Over the last couple days Nick, Andrew, Simon, Shane and myself have been exchanging emails on the above subject. It was considered this might be of interest to others so I have started this new thread.
Rather than precise what has been discuissed to date I, below is the extracted text from our emails:
Exchange of emails to date
Over lunch today had a head to head with my mate Ian.
I'm leaning towards making a single box unit to house a phono stage, line driver and TVA's. On the front panel would be a power on/off switch, source selector switch and volume control only.
The box would be suitably partitioned internally.
In it would go your D3A line driver, Andrews Cascode Phono (PCB based) and the Silk STA-522 transformer volume attenuators with Seiden or Elma 23 position volume control. I would have two inputs and one output using phono plugs. Nick Replied: Yes, sounds like a good idea
Would a single power supply do,with multiple tappings, or best to have seperate power supplies for the phono and line driver? Nick Replied: I would think one good supply for the lot is better than two not so good.
I was thinking the front mounted selector switch could be wired such to activate a relay that switches on the power to the phono as well as routes the input to the phono 'in' plugs when switched to Phono input? So only power to the line driver would be on when playing CD. The on/off switch would only power up the d3a power supply. What you reckon? Would you do this another (better perhaps) way? Nick Replied: Yes, that’s a good way of doing that, CD being passive only.
Hi Colin,
Already, been in contact with Shane on this one.
I think we can do better and perhaps, a bit simpler to build.
To those ends, been scheming up a new design based upon the work I did with/for Simon. (cc'd Simon as he's built the thing).
Basically, Simon seems to like his, but he's had problem with the high current demands of the heaters, same here for my phono which we briefly heard at Witham. I think Simon and myself have a way around this, but building the line driver/buffer into the phono using a 6N6P could perhaps be considered as "guilding the lily" which is what Simon and I did when we put Aikido line stages on the back of the phono.
The Aikido gain stage plus its line driver is only really needed for systems with long cables or an inductive load, for example, a transformer volume control. But, if you have long cables or a TVC then your CD/radio/etc also needs a buffer stage to drive the cables. Why put a buffer in just the phono? So my current thinking is its better to build the buffer 'separately' and let phono do the best it can at one thing only, being a good valve phono and with a reasonable line drive for most situtaions.
Plan is same front-end, as kindly debugged by Simon, followed by a triode, there are lots of posisbilities here heaters are no more than 400mA amps per C3g plus whatever we select as the next triode. PSU is is the region of 30mA-ish per channel. I have an HT PSU on a strip board awaiting my efforts to fix my scope, small DC regulated heater supplies for C3g should be relatively simple, also on a small piece of strip board; we could try a single DC heater supply first off for the total heater and see where we go.
I'm happy to furnish drawings of the cascode, if you prefer. Otherwise, what you suggests sounds like a very good, especially given you will use a TVC and long cables.
Cheers, -- Andrew
Evening chaps.
That's an interesting way of thinking about things Andrew. It would
certainly be interesting to try a triode second stage instead of the Aikido
- say a 6SN7 like you originally had . Perhaps some of the magic comes
from the Aikido, it needs trying to see I guess, wish I had the time. I can
feel that large piece of mdf calling...
The LT reg I built using an LM338 wasn't successful at Witham though I've
had it working for over an hour at home with no problems. I guess it must be
pretty marginal at the moment but I think removing the 1.5A draw of two
6N6Ps drivers should make the reg pretty comfortable.
Pleased to be copied in; I'll look on with interest.
Cheers, Simon.
Hi Simon et al,
Well I think the Aikido is a very good solution, especially if you think each amp should be able to "stand on its own". And, I think AC heating the 6N6P will safely remove the heater issues without added noise.
In Colin's case he's putting a buffer stage in the same box and going for a one box pre-amp so he's got no requirement for an Aikido output stage on his phono.
We need to know more about Shane's system and his plans.
What I'm trying to get to, I guess, is an Aikido is very good but there are other methods that might be more appropriate for a given situation especially if you have long cables/trabsformer volume/control and a valve output on your CD player, which Colin scores a full 3/3 and so needs a buffer anyway so is better building it into his pre section.
This is an option for you, of course, and my point was that doing this frees up the phono's second stage from dual duty of both gain and drive and perhaps increases the various options for the output valve choices.
In all cases, as of my current knowlege, my best guess on the high bang for the buck phono is the C3g front end followed by whaterver takes your fancy and fits with individual gain and drive requirements for the second stage.
cheers, -- Andrew
Interesting stuff!
For myself, I have no need to drive long cables or inductive loads, indeed I'm toying with the idea of building the phono onto an expanded chassis with the 6550 (with an entirely separate power supply), so the simpler triode output will suit me fine.
Shane.
Shane and Colin,
Well in both your cases you now have a good few bits in a single chassis, an integrated and a fully functioning pre, repectively. Now, the C3g front end needs a second triode with a gain of about 25, a bit more or less, depending upon the sensitivity of the power amp. For a standalone device, I'd really be tempted by two more C3g in triode mode but in your case I would recommend, as an less ambitious build, less heater current and a bit less HT current, and probably just as good, and more importantly proven in the Cascode and the Thorsten; the humble ECC88. There's also a couple of Ruski's that could do this but the JJ ECC88 isn't half bad, I have found; a slighly cleaner sound than the Mullards, to my ears.
As for step ups, I can only go with what I know. So, I don't think you can go far wrong with the Lundhals, I have heard these in Nick's phono against my S&B also in his phono and would be stuck to hear the difference. There's also the cheaper so called ex-BBC step ups on e-bay sold by a guy called DR-TRON, these are not as good as the S&B in my system but what can you say for £14 I paid for them. I would start by primary loading these with your desired resistor and place a 1Meg on the secondary, if this sounds too forward move to secondary loading.
Once we get going shall we move this to the Forum?
I've had a brief chat with Steven (Izzy Wizzy) and pointed out this place, he would surely be a useful person to have around. I expect his phono sounds very very good as well. It's interesting he uses a high gm pentode in the latest design.
OK guys I'm looking to source some step up Tx's for the phono stage and wondered which ones you recommend from listening tests/comparisons?
I know Andrew recommends Lundahls but which ones LL9206? These are around £58.00 from Benny at Aqua Blue, but is this price a pair?
I quite fancy a pair SILK Supermalloy MC-step up transformers with nano winding technology (don't you just love all this techno babble!) and assume I would need model ref MC-220 as my rondo bronze cartridge requires 10-200 ohm loading impedance.
Though I now have promised my Welborne Labs remote volume kit in the post (fingers crossed) depending how this compares Nick's Dave Slagle units I may throw caution to the wind and go for a pair the SILK-522 TVA's with Elma 23 position switch in lieu the WL remote.
The LL9206s are the ones I use, and most others I believe.
I got mine direct from Lundahl, think I paid around £80 delivered for the pair IIRC. Benny's showing 52.68 euro inc tax, which is each I think. So a pair including tax and postage works out remarkably similar to buying direct. In fact I suspect there's no difference...
Well if it isn't my money then the S&B's are very good.
The bass, I think, is a tad better than the Llundahl, but I 'd need to spend more time with them really.
The Llundahls are what ever Nick has.
Here's my rough circuit - I need to check it over, especially the operating points and check with Simon where he's at, don't whatever you do go build this yet....at the very least R2 is wrong should be more like 28k, what did you get Simon, in the end.
When you have a mo', I could do with you sticking the LEDs in then measuring the voltages on the Pentode's a, g2 and k. Oh, and letting me know if it sounds OK?
Basically, I'm a little concerned about pushing g2 a bit too hard at the current cathode voltage you have, the LED will be better (higher cathode voltage) but we need to be a bit careful. What I'm after is a g2 of 140v which gives us just about the max dissapation of g2 at that cathode voltage, the current should be just about 4.5mA for which I reckon you need a g2 resistor of ~24k.
After much debate with myself, I've decided to try out the SILK step ups and ordered a pair and hope to have these in the next couple week or so. These are not ex stock but are made to order and matched specific to your MC cartridge.
Andrew,
Basically how does this new phono design differ to your cascode design?
Any chance the new design can be knocked together onto a PCB like you did your cascode?
The new design uses a much lower impedance RIAA section which is driven much harder by the pentode. The RIAA also has much less series resistance as there's no need to place a buffer resistor to match the RIAA impedance to the input valve; put another way it's already the optimum match.
The pentode has even more sensitivity than the cascode you heard, to hopefully pick up more of the goodness on your black stuff.
The back end is essentially the same as the cascode, except there's no C4S constant current source on the ECC88. You could put one on if you wanted, perhaps on a small piece of stripboard.
For a possible upgrade I would put the C4S on the 88, but that's personal preference, some like them, some do not. It will increase the Zout a bit, but with a buffer that's no big deal.
James D originally recommended the C3g as a likely candidate for a phono, I hope I have done the concept justice whilst keeping things clean, simple and hopefully easy to build, therefore attainable.
I think this design would go fine on a bit of stripboard, using quality sockets connected "off the board" making it much more accessible than the cascode, which really needed the PCB...
cheers,
-- Andrew
Last edited by Andrew on Sat Oct 20, 2007 3:07 pm, edited 1 time in total.
. Perhaps some of the magic comes
