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Old 18th July 2011, 03:57 AM   #221
wlowes is offline wlowes  Canada
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It is looking good. Nice clean work. Looks like Russian PIO coupling cap? They are nice.
Always good to take a break and double check the wiring anyway.
Post more pics as you go.
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Old 18th July 2011, 08:38 AM   #222
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Old 18th July 2011, 10:06 PM   #223
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Walter - it's hooked up and all is well.

CD switched on but not playing and turn up the volume to around 12 and there's some hum. Not sure about the input resistor fancy dan loop I made and may make a separate ground for each channel - once I've got my light bulb thing working to discharge the caps :-)
Plus rubber gloves, wellington boots and face mask

Can you see any flaws there somewhere ?

Diodes not here for DEM experiments on Alpha - probably tomorrow then I can have a go at this too.
Did you put an oscon or anything across pin 15 and 26 yet ?

Still enjoying the new sounds ?

Andr
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Old 19th July 2011, 12:41 AM   #224
wlowes is offline wlowes  Canada
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Quote:
Originally Posted by AndrewGM View Post
Walter - it's hooked up and all is well.

CD switched on but not playing and turn up the volume to around 12 and there's some hum. Not sure about the input resistor fancy dan loop I made and may make a separate ground for each channel - once I've got my light bulb thing working to discharge the caps :-)
Plus rubber gloves, wellington boots and face mask

Can you see any flaws there somewhere ?

Andr
Andrew
The wiring all looks correct on the tube pins. I think you have grounding problems. You have a star ground off R1 & R2. I don't see a ground from your RCA negs going to that ground. Also I don't see a ground wire going to ground from pin 9. Basically all ground points should come together at one place, then go to the earth ground at your power outlet. There should be a strong connection between metal chassi and earth ground at near the iec power inlet. In america the iec has 3 prongs, hot neutral and ground. Hot and nuetral go to the bridge rectifier. Your chassis ground and a wire from your star ground all go the the 3rd earth ground point on the iec plug. In the lapmizator guide he has a short section on grounding. All must go to the star point and from there to the earth ground. Make sure the chassis also goes to earth.

Check all your voltages. Anode should be somewhere around 180v. Pretty wide range still ok. 150-200 should work. Filament heaters should be 6.3v. I have run between 5.7 and 7.0 without issue.

I also do not see the source of power to the red and blue filament wires. I see you have these wired in parallel, so you should have 6.3v DC across pins 4&5 of each of the tubes.

Hope this helps. If you still get hum, that can be solved. Likely grounding issue. Your layout is good. There will be no induced noise.

Last edited by wlowes; 19th July 2011 at 12:45 AM.
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Old 19th July 2011, 01:21 AM   #225
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Thanks for the feedback :

Pin 9 not grounded at all - should I ?
RCA socket grounds now have wire to star earth at IEC mains inlet
In fact ALL grounds only go to star at IEC mains inlet
R1 / R2 are on separate ground wires to the RCA's
Both L/R signal ' in ' RCA' grounds are connected to each other - should they be separate ?

I've got so many wires to the star I had to put a bigger bolt in !

Thinking this is wrong now - never understood earthing properly.
I'll check Lucas site for this info too.
It sounds nice though an am pretty pleased with it for a ' first go '
Got some decent wood and will make a nice case for it once I've sorted the hum out.
Then it's the i/v op amp signal straight to the buffer - hope that works out.
I'm sure my Arcam can perform better.

Really appreciate the input Walter - thanks

Andrew
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Old 19th July 2011, 01:25 AM   #226
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Right got it I think - all grounds together - floating ( ? ) then down to the IEC power mains inlet chassis ground via 1 thick or thin wire ?

Thanks again
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Old 19th July 2011, 02:32 AM   #227
wlowes is offline wlowes  Canada
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Great progress Andrew..

Pin 9 should be grounded.

Slightly thicker is good on your main ground bus. Not critical in this set up I think. One place I read to think of all circuits like flowing water trying to find a free path to ground. It will take any path it can find. You want the current to flow away from your delicate signals to the ultimate destination which is earth ground. Not through the chassis (or you).

In my case I used the neg RCA tab as a local star for each channel and brought everything on the tube there. Then I ran those to the negative of the last filter caps.. then heavier wire to the first cap in the CRC filter, then to the iec socket. There is a short wire from the IEC to the chassis at that point. Lots of ways to do it. Mine was kind of a waterfall cascade, and as more piled on I added wire guage. Yours where they all come together at one point is probably best, but a little more wire.

Lukas has a little tutorial on how to track down hum. Make sure all your power wires are twisted. Transformer to bridge, bridge to filter all twisted.

Ultimately I went for super quiet. Bridge then big cap, then choke, then medium cap then separate rc filter for each channel. Even quieter would have been a choke per channel at that last stage. As it is with wires twisted and the three stage filter it is DEAD quiet. Ear tight to tweeter ever so slight hiss (from tube) and no hum. I mean quiet at high volume with ear tight on speaker. I also put small film cap bypasses right across the anode and pin 9 for a nice polishing touch. (this is future tuning.. just get it running for now)

Did I hear you say you are getting music out of it along with a little hum?

How is the sound? It will open up after an hour BTW. new caps and wire..
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Old 19th July 2011, 02:55 AM   #228
wlowes is offline wlowes  Canada
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Quote:
Originally Posted by AndrewGM View Post

Did you put an oscon or anything across pin 15 and 26 yet ?

Still enjoying the new sounds ?

Andr
I was so caught up in your project I missed your question. Yes I am very much enjoying the new sounds. The old clichet that I have to get to know my entire music collection holds. Its like I am on a new level hearing stuff I have not heard before.

I put a 1u MCap across pin 15 & 26. I need to save my last 4 OSCON SEP for another application. Also, I was not sure which way to orient it so I found the non polar film cap a handy way to avoid the question. I also put an old BG 47u in where C227 goes.

Sound is good. I think the 200pf cap on 16&17 was the bees knees however.

I am not going to change anything until this settles in and I get to know the sound. I do think I have to build some kind of super regulator. The feedback from Simon and from Oliver on his Salas shunts seems to suggest at like the DEM they are a must have. It will be a while before I get itchy for the next level though. I will be watching with interest on what you see with the DEM thing over and above your 250pf cap.
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Old 19th July 2011, 08:05 AM   #229
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Andrew, congratulations on getting sound from your new output stage!

If your amp(s) or Arcam have their signal ground connected to safety ground / earth then you've created an earth loop (obvious source of hum) with your new output stage. I know nothing about tubes but normally with DIY gear you will want to connect the chassis to safety earth very thoroughly (for safety) but not usually the signal ground (for the earth loop / hum reason). This is only an issue if something else in the system is connected to safety earth.

If there indeed was a loop you'll need to use insulated phono plugs and make sure there's no other connection from the chassis to signal ground, but this is an *if*.
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Old 19th July 2011, 06:37 PM   #230
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Thanks Simon

The grounding is definitely the issue and will do some tests soon.

Was extremely nervous firing it up for the first time and was a fair distance away at switch on !!!
Now, with your suggestions an Walters I've got to go back and lift and re solder things I've little knowledge of which is equally nerve racking. I have not yet sorted out my ' light bulb cap discharging weapon ' yet either so it's on hold for another day maybe.

So. getting back on thread ( and I'm sorry I kind of moved it away for a day or two ) I have GOOD news.

I am DEM re clocked and it works fine.
In fact it works so damn fine I'm stunned as it's all on the spare Alpha board still crammed with 25 year old caps, NE5532 / OP27, standard diodes, no caps around the dac changed, original tantalums, no SEPC's......nowt !!!!

I'll attach the drawing and photos of the work done later tonight when I can find some ******* batteries for the camera ( kids ! )

I am very happy with this mod to say the least

More later

Andrew

ps Walter, thanks a lot for the encouragement and advice - it sounds so sweet in the upper mid and hf and there's a lot of solidity in the bass registers too which I was not expecting at all. Get rid of the hum and I could get more into this valve thing
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