Hi, I built this schematic for guitar preamp
EF86 for any amplifier
I use it as a preamp to high Z input of an audio card.
The point is that it sounds pretty dull. No chime at all.. Muddy, bassy sound, no sparkle.
Tried with few ef86, old ones from different manufacturers. Mostly grey plated, one of them with silver grid around but no big difference.
I process the sound in amp simulator afterwards and I need to add a trebble booster in the chain to get smth at least close to the sound I like.
Would I benefit to add a cathode follower at the output of the circuit (mosfet)?
Now the sound goes through 680k res after C1 and then 20k log pot to ground, thats it.
Here it is the pehthode chanel bright tone with ef86:
Vox AC15 Heritage Handwired - YouTube
Some ppl didnt even believe it is true when I played them the video, they suspect there is a hidden trebble booster somewhere inside
EF86 for any amplifier
I use it as a preamp to high Z input of an audio card.
The point is that it sounds pretty dull. No chime at all.. Muddy, bassy sound, no sparkle.
Tried with few ef86, old ones from different manufacturers. Mostly grey plated, one of them with silver grid around but no big difference.
I process the sound in amp simulator afterwards and I need to add a trebble booster in the chain to get smth at least close to the sound I like.
Would I benefit to add a cathode follower at the output of the circuit (mosfet)?
Now the sound goes through 680k res after C1 and then 20k log pot to ground, thats it.
Here it is the pehthode chanel bright tone with ef86:
Vox AC15 Heritage Handwired - YouTube
Some ppl didnt even believe it is true when I played them the video, they suspect there is a hidden trebble booster somewhere inside
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This belongs in Instruments and Amps so I'm moving it to the right forum.Thx for moving
The sound card is for guitar, not ordinary line in or dynamic microphone.
Wonder if to start messing with the capacitors as well, the sound is really Nothing like what I hear in the demo.
If clean - it is dull. If start some distortion - it is really bassy and muddy, no clarity at all
The sound card is for guitar, not ordinary line in or dynamic microphone.
Wonder if to start messing with the capacitors as well, the sound is really Nothing like what I hear in the demo.
If clean - it is dull. If start some distortion - it is really bassy and muddy, no clarity at all
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I suspect there are a number of things going on here, the best place to start might be by letting us know the sound card input impedance (resistance and capacitance) as well as that of the cable.
Did you use the recommended or similar caps, it is important in the MI world for tone..
It does sound rather like it is struggling to drive a fairly capacitive input so a CF may well help.
Did you use the recommended or similar caps, it is important in the MI world for tone..
It does sound rather like it is struggling to drive a fairly capacitive input so a CF may well help.
Thx. Sounds not that extraordinary
I will try to find details for the soundcard. Now just experimenting with this: USB Guitar Link Cable Turns PC Into Amp | GeekAlerts
Didnt think it might be that bad, to cut off all the high frequencies.
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http://www.dougcircuits.com/images/genericEF86.png
680k and 20k log pot in series, log pot to ground, wiper -> out. Primitive
Cable is a common microphone cable, nothig special or highend.
I will try to find details for the soundcard. Now just experimenting with this: USB Guitar Link Cable Turns PC Into Amp | GeekAlerts
Didnt think it might be that bad, to cut off all the high frequencies
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http://www.dougcircuits.com/images/genericEF86.png
680k and 20k log pot in series, log pot to ground, wiper -> out. Primitive
Cable is a common microphone cable, nothig special or highend.
Thx, just was reading about it here:
Modifying Guitar Amp Preamp Circuitry
First thing to check!
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Still I dont quite understand how C3 behaves in the original schematic:
http://www.dougcircuits.com/images/genericEF86.png
Better don't touch?
To my common sense and lack deep knowledge, seems that all highs go to ground through a 100/220n cap (screen cap).
But this value seems to be into the original vox schematics.
I read that in some preamps it is omitted, connecting screen grid to cathode as the suppressor grid, but haven't seen any such schematic for guitar.
Modifying Guitar Amp Preamp Circuitry
First thing to check!
---
Still I dont quite understand how C3 behaves in the original schematic:
http://www.dougcircuits.com/images/genericEF86.png
Better don't touch?
To my common sense and lack deep knowledge, seems that all highs go to ground through a 100/220n cap (screen cap).
But this value seems to be into the original vox schematics.
I read that in some preamps it is omitted, connecting screen grid to cathode as the suppressor grid, but haven't seen any such schematic for guitar.
You need the 0.1u screen bypass capacitor, otherwise your gain will be low, so leave that alone, now some suggestions:
1) Get rid of the pentode/triode switch and run in pentode mode only if you want the Vox chime.
2) Change the 680k to 200k, and connect it to the 20k pot, or better yet, replace both with a proper 250k log pot. Too much series resistance is killing the highs, you can add a bright cap across the 680k as suggested by djgibson51, if you do not have any other lower value resistors to replace it.
Jaz
1) Get rid of the pentode/triode switch and run in pentode mode only if you want the Vox chime.
2) Change the 680k to 200k, and connect it to the 20k pot, or better yet, replace both with a proper 250k log pot. Too much series resistance is killing the highs, you can add a bright cap across the 680k as suggested by djgibson51, if you do not have any other lower value resistors to replace it.
Jaz
Thx all!
I have set 680k to prevent high voltage on the output.
Not sure if 250k will give usable output voltage range out, have some such pots at disposal.
The sound card would clip badly, mby even get its input burned.
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Another pros for cathode follower solution?
(eliminating high resistance before output, handling the full voltage amplitude, plus low output impedance)
Still I will try it the simple way first, with a bypass cap on the output resitor.
p.s. the sound card has 250/400k (lo/hi) input impedance, no idea about the capacitance.
Tried both with 0.5m and 3m cables for the guitar, I dont hear such a big difference.
I have set 680k to prevent high voltage on the output.
Not sure if 250k will give usable output voltage range out, have some such pots at disposal.
The sound card would clip badly, mby even get its input burned.
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Another pros for cathode follower solution?
(eliminating high resistance before output, handling the full voltage amplitude, plus low output impedance)
Still I will try it the simple way first, with a bypass cap on the output resitor.
p.s. the sound card has 250/400k (lo/hi) input impedance, no idea about the capacitance.
Tried both with 0.5m and 3m cables for the guitar, I dont hear such a big difference.
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There is no high voltage after the output coupling capacitor, it blocks all the DC from reaching the soundcard. If you are only playing guitar through this preamp, I doubt you can generate enough swing to damage the soundcard's input. But to be safe, you should always have Zener clippers to protect over-voltage to the card.
In this case, I don't think a CF will make a drastic difference, so probably not worth the trouble of adding another tube, but it is up to you.
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