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His Master's Noise: A Thoroughly Modern Tube Phono Preamp
His Master's Noise: A Thoroughly Modern Tube Phono Preamp
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Old 18th July 2017, 09:05 PM   #431
mrdave45 is offline mrdave45  United Kingdom
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I assume you're talking about the ccs and that i don't need to use heatsinks on q1 q3 and q5. I'm already using dn2504 probably the n3-g, that sounds familiar.

I heatsinked the lot as I possibly had heat issues in the impasse preamp and it seems that this preamp is going to generate a lot more heat in a smaller box.
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Old 18th July 2017, 09:38 PM   #432
mrdave45 is offline mrdave45  United Kingdom
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Right, I understand. It's the n5s I've got. The n3s are in the small package and in those positions they really don't disipate much at all.
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Old 19th July 2017, 12:27 AM   #433
jackinnj is offline jackinnj  United States
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His Master's Noise: A Thoroughly Modern Tube Phono Preamp
The TIP50's are the pass devices on the 2-transistor regulators -- they should be heat-sinked.

The first of the DMOS transistors of the CCS bear the brunt of heat dissipation.
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Old 20th July 2017, 06:54 PM   #434
mrdave45 is offline mrdave45  United Kingdom
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It works! Woooooooooooooo. Amps arent even warm yet and it sounds better in all respects! Was feeling a bit down having spent a ton of money on a gyrodec, audiomods and benz cart and being a bit underwhelmed.

The gain for this is spot on for my benz cart at 0.3mV at 3,54cm/s.

Thank you all so much for your help and patience. its really appreciated.

Sadly i will have to get better transformers. Most of the hum is the heater tx but a little underwhelmed that my custom wound hums a little. Any recommendations from the uk? I may also try using a bridge rectifier for the ht on a single wind 250v instead.

Thanks again. Wooooo!!!!
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Old 21st July 2017, 06:57 PM   #435
mrdave45 is offline mrdave45  United Kingdom
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Swapped out the heater tx for a torroid that I had kicking about. It doesn't hum so I'll use that for now.

I checked my plate voltage and although the drop across r3 is almost spot on 20v the plate on one D3a is about 140v and the voltage on the other is about 126v. Under load the 260v reg is 260 on one side and 256 on the other.
Any ideas?
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Old 22nd July 2017, 09:28 AM   #436
frankwilker is offline frankwilker  Germany
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Hi Dave,
thanks for your mail. You wrote to me, Va = 146V. In your post here, 126V. Whats the correct value?
I would first change the tubes from right to left and then the PS from right to left. So you see, from where the wind is blowing.
Another problem in my view is the connecting of the voltage dividier for the heater to one channel.
A solution should be, to connect the voltage dividier for the heater before the regulated PS. I remember, you got 317V. I will do it in the same way.
You have to calculate new values. I think 100K and 27K are good values. This gives you 70V (and needs 2.5mA). Better is to use greater values. So the current the dividier needs is decreased (470k/120K (64V) 150K(76V) 0.5mA).
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Old 25th July 2017, 11:40 AM   #437
mrdave45 is offline mrdave45  United Kingdom
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Right, finally got round to swapping the tubes round.

I think the correct value for the plate on the D3a should be 140v.

Im getting about 138v on one and about 126v on the other. It seems to slowly work its way down to that.

After swapping the D3a tubes around the lower voltage followed the tube.

Is this a sign of a worn or faulty tube?

I remember commenting on one of the other projects that my plate voltage didnt match even though everything else did and there does seem to be a range of acceptable variance but i have no idea what that would be for this.

I measure about 1.18v across the IR diode on both channels. Close enough to each other.

Thanks
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Old 25th July 2017, 01:56 PM   #438
kevinkr is offline kevinkr  United States
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His Master's Noise: A Thoroughly Modern Tube Phono Preamp
Quote:
Originally Posted by mrdave45 View Post
<snip>
Is this a sign of a worn or faulty tube?

<snip>

Thanks
All is well, this is just an indication of the parametric variation tube to tube, and as the tube warms up and settles down to its warmed up operating point. High transconductance types tend to exhibit quite a lot of variation sample to sample.

In some of my early designs I had to match them to the circuit, I learned not to make that mistake as my stash of D3As shrank, and designed circuits that are less sensitive to parametric variations in the tubes.

Mu is essentially independent of operating point variations because of the CCS loading, so this is not something I would worry over.
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Old 25th July 2017, 02:32 PM   #439
mrdave45 is offline mrdave45  United Kingdom
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Fab, thanks. Hopefully they will be reliable!

It turns out my cases are 24cm across and not 23 cm like i thought they were going to be. My hifi rack supports are 47cm apart! Nevermind.
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Old 15th August 2017, 03:06 PM   #440
frankwilker is offline frankwilker  Germany
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Hi guys,
iīm lucky, my system is running, the riaa curve is matched. I couldnīt get the last 0,5 dB to 20 khz. But i think, i donīt hear that.
Sounding is great.
Iīm now using a CSS of 13 mA in the first Stage und 6/8mA in the second Stage.
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