Unfortunately, once you have signal transformers in the mix, costs go up rapidly. Skimp on them and quality goes down rapidly. And I gather that $500 BOM is outside the OP's budget.
Doug, there's a particularly neat trick to do with FETs, but you need a p-FET, and good, quiet p-FETs are hard to come by these days.
Doug, there's a particularly neat trick to do with FETs, but you need a p-FET, and good, quiet p-FETs are hard to come by these days.
The Marantz based kit is interesting. I took a (very quick) look at the schematic. It looks like it (the original Marantz as I don't have schem for the kit) uses pretty decent sized plate load resistors of 270k, of course shunted by the eq network which includes a 330k resistor so about 150k. Not an ideal load I am sure but about 2.4 times rp give or take depending on the bias. The second stage has a very high impedance CF load so the total load is essentially the 270k which is over 4x rp so seems pretty decent there. I can only assume that your kit uses the 12AU7 for the CF for which it should work just fine.
I also see at least one feedback loop and I haven't traced through all of the switching but it looks like there may be another from the output of the CF.
My thought on it is that the kit is not super expensive and is an interesting design. Since it is a separate PCB you could build it and give it a good listen. If you like the sound it doesn't matter what its technical flaws are. If you don't like it then it is a simple matter to put it in a project box and resell it on eBay. Given it is from a classic design I am pretty sure that it would sell and you could recoup at least some of your cost. In the end you will come out with some real personal hands on experience on the subject and that is IMO a huge part of what this hobby is about.
In the end we get all hung up sometimes in the quest for the Holy Grail which is all well and good but it is really about having fun and listening to music. So I say don't be afraid to try something (well don't try discharging filter caps with your tongue
) and see what you get.
I also see at least one feedback loop and I haven't traced through all of the switching but it looks like there may be another from the output of the CF.
My thought on it is that the kit is not super expensive and is an interesting design. Since it is a separate PCB you could build it and give it a good listen. If you like the sound it doesn't matter what its technical flaws are. If you don't like it then it is a simple matter to put it in a project box and resell it on eBay. Given it is from a classic design I am pretty sure that it would sell and you could recoup at least some of your cost. In the end you will come out with some real personal hands on experience on the subject and that is IMO a huge part of what this hobby is about.
In the end we get all hung up sometimes in the quest for the Holy Grail which is all well and good but it is really about having fun and listening to music. So I say don't be afraid to try something (well don't try discharging filter caps with your tongue
) and see what you get.
It's not that I am hung up or anything on the 12AX7 or anything just that I've got a slew of them and they seem to be used so often both in DIY kit forms, many phono schematics and other designs.
I'm starting to appreciate that it's not necessarily the best choice or the cheapest to properly build a phono stage around in the end but surely there's some viable and affordable alternative...not for a penultimate design or performer but something those on a tight budget lets say $250 could fashion and realize credible performance from.
Based on what I'm hearing from Sy, Eli and others the only economical alternative is to utilize a solid-state design? which kind of undermines my desire to have an all-tube chain.
The Marantz based kit is interesting. I took a (very quick) look at the schematic. It looks like it (the original Marantz as I don't have schem for the kit) uses pretty decent sized plate load resistors of 270k, of course shunted by the eq network which includes a 330k resistor so about 150k. Not an ideal load I am sure but about 2.4 times rp give or take depending on the bias. The second stage has a very high impedance CF load so the total load is essentially the 270k which is over 4x rp so seems pretty decent there. I can only assume that your kit uses the 12AU7 for the CF for which it should work just fine.
I also see at least one feedback loop and I haven't traced through all of the switching but it looks like there may be another from the output of the CF.
My thought on it is that the kit is not super expensive and is an interesting design. Since it is a separate PCB you could build it and give it a good listen. If you like the sound it doesn't matter what its technical flaws are. If you don't like it then it is a simple matter to put it in a project box and resell it on eBay. Given it is from a classic design I am pretty sure that it would sell and you could recoup at least some of your cost. In the end you will come out with some real personal hands on experience on the subject and that is IMO a huge part of what this hobby is about.
In the end we get all hung up sometimes in the quest for the Holy Grail which is all well and good but it is really about having fun and listening to music. So I say don't be afraid to try something (well don't try discharging filter caps with your tongue
Thanks to all. Appreciate your comments regarding the Marantz kit (Mahaffer). I was hoping others might offer their opinion on that potential avenue of exploration for those on a tight budget.
It seems if my choices are $500 to infinity for a decent Tube Phono stage build and $250+ for a S/S phono stage that this Marantz 7 PCB kit might be a decent compromise...but again looking for other's expertise.
ma's point is a good one, that you can always resell it. But I've built several stages like that and never ended up keeping them. The undegenerated cathode resistance means the plate resistance skyrockets (that 270k resistor suddenly doesn't look so big). Bass distortion is high and RIAA conformance is unstable because of inadequate upen loop gain. Miller capacitance is still high, which may or may not be an issue for your cartridge.
Sorry, don't mean to be a downer, I've just spent a lot of sweat over the years getting tube phono stages to work right. I'm extremely happy with my current one for MC (His Master's Noise), but am in the throes of getting a new MM stage going.
Sorry, don't mean to be a downer, I've just spent a lot of sweat over the years getting tube phono stages to work right. I'm extremely happy with my current one for MC (His Master's Noise), but am in the throes of getting a new MM stage going.
Thanks Sy, appreciate your candour....often there's no sugar coating the inescapable truth. But, having said that, it seems to me that a workable, affordable and quality phono-stage seems to have fallen through the cracks in the floor of the design cookhouse somewhere along the way.
If the RCA book phono-stage is at the bottom of the rung and the next rung is in the $500 plus range what's a humble DIY' selfer wanting a decent but affordable tube-phono stage to do?
The design that I was toying with at one time (have other more pressing projects right now) was passive two stage with a mu-follower input 12AY7 with LED bias on the bottom 12AU7 on the top. Cathode biased 12AX7 second stage with 12AU7 CF output buffer. After this discussion I went back and looked at the last schematic and realized that the eq. circuitry on the output of the second stage is way too low of impedance so I will need to rework it. If I hope to use 12AX7 in the second stage I will need to redo the eq. for sure and maybe use LED bias there as well. But probably better to redesign for 6CG7 or 6N1P in the second stage if adequate gain can still be obtained.
If I had a sleeve of them I would call it "My savings account", especially made by Telefunken.
To use 12AX7 in something real is more likely to use Dollar bills to start fireplace.
If I had a sleeve of them I would call it "My savings account", especially made by Telefunken.
To use 12AX7 in something real is more likely to use Dollar bills to start fireplace.
Too funny Wavebourn!
But you see the problem faced by beginners and neophytes like myself who are interested in building our first projects but not keen on pouring scarce limited financial resources into poor designs or end-results if something better can be fashioned.
For example, I have a number of 26 and 27 tubes that I hear make for some great projects but these tubes apparently pose a whole host of other design concerns and considerations.
So, like the naive beginner I am, I looked for something based on a little more current and affordable tube and one, at least on first blush, that seems to have been designed for such a purpose in the first place--at least by its ubiquitous application in phono-stages as far back as the early 60s and up until today.
I have no problem using other tubes...but now I have to ask what is a 12AX7 best suited for?
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This brings back to the question of what do you want? A philosophical one indeed.
Like Sakuma when he was buiding amps not that he had a budget problem but
his quest for something that "pleases" his soul.So he tried all the usual tricks
and was starring at the interstage transformer which seem to say to him:
"Sakuma do you build amplifiers to get approval from electronic teachers or
for yourself ", from that moment on he never looked back.
The issue is your constraint that it has to be tubes. Narrowing the constraint to include 12AX7 makes it even tougher. Like I said, you can make a fine solid state stage for pretty low $$$. If your 12AX7 are collectors' items, you can sell them off to finance the construction of a good tube stage using more suitable (but not as treasured by the baseball-card-collector-mentality types) tubes.
It is not funny when naive beginners act like spoiled children, "Give me now the best schematic, or I will call you a bad guy".
As I said already: they are best suited for sale.
I would recommend you to start discussing your wishes/requirements, then people will come with constructive suggestions. From that point the "naive begginner" starts learning.
People already gave you a lot of valuable advices that you even did not consider to evaluate.
I am out of your topics, it is the 2'nd time I tried to help you, but got a rude response.
Welcome to the ignore list!
The 'X7 is a good voltage amplifier, but it can't drive loads. It's acceptable in MM phono preamps, provided you take the high CMiller and poor drive capability into account. You deal with CMiller by careful cart. selection. The drive issue is dealt with by buffering. The tweaked RCA setup I uploaded earlier in this thread is technically competent and not especially costly to build.
If a good performing phono preamp at very modest expense is your goal, SY gave you the unvarnished truth, which is to use "sand". Jim Hagerman's "Bugle" is such a project. BTW, a "Bugle" can be set up to work with either a MM or LOMC cart., but not both at the same time.
As always thanks Sy...I just wanted to understand why the 12AX7s weren't very good for this and it's been made pretty clear now that this tube has some fundamental characteristics/difficulties which preclude it from easy and affordable use as a budget phono stage build.
I'll take what's been offered by everyone with great appreciation and see what I can fashion.
I've learned quite a bit more than I first imagined already...I think...thanks again.
Thanks Eli....time to build and see where it leads me. Appreciate all your input.
Wavebourn. I don't know what happened.
I truly meant that I appreciated your use of humour as a way of directing me where I might best spend my time and resources. I was not being sarcastic when I said "Too Funny!"
I didn't know 12AX7s were of any real monetary value but your point was and is valid.
I have looked at the alternatives offered by everyone, but wanted to know what makes a decent quality tube phono-stage so very difficult to render properly at an affordable price.
If I don't know something, If something is not clear to me...because I am inexperienced, I ask for clarification.
I am certain there is some kind of misunderstanding between us that somehow offended you...I don't recall ever demanding anything or telling anyone here at DIYAudio that they weren't being helpful.
My apologies if I offended you, or anyone else here, somehow. I might be guilty of inexperience, of inquisitiveness and verbosity (as rightfully pointed out earlier in this thread) but, I hope, not of disrespect. Best regards, Leo
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