I know, today a simple 5532 opamp with +/-15v rails, @ 20db gain and 25°C will have ~.0005%THD putting out 9Vrms into a 10k load @ 1kHz.
Next time I get my hands on a JJECC81 I will look inside, thanks for the insight.
I have seen EL34's from China that have Beam plates instead of a suppressor grid
Yes this gets me to laugh, he holds others to different standards then himself apparently.
I suggested the same exact thing over there. Use a switch to change out plate and cathode resistors so you can power down, change a tube and flip a switch. This will much fairer assessment of each triode without much more work and complexity.
At first I kind of was hoping the design was a joke because I mean you really can't call it hifi at all. You have to put forth an effort to purposely design something so incompetent because there are datasheets floating around for the past 60 years with all the suggested design parameters, at the very least one could just copy straight off a datasheet and get good results.
In their eyes we don't get it, but as DF96 states, we actually do all too well. They removed my comment about it being an effect box and said "it doesn't contribute to the thread". Again I have no problem with people building an effect box, I do it all the time but at least call it what it is, a duck is a duck, quack.
> one important parameter they chose not to show is where will plate voltage rest with such different tubes plugged in.
Easily deduced from 100K, 1.2K, B+, and stated values of "Eco".
12AT7 - 'Eco'=1.7V, Ik= 1.417mA, in 100K is 142V drop, B+=250V, "plate rests" at 108.3V above common, 106.6V plate-cathode.
Range of 'Eco' 2.2 to 1.16, drop in 100K ranges 183 to 97, plate rest 67V to 153V.
IMHO, everything is a divider, a ratio. 27% to 61%. Not sure what that means for DIYers who need a guide for a single triode stage.
Easily deduced from 100K, 1.2K, B+, and stated values of "Eco".
12AT7 - 'Eco'=1.7V, Ik= 1.417mA, in 100K is 142V drop, B+=250V, "plate rests" at 108.3V above common, 106.6V plate-cathode.
Range of 'Eco' 2.2 to 1.16, drop in 100K ranges 183 to 97, plate rest 67V to 153V.
IMHO, everything is a divider, a ratio. 27% to 61%. Not sure what that means for DIYers who need a guide for a single triode stage.
That´s the point 🙂
*We* (and many others) can do that easy Math, many won´t and probably trust the design to be something serious or Pro, which it is not.
Maybe they see that Vk varies between 1.16V and 2.2V and vaguely wonder (if they notice or care about that) "hey, around 1 Volt variation, no big deal" ...while the reason for concern is that idle plate voltage rests (with +V=250V) between almost perfect 153V with a 12AX7 there , which allows for some 60V RMS at reasonably symmetrical clipping to terrible 67V which will start to clip very unsymmetrically at some 15V RMS, simply because idle current is too high and load resistance also too high for a 12AU7.
In fact, it´s not an "all purpose tyre" at all; but a 12AX7 optimized preamp (chosen values point to that) "where you "plug other tubes and still works ..... sort of".
Somebody my argue that I´m blowing this out of proportion by considering >10V RMS audio voltages, measurements were made at output levels around 1V RMS, results were no Hi Fi by any means but somewhat acceptable for casual listening.
Thing again: this "thing" is shown amplifying the output of an I Pod which on its own is not enough to fully drive the amp shown.
I checked and it needs 1.1V RMS to reach its full power of 3.2W RMS.
Ok, how much does an I Pod put out?
From an earlier post here in DIYA , they were measured at 0.33V RMS, so proper preamp would be a 4X one.
Now these "universal tires" supply from 10X (unbypassed cathode 12AU7) to 54X in a full gain, bypassed cathode 12AX7 .
As noticed above: "way too much gain for the intended task"
Which also means that audio voltage can reach as much as 18V RMS.
Now that I´m rereading the original page (every time I find something new), it states:
Which brings us to: signal output is way too high, so you are *forced* to set that volume pot very low , full volume (amp driven into clipping) will reaches between 1 and 2 in a scale of 10 for many of these tubes ... talk about a hair trigger.
That, forgetting that an external unit will be driven from a 250k source pot. (it was also mentioned above).
In a nutshell, a nice project for those itching to build "something", also easy "proof" that tubes sound different from SS (such distortion levels will be audible even in a double blind test) so as an effects box it´s fine ... just don´t call it Hi Fi .
Will it at least amplify an I Pod enough to drive a power amp?
Yes, it can also do that, if you like the flavour it imparts to Audio going through.
Hey!!!! bit it has a volume control
*We* (and many others) can do that easy Math, many won´t and probably trust the design to be something serious or Pro, which it is not.
Maybe they see that Vk varies between 1.16V and 2.2V and vaguely wonder (if they notice or care about that) "hey, around 1 Volt variation, no big deal" ...while the reason for concern is that idle plate voltage rests (with +V=250V) between almost perfect 153V with a 12AX7 there , which allows for some 60V RMS at reasonably symmetrical clipping to terrible 67V which will start to clip very unsymmetrically at some 15V RMS, simply because idle current is too high and load resistance also too high for a 12AU7.
In fact, it´s not an "all purpose tyre" at all; but a 12AX7 optimized preamp (chosen values point to that) "where you "plug other tubes and still works ..... sort of".
Somebody my argue that I´m blowing this out of proportion by considering >10V RMS audio voltages, measurements were made at output levels around 1V RMS, results were no Hi Fi by any means but somewhat acceptable for casual listening.
Thing again: this "thing" is shown amplifying the output of an I Pod which on its own is not enough to fully drive the amp shown.
I checked and it needs 1.1V RMS to reach its full power of 3.2W RMS.
Ok, how much does an I Pod put out?
From an earlier post here in DIYA , they were measured at 0.33V RMS, so proper preamp would be a 4X one.
Now these "universal tires" supply from 10X (unbypassed cathode 12AU7) to 54X in a full gain, bypassed cathode 12AX7 .
As noticed above: "way too much gain for the intended task"
Which also means that audio voltage can reach as much as 18V RMS.
Now that I´m rereading the original page (every time I find something new), it states:
Sorry but 1Vpp (typical Ipod output) is neither 1 V peak nor 2V peak to peak.
Which brings us to: signal output is way too high, so you are *forced* to set that volume pot very low , full volume (amp driven into clipping) will reaches between 1 and 2 in a scale of 10 for many of these tubes ... talk about a hair trigger.
That, forgetting that an external unit will be driven from a 250k source pot. (it was also mentioned above).
In a nutshell, a nice project for those itching to build "something", also easy "proof" that tubes sound different from SS (such distortion levels will be audible even in a double blind test) so as an effects box it´s fine ... just don´t call it Hi Fi .
Will it at least amplify an I Pod enough to drive a power amp?
Yes, it can also do that, if you like the flavour it imparts to Audio going through.
Hey!!!! bit it has a volume control
That's the thing, that's one thing that tipped me off to what this device is intended for. As you cleverly pointed out adding this preamp into a system should effect the sound enough to be audible in a DBT. If you are driving an amp with mega bandwidth into some horns or something, the high output impedance of this preamp driving some interconnect capacitance will roll the harsh highs off. Also the volume control at the output makes sure that there is plenty of distortion to "color" things. How much color? As noted if you plug in say a McIntosh CD player that has a fixed output of 2Vrms well you will have much more distortion than say hooking an Ipod up to it that can only put out something like 1Vpeak. Distortion varies with source output signal amplitude which as we know isn't standardized.
Sooooo yes maybe this device was devilishly devised to be well recognized when being placed into any system, especially very transparent systems. An effect box indeed, especially when plugging anything besides a 12AX7 in there.
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> 12AX7 ...some 60V RMS at reasonably symmetrical clipping
I get 41Vrms. I figure plate will bottom above 93V, leaving 60V peak neg swing.
> to terrible 67V ...12AU7.
12AU7 will pull-down nearer 30V. Say 37V peak, 26Vrms.
Any of these would be way ample if the pot was in the front.
I get 41Vrms. I figure plate will bottom above 93V, leaving 60V peak neg swing.
> to terrible 67V ...12AU7.
12AU7 will pull-down nearer 30V. Say 37V peak, 26Vrms.
Any of these would be way ample if the pot was in the front.
"Forget 0.001% THD. You'll likely never get there and any signal generator advertising such a value is blowing smoke. That's -100dBv. For those measurements your talking conditioned lab power, Faraday cages, and high end equipment. It's the same reason that the advertised THD of most SS amplifiers is total hooey. They are theoritical numbers or very controlled lab tests under very clean conditions, not real world operation."
I wonder where he has been for the last 35+ years. Even the IG-18 could be modified to achieve almost that level in 1971!
I wonder where he has been for the last 35+ years. Even the IG-18 could be modified to achieve almost that level in 1971!
Where has he been for the last 35 years? To answer your question from his response in another forum;
Lulz
What would be proper plate and cathode resistor values in this circuit for example for 12AU7 or 12AX7?
For 250v I like Rp=27k and Rk=1k
You should be around Va=135 and Vg-k=-4
The initial plate load value of 100k brings the plate down to ~65v😱
The 12AU7 performs better with more current through it. I find I liked the performance and sound with these sort of values. I am sure others have other examples.
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