View Full Version : Rich's phono stage tinkering
Prompted by falling in love with vinyl again (detailed in the next paragraph should you be interested), I've decided to embark on a few light tweaks to my Eurekon phono stage. I'm very happy overall with the sound it produces but after taking the lid off for a look, curious chap that I am, I recognised that there was definitely room for the odd improvement here and there.
Background: I've had a Moth RCM MKII for a number of years. I've never been that happy with it. It has done some good to some records and left others pretty much unplayable. I'd tried adapting my cleaning technique and using different brushes etc. but some of my favourite albums had been ruined. Couple this with all of the improvements in the digital side of the system over the last year and my Well Tempered was getting used less and less.
Then after stumbling across the Keith Monks stand at the Bristol show at the weekend I got chatting to them about it and decided to buy a couple of bottles of their cleaning fluid to replace the Moth fluid I had always used. I didn't get to use it on arriving home on Saturday (too much post show beer ;-), but Sunday I got to work on some records, and thanks to Messrs. Monks, I not only have records playable that I thought destroyed but a wholly revitalised analogue front end. There are still clicks and pops in my records but you take less notice of this when the rest of it is pinning your jaw to the floor ;-).
Anyway, here is a piccy I took of the inside of my Eurekon:
http://i609.photobucket.com/albums/tt177/lovejoy23uk/Phono%20stage%20insides/DSCF0425.jpg
To be honest, I'm not really sure of this thing's origin. When I bought it, I worked as Saturday guy in Sevenoaks in Cardiff and was in the market for a new phono stage. I'd tried a couple - Tom Evans, Michel, the rest escape me now, but I was close to opting for a Linn Linto. Then a chance conversation with a visitor to the shop changed all that. He was a South African gentleman who was a friend of Andre Nel, designer at Eurekon audio and told me he had one of his phono stages he was selling on before moving back to South Africa and agreed to loan it to me for the weekend. I loved it and bought it from him the week after, and it has sat happily in my system ever since.
I've had the odd Email exchange with Andre Nel and we talked about some improvements to the power supply. This is going back a while now though and I've now managed to lose contact with him. But looking at the top of the board where the power is being fed from a toroidal transformer feeding +/-25V, there is a rather basic LM317/337 setup feeding the circuit. There's plenty of space in the case at the front so I thought that a +/- TeddyReg pair would fit in there rather nicely and almost certainly bring some serious improvements to what is a surprisingly basic supply.
Having then looked around the board a bit more I came to the conclusion that this must have been a prototype, given away by its lack of a serial number and the fact that every single IC is in a chip holder. It also seemed rather strange that they've gone to the trouble of wiring everything up with Kimber Cable and then used chip sockets everywhere.
Being a phono stage dealing with some delicate signals I would have thought chip holders were a bad idea for a final product. Can anyone here vouch for it being worth my while in taking them all out and resoldering each IC directly to the board? I'm not sure I want to start swapping out op-amps, as I say, I'm overall happy with the tonal balance - I'm just looking at the more obvious areas of improvement, and having read up on the op-amps involved, they seem like reasonable choices.
Finally, those electrolytics could probably do with upgrading.
I'd be most interested/grateful for anyone's thoughts on the matter.
StanleyB
02-03-2010, 08:27
The presence of a LM317 does not imply that it is a simple power supply circuit. I have seen some very advanced power supply drawings with the LM317 in it. The LM317 is used for regulation + setting the required voltage output level. Ancillary components around the LM317 could be doing additional jobs such as noise filtering etc.
If you are thinking of replacing the LM317, make sure you know what you are doing! My first suggestion would be to measure the voltage on the output pin of the LM317.
ICs in sockets is not uncommon and was actually quite popular before cost cutting and surface mount made them harder to find in a design. I use them for my opamps, and many PC motherboards still use them for certain chips. That includes the micro processor running at a GHz or two, and the memory chips.
The Grand Wazoo
02-03-2010, 08:39
Rich, sorry if this swerves the thread a bit, but why did you Moth RCM do what it did?
I've had one for years & swear by it - never had the slightest hint of a problem or worry.
Start another thread if you'd like to keep this one on topic.
Cheers
No worries Chris,
Well, it looks like the finger of blame is being pointed at the Moth cleaning fluid I was using as so far using the Keith Monks fluid, every record it has touched it has worked absolute magic on - that's including a handful of classical records I bought from car boot sales for 50p that before now did absolutely nothing for me, now I'm hankering for more.
I do wonder how long that fluid had been in storage before I bought it. Being isopropyl alcohol based I guess there's every chance the alcohol had managed to evaporate leaving me with something rather less effective.
Thanks Stan,
I'm more than happy NOT to be removing all of those chip sockets so your words come as welcome relief on that front ;-).
Having dug around my old Emails from Andre, I found some information on his own experimentation with power supplies. He has noted that better regs have not really improved things and have introduced their own problems. However, double regulation seems to turn up some positive results. This sounds like good news as a TeddyReg between the trafo and the existing regs would be clean, non-intrusive and reversible. Also some better diodes have been suggested in the rectification stage although no types were mentioned.
The one thing I really have overlooked is the use of custom resistors for cartridge loading. The manual recommends the use of custom resistors instead of the DIP switches to get the best results. Hmmmm, now then, what would be the value I'd need for my AT33PTG - I'm guessing around 100ohms... Anyone?
StanleyB
02-03-2010, 09:10
I do wonder how long that fluid had been in storage before I bought it. Being isopropyl alcohol based I guess there's every chance the alcohol had managed to evaporate leaving me with something rather less effective.
It depends on how much alcohol was in the bottle. If the alcohol has evaporated, the bottle content would be reduced by the same amount of alcohol.
StanleyB
02-03-2010, 09:23
However, double regulation seems to turn up some positive results.
I am a firm believer in double and even triple regulation. All my DACs power supplies are designed with double regulation. The TC-7510 5V power supply is even triple regulated. There is a massive improvement in power supply noise rejection and ripple in a double regulated circuit.
Great, time to do a Farnell order then. Thanks for the advice Stan, not to mention making the whole job a lot easier for me :).
Having done a bit more record cleaning, I've noticed that the records I'd previously cleaned with the Moth fluid are now bringing up this white residue when I apply the new fluid. A couple of applications sorts this out and all of the damage is being undone, so this is fantastic news. This Keith Monks' stuff is really VERY VERY good.
Had a pair of high quality 180ohm resistors lying around not doing anything so I thought I'd try those in the custom resistor socket. I don't think the value is spot on for the AT33PTG but the manual was right, it's still better than the DIP switch settings. The words "holy crap" spring to mind. You know when something sounds so good that you can't quite play it loud enough - well, my ears are ringing.. It's a good job the neighbours are out.
Hmmmm, now then, what would be the value I'd need for my AT33PTG - I'm guessing around 100ohms... Anyone?
Interestingly I've been experimenting with that myself with my 33PTG. For a direct MC phono stage I've found 500 Ohms to be good (although you can experiment down to about 200 Ohms). For a step-up transformer, the 184 Ohms that my CineMag SUT presents is absolutely ideal, giving a nice improvement in weight while retaining its treble sparkle.
Thanks Martin, that is interesting.
The DIP switches on my Eurekon only go up as far as 300ohms, but I can put a 500ohm in the custom slot and try that. I need to get a decent quality 500ohm resistor ordered to try it. I have to say though, that the 180ohm resistor in place is making the best music I've ever heard from the AT33PTG, but then I've only ever used the DIP switches before. I'll add a good 500ohm resistor to my Farnell order.
It'll be interesting to know what you think as you may find that you prefer your current 180 Ohm setup. General opinion seems to have it that direct inputs and transformers behave slightly differently, certainly my SUT on 184 Ohms gives the best sound I've yet achieved, so maybe the 33PTG is consistent in this respect? Fab cartridge, isn't it?
Fab cartridge, isn't it?
I was extremely pleased with it from day 1. It replaced both a Dynavector XX2 which I found too rich for my tastes but was incredible with vocals and an Ortofon Kontrapunkt A which I really liked - neither of those carts were slouches, or cheap, but the AT seems to combine the best of both and still keeps pulling new things out of the bag which never cease to amaze me. Surely one of hi-fi's greatest bargains.
Indeed - and for an even bigger bargain, try a Denon DL-103SA, which when partnered optimally competes with cartridges at virtually any price... Isn't that right Martin? ;)
Marco.
It is indeed - the proviso being that it is more fussy about partnering equipment ;)
That, my friend, I cannot deny :)
Marco.
Sounds like I've found my next cartridge then, which by the way I'm ploughing through albums today won't be that far away ;)
Primalsea
02-03-2010, 20:38
Lovejoy, you could replace the power supply caps with new, better ones. It may not be a good idea to increase the capacitance rating though.
Also you may have noticed that there is 8 smaller electrolytic caps. I cant tell from the photo but they look like they might be in the signal path rather than bypass caps for the local power supply rails. If they are bypass caps you could change them for higher quality electrolytics. You could get away with increasing the rating a little but dont go mad. If they are in the signal path you want to try to replace them with a different cap. Depending on the rating you might struggle to get the same rating in say, poly caps (or whatever your choice is) You might be able to replace them with a much lower rating however, ie changing from 100uF to 4.7uF may not cause any problems and in some cases can be beneficial.
Thanks Paul,
Having taken a closer look at the 8 small electrolytics, it turns out they are 100uf Rubycons. It seems the choice of components throughout the board is of pretty good quality, although the power supply caps are 1000uf "Gloria" - not one I've ever heard of. Now that I see the smaller ones are Rubycons, I'll leave those as they are. I think I may change the Gloria ones for something a bit better when I drop in the second regulation stage though.
I'd be cautious tbh, I'd prefer to have some understanding about the circuit before attempting modding anything, its very easy to make something perform far worse if just guessing swapping bits about;)
Sorry for sounding boring but the times I've had to help friends out after they'd been fiddling with something :doh:
If your really sure you want to have a bash my advice is start off simple, note EVERYTHING down you've changed so you can back track later if needed, if unsure of anything leave it until you've confirmed its ok to try
StanleyB
03-03-2010, 14:46
power supply caps are 1000uf "Gloria" - not one I've ever heard of. Now that I see the smaller ones are Rubycons, I'll leave those as they are. I think I may change the Gloria ones for something a bit better when I drop in the second regulation stage though.
Gloria capacitors have been in business for about thirty years now. Very good make. A lot of the popular brand names are now counterfeited in China, so changing for a 'better' one is just the thing that counterfeiters relish in.
Seems it has all been very nicely specced then, which means given the amount of thought gone into it, I'm only going to make things worse by tinkering. This thread has been a massive help - thanks guys. Plus it did get me to drop in some custom resistors, which has made everything sound very live and free of the speakers.
I'll order a couple of good quality different value resistors to try for loading to compare with the current 180ohms and report back, but I think that's as far as I need to go.
A lot of the popular brand names are now counterfeited in China
Plus one Chinese brand, 'CapXon', which should be avoided like the plague.
StanleyB
04-03-2010, 08:15
If you are going to try other resistors, don't get taken in by the apparent brand name. What you should look for is E96 or E192 types, which are listed in the IEC 60063 document. Those are the best quality, but also cost top bucks. Only buy them from reputable companies though, such as RS, Farnell, etc. There are a lot of fakes coming out of China, and sold as genuine well respected brands on eBay by HK and China based sellers.
Time for an update:
Got a couple of different resistors to try from Hi-Fi Collective over the weekend. Dropped in some 500ohm - well 510ohm actually as that was the closest I could get, left it all to warm up and came back for a good listening session with the old 180ohm load resistors fresh in my mind.
Martin, you are right. 500ohm is the business!! If there was one niggly little complaint I had before it was that bass wasn't quite as taut and tuneful as I thought it could be. Now it's all there, plus some extra space around everything and the ability to follow any instrument in the mix is incredible.
It sounds so good, there's no urge to tweak it any further, just enjoy it, and enjoy it, and enjoy it. Many thanks all.
I'm about to post a needledrop in the analogue art section. It'd be grand if you'd have a wee listen.
Glad you've got it sorted, Rich. A cartridge running in its sweet spot is a joy to listen to. What tracking weight are you using?
I'm on 1.8grams, which is where it's been since running it in. I found I had to adjust it up and down a few times during the first 50 hours. It was sounding quite dead at 1.8 for a while so it was right down at 1.4, but now it has plenty of records played, it seems quite happy at 1.8.
What is yours at Martin?
I'm running at 1.85g and it's sounding superb in the Jelco arm. Can't wait to get it in the Dynavector arm :)
Powered by vBulletin® Version 4.2.3 Copyright © 2026 vBulletin Solutions, Inc. All rights reserved.