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PostPosted: 29 Jan 2016, 11:44 
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Hi Marko, :) Something most folks know about me is that I hate hum and noise. My target for any design is a signal to noise of at least 90 db. That is so low that nothing gets through most systems. The current iteration of the Forewatt is typically running about -93dbv for a S/N. Very quiet. So it is easy to put an LED power indicator in it. Any color you like with a series resistor of around 4.7K (lower values for brighter, higher for dimmer) and attach it to the heater circuit. Be sure to get the polarity right and do not attach the ground end of the LED (or resistor) to the actual circuit ground as it will then see the reference votlage on the heater string and go poof. The target range for the heater reference is 65-80 volts so you are fine. The capacitor is likely (if a good brand) to be rated for at least 25% overage so it ought to be OK. I typically use 350 volt rated ones in that location though. 6.88 volts is a bit high. I would replace the "R" in the filter with a regulator a LM317 is fine, but a LT1085 better. Even a LM7806 might do if there is about 3 volts of headroom. Any of them will filter better than the resistor. My newest designs use the LT1085s as they are low drop out regulators and work with as little as 1 volt across them (not great at that level though and 2-5 is far better). The LM317 will be OK with 2-3 volts across it.

Good listening
Bruce

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PostPosted: 29 Jan 2016, 13:56 
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Location: Zagreb, Croatia
gofar99 wrote:
Hi Marko, :) Something most folks know about me is that I hate hum and noise. My target for any design is a signal to noise of at least 90 db. That is so low that nothing gets through most systems. The current iteration of the Forewatt is typically running about -93dbv for a S/N. Very quiet. So it is easy to put an LED power indicator in it. Any color you like with a series resistor of around 4.7K (lower values for brighter, higher for dimmer) and attach it to the heater circuit. Be sure to get the polarity right and do not attach the ground end of the LED (or resistor) to the actual circuit ground as it will then see the reference votlage on the heater string and go poof. The target range for the heater reference is 65-80 volts so you are fine. The capacitor is likely (if a good brand) to be rated for at least 25% overage so it ought to be OK. I typically use 350 volt rated ones in that location though. 6.88 volts is a bit high. I would replace the "R" in the filter with a regulator a LM317 is fine, but a LT1085 better. Even a LM7806 might do if there is about 3 volts of headroom. Any of them will filter better than the resistor. My newest designs use the LT1085s as they are low drop out regulators and work with as little as 1 volt across them (not great at that level though and 2-5 is far better). The LM317 will be OK with 2-3 volts across it.

Good listening
Bruce


Hello Bruce,
this time zone difference between us is killing me. I used LT1084 with 2 leds instead of R2( forward voltage of leds 4,7+1.25=6V, 5.89 to be exact), so it can be done with just 0.8V headroom. R is just 2x0.22R so not much to be gained there. I am using old VCR as a case, pardon the dust.

Thank you once again

Marko


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PostPosted: 14 Feb 2016, 10:21 
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Let me add my praise to Bruce for this fabulous, simple, flexible design. It's a real Gem! :headphones:

I have just finished a Forewatt using an old power transformer from eBay, power supply of my own design ( :geek: ), heater supply also of my own design and Pinnacle 5963 valves (tubes ;) ). Using resistors at various points in the PSU I have a B+ of 217v. I have used Mills resistors in the PSU and PRP PR9372 Series Metal Film resistors elsewhere. Signal caps are Mundorf MKAP MKPs. All Silicon is bypassed, as are the heaters, with 100nF poly caps. From first turn on after building it is close to silent.

My source is my computer (mostly FLAC files) through my highly modified Musical Fidelity V-DAC. I am driving a modified Quad 405 power amp. The sound is amazing. It is the best I have ever heard from my system. It is clean, crystal clear and detailed with great stereo image. I listen mostly to classical chamber music which has taken on a whole new sense of presence. And I haven't even started tweaking yet!

A pair of Oddblocks will be coming soon! Bring them on!!

Thanks again Bruce.


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PostPosted: 14 Feb 2016, 17:15 
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Hi, :D Glad you found it a worthy project. It is deceptively simple, but then I generally feel that a vast majority of equipment out there have features and complications built in that get in the way of the music. The Oddblocks follow the same thought process. No more components than needed to do the job well and each selected for minimal contamination of the signal. Another deceptively simple design.

Good listening
Bruce

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PostPosted: 15 Feb 2016, 03:40 
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Location: Zagreb, Croatia
Hi Bruce,
I agree with a previous poster, soundstage from you preamp is really to die for :)
Can you tell me what you think about ECC99 in this circuit, my amp Zin is lowish 10K, could be a worthwhile considering better impedance matching.
I tried to simulate it, look at the results below.

Image


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PostPosted: 15 Feb 2016, 04:31 
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Bruce,

I agree absolutely with your design philosophy, fewer components in the signal path has to be better. I also try to get the best, smoothest power I can and to leave out any 'bells and whistles'. I think your philosophy has proven merit.

May I seek your advice on two matters please:
1. Is the ECC802S much better than the 5936 I am using? The 802S is very expensive but I am happy to save for it if it's worth the extra money.
2. My device is HUGELY micrphonic. Even the slightest touch to the chasis echoes through the speakers. Is this normal? How can I reduce it? I have decoupled wound components from the chasis using rubber grommits but valve sockets are bolted directly to the chasis. Are valve damper rings any good?

Thanks in advance,
Mark


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PostPosted: 15 Feb 2016, 09:16 
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Hi, The sim looks OK, but I'll run it later here to see if the operating points are good.

The ECC802S should not be that costly. The new production JJs are about $20US which is in line with many new production tubes. I see no advantage to using NOS ones as they would be costly. For other choices I would stick to only long plate (anode) versions of the 12AU7. The small plate versions seem to be to me less musical. YMMV.

I have not had any microphonic issues....I have even dropped one Forewatt while running and it didn't make a sound. It is probably the tubes you used. If different tubes don't fix the problem then you should examine the coupling capacitors by tapping each with something non-conductive to see if one might be bad.

Good listening
Bruce

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PostPosted: 15 Feb 2016, 09:39 
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Hi, I checked the settings for an ECC99. At B+=220V, Cap=1uf, R(caths)=470. I(cath)=8.5ma, V (center)=106, Z(in)=151K, Z(out)=1.16K, GV = 10.3 (20.3db), dissipation each section = 900mw, F3(low)=3HZ, F3(high)= over 1meg with 1K input resistor, with 25K about 150KHZ. V(out) = +51/-49. So with the given B+ the tube seems to be in a good part of the operating range. If you use a different B+ (more than about +/- 10%) then the calculations will not be valid.

It should drive the amps fine as there is about a 1:10 impedance ratio. I would not put a transfomer in the output. No need.

Good listening
Bruce

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PostPosted: 15 Feb 2016, 09:59 
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gofar99 wrote:
Hi, I checked the settings for an ECC99. At B+=220V, Cap=1uf, R(caths)=470. I(cath)=8.5ma, V (center)=106, Z(in)=151K, Z(out)=1.16K, GV = 10.3 (20.3db), dissipation each section = 900mw, F3(low)=3HZ, F3(high)= over 1meg with 1K input resistor, with 25K about 150KHZ. V(out) = +51/-49. So with the given B+ the tube seems to be in a good part of the operating range. If you use a different B+ (more than about +/- 10%) then the calculations will not be valid.

It should drive the amps fine as there is about a 1:10 impedance ratio. I would not put a transfomer in the output. No need.

Good listening
Bruce


Thanks for the doing the math for me Bruce. I will let you know my impressions after I acquire the ECC99 tubes. I think it is imperative to
emphasize that I am already very content with the sound, it is hard to imagine that the tube swapping could bring substantial sonic improvements, but
if it does I would not complain ;)

Kind regards

Marko


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PostPosted: 23 Mar 2016, 16:21 
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I'm planning my second Forewatt!

The first has taken pride of place in my main system. I added LR8 regulators to the B+ and heater ref and substituted the heater regulators with LDO ones. Not sure I can tell the difference, but I can control everything more precisely ;) And it is now absolutely silent.

Just for fun I plan to build my second one the 'old school' way. Tube rectifier, ac heaters, no silicon at all. I want to find out what my father's generation were up against! I'll be interested to see how it sounds and, more importantly, if I can get it quiet.

I'll keep you posted.

Mark


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