engel dela pena said:
Look at the preamp portion of this project, pcb is available.
http://sound.westhost.com/project27.htm
Re: Re: pre amp for gain clone as guitar amp
The above looks exactly like one channel of a Fender Bassman 5f6a but built with op amps rather then 12AX7 tubes. Basically it is just two gain stages with a tone stack between. You might conceder actually using real tubes. They clip naturally without need of that diode network. The above circuit uses a dual p amp and the "AX" tube has two triodes in one package, R and C values in the tone stack are close, bright switch works the same way.... Funny how little has changed in 50 years. (I think the 5f6a is about 50 years old.)
My son is high school age and does not remember the tube era. I took him to the music store just the other day we demoed a small Fender tube amp, the "Champ" with a Strat. After only two or three chords he heard the difference. The tone is much different.
Tube PRE-amps un-like power amps are easy to build because there is no expensive output transformers and the HT power supply can be vary small. 100 mA is very large for a preamp PS.
kscharf said:
The above looks exactly like one channel of a Fender Bassman 5f6a but built with op amps rather then 12AX7 tubes. Basically it is just two gain stages with a tone stack between. You might conceder actually using real tubes. They clip naturally without need of that diode network. The above circuit uses a dual p amp and the "AX" tube has two triodes in one package, R and C values in the tone stack are close, bright switch works the same way.... Funny how little has changed in 50 years. (I think the 5f6a is about 50 years old.)
My son is high school age and does not remember the tube era. I took him to the music store just the other day we demoed a small Fender tube amp, the "Champ" with a Strat. After only two or three chords he heard the difference. The tone is much different.
Tube PRE-amps un-like power amps are easy to build because there is no expensive output transformers and the HT power supply can be vary small. 100 mA is very large for a preamp PS.
you could try the marshall lead 12 layout - http://www.drtube.com/schematics/marshall/3005.gif
no clipping diodes in the preamp
no clipping diodes in the preamp
Re: Re: Re: pre amp for gain clone as guitar amp
I guess using tubes in the low level stages is one way to get the "tube sound" cheaply, though I would think that it was the power stages clipping that actually generated the "crunch" that make tube amps what they are.
A pair of 6L6's (or maybe a quad of them in PP-P) would be about equal in power to a single LM3886 output stage. The cost (tubes, output and power tranny's) will be several orders of magnitude greater though. OTOH, two or three 12AX7's in the preamp would only cost two or three times the price of the op-amp version. (Less if you don't pay for audiophool priced tubes).
ChrisA said:
I guess using tubes in the low level stages is one way to get the "tube sound" cheaply, though I would think that it was the power stages clipping that actually generated the "crunch" that make tube amps what they are.
A pair of 6L6's (or maybe a quad of them in PP-P) would be about equal in power to a single LM3886 output stage. The cost (tubes, output and power tranny's) will be several orders of magnitude greater though. OTOH, two or three 12AX7's in the preamp would only cost two or three times the price of the op-amp version. (Less if you don't pay for audiophool priced tubes).
Re: Re: Re: Re: pre amp for gain clone as guitar amp
It depends on what part of "the sound". Tube amps even when run clean, sound like tubes. If you were a jazz guitarist playing a electro-acustic you'd still be wanting a tube amp, one with a really clean and bright sound.
I think most of that sound is in the preamp. And the rest is in the speaker. Ecept for the case of way-loud bands who over drive their power amps
When overdriven the over drive can happen in the power or the preamp stage. I'd prefer a system that over drives in the pre stage just so that you can run it at lower volume. Many of the old amps would only over drive if you turned the volume up to 8 to 9. But that is not so good for practicing at home late at night.
Many classic recording where made in the studio using a 5 to 18W tube amp with a mic on the speaker cab. Or some times even inside the cab.
You can't compare "power" between tubes and SS by using watts. A 60W tube amp driving a 4x12 cab is concert level loud where as a 60W SS amp is a little weak. The reason is that you simply can't run SS amps to 120%. Because clipping a SS power amp will blow a speaker.
You are correct about cost. Tube power amps are very expensive but tube preamp is not.
Back on-topic: You asked what was "best". Not cheapest or easiest to build so I thought "a Fender Bassman-style front end done with tubes" But op amps save you money and bulk.
kscharf said:
It depends on what part of "the sound". Tube amps even when run clean, sound like tubes. If you were a jazz guitarist playing a electro-acustic you'd still be wanting a tube amp, one with a really clean and bright sound.
I think most of that sound is in the preamp. And the rest is in the speaker. Ecept for the case of way-loud bands who over drive their power amps
When overdriven the over drive can happen in the power or the preamp stage. I'd prefer a system that over drives in the pre stage just so that you can run it at lower volume. Many of the old amps would only over drive if you turned the volume up to 8 to 9. But that is not so good for practicing at home late at night.
Many classic recording where made in the studio using a 5 to 18W tube amp with a mic on the speaker cab. Or some times even inside the cab.
You can't compare "power" between tubes and SS by using watts. A 60W tube amp driving a 4x12 cab is concert level loud where as a 60W SS amp is a little weak. The reason is that you simply can't run SS amps to 120%. Because clipping a SS power amp will blow a speaker.
You are correct about cost. Tube power amps are very expensive but tube preamp is not.
Back on-topic: You asked what was "best". Not cheapest or easiest to build so I thought "a Fender Bassman-style front end done with tubes" But op amps save you money and bulk.
I am just finnishing building a guitar amp useing a different Power amp IC ( A Bridged 140W TDA7293) ....
This is the Preamp Design I am useing , I just cobbled it together from other curcuits but is simular to a design I have used before ...
It has a Very heavy nice squealy metal tone with the Gain Cranked and does a nice cleaner bluesy tone with the Gain lower and the Tone controll has a lot of Control and versitility.....
For a Power supply I use a 12v ac Transformer for the Heaters and run a Voltage doubler to get +/-15v for the Opamps and power the Plate off of the Positive Rail of the Chipamp PSU ......
Cheers
Sorry the Schematic is pretty crappy quality , I had to resize it to post it ....
This is the Preamp Design I am useing , I just cobbled it together from other curcuits but is simular to a design I have used before ...
It has a Very heavy nice squealy metal tone with the Gain Cranked and does a nice cleaner bluesy tone with the Gain lower and the Tone controll has a lot of Control and versitility.....
For a Power supply I use a 12v ac Transformer for the Heaters and run a Voltage doubler to get +/-15v for the Opamps and power the Plate off of the Positive Rail of the Chipamp PSU ......
Cheers
Sorry the Schematic is pretty crappy quality , I had to resize it to post it ....
Re: Re: Re: Re: Re: pre amp for gain clone as guitar amp
That's probably why the amps have two or three gain controls. The final gain control is just before the power amp and sets the actual volume. The first gain control if cranked up all the way will drive the final stage of the preamp into clipping, yet you can turn down the gain to the power amp to limit the volume.
ChrisA said:
That's probably why the amps have two or three gain controls. The final gain control is just before the power amp and sets the actual volume. The first gain control if cranked up all the way will drive the final stage of the preamp into clipping, yet you can turn down the gain to the power amp to limit the volume.
Another good preamp route is something like a two channel type: Rocktron Gainiac/Silver Dragon or the newer Seymour Duncan line. Perhaps run a good compressor for the clean channel and A/B.
If your already running power for your chip amp that's a great way to power the tubes enough to get some colour. The above schematic is a beautiful approach.
Tube preamps rule for tone that you, the player, can connect with. Go this route if at all possible and ASAP!
If your already running power for your chip amp that's a great way to power the tubes enough to get some colour. The above schematic is a beautiful approach.
Tube preamps rule for tone that you, the player, can connect with. Go this route if at all possible and ASAP!
guitaristz said:
If you want to run a preamp tube off a small transformer, for $20.01 you can buy a "real" power transformer from Edcor that has enogh power for three preamp tubes and runs them at a real voltage (well over 200V DC) Or if $20 is to much find and old 500ma 12V power cube (wall wort) and salvage the transformer. Wire the 12V side to your 12V AC that is powering the tube heaters you will get 120V AC on the other side. Use a diode bridge and cap and the final DC voltage is about 140 at the tube plate. Cost for this can be nearly zero if you can salvage the parts of old PC power supplies and the like.
You will get the best tone by far if you go all tube. The power amp stage in a guitar amp really does add color to the sound. Using one tube in the preampis not the same.
Look up "firefly" or "high octane" at the ax84.com web site. You can build one of those all tube amps for about $250.
That Edcor company looks great. I see the preamp transformer here:http://www.edcorusa.com/Products/ShowProduct.aspx?ID=598
Still, what would be REALLY nice is that is a toroid form—like the one used in a Lee Jackson Prefect Connection preamp.
Even better would be added dual 25Vac as well for our chip.
So something like:
175-0-175) at 60mA
and
6.3V (3.15-0-3.15) at 2A
and
18V+18V at 250VA
With all the amp modellers out there this could yield something quite useful
ChrisA~ good point, still I've fine tuned/revoiced a few guitar amps via the preamp out and headphones and got some really nice tones
Still, what would be REALLY nice is that is a toroid form—like the one used in a Lee Jackson Prefect Connection preamp.
Even better would be added dual 25Vac as well for our chip.
So something like:
175-0-175) at 60mA
and
6.3V (3.15-0-3.15) at 2A
and
18V+18V at 250VA
With all the amp modellers out there this could yield something quite useful
ChrisA~ good point, still I've fine tuned/revoiced a few guitar amps via the preamp out and headphones and got some really nice tones
guitaristz said:
Edcor will make custom transformers for not much more than the price of their stock units. Call them. All you are asking for is a one more secondary winding on top of a stock unit.
one other option is to make a voltage tippler with some caps and diodes from the 6.3 secondary. You don't need all of those amps. The preamp tubes use only 0.3 amps each of the 6.3V so there is plenty of current to support a voltage tippler.
And about the sound coming from the preamp vs. the power section. I think the real answer is that it's additive. And it continues with the speaker too. Some of that distortion you hear at high volume is the speaker cone breaking up and no longer acting as a solid, mass but something more flexible
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