thery need a separate ps board.
I'm trying really hard to get this all onto a single PCB at is ~50mmx80mm; it may need to be a bit bigger. I get a few extra db noise reduction in simulations (recall its pretty low at the moment) by smoothing the 'B+' a bit more before it hits the main regulator. What I need to find out is a) does this make a measureable difference, b) does this make an audible difference. That's my next job.

cheers,

Andrew
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#30

Post by Clive »

Andrew wrote:
I've not heard Rod's modules, not even studied his circuit - this is deliberate.

I'm using a "current source" so there should be no feedback into the signal on the cathode.
Sounds great, I read up on the link you gave, it sounds like the circuit should be as good as it gets.

50 x 80 would be ideal as this is the same size as my current heaters. I could even suggest where the mounting holes go.....:-)
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