I have a cheap little Champ kit chassis, just vol & master vol but I might add a 'bright' switch across that vol; one 6V6, really small cheap transformers. I don't really want to mess with it, it is what it is, really small and convenient, but occasionally it could be more.
I have a range of power transformers and chokes, a 15-watt single-ended output transformer, a KT-120, some EL34's. I've seen some nice KT-80 guitar power amp circuits using a smallish power transformer and the same output transformer I have. Even the smallish power transformers will handle the higher filament requirements of the KT-120 when there's no preamp to drive.
I guess I should evaluate the noise level of the champ, and see whether it would still be acceptable boosted. It has AC heaters, wires are not even twisted, and the heaters are not raised with DC divided off the B+. It's never seemed very noisy to me, but then again it's never been very loud.
If I just made a simple 'champ-booster' meant to work with MY champ amp, what's the simplest circuit? I imagine I could just bypass the champ's output transformer and capacitor-couple right to a level resistor and grid-stopper on the KT120. That would make this 'champ booster' really small and simple with a very very small parts count. But...that's a few hundred volts, so perhaps I would not want a high-voltage cable to an external 'champ booster' in its own head cabinet.
Or...instead of a head and booser head, I have a JBL 10" guitar speaker that would make a nice combo with the Champ, and I have a JBL 15" guitar speaker that would be nice in an another cab with its own 'booster' amp when I want more bass and volume.
Is it practical or safe to have an external cord with 300 volts?
Or should I put a more moderate line-level out on the champ and add one more tube to the 'booster' and make it into a more versatile normal power amp to use with the champ or a preamp etc. Might even be nice to plug my tube proverb between the two.
BTW I do have many bigger amps, so this is just a fun project, not a neccessity. At first I had grand ideas, then realized that part of the fun is something very compact and portable and convenient, and a Champ combo is simple and convenient, and a really simple powered extension cabinet might be really cool.
I have a range of power transformers and chokes, a 15-watt single-ended output transformer, a KT-120, some EL34's. I've seen some nice KT-80 guitar power amp circuits using a smallish power transformer and the same output transformer I have. Even the smallish power transformers will handle the higher filament requirements of the KT-120 when there's no preamp to drive.
I guess I should evaluate the noise level of the champ, and see whether it would still be acceptable boosted. It has AC heaters, wires are not even twisted, and the heaters are not raised with DC divided off the B+. It's never seemed very noisy to me, but then again it's never been very loud.
If I just made a simple 'champ-booster' meant to work with MY champ amp, what's the simplest circuit? I imagine I could just bypass the champ's output transformer and capacitor-couple right to a level resistor and grid-stopper on the KT120. That would make this 'champ booster' really small and simple with a very very small parts count. But...that's a few hundred volts, so perhaps I would not want a high-voltage cable to an external 'champ booster' in its own head cabinet.
Or...instead of a head and booser head, I have a JBL 10" guitar speaker that would make a nice combo with the Champ, and I have a JBL 15" guitar speaker that would be nice in an another cab with its own 'booster' amp when I want more bass and volume.
Is it practical or safe to have an external cord with 300 volts?
Or should I put a more moderate line-level out on the champ and add one more tube to the 'booster' and make it into a more versatile normal power amp to use with the champ or a preamp etc. Might even be nice to plug my tube proverb between the two.
BTW I do have many bigger amps, so this is just a fun project, not a neccessity. At first I had grand ideas, then realized that part of the fun is something very compact and portable and convenient, and a Champ combo is simple and convenient, and a really simple powered extension cabinet might be really cool.
Hi,
You've alluded to the simplest option, build the 10" combo.
Fit some form of attenuated out driven from the speaker terminals.
I'd use a simple chip amp in the extension cabinet, and use
ESP's variable impedance circuit Variable Amplifier Impedance
to tune its basic cabinet sound.
As long as the Champ does all its stuff before the chipamp
can possibly clip, you'll just get a bigger Champ* effectively.
Easy to arrange with say a 68W chip amp.
rgds, sreten.
* Not quite depending on lots of things, but why complicate it ?
You've alluded to the simplest option, build the 10" combo.
Fit some form of attenuated out driven from the speaker terminals.
I'd use a simple chip amp in the extension cabinet, and use
ESP's variable impedance circuit Variable Amplifier Impedance
to tune its basic cabinet sound.
As long as the Champ does all its stuff before the chipamp
can possibly clip, you'll just get a bigger Champ* effectively.
Easy to arrange with say a 68W chip amp.
rgds, sreten.
* Not quite depending on lots of things, but why complicate it ?
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Back when I was making "Turbo Champ's" I stuck an attenuated speaker output (speaker still live) on one of them and plugged it into the input jacks on a 400 watt solid state Carver cube which fed a pair of 4 X 12 cabinets.....it ROCKED. The original Carver M-400 "magnetic field amp" carried all sorts of warnings not to do this since it had virtually no heat sinks, but if I hammered on it until it got mad, it just shut down until I turned it down a bit.
A chip amp would probably work good, but when I get a chance I want to try the 300 watt class D board I got from China for $50.
A chip amp would probably work good, but when I get a chance I want to try the 300 watt class D board I got from China for $50.
Hi,
A cautionary note regarding speakers - I added
a 1x15 to my 4x10 bass combo and the 1x15
totally blew away the 4x10's midrange.
Fortunately a bass playing friend using a 1x15
combo found it a bit dull. So a speaker swap
was done and worked out great. The 15" I
got integrated much better, and his combo
gained a much more aggressive midrange.
rgds, sreten.
A cautionary note regarding speakers - I added
a 1x15 to my 4x10 bass combo and the 1x15
totally blew away the 4x10's midrange.
Fortunately a bass playing friend using a 1x15
combo found it a bit dull. So a speaker swap
was done and worked out great. The 15" I
got integrated much better, and his combo
gained a much more aggressive midrange.
rgds, sreten.
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I'm currently building a unit that acts as dummy load or power soak and will have a transformer-coupled balanced or unbalanced line out. And I've plenty of solid-state power amps, so I don't need a chip amp. But I was kind of looking for a fun tube project to use the transformers and tubes.
It might make more sense to build a second slightly larger champ with an EL34. I'll make better decisions with better data, so I need to find the transformers and figure out exactly what each puts out.
It might make more sense to build a second slightly larger champ with an EL34. I'll make better decisions with better data, so I need to find the transformers and figure out exactly what each puts out.
I'd be interested to find out more about your loadbox/power soak. So far, the only good DIY circuit along these lines which I know about is the Aiken reactive load (which I've built and works well).
It was my opinion that the only load that acts like a speaker is......a speaker. That's why I left the Turbo Champ's speaker connected. You can't hear the 5 watt Champ sitting on the ground near 8 X 12's fed over 300 watts. Do not set the Champ on top of the big cabinet if the speaker is still connected. It can act like a microphone and make a very loud feedback.
I have made simple tube boosters. First decide if you want SE or P-P. Find two OPT's of the appropriate flavor, one for the output, and a small one for the driver. The easiest method is to use a reverse connected OPT to drive the grid of the output tube. Bias is applied to the cold end of an SE OPT or the CT of a P-P OPT. For cathode bias ground the cold end or CT. The rest is pretty much standard power supply and OPT stuff. The load for the Champ can be a typical resistor or speaker simulator on its output with the driver transformer in parallel. A 10K to 50K resistor across the transformer secondary may reduce transformer ringing and improve the tone. Alternatively you can connect the transformer directly to the Champ's output and place the load/simulator on it's primary, grid(s) of output tube(s). Much smaller inductors are needed in the simulator circuit.
I have made simple tube boosters. First decide if you want SE or P-P. Find two OPT's of the appropriate flavor, one for the output, and a small one for the driver. The easiest method is to use a reverse connected OPT to drive the grid of the output tube. Bias is applied to the cold end of an SE OPT or the CT of a P-P OPT. For cathode bias ground the cold end or CT. The rest is pretty much standard power supply and OPT stuff. The load for the Champ can be a typical resistor or speaker simulator on its output with the driver transformer in parallel. A 10K to 50K resistor across the transformer secondary may reduce transformer ringing and improve the tone. Alternatively you can connect the transformer directly to the Champ's output and place the load/simulator on it's primary, grid(s) of output tube(s). Much smaller inductors are needed in the simulator circuit.
Interesting idea, running an output transformer in reverse to get enough drive so the booster doesn't need a driver stage; we're still talking about a very small inexpensive Champ transformer. The champ puts out so little power that any tone-shaping can use inexpensive crossover parts, no need to get the really good stuff.
The power soak is not really for this project, it's got to serve for testing big transistorized amps as a dummy load but also work as a direct box for whatever I throw at it, and as a power reducer too.
For the power soak, so far I have $5000.00 worth of square metal-film 300-watt 10-ohm power resistors that bolt to a heatsink, I got all 12 used for $30; a 10" X10" aluminum plate 1/2" thick, and a 10" X 5.5" heatsink with very very deep fins. The mechanical layout will be big L-shaped spine of thick aluminum, forming the bottom of a box with the resistors bolted to it, and rising vertically across the back of the box and above it, with the heatsink bolted to the vertical plate over the front of the box (vertical fins) and some aluminum c-channels bolted to the back (cheaper than heat-sink).
I haven't bought the box yet, until I have all the components and know exactly how much room I need.
The truth is that I never did really understand the Marshall power soak, or most inductive loads. I guess the Aiken is really trying to load the amp like a speaker would. So you've built one; did you have a switch for the resonant portion? What were your impressions in actual use? I used to have some Marshall Power Brakes and also some Scholz Power Soaks, bought used. Some of the Power Soaks have burned circuit boards and burned cracked resistors. I didn't get to try the inductive brakes against the resistive soaks in a real A/B comparison, and had to sell them all in hard economic times a few years back.
I was hoping to afford this large balanced line out transformer, which I've used in mixing board balanced outputs; it handles quite a large signal cleanly when necessary:
http://www.jensen-transformers.com/datashts/11bmcf.pdf IMHO it's definitely the king of output transformers. But for that expense, I might just mount it on its own chassis where it can be most versatile.
For that matter, I could make the resonant inductive/capacitive load a separate plug-in chassis too.
I would be simple and versatile to make several units on individual chassis that plug together:
1) Reactive amp load
2) power reducer that make the output 1/4 the input power
3) tone shaper & balanced output transformer
4) variable output switch-based output pad or a normal commercial resistive unit if I can afford it.
Thanks for the link, it's making me think and I'm going to have to read it more than once. But what's your opinion of the inductive amp load from a man who owns one?
For the power soak, so far I have $5000.00 worth of square metal-film 300-watt 10-ohm power resistors that bolt to a heatsink, I got all 12 used for $30; a 10" X10" aluminum plate 1/2" thick, and a 10" X 5.5" heatsink with very very deep fins. The mechanical layout will be big L-shaped spine of thick aluminum, forming the bottom of a box with the resistors bolted to it, and rising vertically across the back of the box and above it, with the heatsink bolted to the vertical plate over the front of the box (vertical fins) and some aluminum c-channels bolted to the back (cheaper than heat-sink).
I haven't bought the box yet, until I have all the components and know exactly how much room I need.
The truth is that I never did really understand the Marshall power soak, or most inductive loads. I guess the Aiken is really trying to load the amp like a speaker would. So you've built one; did you have a switch for the resonant portion? What were your impressions in actual use? I used to have some Marshall Power Brakes and also some Scholz Power Soaks, bought used. Some of the Power Soaks have burned circuit boards and burned cracked resistors. I didn't get to try the inductive brakes against the resistive soaks in a real A/B comparison, and had to sell them all in hard economic times a few years back.
I was hoping to afford this large balanced line out transformer, which I've used in mixing board balanced outputs; it handles quite a large signal cleanly when necessary:
http://www.jensen-transformers.com/datashts/11bmcf.pdf IMHO it's definitely the king of output transformers. But for that expense, I might just mount it on its own chassis where it can be most versatile.
For that matter, I could make the resonant inductive/capacitive load a separate plug-in chassis too.
I would be simple and versatile to make several units on individual chassis that plug together:
1) Reactive amp load
2) power reducer that make the output 1/4 the input power
3) tone shaper & balanced output transformer
4) variable output switch-based output pad or a normal commercial resistive unit if I can afford it.
Thanks for the link, it's making me think and I'm going to have to read it more than once. But what's your opinion of the inductive amp load from a man who owns one?
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The Aiken design is very good. It's interesting to be able to hear the raw amp output. It sounds awful 
but it shows you how important the speaker is in creating the final sound.
You need to use a cab sim eg LeCab. Convolution is best. Lots of free IR's on the net but most of my best results so far have been with some commercial ones from Ownhammer. Often I'll mix and match more than one IR to get the final sound.
I'd strongly recommend using the ERSE inductors mentioned in the gearpage thread. These are known to work. The OP ran into some saturation problems when he tried winding his own.
You wouldn't go wrong with one of their big, fat pulseX caps either although in my own I did use some cheaper electrolytics with a high ripple current rating in a series/parallel array. I'm about to upgrade it for 15W and will probably cheap out again and use four of these Nichicon CS.
I didn't add the resistive/reactive switch because I was in too much of a rush to try it out
I use mine when I need practice or work silently. You do lose a little bit of the character imparted by a real speaker but it's pretty good. On the plus side you have a lot of freedom to shape the sound with different impulse responses.
I guess decent headphones will be a requirement. An old pair of Sony MDR V6 work for me. In a well-worn set the earpiece foam starts to collapse a little moving the drivers a few mm closer to your ears - that fills out the bottom end.
Some samples of a 5F1 Champ:
https://dl.dropboxusercontent.com/u/93545279/clips/5F1-champ-no-NFB-2.wav
https://dl.dropboxusercontent.com/u/93545279/clips/5F1-ownhammer-sample.wav
https://dl.dropboxusercontent.com/u/93545279/clips/5F1-scumblack-and-blue.wav
https://dl.dropboxusercontent.com/u/93545279/clips/rockett-animal-sample.wav
https://dl.dropboxusercontent.com/u/93545279/clips/coil-taps-tm-2014-06-11T22:43:00.wav
but it shows you how important the speaker is in creating the final sound.You need to use a cab sim eg LeCab. Convolution is best. Lots of free IR's on the net but most of my best results so far have been with some commercial ones from Ownhammer. Often I'll mix and match more than one IR to get the final sound.
I'd strongly recommend using the ERSE inductors mentioned in the gearpage thread. These are known to work. The OP ran into some saturation problems when he tried winding his own.
You wouldn't go wrong with one of their big, fat pulseX caps either although in my own I did use some cheaper electrolytics with a high ripple current rating in a series/parallel array. I'm about to upgrade it for 15W and will probably cheap out again and use four of these Nichicon CS.
I didn't add the resistive/reactive switch because I was in too much of a rush to try it out
I use mine when I need practice or work silently. You do lose a little bit of the character imparted by a real speaker but it's pretty good. On the plus side you have a lot of freedom to shape the sound with different impulse responses.
I guess decent headphones will be a requirement. An old pair of Sony MDR V6 work for me. In a well-worn set the earpiece foam starts to collapse a little moving the drivers a few mm closer to your ears - that fills out the bottom end.
Some samples of a 5F1 Champ:
https://dl.dropboxusercontent.com/u/93545279/clips/5F1-champ-no-NFB-2.wav
https://dl.dropboxusercontent.com/u/93545279/clips/5F1-ownhammer-sample.wav
https://dl.dropboxusercontent.com/u/93545279/clips/5F1-scumblack-and-blue.wav
https://dl.dropboxusercontent.com/u/93545279/clips/rockett-animal-sample.wav
https://dl.dropboxusercontent.com/u/93545279/clips/coil-taps-tm-2014-06-11T22:43:00.wav
An interesting idea:
If the input to the "soak" was a power transformer wired in reverse, the unit could have inputs for multiple impedances, yet use just one configuration of the load and resonance circuits of resistors, capacitors, and inductors. And...the voltage ratings would increase but the current requirements drop, which might save a lot of money...after buying that $300 output transformer, unfortunately.
I do already have some output transformers which might be suitable for use in a soak to work on a range of amps of various power outputs. I have one transformer that's meant for 4 EL84's. I have another one that's meant for 8 KT88's.
But...it's a LOT of money and weight just to make it more flexible in what inputs it accepts. Then again, compared to the way some mfgrs of resistive units make you buy a different unit to match each amp output impedance seems wasteful too.
If the input to the "soak" was a power transformer wired in reverse, the unit could have inputs for multiple impedances, yet use just one configuration of the load and resonance circuits of resistors, capacitors, and inductors. And...the voltage ratings would increase but the current requirements drop, which might save a lot of money...after buying that $300 output transformer, unfortunately.
I do already have some output transformers which might be suitable for use in a soak to work on a range of amps of various power outputs. I have one transformer that's meant for 4 EL84's. I have another one that's meant for 8 KT88's.
But...it's a LOT of money and weight just to make it more flexible in what inputs it accepts. Then again, compared to the way some mfgrs of resistive units make you buy a different unit to match each amp output impedance seems wasteful too.
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The Aiken design looks like the best currently available, but here's an interesting quote:
"It is not self-evident that a traditional guitar speaker is the gold standard of guitar tone to any given listener's ears. I think it could be interesting to experiment with radically different impedance curves."
from user torquil on thegearpage.net in that thread about the Aiken.
"It is not self-evident that a traditional guitar speaker is the gold standard of guitar tone to any given listener's ears. I think it could be interesting to experiment with radically different impedance curves."
from user torquil on thegearpage.net in that thread about the Aiken.
FWIW I have built and sold lots of guitar specific powered boosters for small (<20W) tube amps.
Configuration is : an input attenuator (I tap the 8 to 20V RMS signal present directly at speaker terminals), a 60 or 100W SS amp (a chipamp would be fine, of course) and either 1 or 2 x 12" speakers, 2 x 10" ones or the odd 15".
No need for inductive loads or compensation, since I leave the original speaker(s) in place, which preserves original reactive load better than any simulation, keeps interaction alive, etc. and, as noted above, is *drowned* by the new booster.
And even if it´s not .... that´s the sound we are trying to get, only louder
A big point which keeps it simple is that I only use guitar speakers, so the response curve is "built in" by default.
It would be very different if a wide range powered cabinet (think JBL EON and such) were used because thare that flat frequency response is miles away from what we need.
Configuration is : an input attenuator (I tap the 8 to 20V RMS signal present directly at speaker terminals), a 60 or 100W SS amp (a chipamp would be fine, of course) and either 1 or 2 x 12" speakers, 2 x 10" ones or the odd 15".
No need for inductive loads or compensation, since I leave the original speaker(s) in place, which preserves original reactive load better than any simulation, keeps interaction alive, etc. and, as noted above, is *drowned* by the new booster.
And even if it´s not .... that´s the sound we are trying to get, only louder
A big point which keeps it simple is that I only use guitar speakers, so the response curve is "built in" by default.
It would be very different if a wide range powered cabinet (think JBL EON and such) were used because thare that flat frequency response is miles away from what we need.
Sorry but 6" size and small enclosure means not much bass capacity.
A 6" speaker which I like is the Jensen MOD 6" but it´s even sharper and probably has less bass.
In 6" size I gess you already have something as close as possible to your needs.
*If* you could use a larger speaker (ideally a 12" but worst case a 10") you will have a much wider selection to pick from.
A 6" speaker which I like is the Jensen MOD 6" but it´s even sharper and probably has less bass.
In 6" size I gess you already have something as close as possible to your needs.
*If* you could use a larger speaker (ideally a 12" but worst case a 10") you will have a much wider selection to pick from.
Thank you Jim for your friendly response. In my workshed I can compare with different cabs containing one 8", 12" and 15" speaker each.
Obviously the 15" sounds bests, haha!
nonetheless I try to make the most of the tiny Box with 6.5" driver.
Meanwhile there has been audible improvement by adding some bass boost. The price to pay will be recuded over all power - so I will have to find my personal compromise.
Additionally some treble cut seems appropriate as the PA6/100 delivers a bit too much "sss".
Next time I will do some rough frequency measurement with Arta - my goal is a close to linear response down to about 100Hz.
At the time the cutoff is above 200Hz.
kind regards
Obviously the 15" sounds bests, haha!
nonetheless I try to make the most of the tiny Box with 6.5" driver.
Meanwhile there has been audible improvement by adding some bass boost. The price to pay will be recuded over all power - so I will have to find my personal compromise.
Additionally some treble cut seems appropriate as the PA6/100 delivers a bit too much "sss".
Next time I will do some rough frequency measurement with Arta - my goal is a close to linear response down to about 100Hz.
At the time the cutoff is above 200Hz.
kind regards
I use a pair of Dayton PA165-8's in a 1 cubic foot enclosure with a bullet tweeter for response out to 18 KHz. There is a 2 X 3 inch rectangular port 3/4 inches long (a cutout in the plywood, no port extension). The response is flat to to 70Hz then drops like a rock below that. I use a 125 WPC tube amp to drive a pair of these cabinets (4 PA165's and 2 tweeters total) for guitar amp duty. They sound awesome with a digital piano too.
I add a PA380 fed by a TI 300 watt class D chip in a 4 cubic foot box when I need to go to 40 Hz for PA, bass guitar or EDM synthesizer.
https://www.parts-express.com/dayton-audio-pa165-8-6-pa-driver-speaker--295-015
https://www.parts-express.com/dayton-audio-pa380-8-15-pro-woofer--295-034
I add a PA380 fed by a TI 300 watt class D chip in a 4 cubic foot box when I need to go to 40 Hz for PA, bass guitar or EDM synthesizer.
https://www.parts-express.com/dayton-audio-pa165-8-6-pa-driver-speaker--295-015
https://www.parts-express.com/dayton-audio-pa380-8-15-pro-woofer--295-034
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