OTL amps for guitar duty

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Hummm , i see one piece of sarcastic position here, or is the google translate?, or not undestand to me very goog by one moment?
I am spanish, an is dificult, for my the perfect expresión, I say reference to this is more sensitive to tone instrument, an not enmascarate nothing....

Nothing relationship whit the magic of cable, or the light of the cosmos, or blue pitufs.

Bad boys.
 
We've built a lot of guitar amps in our shop. Several of my employees build guitar amps which they play in their bands. None have come anywhere near the transparency of our OTL guitar amp; its much easier to hear the difference between a really good pickup and a cheap one, as well as the character of the guitar cable itself.

That's your experience.My experience is that most OPT's used in guitar amps are bad, including those from notorious firms.... I guess the one you used was no exception. For me OTL's have more troubles than advantages.

P.S.
I am actually assuming that one is sure about all the other things because often people attribute things to the wrong cause. The output transformer is often the scapegoat for other troubles that people are unable to spot. 99% of users of OTP's do not really know how it works and so it's easy to make up their mind about the "transparency" tale. That's just snake oil theory. a proper transformer can more transparent than any other electronic component. In the case of guitar amp where the bandwidth is even narrower that is absolutely true.
Personal beliefs, including generic comments about the sound, with no objective proof repeated over and over at some point become the truth. Real thing is different.
 
Transparency and OTLs are two things that are often found together. IOW OTLs have been known for being really transparent for decades so this is nothing new.

I agree that a good transformer properly set up is quite transparent, but its also been my experience (over 4 decades now) that any transformer coupled amp we could get our hands on (and over the decades, that's been hundreds) just isn't going to be as transparent, and that includes amps that overall cost quite a bit more.

In that latter regard, one reason to go OTL is its less expensive. Unless you are going low power, output tubes tend to cost less than output transformers of the same power.

My advice is 'try it'. I find most of the push back I get comes from people who haven't.
 
Transparency and OTLs are two things that are often found together. IOW OTLs have been known for being really transparent for decades so this is nothing new.
In my experience they are only transparent on the bench driving a resistor. Not so transparent when driving real loudspeakers. They are actually quite fussy when it comes down to mate them with loudspeakers. Proper solid state amps are better for me if no transformer.

I agree that a good transformer properly set up is quite transparent, but its also been my experience (over 4 decades now) that any transformer coupled amp we could get our hands on (and over the decades, that's been hundreds) just isn't going to be as transparent, and that includes amps that overall cost quite a bit more.
Be assured that if the OTL made a better guitar amp it would be at least a common solution among top of the range custom amps. Instead it isn't.

In that latter regard, one reason to go OTL is its less expensive. Unless you are going low power, output tubes tend to cost less than output transformers of the same power.
Less expensive? Are you joking? I can do a 10W class A amplifier with 3 valves 1xECC83 and 2xPCL86, high quality capacitors and high quality transformers. The amp has two independent channels, one clean and one high gain with individual tone controls, presence switch. Only the first 1/2 ECC83 and output stage is in common. The clean channel outputs 10W super clean and 12W with some distortion (mostly 3rd and 2nd harmonics which results in a very light warm crunch when playing).

The output transformer is 16K plate-to-plate (a long story....) and weights less than 1Kg. Total parts cost is about 70 euros + 90 euros for the Eminence Legend 1028K + 30 euros for the reverb. If someone wants to buy it he would have to pay more because I have done the transformer myself however this would cost about 50 euros.

Can you make a 10W class A OTL amp for about 100 euros (excluding the loudspeaker driver and the reverb tank)?
I really doubt it.


My advice is 'try it'. I find most of the push back I get comes from people who haven't.
I haven't tried for a guitar amp because I have tried for HiFi. Not good enough for me. Very fussy and thus anything but transparent in most cases.
For a guitar amp it should be easier however the sound of guitar amp is heavily dependent on the guitar, tone controls, effects of various types, speaker, gain stage that talking about the transparency of the output stage is like talking about everything and nothing at the same time.....
 
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That almost sounds like a Challenge.

Isn't this how the HBAC started?

Let's see, 100 Euros is $114 USD as of 5 minutes ago......

Unfortunately those 6 inch Eminence guitar speakers that I have are 4 ohms.....

So assuming a 32 ohm load, and a 10 watt class A OTL, I'm guessing 4 X $3 output tubes, another 4 X $3 small signal tubes, a $35 power transformer, leaving about $55 USD for the rest of the parts......10 watt OTL amp, probably. Pretty case and fancy knobs, probably not.
 
I don't know, I didn't start this one....I would assume SS rectifiers are OK. Mosfets? I'll use them if it is the right thing for the circuit.

The more I think about this the crazier it seems. I think I can do a 10 watt class A OTL. I figure that it will burn about 150 watts to make 10. The green police will have my number from the heat signature of 70 watts worth of tube heaters.

I have been working on an equally insane project, a music synthesizer built with vacuum tubes. Which is crazier, a tube synth, or an OTL guitar amp. Maybe I'll just build both and connect them together.
 
Isn't this how the HBAC started?

Let's see, 100 Euros is $114 USD as of 5 minutes ago......

Unfortunately those 6 inch Eminence guitar speakers that I have are 4 ohms.....

So assuming a 32 ohm load, and a 10 watt class A OTL, I'm guessing 4 X $3 output tubes, another 4 X $3 small signal tubes, a $35 power transformer, leaving about $55 USD for the rest of the parts......10 watt OTL amp, probably. Pretty case and fancy knobs, probably not.

In the 100 euros/$114 also the metal chassis for the amp and the wood cabinet all put together and finished for a combo amp are included. Only the driver/drivers and the reverb tank are extra.
 
While taking a break from shoveling the snow, ice and frozen mud that has taken over my driveway I decided to read back over some of this thread. Intrigued by SemerFi's circuit and its PNP current mirrors I remembered some of my experiments from many years ago.

At that time I was still an engineer working at a large Motorola plant and silicon from On Semiconductor (used to be Motorola) was FREE.....did I blow up silicon? Truth is, I have fried more sand than vacuum tubes in my 50+ years of electronics experiments.

From post #41 Gnobuddy said:

what if we use a current mirror, arranged to force an output transistor to exactly duplicate the current in the output valve? Now the transistor should sound exactly like the valve.........we can modify the current mirror so that the second branch not only mirrors, but also multiplies, the current from the output valve? Then we could deliver triple, or quadruple, the current to the speaker

At the time I was making SET HiFi amps and I got the idea of making a boosted version of the 45 DHT tube. Armed with a box full of the biggest and baddest high voltage audio transistors that ON Semi makes, I went down this road.....only to wind up with a box full of toasted silicon.

the transistor could be run off a much lower voltage B+ rail than the pentode. This would reduce problems with second-breakdown of the transistor.

YES, I had rediscovered secondary breakdown. running the transistor into the OPT, which was then connected to a lower voltage supply helped, and this allowed the use of a 600 ohm OPT. This is where my path took a different turn.

We have found a way to drive a chosen tube in a way that gives us a good sounding low powered amp. We know how how to mirror this current and multiply it and use it to drive say an OPT, which can present us with all sorts of inductive kick back voltages and currents which will kill the silicon, so....

Stick the mirrored side current into the cathode of a BIG fat TV sweep tube that has no problem eating whatever the OPT throws back at us. So, I tried mirroring the current of my little 45 tube, multiplied into the cathode of a big sweep tube, with both plates tied together feeding an OPT.....it works!

It is logical that a bunch of 6AS7, 6336 or 6528 triodes could be driven by the mirror and fed directly to the speaker.
 
¿Puedes hacer un amplificador OTL de clase A de 10 vatios por unos 100 euros (excluyendo el controlador del altavoz y el tanque de reverberación)?
Realmente lo dudo.
.

Is very ovius, yes...

This Amp you to coment, but of one only extreme, it is OTL, whit pcl86, or more way whit 1ecc83 an 2 EL86....yes 10 watts in OTl...of new...

An it can ser more less (too) price :), by not put the output transformer, jiji

The Eminence wizzar whit 16 ohms it more way for you purposes....whit 102,8 db (103db), it way for my

Less cost
Less weigth,
Whit 800 ohms cone 6" more much less price , i pay for this cone 5$ :).

The sound of guitar, is one part is in all chain of the sound since guitar to amp, and finality to speaker.

All chain in higth impedance in 800 or 600 ohms if this posible, and eliminate the block of output ( ladrille the output transformer)

I inclusive conduct the OTL of this type whit 16 ohms, of this form), and whit standars speakers whit others compensatións at one identical volume to compare whit 800 ohms in OTL.

Transparence not is one oblique expresión, it is not obstaculize, and not deteriorate the signal by the road.

This it is work in this moment and very less cost, in combo format , yes.

And include and more merit, this in higth and in low tensión,

in less voltaje less power ok but yes

Very big qualite, in some years you see one standar, in guitar this is only short time

Regards.
 
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I have in my saloon one venerable fender blackface of 1965, original not reissue, other fender deluxe tweed point to point,
One Champtone thirty teen, one fender champ ptp, and others...very big list for cite here all,

But i select for playing more good experience whit my guitar first the OTL of direct output, or capacitance output
Independent of the power of this.


Is more musical and tridimensional, and more sensitive at the pulsatión.

And less price, of course
 
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In my experience they are only transparent on the bench driving a resistor. Not so transparent when driving real loudspeakers. They are actually quite fussy when it comes down to mate them with loudspeakers. Proper solid state amps are better for me if no transformer.


Be assured that if the OTL made a better guitar amp it would be at least a common solution among top of the range custom amps. Instead it isn't.


Less expensive? Are you joking? I can do a 10W class A amplifier with 3 valves 1xECC83 and 2xPCL86, high quality capacitors and high quality transformers. The amp has two independent channels, one clean and one high gain with individual tone controls, presence switch. Only the first 1/2 ECC83 and output stage is in common. The clean channel outputs 10W super clean and 12W with some distortion (mostly 3rd and 2nd harmonics which results in a very light warm crunch when playing).

The output transformer is 16K plate-to-plate (a long story....) and weights less than 1Kg. Total parts cost is about 70 euros + 90 euros for the Eminence Legend 1028K + 30 euros for the reverb. If someone wants to buy it he would have to pay more because I have done the transformer myself however this would cost about 50 euros.

Can you make a 10W class A OTL amp for about 100 euros (excluding the loudspeaker driver and the reverb tank)?
I really doubt it.



I haven't tried for a guitar amp because I have tried for HiFi. Not good enough for me. Very fussy and thus anything but transparent in most cases.
For a guitar amp it should be easier however the sound of guitar amp is heavily dependent on the guitar, tone controls, effects of various types, speaker, gain stage that talking about the transparency of the output stage is like talking about everything and nothing at the same time.....


Hm. You say you've not tried it but you say 'in your experience' that the amp is only transparent driving a resistor. Can't have it both ways- I have to assume that the first statement is about a thing that didn't happen.


FWIW I get this sort of thing a lot, but I've been doing this successfully for a living for over 42 years so I know it works. If you don't want to try it, no skin off my back.



OTLs have an economy of scale- the bigger you make them the more efficient they are. But if you really wanted to make an OTL for under 100 Euros you could do it if you knew where to get the parts.
 
Hm. You say you've not tried it but you say 'in your experience' that the amp is only transparent driving a resistor. Can't have it both ways- I have to assume that the first statement is about a thing that didn't happen.
hmmm instead I have more and more doubts that you know and understand what makes the sound in guitar amp.

FWIW I get this sort of thing a lot, but I've been doing this successfully for a living for over 42 years so I know it works. If you don't want to try it, no skin off my back.
Successfully for you, I say. I have done my experience with OTLs in HiFi and they are inferior. In HiFi there are more precise rules on what an amplifier is supposed to do and they are inferior. Sorry to upset you but that is. For what other reason should they be better in guitar amp if the signature of the output transformer is diminished because of the narrower bandwidth?

OTLs have an economy of scale- the bigger you make them the more efficient they are. But if you really wanted to make an OTL for under 100 Euros you could do it if you knew where to get the parts.

Again I doubt you are aware of what a guitar amp should look like and what should do. People don't want a big amp but a great amp which should be as small and light as possible. Big and heavy amps no one wants them anymore......
I don't need to buy the parts. I already have them. I have a couple of quads of 6AS7G's by RCA and some 6080's by GEC. Made in 60ies....but I prefer them with an output transformer.
 
.

Is very ovius, yes...

This Amp you to coment, but of one only extreme, it is OTL, whit pcl86, or more way whit 1ecc83 an 2 EL86....yes 10 watts in OTl...of new...
.

And what speakers is going to drive with 2xEL86? 6" cheap cones? Haha. Then where is this superior performance???? If you don't spend in the amp to make it under 100 euros you will have to spend money on speakers and the size will not be compact. Useless in practice. Try to sell such an amp and see how many musicians would buy it. A guitar amp MUST be practical too even if you are not a professional because if you have to go around to play with friends after a while I am pretty confident you will leave at home and use a more practical one.
 
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hmmm instead I have more and more doubts that you know and understand what makes the sound in guitar amp.


Successfully for you, I say. I have done my experience with OTLs in HiFi and they are inferior. In HiFi there are more precise rules on what an amplifier is supposed to do and they are inferior. Sorry to upset you but that is. For what other reason should they be better in guitar amp if the signature of the output transformer is diminished because of the narrower bandwidth?



Again I doubt you are aware of what a guitar amp should look like and what should do. People don't want a big amp but a great amp which should be as small and light as possible. Big and heavy amps no one wants them anymore......
I don't need to buy the parts. I already have them. I have a couple of quads of 6AS7G's by RCA and some 6080's by GEC. Made in 60ies....but I prefer them with an output transformer.


You can make an OTL guitar amp lighter than one that has an output transformer, unless the OTL is going to be inefficient by being too small. IME 20 watts is about as low power as you can get away with unless you really increase the loudspeaker load impedance.



I've won many awards and gotten plenty of nice reviews in the high end press so no worries there. I also play in a band; Music | Thunderbolt Pagoda
I've worked on many guitar amps over the decades. We used to build a Plexi knock off for an amp company back before they were driven out by the recession.



All of my employees play guitar. The only reason OTL guitar amps aren't more common is the simple fact that guitar players expect to see one of only a few power tubes types (KT88, 6L6, etc.) in an amp and if its something else they get freaked out.



I've run into a lot of mythology about OTLs in the last 40 years. The most common is actually that they are unreliable. That is only true if the circuit used is a totem-pole. Circlotron OTLs tend to be much more reliable. As far as speaker choice goes, SETs are as picky as OTLs are and SETs are doing quite well so no worries.
 
You can make an OTL guitar amp lighter than one that has an output transformer, unless the OTL is going to be inefficient by being too small. IME 20 watts is about as low power as you can get away with unless you really increase the loudspeaker load impedance.
HOW??? Can you make a REAL example instead of going round in circles?

Then I have to remind you the TIPS I gave you to make it lighter in post 143.

I have made a real example of a 10W class A amplifier, including the actual Eminence driver it is using.

At 20W power level things become even worse for an OTL because for a 20W amplifier with output transformer I will only need 2x12AX7 and 2xEL84. Just one more tiny 12AX7 consuming little power. The PSU transformer will be a bit bigger of course but that's true for any amp.
I have made output transformer on 22x22 mm core size and it actually has HiFi performance! It could be even reduced to 20x20 accepting a bit more DC resistance but nothing really to worry about. Same as before for the 10W with PCL86's but 8K instead of 16K. I prefer the 22x22 because I can easily find the covers.....so not much weight added for 2x the output power.

I've won many awards and gotten plenty of nice reviews in the high end press so no worries there. I also play in a band; Music | Thunderbolt Pagoda
I've worked on many guitar amps over the decades. We used to build a Plexi knock off for an amp company back before they were driven out by the recession.

So why do you keep going round in circles? Where is this lighter 20W amplifier?

All of my employees play guitar. The only reason OTL guitar amps aren't more common is the simple fact that guitar players expect to see one of only a few power tubes types (KT88, 6L6, etc.) in an amp and if its something else they get freaked out.
Apart from people beliefs and expectations the true reason why OTL amplifiers are not popular, never were and never will is that the best speakers have low impedance. A 32-150-600-800R driver will never be as good as a 4-8R driver. That's physics. The first thing that can be noticed is that all things being equal a lower impedance driver will be more efficient, if done right.

I've run into a lot of mythology about OTLs in the last 40 years. The most common is actually that they are unreliable. That is only true if the circuit used is a totem-pole. Circlotron OTLs tend to be much more reliable. As far as speaker choice goes, SETs are as picky as OTLs are and SETs are doing quite well so no worries.

That's not mythology it was true at beginning. It's rather bad reputation that never went away. The mythology is that the absence of the output transformer makes them better. Better for what?
SE or PP amps can be both with or without transformer. Surely a SE OTL is the worst amp one can think of...
 
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This thread is also starting off in much the same way the HBAC did too.

Note:
HBAC = Hundred Buck Amp Challenge thread

The Hundred-Buck Amp Challenge

I have made a real example of a 10W class A amplifier

I started making guitar amps in the 60's as a kid with no money. My only parts store was the county trash dump where hundreds of old TV's, radios, and HiFi consoles went to die. The prices were good though, free, just bring some tools and a shopping bag. I started making Champ clones, many with TV tubes.

I have had a guitar in my hands off and on for nearly 60 years, and built hundreds of amps. Some were sold, some given away, and others just used for a while, then robbed for parts. Most used tubes, but I did go through a solid state phase in the 70's and early 80's since silicon was free. In the 90's I did make soemguitar amps for sale. They were either "Turbo Champs" a SE design with anything from a 6V6 to a KT88 making from 5 to 15 watts, or push pull amps of 35 to 100 watts. I started Tubelab, making HiFi amps in the early 2000's. Every one of my HiFi designs had to eat my guitar playing with at least 10 DB of overdrive as part of its initial "torture testing." Ever play guitar through 300B's? I have, in both SE and push pull.

The amp I currently use is a 4 watt push pull job I built for about $45 cabinet and chassis included, for the HBAC. It was deemed that the current cost of 12AX7 / ECC83 was too much for most builders to use in their amps. It would be interesting to see how your amp was built for 100 euros when 20 of them went for tubes.

I have however NEVER played guitar through an OTL, and even though the engineer in me says I would prefer a transformer driven speaker, I will reserve judgment until I actually TRY it.

I am currently in the midst of a redesign of my TSE product, as after 14 years of sales some of the parts have gone extinct. Once that is done, I may tinker with some sort of OTL.

As has been stated 10 watts is kind of an odd spot for an OTL with conventional speakers. The 600 ohm speaker stuff is far too oddball, and hard to find. 2 X 16 ohm speakers, or 4 X 8 ohm speakers is far more conventional. I could rewire the speakers that I currently use, and know to make a 32 ohm load.

Getting 10 watts across that 32 ohm load needs about 18 volts RMS and 600 mA of idle current in class A. The cheapest power transformer is an isolation transformer with 2 X 120 volt windings......that's a lot of wasted power to make 10 watts. I have a big box full of used 6AS7's some 6336's and 6528's, but to make the 100 euro mark some cheap tubes are needed. I dug through my collection and found some TV sweep tubes that currently list for $3 and have a peak current rating of over 1 amp each......

Surely a SE OTL is the worst amp one can think of...

Maybe I'll start there. It's easy, and I only need about 50 volts peak to peak swing across the speaker.

Ralph, I followed the link to the Bandcamp page and listened while I typed this. I was intrigued to see a real "beast full of tape strips" kind of Mellotron.
 
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