I find it hard to believe that no-one has posted this question to this forum before, so here goes...
I'm a jazz and blues guitarist. I play 'clean' but actually I like the kinds of sounds you get from a Gibson-style humbucking pickup on a hollow-body/archtop electric guitar into a classic tube amp like Fender Vibrolux or Deluxe combo amps.
I have one of those amps, but I don't gig anymore, and it's just too heavy.
Now that there are all these great cheap power amps available, I thought it might be nice to wire up a guitar preamp that emulates the sound of a late 1960s Fender 'black-face' combo amp. Of course the sound of the amp is hugely influenced by the output stage including output transformer, choice of speaker, what cabinet the speaker is in, and so on.
I do find that you can make a low pass filter that simulates the high frequency roll-off of a classic guitar speaker like Jensen C12N or similar.
What I don't know is how to emulate the nice compression effect one gets from a Fender Deluxe Reverb played at a moderate volume level. Not 'distorted' in the rock sense, no fuzz to its tone, but 'enriched', 'warmed up'.
Do you think it would be possible to put a cathode follower at the output of a Fender 'clean channel' with 12AX7 and tone stack, and bias an output stage CF up so that it compresses easily? Or maybe use a pentode after the tone stack and set it up so that it has little headroom, so compresses the 'clean' signal?
Has anyone tried these things?
Just curious if someone has built something like this that has worked out for them.
Thanks.
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I'm a jazz and blues guitarist. I play 'clean' but actually I like the kinds of sounds you get from a Gibson-style humbucking pickup on a hollow-body/archtop electric guitar into a classic tube amp like Fender Vibrolux or Deluxe combo amps.
I have one of those amps, but I don't gig anymore, and it's just too heavy.
Now that there are all these great cheap power amps available, I thought it might be nice to wire up a guitar preamp that emulates the sound of a late 1960s Fender 'black-face' combo amp. Of course the sound of the amp is hugely influenced by the output stage including output transformer, choice of speaker, what cabinet the speaker is in, and so on.
I do find that you can make a low pass filter that simulates the high frequency roll-off of a classic guitar speaker like Jensen C12N or similar.
What I don't know is how to emulate the nice compression effect one gets from a Fender Deluxe Reverb played at a moderate volume level. Not 'distorted' in the rock sense, no fuzz to its tone, but 'enriched', 'warmed up'.
Do you think it would be possible to put a cathode follower at the output of a Fender 'clean channel' with 12AX7 and tone stack, and bias an output stage CF up so that it compresses easily? Or maybe use a pentode after the tone stack and set it up so that it has little headroom, so compresses the 'clean' signal?
Has anyone tried these things?
Just curious if someone has built something like this that has worked out for them.
Thanks.
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To get the compression effect you need to drive a pentode, hard.
A mini-micro power stage, even if 0.1W output or less.
Follow it by a "speaker emulator", thyereare many good circuits around, and with that signal you drive anything, including a Class D ampand a Guitar speaker, at any level you want, since sound is already "tube flavoured" the good way.
A mini-micro power stage, even if 0.1W output or less.
Follow it by a "speaker emulator", thyereare many good circuits around, and with that signal you drive anything, including a Class D ampand a Guitar speaker, at any level you want, since sound is already "tube flavoured" the good way.
I did a 5E3 Deluxe with a pair of 6AK6's for output tubes using a 70V line transformer (although I would suggest the Hammond 125A). You could build up a whole BF Reverb in a small package. 13" wide, no long tank, sorry. The board is for a Marshal inspired build though.
Needs an extra hole, could take the place of the speaker jack hole. I was going to go SS for the reverb and recovery. Since you do not plan to rock out too much a regular BF four triodes should do. Reverb return in the other side of the phase inverter should do,
Needs an extra hole, could take the place of the speaker jack hole. I was going to go SS for the reverb and recovery. Since you do not plan to rock out too much a regular BF four triodes should do. Reverb return in the other side of the phase inverter should do,
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I have a vintage Jensen C12N I'd like to use. I'd put that in an open back cabinet.
I'd drive that with some kind of power amp. I have an old Hafler 50wpc amp I can use. It's bridgeable, so that offers plenty of power, and it's a small-ish unit.
My question is, if I already have an authentic vintage guitar cab, what would the 'speaker emulator' do for me? In my head, I see it superimposing a 'classic cab' frequency response on top of another speaker cabinet. Too much of a good thing?
The micro-power output stage is a nice idea. Maybe a single-ended 12C5 into a 3k:600 output transformer(?).
I don't use reverb, and I have a power amp, so I'm thinking this would be a preamp with tone controls only. I'm not even sure I need more than a single Fender-style 'Tone' control. When I played my Fender Deluxe Reverb, I'd leave the Treble control at about 1 and the Bass control at about 2. It turns out that's electronically 'flat' response from the tone stack. It seems I don't like to boost highs or lows.
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You could try a single tube preamp. Run that into a SS amp and see if you like it. If it is not 'enough' for you then you can add on around it. Some warm up the signal with a boost in front of the first stage. You could add in behind but I am guessing you may not need it. I would not bother with a current hog like the 12C5. I would just use a 12V switching wallwart adapter and make or buy a high voltage switching circuit.
Mind you if you forgo the switching amplifier and do not mind the weight of an output transformer you could have a real tube output stage putting out about 15-20W using a laptop power supply and a HV switched supply.
Mind you if you forgo the switching amplifier and do not mind the weight of an output transformer you could have a real tube output stage putting out about 15-20W using a laptop power supply and a HV switched supply.
Hmmm...
I simulated a three tube circuit using a 12AT7 into a Fender tone stack, into a 6AU6A pentode, into a 12AT7 cathode follower.
I used a simple one-capacitor low pass filter to roll off above 5kHz, because there's nothing up there I'd want to hear from a guitar except noise and excess sizzle.
Part of this project is to use parts I have on hand. I have a pulled Fender Deluxe Reverb OPT in the closet. I'm not sure I want to use that for this. I'm really thinking of a pre-amp to plug into any old thing, including a headphone amp, class D power amp, etc.
I think I don't need a speaker emulation circuit. As I mentioned before, I have a couple of nice old 12" guitar speakers, including a Jensen C12N from the 1960s that I'd like to use in a 1-12" open back cab (that's the sound I like).
I have a couple of small class D amps I can throw at this. I don't even need any gain. It's really just the tube tone and the tone stack I'm after.
I really liked the old Gibson GA-50 guitar amp, which used a 6SJ7 pentode input tube into a 6SN7 paraphase phase splitter into a pair of 6L6 pentodes. It ran the 6L6s quite hot, and only made about 20 watts. That got me interested in the sound of a pentode as a voltage amplifier stage.
In simulation, it looks like using a large value 100k plate resistor on a 6AU6A gives you more gain and higher levels of 3rd order harmonic. Reduce the value of the plate resistor to 33k and you get less gain with the 2nd order harmonic completely dominating.
Also in simulation, removing the cathode bypass capacitor (Ck) from the 6AU6A reduces the gain (of course) but changes the character of the harmonic distortion to very much like a triode, practically all 2nd order. There's a lot of design flexibility there.
Edit to add: I wonder, how much THD begins to sound 'dirty' on an electric guitar? In the simulated circuit, it looks like the input stage 12AT7 produces 0.8% or more THD with 100mV peak input. I think the rule of thumb is that you can hear 0.1% THD if it's all 2nd harmonic, but just barely. Is 1% 2HD a lot for a guitar? Or would that still qualify as a 'clean' sound?
Here's what I was working on...
I simulated a three tube circuit using a 12AT7 into a Fender tone stack, into a 6AU6A pentode, into a 12AT7 cathode follower.
I used a simple one-capacitor low pass filter to roll off above 5kHz, because there's nothing up there I'd want to hear from a guitar except noise and excess sizzle.
Part of this project is to use parts I have on hand. I have a pulled Fender Deluxe Reverb OPT in the closet. I'm not sure I want to use that for this. I'm really thinking of a pre-amp to plug into any old thing, including a headphone amp, class D power amp, etc.
I think I don't need a speaker emulation circuit. As I mentioned before, I have a couple of nice old 12" guitar speakers, including a Jensen C12N from the 1960s that I'd like to use in a 1-12" open back cab (that's the sound I like).
I have a couple of small class D amps I can throw at this. I don't even need any gain. It's really just the tube tone and the tone stack I'm after.
I really liked the old Gibson GA-50 guitar amp, which used a 6SJ7 pentode input tube into a 6SN7 paraphase phase splitter into a pair of 6L6 pentodes. It ran the 6L6s quite hot, and only made about 20 watts. That got me interested in the sound of a pentode as a voltage amplifier stage.
In simulation, it looks like using a large value 100k plate resistor on a 6AU6A gives you more gain and higher levels of 3rd order harmonic. Reduce the value of the plate resistor to 33k and you get less gain with the 2nd order harmonic completely dominating.
Also in simulation, removing the cathode bypass capacitor (Ck) from the 6AU6A reduces the gain (of course) but changes the character of the harmonic distortion to very much like a triode, practically all 2nd order. There's a lot of design flexibility there.
Edit to add: I wonder, how much THD begins to sound 'dirty' on an electric guitar? In the simulated circuit, it looks like the input stage 12AT7 produces 0.8% or more THD with 100mV peak input. I think the rule of thumb is that you can hear 0.1% THD if it's all 2nd harmonic, but just barely. Is 1% 2HD a lot for a guitar? Or would that still qualify as a 'clean' sound?
Here's what I was working on...
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So something like 4% THD (but not clipping) would still sound like a 'clean' guitar sound?
In that case, I might be on the right track for a 'warmed up' or 'fattened up' clean sound.
I'm a guitarist, played professionally for about 15 years. I've played through a kazillion different 'clean' guitar amps from Roland Jazz Chorus to Polytone Mini-Brute to Fender Vibrolux Reverb to Fender Twin Reverb to Roland Cube to Gibson GA-50 to others I can't remember. There is something nice about a bit of dynamics compression and some added 'fatness' to the sound. It feels good to play through an amp that gives you that.
What is it about a well-working, vintage Fender Vibrolux Reverb or Fender Deluxe Reverb that works so well for jazz guitar playing? There's a kind of 'saturation' to the sound, a certain enhancement. It's a little muddy, especially in the bass notes, but it's not over the top. It's also not 'glassy' and 'hard' sounding like a Mesa Boogie or Soldano or other high-gain rock-oriented tube amp.
That circuit I simulated in the previous post delivers way too many volts out, but its cleanest sound has about 3% THD. Would that be the added 'saturation' I desire? I don't know. I guess I'm going to have to build one and see.
I also found that I could use pentode-triode like 6U8A, 6GH8A, 6BL8, etc. Use the pentode as the first stage, the triode as a cathode follower. A Fender tone stack introduces a lot of insertion loss, so the gain winds up being only 10dB. I guess it could use a single-knob tone control for least insertion loss. THD is 1.8% as shown.
In that case, I might be on the right track for a 'warmed up' or 'fattened up' clean sound.
I'm a guitarist, played professionally for about 15 years. I've played through a kazillion different 'clean' guitar amps from Roland Jazz Chorus to Polytone Mini-Brute to Fender Vibrolux Reverb to Fender Twin Reverb to Roland Cube to Gibson GA-50 to others I can't remember. There is something nice about a bit of dynamics compression and some added 'fatness' to the sound. It feels good to play through an amp that gives you that.
What is it about a well-working, vintage Fender Vibrolux Reverb or Fender Deluxe Reverb that works so well for jazz guitar playing? There's a kind of 'saturation' to the sound, a certain enhancement. It's a little muddy, especially in the bass notes, but it's not over the top. It's also not 'glassy' and 'hard' sounding like a Mesa Boogie or Soldano or other high-gain rock-oriented tube amp.
That circuit I simulated in the previous post delivers way too many volts out, but its cleanest sound has about 3% THD. Would that be the added 'saturation' I desire? I don't know. I guess I'm going to have to build one and see.
I also found that I could use pentode-triode like 6U8A, 6GH8A, 6BL8, etc. Use the pentode as the first stage, the triode as a cathode follower. A Fender tone stack introduces a lot of insertion loss, so the gain winds up being only 10dB. I guess it could use a single-knob tone control for least insertion loss. THD is 1.8% as shown.
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Not sure if I would use a 6AU6, a 6AK5 is suppose to sound better. One thing I did do with a 6AU6 I have about 50 of them) is had pots for the cathode, plat and screen resistors and fiddled about with them and found the best sound by ear. I ran a triode in front of it as well as behind. I do not recall getting too excited about it although that was many years ago and I had a lot of ideas to try.
I used a Paraphase inverter in one amp and unbalanced the signal going to the output tubes. Even clean it fattened up the sound. I have an idea I will get to one of these days of driving a tube inverter and then running the two signals into an opamp then a SS amp.
I used a Paraphase inverter in one amp and unbalanced the signal going to the output tubes. Even clean it fattened up the sound. I have an idea I will get to one of these days of driving a tube inverter and then running the two signals into an opamp then a SS amp.
I believe the reason a paraphase inverter fattens up the sound is that they almost always suffer from imbalance, which increases 2nd harmonic distortion and other even order harmonics as well. I wonder...
You know those OddWatt amp designs, with the self-splitting output stage using EL84s? It's basically an LTP with its plates fed straight to the PP OPT primary. That could be an interesting way to get the sound of a push-pull amp at line level. Choose the transformer for the desired stepdown ratio. Adjust the imbalance of the LTP to get the desired harmonic structure. Perhaps push-pull 6N6P?
In the circuit I was working on, in simulation I found that the 6AU6 with a smaller value of plate load resistor produces predominantly 2nd order harmonic distortion, and lots of it too.
I substituted a 6AK5 model into the proposed circuit and it looks very similar to the 6AU6 electrically. Even the predicted THD was similar. I guess they're similar but sound different.
I have a sleeve of 6AC7. That might be fun to try in real life. It shows just a bit more gain than the others in simulation, because it has higher gm.
I also have a few 6SJ7 around. That sims almost exactly the same as 6AU6, so that would be usable too.
You know those OddWatt amp designs, with the self-splitting output stage using EL84s? It's basically an LTP with its plates fed straight to the PP OPT primary. That could be an interesting way to get the sound of a push-pull amp at line level. Choose the transformer for the desired stepdown ratio. Adjust the imbalance of the LTP to get the desired harmonic structure. Perhaps push-pull 6N6P?
In the circuit I was working on, in simulation I found that the 6AU6 with a smaller value of plate load resistor produces predominantly 2nd order harmonic distortion, and lots of it too.
I substituted a 6AK5 model into the proposed circuit and it looks very similar to the 6AU6 electrically. Even the predicted THD was similar. I guess they're similar but sound different.
I have a sleeve of 6AC7. That might be fun to try in real life. It shows just a bit more gain than the others in simulation, because it has higher gm.
I also have a few 6SJ7 around. That sims almost exactly the same as 6AU6, so that would be usable too.
What about semi-remote or remote-cutoff triodes and pentodes?
They have grids wound with uneven spacing, so they're variable-gm.
There must be some that are wound so that their gm goes down as signal level input goes up. That would make a sort of automatic compressor.
Has anyone experimented with those as part of a guitar preamp?
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They have grids wound with uneven spacing, so they're variable-gm.
There must be some that are wound so that their gm goes down as signal level input goes up. That would make a sort of automatic compressor.
Has anyone experimented with those as part of a guitar preamp?
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I'll give you one free spin with Google before I hand this over.
remote-cutoff triodes and pentodes compressor - Google Search
remote-cutoff triodes and pentodes compressor - Google Search
Hey PRR, thanks.
What makes a good amp for jazz guitar is a very subjective thing.
I know a lot of jazz guitarists and I don't remember any actually liking the Roland Jazz Chorus amps for very long. I certainly never did. 'Hard' sounding. Not for me. YMMV.
Fender Twin Reverb of course is a classic (just ask Kenny Burrell or George Benson). Way too heavy though. I mean... waaaaay too heavy.
I had an Ampeg VT-40 when I was a teenager! What a great amp that was! But again, a real back breaker. Ugh.
I think there are as many ideas about what makes a good guitar amp as there are jazz guitar players.
There is a school of jazz players -- especially fingerstyle, chordal arrangement players -- who prefer extremely clean sound, I suppose so you can hear all the notes in the chords and polyphony. There is a different school of jazz players who play a lot of single note lines, who prefer a more 'enriched' tone, with some harmonic distortion added (think the tone of Peter Bernstein, for instance, who plays through a Fender Vibrolux Reverb). Pete's tone is what I'm thinking.
For instance:
Peter Bernstein - Chant - YouTube
Kenny Burrell's tone is the one to die for. Like this:
Tin Tin Deo - Kenny Burrell - YouTube
I believe Kenny would have recorded that through a Fender amp, maybe his Twin Reverb with (back-breakingly heavy JBL speakers), which I had the privilege to hear him play at the Village Vanguard some years ago. (Man, what a sound!)
So yeah, I'm a Fender guy. I have a Deluxe Reverb in which I swapped the OPT for one from a Bassman and a Thordarson power transformer, with push-pull 6L6s. It gets a mighty 35 watts, which is all I ever needed, even on the loudest gigs.
The Deluxe Reverb has a nice way of 'enriching' the sound, I think because it has a lot of gain and its output stage has little NFB around it (it overdrives quite easily, unlike a Twin Reverb).
Of course there's Jim Hall's tone, which was different, but also somewhat 'furry'. Jim used a Gibson GA-50 for many years, which was a push-pull 6L6 combo amp with a pentode input stage and a paraphase phase splitter. Like this:
Without a Song (Remastered) - YouTube
Anyhow, I hope those examples help illustrate the tone I'm hoping to find in a smaller box. I can't play like that, though. But "I Can Dream, Can't I"?
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What makes a good amp for jazz guitar is a very subjective thing.
I know a lot of jazz guitarists and I don't remember any actually liking the Roland Jazz Chorus amps for very long. I certainly never did. 'Hard' sounding. Not for me. YMMV.
Fender Twin Reverb of course is a classic (just ask Kenny Burrell or George Benson). Way too heavy though. I mean... waaaaay too heavy.
I had an Ampeg VT-40 when I was a teenager! What a great amp that was! But again, a real back breaker. Ugh.
I think there are as many ideas about what makes a good guitar amp as there are jazz guitar players.
There is a school of jazz players -- especially fingerstyle, chordal arrangement players -- who prefer extremely clean sound, I suppose so you can hear all the notes in the chords and polyphony. There is a different school of jazz players who play a lot of single note lines, who prefer a more 'enriched' tone, with some harmonic distortion added (think the tone of Peter Bernstein, for instance, who plays through a Fender Vibrolux Reverb). Pete's tone is what I'm thinking.
For instance:
Peter Bernstein - Chant - YouTube
Kenny Burrell's tone is the one to die for. Like this:
Tin Tin Deo - Kenny Burrell - YouTube
I believe Kenny would have recorded that through a Fender amp, maybe his Twin Reverb with (back-breakingly heavy JBL speakers), which I had the privilege to hear him play at the Village Vanguard some years ago. (Man, what a sound!)
So yeah, I'm a Fender guy. I have a Deluxe Reverb in which I swapped the OPT for one from a Bassman and a Thordarson power transformer, with push-pull 6L6s. It gets a mighty 35 watts, which is all I ever needed, even on the loudest gigs.
The Deluxe Reverb has a nice way of 'enriching' the sound, I think because it has a lot of gain and its output stage has little NFB around it (it overdrives quite easily, unlike a Twin Reverb).
Of course there's Jim Hall's tone, which was different, but also somewhat 'furry'. Jim used a Gibson GA-50 for many years, which was a push-pull 6L6 combo amp with a pentode input stage and a paraphase phase splitter. Like this:
Without a Song (Remastered) - YouTube
Anyhow, I hope those examples help illustrate the tone I'm hoping to find in a smaller box. I can't play like that, though. But "I Can Dream, Can't I"?
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Thanks. However, I don't see a discussion of using a semi-remote or remote-cutoff tube as a gain stage in a guitar amp specifically, or what that sounds like. Lots of discussion of how to use them in a variable-mu compressor, which is helpful.
Most discussions talk about simply 'adding distortion', whatever that means to whomever is typing at the moment. Like so:
https://www.diyaudio.com/forums/tubes-valves/174475-emulating-remote-cut-2.html#post2319123
There are lots of discussions that don't lead to any kind of 'I tried it myself and here is what I think' kinds of conclusions...
What is a Remote Cutoff Pentode - AMPAGE Archive
What happens if one simply uses a 6ES8 or a triode-wired 6BA6 as a voltage amp stage in a guitar amp? Do you get any 'compression' at higher signal levels, or just more THD? I'm thinking I'd like to add 2nd harmonic, but not to the point of rock-style clipped 'overdrive.' I suppose I'll just have to buy a few remote-cutoff tubes and try 'em. Maybe I have some remote-cutoff pentodes in one of the junk boxes... Any recommendations on one that might be useful? 6SS7? 6SK7? 6BA6?
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Yes, most specifically the late Fred Nachbaur who put a small amp emulator in his Dogzilla
There's also bunch of people playing with microamps putting out below 2W (and 10db below). Probably the best known are those on Rob Robinette's site - e.g. the Bassman Micro
Run one of those into a low-efficiency (but appropriate F3) mini speaker (or emulator) and feed your main amp from there.
And yet we can learn how others have used the tubes, which are more viable, even if it is not necessarily for a guitar signal. Mind you, they are trying to do the same as you, adding to the sound without running into clipping. They might even us it on a guitar signal. Stranger things have happened.
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