phono stage

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simon
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#16

Post by simon »

I finally got around to trying a couple of 1N4007 dioides in place of the C3g cathode resistors on Wednesday evening. Just as Andrew predicted this increased the gain quite a bit. I'd say it is roughly equivalent to my PHONO II now, perhaps not quite as loud, but in that ball park. No obvious detriment to the sound that I could hear either. Should I think about leds now?

When I was struggling for gain I did try some 5751s in place of the 6N1Ps. This did give more gain, and I listened for a little while, but I think I prefer the 6N1Ps. Wouldn't want to stake a lot of money on it though. I have some Mullard ECC83s I could try some time, this would give me lots of gain now :) .
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#17

Post by Andrew »

Hi Simon,

Yes, I would suspect LEDs might be better. What's the rough cathode voltage with the diodes in?

cheers,

-- Andrew
simon
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#18

Post by simon »

A smidge over 1.4V. If I remember correctly it was just over 1.7V with the 82R resistors. In his book MJ provides a table with voltage drop for various diodes. Can't remember now which was the most appropriate but I seem to remember it being something "simple", so will any old led do like one of these say: http://www.rapidonline.com/productinfo. ... 0#techspec?
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Nick
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#19

Post by Nick »

I believe some LED's are noisier than others, but I think Andrew is the man for that.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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#20

Post by Andrew »

Well, I'm no expert but what I looked for, as Nick said, was a combo of quiteness and a good impedance curve.

I started, by having a search around to see what others recommended and ran into the one used on the Bottlehead C4S, the HLMP-6000. This is now made by Avago, ex-Agilent semiconductors and before that ex-HP semiconductor, its a subminature standard red LED, there was a normal sized one which was even better but you can't get hold of it anymore.

Old fashioned standard red types are apparently less noisy, it's do with the materials involved.

There's a reasonable thread on the Bottlehead forum http://www.audioasylum.com/scripts/t.pl ... ad&m=24579. I used to have a better link but can't find it now, must be what you type into Google.

Looking into why they thought it was good was that if you look at the attached graph the standard red is almost vertical within its useful range, say 1-50ma, indicating good linearity and low dynamic impedance, if I recall it was over 10 to 100 times less than many others.

I wish I had the time for a more extensive study, in the end this was all good enough for me. You might find better if you have time to study the data sheets.

[edit] Found the thread I was after, try here http://www.nmr.mgh.harvard.edu/~reese/j ... v02_v.html Manfred Huber did the work and discussed it on Joelist back in 2001.

cheers,

-- Andrew
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shaun
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#21

Post by shaun »

hi Simon

it's great to hear that your phono is getting there :D

i'm still at the ordering stage with the PSU components but that should be sorted soon. i'm lookind to build a bit of a beast PSU (as phono's go) with a variable supply of 230-350v at 100ma or so as this will give some room for experimentation with a variety of circuits.

i'm working flat out at the moment so times a bit short

take care

shaun
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#22

Post by simon »

Went over to Nick's last night for another fun evening. Listened to his latest 6c33c amps which you won't be surprised to hear sound very nice. The bass is really something special, powerful and controlled but doesn't overpower the rest of the music at all. Hearing them made me realise how other amps seemed to do this. At first I found the treble rather too much, quite harsh and uncomfortable. By the end of the evening I'd realised that it wasn't the amps it was just ruthlessly transparent of the digital recordings we'd listened to earlier.

The amps are already very impressive but with fancy coupling caps and nice opts these could be killers. But they're not a relaxing listen, these are party amps, amps to make you shake yer thang :D . Nice to have the option of 300B, 45, 211... 8)

So, down to the purpose of the visit - to test the RIAA of the C3g/Aikido phono (PMed you earlier Andrew). Following Nick's LCR is never going to be easy but it's fair to say it sounded awful. Because the 6c33c amps tell you exactly what's going on. So on the bench Nick checked the RIAA with his inverse RIAA and the right channel was pretty good - the square wave was pretty much square. The left channel was rubbish though, so we started checking each bit. I've looked it over a number of times and not seen anything, but last night I saw it pretty much straight away - I had a 68R resistor in the RIAA where I should have had a 680R. No wonder it sounded rough. Doh! and double Doh!

Plugging it back in with Nick's valve reg bench supply it sounded much better now the RIAA was correct, especially after it warmed up after a few minutes. It doesn't have the coherence and detail of the LCR but it was better than (he whispers) the PHONO II, which sounded pedestrian and slow in comparison (tin hat on, incoming!). I'd probably put the C3g phono closer to the PHONO II than the LCR, but that's largely because the LCR is such a lovely, lovely phono. Still, not bad for maybe £60 of bits (excluding PSU). A credit to Andrew and his design.

Next step is to try a regulated PSU, and play with coupling caps to see if I can tidy things up a little.

Thanks to both Nick and Andrew, I think the next round is mine :) .
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#23

Post by shaun »

hi all

well i've finally go round to ordering the TX and choke for the psu so it should be arriving in a week or so. :D

simon i'm using the very reg you found on steve B's tube based regulator primer and have been pretty happy with it, i'm using boyh sides of the 6080 in paralel for the pass valve. mine is set fot 220v output which according to steve about the max in this configuration. for 250v out you could try an OA2 (150v) and rearange the potential devider and tickle the raw B+ up a tad with a small cap before the choke. i'm looking for about 300v so intent to do the same thing with 2 OB2 in series (200v) and change the potential devider to 100k top and 200k bottom (50k top-100k multiturn-150k bottom to allow some adjustment of the output voltage) which i think should work ok :P .

thanks for the comments on your phono it sounds like you've had a result with that.

i spent an interesting evening with dave dove listening to his lovely aikido driven 300b and was impressed. i also had the chance to listen to his JB e88cc phono and was likewise very impressed with the sound of that. i think i may have to add that to the list of things to try. :twisted:

thanks all for the input

take care

shaun
simon
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#24

Post by simon »

Hi Shaun,

Thanks for the pointers on the reg, that's really useful. I popped over to Steve The Shadow's on Saturday and as well as hearing his new PP amp and the new-super-improved Metronomes I scored a borrow of JJ EL509s and 6080s. Thanks Steve. Thought Steve's combo sounded really good - a PP amp I think I could live with... The Metronomes shocked me with how much bass they now have, even more so for a tiny 4" driver. There's more than there used to be with the subwoofer and it's much cleaner and more accurate now too I reckon.

Anyway, back to regs. Have you simply paralleled the 6080 then, nothing more fancy? Have you tried them in cascode at all? That might make the heaters a little more tricky perhaps. I'm going to use the 6.3V winding in the mains tx for the pass and error tubes in the reg, so I need a separate 6.3V supply for the phono heaters which I'm working on first. I've got a 7.5V tx which I'm trying to rectify with these SB350 Schottkys in a bridge: http://www.rapidonline.com/productinfo. ... leno=66258
But I'm beginning to wonder if they're not the right thing to be using as I'm getting a lot of AC as well as DC on the output of the bridge according to my DMM... Something's not right but I'm not sure what yet.

I haven't heard Dave's Aikido 300B but I'd really like to sometime - hope he makes another fest sometime. I know he really rates Brosky's phonos, definitely another to add to the long list.

Simon.
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#25

Post by shaun »

hi simon

yes just plain vanilla parallel 6080 but i'm thinking on that at the moment :D

take care

shaun
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#26

Post by shaun »

hi all

i've built the regs for the phono stage experiments and just have some fillament supplies to do next then it's time to play :D i'll let you know how it goes.

take care

shaun
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