This is my first attempt with tubes. It is a modified version of the Engel preamp with ECH83, btw which cost me 2.5Eur at a local store. Here is the schematic
(http://www.diale.org/img/ECH83pre.jpg)
There is a similar version here (http://www.diystompboxes.com/smfforum/index.php?topic=56490.msg436475#msg436475). My mods are in red.
I'm pretty happy with it, but there is always a hiss in the background. I've started with the triode part only and the hiss was initially there, and then coupled the heptode part. Is this hiss common or I'm using a broken tube? Any experience with this pre?
Thanks.
tca
looks cool... have you built it already? Any sound clips?
Quote from: J0K3RX on July 11, 2012, 03:40:58 PM
looks cool... have you built it already? Any sound clips?
Yes it is build just beside me... I'll post some sound samples tomorrow (is getting dark here now).
Here is the picture (didn't found any 9 pin socket for the tube)
(http://www.diale.org/img/ECH83pre_bb.jpg)
I made a dual version of this a couple of months ago, basically just the stock version with a fixed resistor replacing the 1M gain pot from V+ (I can't remember the value, but it was between 50k and 100k), the volume leaving the first preamp was the gain into the second. It ran from 12V so the heaters were wired in series.
There was a bit of a hiss, but nothing too distracting. I just thought it was due to the amount of gain it had. It went from nice breakup crunch to high gain thrashy sounds to full on extreme compressed fuzziness! And when I say extreme compressed fuzziness, the gain knob didn't increase the overall volume after about 11 o'clock, it was more like an auto volume limiter you find on camcorders and the like, but with more fuzzzzzz!
It's in bits at the moment, it was too much for me! I'm planning something else with it, but I won't be able to start on that little project until I've got my current projects out of the way...
Hi Wayne thanks for your reply.
Quote from: weasle76 on July 11, 2012, 04:14:17 PM
I made a dual version of this a couple of months ago...
I have an extra tube just waiting to be used!
Quote from: weasle76 on July 11, 2012, 04:14:17 PM
There was a bit of a hiss, but nothing too distracting. I just thought it was due to the amount of gain it had. It went from nice breakup crunch to high gain thrashy sounds to full on extreme compressed fuzziness! And when I say extreme compressed fuzziness, the gain knob didn't increase the overall volume after about 11 o'clock, it was more like an auto volume limiter you find on camcorders and the like, but with more fuzzzzzz!
You are right, it has a lot of gain, not nice for playing at low volumes, it sounds lovely when overdriven and is very clean. I've to check that fuzz that you mention. Powering with 12v is a good idea.
I'm going to test it with other amps to see what happens to the hiss, probably is just my crappy SS amp!
Thanks again. Cheers.
P.S. edit
Just found your entries on this pre (http://www.diystompboxes.com/smfforum/index.php?topic=96011.0).
No problem, glad I could contribute!
I've got everything ripped apart at the moment, re-building and modifying pretty much everything I've done (due to boredom and a few minor issues) including the twin tube noise monster! once I've got the stomps done, I'm planning on making a full tube pre to replace the current one in my all ss amp. That'll be fun, but I like a challenge!
The noise I was getting when not playing wasn't much worse than other dirt boxes, so I didn't think anything of it. But if you're thinking of running one into another, it'll need to be tamed a little because each stage is quite loud (something I would have discovered if I'd breadboarded first instead of just building it!)
Good luck with the rest of your build!
Oh, and I forgot to mention where I saw it first: Mullard Reference Manual of Transistor Circuits (http://archive.org/details/MullardReferenceManualOfTransistorCircuits), pg. 157
(http://www.diale.org/img/ECH83pre_mullard.jpg)
and then googled ECH83.
When I started it, I just saw the post you linked to then hit up google and found the engel site. I liked the idea of using the TMB tonestack that he shows, but never got round to trying it. Once I get started with my full pre amp, I'll be abusing the breadboard!
Just recorded some sound samples (http://www.diale.org/ech83/).
Cheers.
sounds nice to me!
Just a few more comments, while the tube support doesn't arrive by mail.
Just replaced the 100k resistors with the 47k, less gain but ok, tone remains good. Just fix the hiss (bad connection to ground)!
The most amazing thing is that the circuit works fine with 6V, the same voltage as the heater... and now we have tube preamp that runs on 6V (as stated in the datasheet)!
Cheers.
I'm happy my design catches some attention! That's really cool. If I was an American, I'd copyright it. But as far as I'm from Israel I don't care.
If you still have hiss problems I'd check two things:
1. Grid resistor of the triode (I've got 47K instead of 10M)
2. Connections, connections!
After all, although the preamp works and the most wonderful thing is the low voltage, I'm not really happy with the sound of the valve. It a bit mid-heavy, without too much bottom. Othervise I'd use it all the time.
I'm much more satisfied with the sound of american spacecharge tubes, like 12AJ6.
Any reason for 9V not 12V?
@Engel
I was trying a similar amp design (squirrel monkey) http://www.solorb.com/elect/musiccirc/squirrelmonkey1/ (http://www.solorb.com/elect/musiccirc/squirrelmonkey1/) when I thought of putting it in a pedal, but the compactron did not play well with low voltage.
So here was what I came up with, http://www.diystompboxes.com/smfforum/index.php?topic=97383.0 (http://www.diystompboxes.com/smfforum/index.php?topic=97383.0)
I like your gain method though and may have to look into a mod.
Quote from: Kesh on August 23, 2012, 08:40:24 AM
Any reason for 9V not 12V?
You can power it with 12v (it is a autoradio tube).
The datasheet says 6v for the heater, but I've tested it with 9V and it works. Probably it will reduce the life span of the tube.
very nice :D
i'm hearing a lot of bass 8)
How much current is needed for heater? Would 78L06 be sufficient, or I have to use 7806?
heater is 6V3 at 300mA, from the datasheet I saw.
OK, thanks, that means that I can not use 78L06, since it has maximum of 100mA. :icon_cry:
Original design can be found here: http://meatexz.com/engel-sound/ECH83preamp.html (http://meatexz.com/engel-sound/ECH83preamp.html)
I built the pedal using this schematic:
(http://i67.tinypic.com/i1jnu9.jpg)
But I have nothing at the output. I tried to follow signal using oscilloscope, it is present only at the pin 9, and then nothing. Voltages (DC) on pins:
1: 7.54
2: 0.01
3: 0.00
4: 0.00
5: 6.05
6: 6.05
7: 7.54
8: 8.83
9: 0.00
This is my first tube build, so please help! Really have no idea what's wrong. Tube is ECH83, and it is completely cold. Power supply is capable of 1.5A, so I presume there is enough current for heater. Maybe BC549C I used is not capable to deliver enough current?
Tube symbol in my schematic is not correct, my PCB software doesn't have it, but pins are connected by numbers as in original schematic.
Looks like I have reversed tube pins :(
New PCB finally arrived and now I can tell that this baby works fine! I tried with 9/18V switch, but found out that 9V sucks, so I put a jumper to 18V instead of switch. Also, I get approx. 16V instead of 18V for some reason. LT1044 used as a charge pump.
One thing I noticed is that it is always working as some kind of distortion, e.g. no clean sound, so I Googled a little bit and tried with potentiometers instead of 47k anode resistors. Now it is possible to get almost clean and really distorted sound, so I like this much more than original. I used stereo A100k pot to control drive simultaneously.
Someone somewhere noticed that it is better to put 1M pull down resistor instead of 47k at the input. Didn't try that (this one is not easily accessible on my PCB), so I would appreciate if anyone could comment this. Why it should be better?
Also, the sound is OK, but there is some kind of hiss. Part of it definitely comes from pedal still not being boxed, so I will report about this when I put it into the enclosure and properly shield.
(http://i64.tinypic.com/28u74zq.jpg)
8)
Looks good!
Care to share the PCB drawings?
Cheers.
Here they are:
(http://i63.tinypic.com/14jumnp.jpg)
(http://i66.tinypic.com/2607io7.jpg)
Please have in mind that DRIVE pot is stereo 100k, mid lugs are connected together and to mid hole on PCB, and CCW lugs go to PCB separated (one to CCW hole of drive pot, another to CCW1 hole on PCB). CW lugs are not connected.
And this is the final schematic:
(http://i65.tinypic.com/f03xqb.jpg)
Looked at your schematic and thought it won't work then realized you have not swapped tub parts to the correct pin. Looking up the original, pin 9 is the grid which has the 47k input resistor. The lower resistor loads down your pickups. As far as the hiss goes, that is what happens when you keep adding more elements between the grid and plate. When used in the application it was designed for, radio receiver, the hiss is not an issue.
Well, I have updated schematic and drew triode/pentode symbols, so the last one is just like original. I only modded it to allow variable grid resistance. But I don't understand what do you mean with "adding more elements between grid and plate". Actually, I can see only one capacitor between B grid and A plate?
I put this into the box and shielded, but noise is still there. Some kind of continuous high frequency hiss. I will investigate further. Maybe this LT1044 generates that?
This is what can be heard when I turn this pedal on. Sound is cricket-like and it is continuous, doesn't stop or change and when I play it is heard together with guitar. Does anybody have an idea what it could be?
Sounds like the LT1044 switching frequency bleeding through. You may have to force it to oscillate at a higher frequency beyond audibility.
I thought so, but I have already connected it to run at a higher frequency (pin 1 connected to +9V). Maybe I bought a remarked 7660? Who knows? I will try to replace it with LT1054, which I am sure is original one and can be boosted to higher frequency. Unfortunately, I didn't socket that IC, so it would be a little complicated to replace. :(
Now I replaced LTC1044 with LT1054 and the hiss is gone. Seems it was really remarked 7660A. Really nice sound!!!
Quote from: tca on July 11, 2012, 10:10:45 AM
This is my first attempt with tubes. It is a modified version of the Engel preamp with ECH83, btw which cost me 2.5Eur at a local store. Here is the schematic
(http://www.diale.org/img/ECH83pre.jpg)
There is a similar version here (http://www.diystompboxes.com/smfforum/index.php?topic=56490.msg436475#msg436475). My mods are in red.
Is there any difference in sound regarding change of pull down resistor from 47k to 10M? Why did you do that?
47K off a naked guitar is maybe a little more loading than we like. It would tend to reduce the treble brightness. It may be about-the-same on some guitars, and if you are coming from another pedal rather than direct from guitar.
10Meg is plenty high for any axe. It may be a bit high for the tube, though at this low voltage this is not a concern.
tca knows what he is doing. You could just take his values.
Or for another few cents, you could try 47K, 1Meg, 10Meg, see if there is any difference in your setup. Put the 10Meg in permanently, then tack 1Meg or 47K across it for lower values. It won't be "wow!" (unless the tube is off-bias with large resistor). It may be "bit more sizzle" or something.
OK, I'll try that. What do you think about putting double potentiometer in series with anode resistors, just like I did here (see my previous schematic)? I like the sound I get, but I'm in doubt if that will do any harm to the tube?
I am a bit confused by these drawings but the triode and pentode don't appear to have cathode resistors.
If this is the case what you have are what's known as Mu amplifiers which have unrestricted gains, which would be sure to cause all sorts of horrible noises.
The gain of each stage is approximately the anode resistance divided by the cathode resistance so with no cathode resistors the gain is flat out or as much gain as the tube is capable of - hence the name, Mu.
Typical values are about 1k to 1.5k (1.5k are what are used in Fender amplifiers)
OK, but I don't have strange noises at all after replacing LTC1044 with LT1054. This sounds from pretty clean to overdriven, and that's all. I was also a little bit puzzled with absence of cathode resistor, but I tried it and it works.
In Philips data handbook it is also shown without cathode resistor, see here:
http://www.radiomuseum.org/forumdata/users/1511/Ph-DataECH83.JPG (http://www.radiomuseum.org/forumdata/users/1511/Ph-DataECH83.JPG)
Ok, that's fair enough. I am not familiar with this type of bottle so I don't know what it's mu is.
I used to have an old MusicMan hybrid amplifier and they put one 12ax7 in it for the distortion sound. Half of it was wired up as a mu amp and it sounded like crap. They ended up changing that part of the circuit in a new revision.
If you added a cathode resistor, you would get a cathode-coupled multivibrator that would oscillate. I don't know what value of cathode resistor would do it but I would avoid any cathode resistor. The standard use for this tube is an oscillator-mixer in a radio where the triode oscillator generates its own negative grid bias and the pentagrid side is biased by the negative automatic volume control bias derived from the detector stage. But at 9 volts on the plate, you don't have to worry about excessive dissipation.
I am running it at 18V and it is fine. I will try 24V in next build. What about plate/anode resistors and potentiometers, would they cause any trouble in time? :icon_question: Everything works fine for now.
This is most recent schematic, I hope it is clear:
(http://i64.tinypic.com/nvy47.jpg)
Drive potentiometer is stereo B100k, but I don't have symbol for that, so I drew two standard pots.
Do I need C4 and C6? I just drew them, but I didn't put them on board.
R10 is there for test purposes - to see what happens when input impedance is lower.
Also, I found that gain pot is better if it is 500k. Pretty unusable from 500k to 1M.
I have settled down with 3M3 pull down resistor, and it makes huge difference to 47k! Really much more treble!
really cool timing, i just bought an ECH83 as in like 3 days ago and this post has been of huge help. i'm definitely going to make it and use it as an external preamp for my 12v valve amp :D
~Aran
This one works fine right now, but I have only one problem - if I connect it to power supply with other pedals (daisy chain, I know, I know... :-[) it produces some kind of hum sound. Connected to separate PS, works really fine. This is my final schematics, showing charge pump with 555. And I have added a trim pot so I can adjust the point where gain doesn't produce "choke" effect which I don't like.
(http://i67.tinypic.com/2wbwa54.jpg)
I also experience a slight vibrato with this pedal. Does anyone have an idea why?
Quote from: rankot on May 10, 2017, 07:31:27 AM
This one works fine right now, but I have only one problem - if I connect it to power supply with other pedals (daisy chain, I know, I know... :-[) it produces some kind of hum sound. Connected to separate PS, works really fine.
You have a ground loop somewhere, that is what produces the hum sound when you use the same supply but not a different one.
João
It was actually a bad cable from bass to preamp - had a break somewhere in shielding :) Pre works fine right now, I am still experimenting with power supplies.
Hi all,
Here's my go at tweaking the original schematic. I turned the original gain pot that sets the voltage on all those grids tied together into a trimmer (to be set at the point just before the volume breaks down when you turn down the resistance), and added a pot between the first and second stage to become the new gain pot. I found it was a bit easier to dial in the required amount of overdrive that way. I also changed the values of the first capacitor and resistor but I didn't find it made much difference. All in all it makes a nice overdrive pedal this way.
(https://s22.postimg.cc/gohs3h65p/ECH83svm.gif) (https://postimg.cc/image/gohs3h65p/)
If you modulate the voltage on the upper grids on the hexode section, you can make this into a tremolo.
I"m back to this one, because although it sounds nice, the GAIN pot is scratchy, so I wanted to change this completely and have a tone stack instead of gain.
However, during LTspice experimenting with the schematics, I've encountered a strange thing: when G1 is used as control grid, G3 connected to cathode, G2+G4 connected to B+ (actually used as a screen), everything looks normal if B+ is 18V, but if I change it to 27V, suddenly anode voltage goes negative, to -24V???
(https://s26.postimg.cc/dv09fyfm1/ECH83anodevoltage.jpg)
Is it a bad tube model, or the same will happen with the real tube. More important, if the same happens to real tube, will it be damaged?
Quote from: rankot on August 17, 2018, 03:31:20 AM
Is it bad tube model, or the same will happen with the real tube.
Tube models are unrealible at low voltages, so probably this.
Quote
More important, if the same happens to real tube, will it be damaged?
Lol, a tube would laugh in the face of your puny -24V! :icon_lol: But seriously, you won't get -24V in real life, the sim is lying.
Well, I supposed it was some kind of sim error. Actually, I will try it with a pedal and see what happens. :icon_biggrin:
OK, after half a day of experimenting, this is MY FINAL schematic for this baby (and I mean FINAL) ;D
http://docdro.id/Oj4Jc3D (http://docdro.id/Oj4Jc3D)
I used Ra of 100k for triode and 82k for hexode; also kept gain pot from kozmix's schematic. 1N4148 diode used for cathode biasing, and added a DRIVE switch, so G3 can be connected to B+ or to ground (later is lower gain). G2+G4 are connected directly to B+, no screen resistor there, because every value bigger than 5k reduced final amplification.
> However, during LTspice experimenting with the schematics
There is no negative supply. HOW can it go wildly negative??
However I note your 2nd stage has no return for cathode current. A real tube would cut-off. A SPICE tube may have internal "current sources" which, unlike the things we call "CCS:, are actual SOURCES and will force node voltage to whatever to keep their assigned current flowing.
So just like all this "Don't work!" pleas: check your wiring!
Quote from: PRR on August 17, 2018, 08:32:45 PM
There is no negative supply. HOW can it go wildly negative??
That's exactly what I though when saw the result, but it's better to ask someone with more knowledge.
Quote from: PRR on August 17, 2018, 08:32:45 PM
However I note your 2nd stage has no return for cathode current.
ECH83 has a common cathode connection (labelled as "C" net on my schematic), so actually both triode and heptode share the same cathode connection to ground through 1N4148. It is not troubling LTspice, since results are as expected most of the time, but sometimes they just go crazy
Anyway, I rebuilt it using the last schematic posted (http://docdro.id/Oj4Jc3D (http://docdro.id/Oj4Jc3D)) and it works really nice, most of the time as a warm, clean boost.
Hey, is this preamp still sounding nice? ;) :) I have a few ECH83. Built the distortion schematic we can find on the web, but wasn't that impressed with it.
I am looking for a nice, clean and warm tube sound. Would like to add a tone stack as well.. :)
João
I'm afraid that tone stack will loose too much of a volume.
So, is that the only problem? the tone stack? perhaps a buffer before??
I have a few of these tubes, as well as some 6N2P, and would like to build a nice starved plate, clean preamp. For overdrive, I have all my other pedals. :)
João
If you don't need it to overdrive, the tonestack will not make any harm.
True. I need it to boost the signal a bit, and color it nicely, that's it :)
João
I've been writing to Mr. Derk Reefman, who is one of the guys behind utracer (http://www.dos4ever.com/uTracer3/uTracer3_pag14.html (http://www.dos4ever.com/uTracer3/uTracer3_pag14.html)). I was initially asking him about various params for remote cutoff pentode and heptode modelling, and during that discussion, I've sent him a schematic for this preamp. He noted that G3 shall be connected to ground, or to cathode potential (to conserve tube and extend it's life), and not to anode or even worse B+. My question is why? I don't have a book covering heptode, so I must admit my knowledge on this topic is really poor.
(https://i.postimg.cc/3wj3DKy4/ech83-g3.jpg)
> G3 shall be connected to ground, or to cathode
At LOW voltage, <12V, I would not worry about it.
And specifically the ECH83... the datasheet (http://www.mif.pg.gda.pl/homepages/frank/sheets/030/e/ECH83.pdf) says "as RF or IF amplifier" Vg2+g3+g4 can be run at full supply voltage. See also graphs G H I.