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Old 5th October 2007, 09:27 PM   #11
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Default The more you know the less the better

The header is a quote from Billy Connellys Grandmother or at least that what he said in one show at the opera house that I went to.Having said that it seems all goes a murky grey when dealing with tubes. You learn one thing.. then you find out all to often how much you dont know.... Enough of the tube grown philosophy.
Shoog, the psu is an adaptation of a circuit dubbed the lsdy powersupply that has been modified by a chap.. heres the url if you want to see the article
http://eshop.diyclub.biz/article_info.php?articles_id=3
It is fairly similar to a ciruit published in a HP test instrument manual so i hope that its ok... i mean its quiet enough and i would be at a losss to better it anyway.(unless you wish to share any designs)
I am readying myself to build some 300b monoblocs and i have done some research on the input caps topic. Many suggest no cap but straigh t to an inductor or if you use a clc initially then the first value of c should be like 5uF. Then theres the concept of ppropylene caps rahter than electrolytics..apart from their sheer size, there is little to detract from a ppylene cap.
I might reduce the value of the caps i have in the phono stage from 47uf in nichicon to 22uF in rubycon i have ,47uf caps strapped across them as well at this point....
So where to from here
Any other suggestions? I might give Mr Connellys grandmother a call... maybe she knows
Thanks to all
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Old 6th October 2007, 12:39 AM   #12
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I think your power supply sounds fine. When I said oversized caps I meant in the 1000uf range.

My guess is that its a simple layout issue. I have my cartridge load resistors and caps mounted on the phono sockets - might be worth a try.
Did you get any improvement with the mods you already performed.

Shoog
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Old 6th October 2007, 10:33 PM   #13
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I built the Hagerman Cornet Octal from the circuit diagram a couple of years back and itís sitting here in front of me. I had a number of phonos laying about a bottlehead seduction and ARC SP3. The Cornet sound best of the three. I even took it to a phonostage shoot out hosted by the local tube audio club and it came in second only to the Artemis Lab PH1. That said Iíve moved on to a concoction of my own and the Cornet is relegated as a loaner to friends.

In my experience the circuit is sensitive to the gain stage tubes and follower (duh!). Other points of pain are: R9, C5 and C8. R7 may also play a role but by then I hit the wall with the Cornet.

My Cornet can sound annoying with too much emphasis in the high frequencies. This situation manifested when I put a Sylvania VT-231 in the follower position. This tube gave the impression of adding detail to the phonostage but on the long run shifted the tone to the treble and added some perceive distortion to loud high frequency passages. I finally settled with a RCA 6SN7GTB black-plate. This tube shifted the tone to the midrange and distort less than the VT. You can also try different 6SL7s. The reason I built the Cornet was that I scored a bunch of 6SL7s at a garage sale. I rolled the tubes until the phonestage gave me a well balanced smooth sound using a Sylvania 6SL7WGT and Tung-Sol 6SL7WGT. You mentioned using BIMAR tubes which Iím sure are good tubes but in my experience 6SN7s are notorious for having different tone and the 6SL7 is a rather squeaky tube.

Another soft spot is R9. You may want to try different resistors here. I found that a Kiwami would soften the tone a bit but the best to date is a mil-spec metal foil resistor I found at a surplus store as having a clean neutral sound. The next component I found helpful to try is C8. If rolling the 6SN7 or 6SL7 does not offer relief try a PIO in this position. I settled on a Russian K40Y9 .47uf paralleled with a Russian K72 Teflon. I found C5 to not be so fussy regarding tone but had an impact regarding distortion. I settled with a K72 Teflon.

Finally my PS is nothing like the one in the circuit diagram. I like to use the bare minimum capacitance in conjunction with a tank circuit to minimize ripple. All electrolytic caps are bypassed with K40s or some sort of PIO for the parts box. I found the PS design played a big role to minimize distortion but less on tone.

Hope this help.

cheers

33dot33rpm
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Old 8th October 2007, 07:31 AM   #14
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Default Thanks for the info 33dot33rpm

Hi
I will look into this..
I run carbon resistors throughout the phono section... try getting good resistors in australia before banishing me to the corner.
I tired shoogs suggestions.. it did make a subtle but palpable difference.. smoother being one perception..
The thing is I believe one channell sounds really nice whilst the other suffers the unpleasantness....
I still think this phono stage sounds great so i will instigate all the suggestions of 33 dot.
Only one question..
Where does a clueless fellah from australia find these fabled pios and teflon?
Ok Ok a second question whats a tank psu?
I am beggining to think my psu is overkill and perhaps contributing to the problem...
Many thanks to all of you
Nick
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Old 8th October 2007, 09:59 AM   #15
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Default Re: Thanks for the info 33dot33rpm

Quote:
Originally posted by duderduderini

I run carbon resistors throughout the phono section... .

I'm not sure that this is a good idea.... .these types contribute raising the noise floor-...others agree ?


richj
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Old 8th October 2007, 10:51 AM   #16
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Default Tube rolling does help somewhat

i tried some rolling.. found the smoked glass variants did smooth out sound somewhat. Curiously one channel exhibits this problem. I have tried to attend to layout as much as i can.
If anyone has recommendations re resistors I will take them up. As I said Australia is not the place for audiophile anything.. it exists but expensive.
Thanks
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Old 8th October 2007, 12:01 PM   #17
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Default What did you end up making instead?

Hi 33dot33rpm
So what did you end up settling on for your phono section?
Cheers
Nick
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Old 8th October 2007, 12:33 PM   #18
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Default resistor noise

I found this document published by Vishay re resistor noise
http://www.vishay.com/doc?49435
It might be of interest to many
Cheers
Nick
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Old 8th October 2007, 08:31 PM   #19
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Hi Nick,

Well it makes perfect sense to me that the smoked glass tube would make the phono sound smoother!:^) You didnít mention that fact that one channel sounds good and the other sounds bad. That would indicate some kind of fault in your circuit. Have you tried running just one channel at a time to the same input of your linestage (donít forget to use the same channel from your source to the phono)? If the same channel is still treble annoying then you can systematically go through the ďbadĒ circuit.

I would do the obvious first. If after rolling the tubes the same channel is still annoying this would be my procedure.

1) Clean and tighten the tube sockets of the channel in question
2) Reheat all solder joints of the bad channel
3) Swap the B+ of the L-R channels. (assuming you are using duel power supply or split and isolated the B+ somewhere up stream)
4) Swap C8 L-R channels.
5) Swap C5 L-R channels
6) Swap R3 L-R channels
7) Swap R5 L-R channels
8) Swap R3 L-R channels
9) Swap R6, R18 L-R channels
10) Keep swapping until the treble problem shifts to the other channel or goes away.

For the Russian capacitors just do ebay and search for ďTeflon CapacitorĒ and K40Y9. I got mine from Alexer1 and KWtubes.

Regarding carbon resistors yes carbon composite do tend to get noisy and drift with time but I have yet to have any noise problems with carbon films. Also note that rule of thumb is to use carbon comps for grid stoppers so go figure.

A tank circuit is to use a choke to resonate @ 120hz (for us American blokes) out of phase with the ripple coming from the rectifier thus reduce the amplitude. This is accomplished by attaching a small capacitor across the choke. Do a web search for tank circuit and you will find some helpful sites to design the circuit. With this setup I only need 200uf total of electrolytic caps to reduce ripple to a value barely detectable on my scope. In my experience too much electrolytic capacitors in the B+ dulls the sound and adds distortion. I donít like regulated PS because Iím too lazy to design and build them.

As for my final phonostage design Iím using the EF86 family of tubes wired for triode op, passive EQ (gain - eq Ė gain no follower). The phono lacks gain but is enough for my mm cart. The thing sounds really good and is slated for another shoot out in the near future. I hope it will beat the Artemis PH1.


cheers

33dot33rpm
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Old 8th October 2007, 10:23 PM   #20
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Default Tank Circuit

Hi 33 dot
You do mean a parrallel resonant band stop filter tuned to 100Hz? (our supply is 50Hz). Do you deploy any other filtration in the form of clc rc etc?
Thanks
WIll get on to your other suggestions later tonight. I have had a good listen to the phono stage again and I am still not 100% that it only occurs in one chanell (it definitely sounds better on to the other though)but i will go and do the checks you suggested.
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