CECAA850 Posted November 10, 2015 Share Posted November 10, 2015 Seriously? This preamp will not be able to drive heavy loads or long interconnects. The 12AU7 is terribly non linear why would you want to input a 1-2Vrms signal into it and then attenuate all the gain away? All you do is add distortion :/ Sincerely disappointed. This is the pre-amp I was asked to build, and, many who have built it, like it. Like I said before, I am going to "do my thing" with it and I suspect my changes will make it better. So you will be doing "your thing" (which I am sure is a "trade secret") which will render it a different preamp. Correction; you are not building that preamp then. Your questions come off as accusatory. I don't know what the problem is but try to lighten up a bit if you would. 2 Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted November 10, 2015 Share Posted November 10, 2015 I am not really accusing anyone of anything. Matt's intention is to build this for a customer but also offer it to any other forum member for sale. I just want forum members to understand the shortcomings of the design. Matt then makes things confusing to people interested in this by saying he is going to change the circuit, I am merely pointing out he is presenting one circuit and building something different. If changes are made present them and make an argument on why and how they will effect performance. Just my 2 pennies, no accusations, I just like clarification. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted November 10, 2015 Share Posted November 10, 2015 I am not really accusing anyone of anything. Matt's intention is to build this for a customer but also offer it to any other forum member for sale. I just want forum members to understand the shortcomings of the design. Matt then makes things confusing to people interested in this by saying he is going to change the circuit, I am merely pointing out he is presenting one circuit and building something different. If changes are made present them and make an argument on why and how they will effect performance. Just my 2 pennies, no accusations, I just like clarification. That was a great post, thanks. Most prefer discussions as opposed to arguments. I appreciate it. Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted November 10, 2015 Share Posted November 10, 2015 No worries! Matt makes beautiful amps and I don't want him to polish a turd so to say. And if he makes circuit adjustments I am sure customers are going to want to know about the added performance of things like distortion and output impedance. I mean honestly looking at the distortion chart on the linked project page who would want >1% THD from just a preamp. Quote Link to comment Share on other sites More sharing options...
minermark Posted November 10, 2015 Share Posted November 10, 2015 Toolshedamps: Iv been following the thread, myself in electronics since the 60s and everything Ham. Iv not "Seen It All" but dam close. I like the Design, and as with any design, Tweeks can be astounding, the fun of the hobby. Sounds like you are very willing to assist DIY builders, and man could this world use more guys like that, well done. May i just throw this out there for something for you to also consider, offer some of these Amp pieces sized and predrilled, you know, not exactly like a kit, but just some helpfull goodies for the DIYs. Of the many people iv assisted over the years, the one constant i saw was, a guy with this kind of hobby will make a space and set up a bench, invest in soldering and more than willing to learn, however iv witnessed many ready to jump on something like this, but do not have a drillpress, or wood/metalworking knowhow. so they give in and just buy assembled. My two cents Keep up the good Work/Designs/Tweeks :emotion-21: 3 Quote Link to comment Share on other sites More sharing options...
mike stehr Posted November 10, 2015 Share Posted November 10, 2015 Seriously? This preamp will not be able to drive heavy loads or long interconnects. The 12AU7 is terribly non linear why would you want to input a 1-2Vrms signal into it and then attenuate all the gain away? All you do is add distortion :/ Sincerely disappointed. I thought a preamplifier is called a preamplifier because it has circuits in itself like phono, tape, etc...The project pointed out is a linestage from what I can understand. Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted November 10, 2015 Share Posted November 10, 2015 I am starting to understand it's an effect box. Input a signal and it will add some pleasing harmonic distortion. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted November 10, 2015 Share Posted November 10, 2015 I had a Admiral push-pull 6BQ5 console amplifier. The original driver section had 12AU7, which I think was the cathodyne topology. Ramped it up on a variac, replaced some bad decoupling/coupling caps, and got it powered up in stock form I suppose. Sounded terrible...a raspy bloated unglued kind of sound. So I used the Dynaco paraphase splitter driver circuit that is published online, and set-up the amplifier using 12AX7. Didn't do anything with tweaking in feedback with a scope, I just used the suggested value feedback resistor in the schematic. The amplifier had a cleaner more settled sound then. Was it the type driver/splitter topology? Or the 12AU7? I know 12AU7 has it's place, but JPM isn't the first person mentioning the non-linearity of 12AU7 that I've come across. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted November 10, 2015 Share Posted November 10, 2015 I know 12AU7 has it's place, but JPM isn't the first person mentioning the non-linearity of 12AU7 that I've come across. Then I like non-linearity. My favorite pre-amp at home has three 12AU7's in it. Not only does it sound phenomenal, Maynard was extremely impressed with how it measured on his scope. Quote Link to comment Share on other sites More sharing options...
Matthews Posted November 10, 2015 Share Posted November 10, 2015 I am starting to understand it's an effect box. Input a signal and it will add some pleasing harmonic distortion. Let us see some of your designs, "xxJPMxx"? Let us see what you have built... Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted November 10, 2015 Share Posted November 10, 2015 Then I like non-linearity. My favorite pre-amp at home has three 12AU7's in it. Not only does it sound phenomenal, Maynard was extremely impressed with how it measured on his scope. Some people like the added distortion. Besides we don't know any details of that circuit, it could have feedback, or it could simply cut down on distortion by just moving the volume control Here is the issue with that schematic. The volume control is at the output and today's sources put out 1-2Vrms. I count with that load line 30V swing at the plate from -2 to 0v and 20V swing from -2 to -4. So you have a source say putting out 4V peak to peak (1.4Vrms) and you have a amp hooked up with an input Z of 100k, You are going to get 48V peak to peak (17Vrms) w/ 3% THD. Then you are going to attenuate that 17Vrms down to 1Vrms to drive the input of the amp. So you have gone from 1.4Vrms to 1Vrms and added 3% THD distortion. Not a great design. Most people only need a volume control w/ buffer for today's sources to drive today's amps. Green line is the load, blue dot is the operating point. 1 Quote Link to comment Share on other sites More sharing options...
ToolShedAmps Posted November 10, 2015 Share Posted November 10, 2015 Honestly, I believe it to be a function of operating point. Rarely is it a specific tubes fault. Almost EVERY tube has a linear region on it's data sheet that allows for low distortion. Some tubes respond better to loading and type of bias than other tubes as well. It more or less becomes a function of what the "chef" is doing with the ingredients than the ingredients themselves. BTW, I know this sounds vague, but, in reality there is no better way to explain it. Short story; awhile back I had the opportunity to pick up a pair of WE 437a's for not terribly that much money. So I proceeded to design a single-gain stage with it (bread-board). I think EVERYONE would agree that this tube is exceedingly linear with as close to zero distortion based on it's curves and plot. Well, it was NON-MUSICAL. Sterile, Dry, let me be perfectly clear, I tried everything I could think of trying to get it to sound good, inductive loading, inductive-parafeed, 9v battery, LED's, you name it. BLAH. My point is, without a "little" 2nd order distortion, it may as well be a transistor..... Cheers! Matt. Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted November 10, 2015 Share Posted November 10, 2015 Let us see some of your designs, "xxJPMxx"? Let us see what you have built... I just use a tube buffer I made for a line stage. 1kHz @ 1Vrms < .01% THD into 100k load, .04% into 10k. I made a linestage with gain with similar results and no feedback too. But like I said I don't need any gain. R1 and R2 is just a 100K volume control. Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted November 10, 2015 Share Posted November 10, 2015 My point is, without a "little" 2nd order distortion I agree. But if you build that and measure distortion I am willing to bet it will be in excess of 1% which in my opinion is too much for a preamp. Honestly, I believe it to be a function of operating point. Rarely is it a specific tubes fault. Almost EVERY tube has a linear region on it's data sheet that allows for low distortion. Some tubes respond better to loading and type of bias than other tubes as well. It more or less becomes a function of what the "chef" is doing with the ingredients than the ingredients themselves. Yes that's all well and good but you are cloning a design, the 4s preamp. Right? Or are you making a common cathode gain stage of your own creation using the 12AU7? Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted November 10, 2015 Share Posted November 10, 2015 Besides we don't know any details of that circuit, I don't either It's a Transcendant Sound Grounded Grid preamp built from a kit. I can post pictures of the guts but I have no idea of how it works. Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted November 10, 2015 Share Posted November 10, 2015 It's a Transcendant Sound Grounded Grid preamp built from a kit. I can post pictures of the guts but I have no idea of how it works. I have always wanted to hear one of those. I was once interested in the design because I thought to myself "hmm......why would somebody use a grounded grid topology for audio, I mean it's usually used for RF amplification". Then I looked at the circuit and saw it was actually not a grounded grid amplfifier, go figure :/ It was something like an umbalanced LTP (differential amp), with half of it resembling an SRPP w/ local feedback. I like strange designs even if they are named wrong! You say it sounds good along with others I know that have heard it. I like those sort of designs were you use a triode as an active load, gain won't change with tube age Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted November 10, 2015 Share Posted November 10, 2015 I only have the pre-amp which I LOVE. I've yet to read where someone had one and didn't like it. I don't have one of their amps yet but if I keep my nose clean between now and Christmas I may get one of their amp kits. Quote Link to comment Share on other sites More sharing options...
richieb Posted November 10, 2015 Share Posted November 10, 2015 Seriously? This preamp will not be able to drive heavy loads or long interconnects. The 12AU7 is terribly non linear why would you want to input a 1-2Vrms signal into it and then attenuate all the gain away? All you do is add distortion :/ Sincerely disappointed. This is the pre-amp I was asked to build, and, many who have built it, like it. Like I said before, I am going to "do my thing" with it and I suspect my changes will make it better. So you will be doing "your thing" (which I am sure is a "trade secret") which will render it a different preamp. Correction; you are not building that preamp then. Your questions come off as accusatory. I don't know what the problem is but try to lighten up a bit if you would. CEC, I couldn't agree more. Had I been Toolshed I would have cut communication with JPM long ago. Nothing but opinionated and argumentative. While the design aspects are way over my head I've owned every amp configuration you can think of. (No OTL yet) Every design can be tweaked and messaged to find that sweet spot. Toolshed, build as you see fit, sales will dictate what if any corrections should follow. Or sub-contract to JPM, he seems to have all the answers and would certainly know how to communicate with customers! 1 Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted November 10, 2015 Share Posted November 10, 2015 (edited) Nothing but opinionated and argumentative. It's electricity, you can only do certain things with it. Physics hasn't changed the last time I checked. I have said nothing but nice things about his amps, I haven't heard one but even I said I am sure they sound goodt. They look like a million bucks too!! I only have the people buying the gear in mind so I ask questions that seem on topic. For instance the power out discretion when changing tubes, the screen dissipation rating when switching tubes, etc..... That was with his amps. The 4s preamp is going to be a collaborative "open source" project, I thought it was encouraged to discuss the design? I ask a lot of questions, people either can answer them or they can't answer them. A lot of times people get angry because they can't answer them. Edited November 10, 2015 by xxJPMxx Quote Link to comment Share on other sites More sharing options...
xxJPMxx Posted November 10, 2015 Share Posted November 10, 2015 Oh and some of us that build gear also buy gear from other builders, I am listening to one of Nosvalves stereo VRD's right now as I type. Quote Link to comment Share on other sites More sharing options...
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