Sorry if some of these questions sounds pretty basic, but this is my first attempt at anything involving tubes, so please bear with me.
i've been collecting/butchering old equipment for parts, and i'm just about to start on the Marantz 7 pre. First off, i've got a 6x4 rectifier, and i was wondering if this would be strong enough to supply both channels (models in PSU designer say that it gives up). Also, the transformer i have has a 6.3v tap for the heaters, and i was wondering if it was worth running these at DC, or just leaving them how they are.
Another thing, do i need to include the balance pot, and does the volume pot need to be so large (not so easy to get hold of).
And finally, i believe there are various mods/updates you can do to this circuit, but i can't seem to find any. I did read somewhere that there is an improvement if you run a B+ of 250v to all tubes.
Any help is most appreciated.
Thanks,
Hamish
i've been collecting/butchering old equipment for parts, and i'm just about to start on the Marantz 7 pre. First off, i've got a 6x4 rectifier, and i was wondering if this would be strong enough to supply both channels (models in PSU designer say that it gives up). Also, the transformer i have has a 6.3v tap for the heaters, and i was wondering if it was worth running these at DC, or just leaving them how they are.
Another thing, do i need to include the balance pot, and does the volume pot need to be so large (not so easy to get hold of).
And finally, i believe there are various mods/updates you can do to this circuit, but i can't seem to find any. I did read somewhere that there is an improvement if you run a B+ of 250v to all tubes.
Any help is most appreciated.
Thanks,
Hamish
Attachments
According to the duncanamps.com database (well worth downloading btw) a 6x4 can handle 70mA at 325V. So I think it would be just cruising along in your application.
In my opinion, it is definitely worth running 12AX7 on DC heaters. Reduces noise and hum by quite a lot. A diode bridge followed by C-R-C filtering will do nicely, adjust the R to get 6.3 V exactly. Also ground one side of the filaments.
You can omit the balance pot if you like just use resistors.
In my opinion, it is definitely worth running 12AX7 on DC heaters. Reduces noise and hum by quite a lot. A diode bridge followed by C-R-C filtering will do nicely, adjust the R to get 6.3 V exactly. Also ground one side of the filaments.
You can omit the balance pot if you like just use resistors.
Hamish said:
DONT!
It's a huge piece of crap, speaking from the experience of owning an original which was then modified all over the place (regs, caps, resistors, topology) before being restored and sold on to a collector.
Yuk! Yuk! Yuk!
The worst aspects of tubiness and poor resolution.
For your time and effort you can do much better. Use another design.
The only reason I'd like to own one today is so that I could sell it on again to another collector for an obscene amount of money.
Any suggestions then? i like this one because the 12ax7's are pretty easy to get and i have a few here anyway. I want a REALLY good phono stage (but not too complicated). That's my main aim.
fdegrove,
i found this on another thread, and you mention having done a phono stage similar. Could i get any more information on that, if possible? Obviously ye olde Marantz 7 is a reviled piece of equipment around here..........
fdegrove,
i found this on another thread, and you mention having done a phono stage similar. Could i get any more information on that, if possible? Obviously ye olde Marantz 7 is a reviled piece of equipment around here..........
Attachments
Hi,
Did I?
Hmmmm....I probably referred to the output stage I think.
The image you posted is nothing more than an anodefollower, RC coupled into another anode follower, direct coupled into a White cathode follower with NFB applied from output to input.
It may be some linestage but it certainly isn't a phono stage...
Cheers,
Did I?
Hmmmm....I probably referred to the output stage I think.
The image you posted is nothing more than an anodefollower, RC coupled into another anode follower, direct coupled into a White cathode follower with NFB applied from output to input.
It may be some linestage but it certainly isn't a phono stage...
Cheers,
Well, i'm aware it isn't a phono stage.........
but it shouldn't be too hard to work an active RIAA eq into the NFB (hopefully). So this should sound ok as line level pre? Sorry, but i have zero experience with tube topologies and sounds.
here's the thread: http://www.diyaudio.com/forums/showthread.php?s=&threadid=5985&highlight=12ax7+preamp
but it shouldn't be too hard to work an active RIAA eq into the NFB (hopefully). So this should sound ok as line level pre? Sorry, but i have zero experience with tube topologies and sounds.
here's the thread: http://www.diyaudio.com/forums/showthread.php?s=&threadid=5985&highlight=12ax7+preamp
Hi,
Sure, recommendations are easy enough to hand out....
Actually producing a good phono stage is another chapter entirely....
MC compatible ones are a living nightmare if you want, like myself stubbornly adhere to valves...
I've got a thousand ideas floating in my mind none of which is perfect but perfection is not of this world anyway...he, he...
Cheers,
Sure, recommendations are easy enough to hand out....
Actually producing a good phono stage is another chapter entirely....
MC compatible ones are a living nightmare if you want, like myself stubbornly adhere to valves...
I've got a thousand ideas floating in my mind none of which is perfect but perfection is not of this world anyway...he, he...
Cheers,
Hamish said:
IMO/IME, you'll not get a really good phono stage with 12AX7's. And not with feedback either.
Before I recommend anything, how much gain do you want, and what sort of input voltage are you thinking of using? This will largely determine what sort of topologies will work.
As for tube availability, do you have a credit card? If so, then tubes are not an issue to obtain. There are a number of US vendors for instance that will have a few tubes to Brisvegas within 7 working days (I'm in the bush and that's how long they take to me) and the postage is decent. Europe takes a bit longer. There are some in Oz too like David Crittle at Retrovox whom I'd highly recommend.
As an example, a simple resistive loaded 6BX7 or 12B4A would be a hell of a lot better than the 7C for a linestage, and the tubes are 7 and 3 USD respectively for real NOS stuff. One stage and no NFB, and for a further improvement use a Lundahl choke, or a CCS to make a mu stage.
Thanks Frank. If you think of any "less than ideal" preamps that might do the trick, let me know
I'm not keen enough yet for a MC. I'm just about to send a Grace F-9 down to Garrot brothers for a rebuild, so i'll be using a MM for a while to get my money's worth.
I'm not really after perfection in the linestage, in fact that is probably the last thing i want. I just want something that's not too hard as a first project, and musical. That's all. I got my first taste of tubes with an Akai M-8 i picked up for next to nothing, and now i want more!
Thanks again, Frank.
Hamish
I'm not keen enough yet for a MC. I'm just about to send a Grace F-9 down to Garrot brothers for a rebuild, so i'll be using a MM for a while to get my money's worth.
I'm not really after perfection in the linestage, in fact that is probably the last thing i want. I just want something that's not too hard as a first project, and musical. That's all. I got my first taste of tubes with an Akai M-8 i picked up for next to nothing, and now i want more!
Thanks again, Frank.
Hamish
Hamish said:
Here's a setup for a 12B4A in a line stage.
B+ 300V
Ia 25 - 30mA
Ranode = 6 - 7K
Vg -12.5 (@ 30mA / 6k)
Rk 410R
rp = 950R
u = 6.4
6k anode load will dissipate 5.4W, so I'd suggest 2 x 12W Mills 12k in //
Bypassed, gain will be 5.5 and Zout 820R. Unbypassed 3.8 and 2k4.
A similar design was discussed in this previous thread.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=19446
Let me know what you have in the way of power supply iron, transformers and chokes, as well as caps and I'll tweak the values for you.
I may also have some spare 12B4A's here, and if not, I'm going to order a few other tubes from the US next week and could add some in if you like.
As far as power supply goes, i've got a 260-0-260 transformer i nicked from an old AWA receiver (with a 6x4 rectifier). I haven't got anything in the way of caps yet (there are some, but they're no doubt too old to be used). I was just going to run up a supply on PSU designer with a simple RC filter to keep things cheap and cheerful. Chokes seem to be a shade pricey.
I got a few tubes out of that receiver if they're of any use: some 6au6's, a 6be6, some 6aq5's, and a 6n8 (an oscillator i think). They're all old AWA tubes so i don't know how good they are...............
I got a few tubes out of that receiver if they're of any use: some 6au6's, a 6be6, some 6aq5's, and a 6n8 (an oscillator i think). They're all old AWA tubes so i don't know how good they are...............
And a bit more modern one... found at Vacuum State Electronics.
dave
An externally hosted image should be here but it was not working when we last tested it.
dave
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