Bridging tube amp combo with Solid state power amp

[GERPUD]

Hi,

I'm trying to get more power from a 9W SE tube amp.
I was thinking that I could achieve that by bridging the 9W amp with a solid state power amp.
The signal of the SS amp would come from the speaker signal of the tube amp using a high resistance trip pot the lower the voltage without draining power from the tube amp. The signal would go through an inverting opamp and then through a LM3866 amplifier kit.
See the diagram.

Would that set up work?

Thank!

[GERPUD]

I forgot the schematic...

[JMFahey]

First of all, congratulations on a new idea.
Lateral thinking at its best.

The idea is perfect in theory, but in this particular case, there's one practical problem.

When you bridge amps, you get twice the voltage on the speaker, and twice the current, so 4 times as much power. Good.

That works well with SS amps wich can supply lots of current.

Now Tubes are current limited, so that also limits available power.

What you are doing, by bridging, is accurately copying signal voltage fed to thye speaker , injecting that into an SS amp (the "other half") and feeding that to a speaker (in this case, the other speaker lug).

You might go all the way and plain drive the original speaker with the 9W`tube amp, tap and pad some of the signal present at speaker terminals and use that to drive a plain SS amp which drives other speaker(s).
These speakers will receive the exact same waveform delivered by the tube amp into a speaker and sound exactly the same, only louder.

After all the speaker does not know what kind of amp is driving it, will simply react to voltage applied to its terminals.

[GERPUD]

Maybe I'm wrong, but when "bridging" you don't need the same power on both amp, because they are out of phase and connected to different speaker terminal. The two amps increase voltage differential across the speaker, and they each provide the current they are able to feed.
What you propose is parallel amplifiers, that would need to be the exact same power to be able to be on the same speaker. The signal do not have to be out of phase in this configuration.
The goal of this mod is to make a little combo amp power enough to play with a drum AND stay little and lightweight, while getting the same (hopefully) the same tube sound. Adding speakers is not "lightweight"!

[Leo_Gnardo]

A little reading on "bridging" amps promises amazing and incredible results, which in real life are generally not achieved.

In all the time I've been involved in big PA since mid 70's, I AVOID bridging amps unless set up for fail-safe operation*. Those ARE big solid state power amps and require near-as-possible identical operation of both amps involved in the bridge, both amps located in the same chassis (commonly called a "stereo" power amp regardless of how it is used). I would not attempt bridging in any other way.

When in "bridge" mode you're no longer using ground as a reference point and handy source of gazillions of electrons. Instead you have a hi-current "tennis game" where all the current supplied by one amp is sent thru speakers, and that same current must be "sinked" by its bridging mate. Then vice versa on the other swing of the signal. See why they have to be identical? The amps also have to be amenable to accepting lots of current arriving at their output terminals when they're on the "sink" half of the cycle, by far not all amps can do this.

What you are proposing is a sort of half ass bridge, with dissimilar amps (!?!), lotta work to gain just a couple of watts. Plus a very good possibility of wrecking your amps. You'd be much better off reaching for your wattage requirements in a more conventional way, whether you choose tube or solid state. One way (as Juan proposed) is to drive a resistor load with your tube gem, run a voltage divider from the speaker output to the input of any competent big-watt power amp then you can dial up lots more volume while still retaining the sonic character of your favorite little tube amp.

- - - - - -

Fail-safe, as in wired like Clair Bros racks. Multi-pin inputs and outputs, no fiddle faddle with "which amp's the lo, mid, hi" and "which wire goes to which speaker." There's no time for guesswork, also no room for error at multimillion $$$$ concerts. Me, I prefer to have no technical problems even at low-budget shows.

[GERPUD]

Thanks for the answer.
I had the feeling tha it was not possible, but without your answer, in the doubt, i'd try it and fail.
You are saving me a lot of time.
I'm still trying to figure out how this 'tone enhancer' is working....
http://hoelectronics.com/wordpress/138-2/
It is becomming an obssession....

Mr Ho told me that there were no dummy load and at minimum level you still get 25% of the amp. So i though that 'bridging' was part of the answer...
Any clue how i could achieve that tone enhancer?

[Leo_Gnardo]

I'm still trying to figure out how this 'tone enhancer' is working....
http://hoelectronics.com/wordpress/138-2/
It is becomming an obssession....

Mr Ho told me that there were no dummy load and at minimum level you still get 25% of the amp. So i though that 'bridging' was part of the answer...
Any clue how i could achieve that tone enhancer?

14 HO website views so far, including you and me.

I would call it a volume enhancer, presumably your "tone" is carried through. Hey with a little more volume it sounds better, I guess.

Having a blink at the inside photo, simple as could be, a basic bipolar power supply, pair of output transistors & 5W "ant coffin" resistors, and what appears to be another transformer for audio. I can only guess that this is something along the lines of "booster amps" of the 1930's onwards. Some big theatre amps (RCA, Altec) rated @ 300 watts, had practically no "front end", because you needed about a 40W amp to drive the input. Such was the technology of the time. Ho's amp boosts your 50W to a 100W, he claims, not really all that much when you come down to it, barely perceptibly louder. For all that, Mr. Ho can keep his "secrets".

Try the method Juan & I suggested. The sky is the limit, you can distribute to as many power amps & speakers as you like. Here's a photo of a stage where the technique is in full bloom. Each column of speakers handles one instrument, lead guitar, rhythm guitar, bass, piano, drums. Takes the heat off the PA system which in this case just handles vocals - that's the semi-cylindrical array hanging over center stage.

[GERPUD]

I know that JMFashey will work very well, but i'm looking something that i can add in the small cabinet so i get more power with the same good sound.
Your picture is impressive! It is not exactly a lightweight set up!

http://www.tubecad.com/2014/02/blog0280.htm

I found that site that explain how to boost a subwoofer from a lm3886 (like i was planning!).
The solid state seems to add the signal to the same line than the primary amplifier. Definately not a bridged amplifiers. More like i'd like to do.

Very interesting...

[GERPUD]

See the schematic
The opamp is a lm3886.

Would it work? (It is more likely to work since it is not my design....)

[cbass]

I'm still trying to figure out how this 'tone enhancer' is working....
http://hoelectronics.com/wordpress/138-2/
It is becomming an obssession....

Mr Ho told me that there were no dummy load and at minimum level you still get 25% of the amp. So i though that 'bridging' was part of the answer...
Any clue how i could achieve that tone enhancer?

14 HO website views so far, including you and me.

I would call it a volume enhancer, presumably your "tone" is carried through. Hey with a little more volume it sounds better, I guess.

Having a blink at the inside photo, simple as could be, a basic bipolar power supply, pair of output transistors & 5W "ant coffin" resistors, and what appears to be another transformer for audio. I can only guess that this is something along the lines of "booster amps" of the 1930's onwards. Some big theatre amps (RCA, Altec) rated @ 300 watts, had practically no "front end", because you needed about a 40W amp to drive the input. Such was the technology of the time. Ho's amp boosts your 50W to a 100W, he claims, not really all that much when you come down to it, barely perceptibly louder. For all that, Mr. Ho can keep his "secrets".

Try the method Juan & I suggested. The sky is the limit, you can distribute to as many power amps & speakers as you like. Here's a photo of a stage where the technique is in full bloom. Each column of speakers handles one instrument, lead guitar, rhythm guitar, bass, piano, drums. Takes the heat off the PA system which in this case just handles vocals - that's the semi-cylindrical array hanging over center stage.

Hmm that rig looks kinda familiar

[ubxf]

may be something like this would work
http://www.badcatamps.com/unleash.html

[GERPUD]

I saw the badcar unleach.
What it does, it attenuates all the output with a dummy load and then reaplify everything with a class d. I don't like the idea. Not best for the tone.

I simply want to add power to the existing amp.
I think i found the answer:
http://www.tubecad.com/2014/03/blog0283.htm

Very very interesting!

[10thTx]

I used a very inexpensive 8 ohm 100w resistor from Parts Express and then a Huges & Kettner Red Box with a 7 watt push/pull amp.

http://www.parts-express.com/8-ohm-100w ... r--019-020

Works great! With the Red Box, you can plug an XLR into a PA system or a solid state power amp that accepts an XLR.

http://hughes-and-kettner.com/products/redbox-5/

It has worked without any problems for almost 2 yrs.

with respect, 10thtx

[JMFahey]

I know that JMFahey will work very well, but i'm looking something that i can add in the small cabinet so i get more power with the same good sound.

http://www.tubecad.com/2014/02/blog0280.htm

I found that site that explain how to boost a subwoofer from a lm3886 (like i was planning!).
The solid state seems to add the signal to the same line than the primary amplifier. Definately not a bridged amplifiers. More like i'd like to do.

Very interesting...

I see where you're coming from.
You are adding SS power ; whether it's Class AB or D (digital) it's irrelevant, it's still SS.
You can't like one and diss the other, because they are functionally the same.

That said, SS can faithfully reproduce Tube sound, to be more precise waveforms, just take care not to overdrive it

Easy to do if you have more power (say 2X) than what you'll actually use.

That's why the suggestion of using a 50W amp to actually drive it to 15/20/25W .

If you do not clip it and drive it with a tube amp produced waveform, it will faithfully reproduce it, only at higher level.
Sound will be the same, it will not be "bad for the tone"

I'm still trying to figure out how this 'tone enhancer' is working....
http://hoelectronics.com/wordpress/138-2/
It is becomming an obssession....

I think I know how it works.

In one of the woofer booster examples you show an original amp driving it through a 0.1 ohms resistor, and a ""parallel follower" providing same voltage but extra current.
Very popular now , usually paralleling chipamps for greater power.

Only problem is, you get more current available but still same voltage, so only way to get more power is to drive a lower impedance load, such as more speakers (what you want to avoid )

I guess (but I'm usually quite accurate) that Ho uses a 1:2 step up input transformer, so he gets 2X voltage, 4X power ... only problem is he will also need 2X current at 2X impedance or 4X current at same impedance.
The power transistors will provide 75% of that, and the original amp its original current ... 25% of the "new, improved" one.
What Ho claims, by the way

Only practical problem is weird up/down impedance shifting ... taken care of by large input and output transformers.
Brilliant

Back to your proble, since you want to keep weight down, please:
1) show your current SE 9W amp.
Is it a combo? .... Head and cabinet?
2) what speaker are you currently using with it?

Might suggest a solution same sounding and much lighter than Ho's

[GERPUD]

Your explanation makes a lot of sense! I think you got it!

I have a fender Ramparte Combo 9W 2x12ax7 + 1x6L6GC (soon modified to be KT66). The OT has no specs on it. It says only Japan and a number that Google cannot find. The dimensions are matching perfectly Weber W022913.
I've changed the speaker to a Eminence V128 (120W RMS, 8ohm).

I'm very curious to know what would be your solution!!!

My obsession with that pushed me to do more researches. I'v found that Tubecad has discussed about that in several blogs. He presented so many different solutions. One of them can have endless gain, the power of the amp is "reused", there is no problems with impedance matching, and the "stock" OT can be used (some solution need 16 ohm OT). The circuit is using a simple LM4780.
http://www.tubecad.com/2013/04/blog0261.htm
However, he doesn't give enough explanation and details for me to be able to build it.
Anyone as done it? Any better solutions?

Thanks!!!