Advise Please Dear Tube Gurus

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Dear Tube Gurus in this thread,

I have little experience with tube amps, but have a good understanding of general principles, and am all ears! I also have a fine ear and appreciate quality. I used to have a wonderful Heathkit tube amp that had a lovely warm sound on my full range quarter waves I made, but those got lost in a move ;-(

Please help me with a new project.

How it all started...
I have been experimenting with DML louspeakers of late and just love them. I started with Pink Pather Foamies, but rapidly graduated to warm guitar tonewood panels that round off that annoying edgy harshness of extruded EPS.

Now I read that DMLs are great for avoiding feedback, making them great for sound reinforcement. Techtonic Audio Labs who acquired the patents from NXT... So, curious, I tested mine with my Takamine N-10 with my sensitive Fishman neodymium pickup and my DMLs. Nothing, no feedback, not even with the amp cranked way up. Sooo koool.

So, here is my project:
A stereo acoustic guitar tube amp in a DML briefcase format.

Not knowing much about tube amps, I bought some inexpensive ones to test, a stereo preamp (6J1) that I want to stack L+R for gain and overdrive (mono), and a 3+3W power amp (6P1, stereo).

My proposed circuit diagram is here:
Dropbox - AcousticGuitarAmp.png

The preamp is a 6J1 type. No questions here, simple 12 VAC supply. Now, perhaps this preamp was not a good choice (perhaps even EQ'd for a phono pickup, oops!), most guitar amps use 12AX7s tubes, whatever... any ideas or suggestions on this appreciated?). The preamp is here (got it on sale):
aassembled ac 12v 1a 6j1 preamp tube preamp amplifier board preamplifier module pre-amp headphone bile buffer stereo bass hifi x10-d Sale - Banggood.com

The question I have regard mostly the proper hookup of the the power amp, the classic 6P1 JCDQ-11
Many input voltages (0-230-230 and 6.3V), what appears to be options (diodes, a coil,..??) . Transformers (input and output) are mostly my issue.
Dropbox - JCDQ-11-6P1TubeAmp.png - Simplify your life
The power amp is to be found here (got it on sale):
jcdq11 tube amplifier 6n1+6p1 valve stereo amplifier board filament ac power supply + 3pcs tubes Sale - Banggood.com

Please advise. All comments, feedback, suggestions and warnings will be taken most seriously and they will be greatly appreciated. Many thanks in advance. Will share the results on INSTRUCTABLES if good.

Any hints where to get cheap reliable components will also be greatly appreciated. Such transformers appear to be quite specialized. Many thanks in advance,

Paul.
Quebec City, Canada.
 
Paul Isabelle;5768812 [I said:
Please advise[/I]. All comments, feedback, suggestions and warnings will be taken most seriously ..
a) do your homework. You've already demonstrated that you don't know what you want or how to build it but you're dogmatic about what it should be built from. Oh, and that we're all going to be instafamous as well.

b) Calm down and build an existing, known good design. Preferably a modern incarnation of a classic circuit so that the safety issues (e.g. death caps) have been dealt with. Or at least map the circuit you have onto a working, safe design and build.

c) provide some detail on how your speakers differ from normal speakers (it's your project not our project) and what sort of sound you're after (you've mentioned Acoustic, which means you've got half a chance for project #1 )

Homework reading starts with Rob Robinette.
and the $100 amp challenge thread.
 
Member
Joined 2004
Paid Member
Dear Tube Gurus in this thread,



My proposed circuit diagram is here:
Dropbox - AcousticGuitarAmp.png


The question I have regard mostly the proper hookup of the the power amp, the classic 6P1 JCDQ-11
Many input voltages (0-230-230 and 6.3V), what appears to be options (diodes, a coil,..??) . Transformers (input and output) are mostly my issue.
Dropbox - JCDQ-11-6P1TubeAmp.png - Simplify your life
The power amp is to be found here (got it on sale):
jcdq11 tube amplifier 6n1+6p1 valve stereo amplifier board filament ac power supply + 3pcs tubes Sale - Banggood.com

[


Paul, good luck with your project. You will learn a lot while doing it.

I am not a guitar man, so I don’t know the merit of the amps you bought, but I can provide a few comment which hopefully will be helpful:

1. Your proposal to use a stereo preamp and run the mono guitar signal through it in series seems doubtful to me. It may completely overload the second input, especially since the preamp has (presumable) a standard stereo volume control. I hope guitar amp experts will provide definitive answers.

2. The stereo power amp - you are using it to amplify two mono signals feeding two loudspeakers, right? Why two loudspeakers? Will 3 watts per speaker be enough? Mr. Thoglette requested more info on your speakers which will help answer the question if 3watt are enough.

3. The power amp link on Banggood.com, if you pick the “read more information” button, shows the schematic, which tells clearly how to hook up the transformer and choke. If the schematic does NOT help you, you need to do the homework as Thoglette suggested, before building anything. There is also a photo that shows how to hook up the PCB; note that while only one line is drawn there are actually two wires going to each tube’s 6.3 Vac heaters.

4. The power transf. needed is a 230v-0-230v center tapped transormer, which needs only two diodes for a fulwave rectification. (4 diode bridge needed for a 230v transf. without center tap). Antek Inc has a transformer that is perfect and costs around $35. See: AS-1T230 - 100VA 230V Transformer - AnTek Products Corp This is a 100VA transformer that you could reuse when you build you next push-pull EL84/6v6 amplifier :D and also provides two heater windings with enough current for the future.

5. I don’t know what impedance your output tubes like to see, or whether your speaker is 8or 4 ohm , so hopefully Banggood provided this information somewhere. You will probably find a reasonably price and suitable transformer at Edcor, like this one at under $22 each. EDCOR - XSE10-8K Edcor also makes chokes.
 
Thank you for your answer thoglette,

Dogmatic I am not ;-). I have a vision of what I want, however, knowing how to get there is another thing ;-)

What I want simply does not exist, such existing designs do not exist. However, from what I suspect from tone of your comment, the tube amp portion of my project is perhaps a black art and the components I selected are not even appropriate. My mistake.

I am tinkering...learning...and fully aware that I may (probably will), hit the wall. But, you have to start somewhere... (should have started with my homework first I guess...)

Insulted? Nope. I am here to listen and learn. I appreciate your feedback and accept it with humility.

...Rob Robinette...and the 100$ amp challenge.
That is exactly what I needed. Thanks for the homework teach!

Cheers,
Paul.
 
Thanks Professor Thoglette! Great homework you gave me.
Rob Robinette has a fabulous website that walks us through. Perfect!

Thank you Francois! I did not see the "read more info" button or the link did not work.
Yes, of course, there are two 6.3V wires, I was just "pointing" to the area.
The output transformer info will be much useful. Thanks.

The power amp is stereo because most guitar reverb effects have stereo outputs. I find this stereo reverb most rich and interesting and it always irked me to plug it into a mono amp.

The preamp stages on most guitar amps I have seen appear to use the 12AX7 tube. There must be a reason for this. Perhaps the 6J1 will have too much gain and overload (maybe that could be cool ;-)

For sure, I will read up more about all this before proceeding with anything.

Paul.
 
The preamp stages on most guitar amps I have seen appear to use the 12AX7 tube. There must be a reason for this. Perhaps the 6J1 will have too much gain and overload (maybe that could be cool ;-)
The 12ax7 is the small block chev of guitar preamp tubes. Cheap and common from the 50's to today.

6J1 appears to be very similar to a 6AK5 also known as 5654 also known as EF95 (according to this and that). But the TDSL doesn't list them as direct substitutes.

Generally, pentodes as inputs in guitar amps are considered "challenging" due to microphonics and high gain (there's a recent thread here on this somewhere or see the Valve Wizard page).
 
I am guessing this schematic.


201508291822311521.jpg


And this.


5cd3ff69-de62-44c6-82b1-a6394927255c.jpg



I'll try pasting the dropbox link


An externally hosted image should be here but it was not working when we last tested it.



An externally hosted image should be here but it was not working when we last tested it.



A poster on tdpri.com used the same preamp board (more or less, there seems to be a few different ones with minor changes) and it sort of worked, do not recall the details but he was going into a SS power amp. You might want a master volume coming into the power amp and a two input hi/low jacks or a pad to reduce the input signal for a cleaner sound.
 
Last edited:
Sorry for this but so far "you do NOT have a tube guitar amplifier" but just "2 boards with sockets and tubes". :(

You still need (way more expensive than what you already bought)

* Power amp power transformer

* preamp power transformer

* two output thansformers

* one filter choke

And then you will have a "tube preamp" unsuitable for an Acoustic Guitar, 2 meager 3W (I suspect closer to 1 or 1.5W :rolleyes: ) amplifiers and then you will still need some kind of chassis and cabinet.

Almost forgot: 2 speakers and their enclosures.

Sorry for the example but you want to build a car and so far only have one rear wheel and the fuel tank.

Suggestion:

Tubes are not the best option, by far, for acoustic guitars, 99% out there are Solid State ... for a good reason: transparent, clean, powerful ... did I mention lighter and cheaper?
Just check Guitar Center, Musician´s Friend, Sweetwater, etc. and check what do they offer ... there´s a reason for that.
FWIW I do not know any Tube amplifier for Acoustic Guitar, go figure.

Try to get an SS Acoustic Guitar preamp instead, two SS power amplifiers, a couple 8" or 10" speakers plus a couple Tweeters, Piezo is fine and popular here and en up with a very useful and good sounding system.

If you want to keep it small and portable you may get amplifiers which can run from a 12V battery , and a couple 5" or 6" full range (for a Guitar that is) speakers by a recognized manufacturer, such as Jensen MOD 5 or the equivalent by Celestion, both around 20/25W RMS , their size allows them to supply excellent highs in this role.

The flat speakers are not new, they were invented by Argentine Engineer Jose Bertagni in 1970 :rolleyes: and distributed by Philips worldwide.

I guess the original patent run out so now NXP can make their version.
Pity they claim they invented them :confused:

PS: you are not experiencing feedback only because of the meager power output and probably low preamp gain ... wait until you rise level to compete with a drummer or amplified instruments :(

EDIT:
* thanks Printer 2 :)

* almost forgot: the 6J1 preamp does not even have volume or tone controls ; a pot at the very input jack does not qualify, you might as well control everything from Guitar´s own volume and tone controls. (hint: cheesy idea)
 
Last edited:
I have a cool briefcase I have waiting to make a little PA for a relative when he does little house concerts. I will have two woofers, mono though and fed by a 20W amp. The tweeters will be fed by their own amp, with an electronic crossover between them. A compressor might find it's way in there. A separate amp for his guitars mind you, that one I have partly built, delayed for life-gets-in-the-way reasons.


The boards you have could give you some kind of sound although an experienced person might be able to take the components and get more out of it. Mind you that would be for an electric guitar, for acoustic you may need a little more power. It all depends on what you will be doing with it. If it is to play at home and complement the sound of an acoustic then it might do. It might be better to identify what you want, maybe even look at manufactured equipment and say you want something equivalent to XXX. Then work your way backwards from the speakers, power amp, preamp. The ampunt of sound you want will dictate the speakers, the speakers the power amp, the preamp then into the power amp.
 
...DML louspeakers...Takamine N-10...Fishman pickup...
I don't know about acoustic-electric guitar, but I think using a DML for an electric guitar would be an interesting experiment. Traditional electric guitar speakers suffer from very poor treble dispersion, so if a DML can improve on that, it would be a worthwhile improvement.

Also guitar speaker cabs are pretty large, and if the entire front face was a DML, the panel should be big enough to work well.

I had that idea (e-guitar combo amp where the entire front face is a speaker) several years ago, but I was missing the crucial piece you contributed: using a distributed mode loudspeaker, rather than trying to make a rigid piston front panel light enough to work as a conventional speaker.

For your project, my suggestion is to break it down into smaller stages, and implement one stage at a time. For example, as step one, build the DML speaker, and mount it in the briefcase.

Step two can be driving the briefcase DML speaker using an existing guitar amp (even one borrowed from a friend.)

If the DML idea works out, then step three can be to use your own power amp, possibly a cheap solid-state class D module from Ebay or Amazon, using a guitar pedal (for example a clean boost pedal or graphic EQ pedal) as your guitar "preamp".

Finally, step four can be creating your own guitar preamp as well, finishing off the project.

IMO this sort of modular approach will give you a better chance of success, compared to trying out half a dozen new and untested ideas all at the same time.


-Gnobuddy
 
. Traditional electric guitar speakers suffer from very poor treble dispersion, so if a DML can improve on that, it would be a worthwhile improvement.
It'll be interesting for sure. My travel system has small NXT DMLs (great for carry on). They certainly behave differently to direct radiators, ribbons or electrostatics. They don't image.

Still better than listening to the laptop or most hotel TV speakers.

I'm getting the popcorn.....
 
Because it disappeared.

I wonder why :rolleyes:
Yes, that thought crossed my mind as well. :D A pair of 6V6 outut tubes is a very expensive, very heavy, very unreliable way to get just a few watts of acoustic guitar amplification.

But, trying to keep an open mind, I think there is some chance that the nonlinearity of a valve preamp might help to tame (compress) those harsh piezo transients that some acoustic-electric guitars put out, and which sound particularly nasty when turned up loud.

One of my Takamine guitars includes a 12AU7 in the onboard "Cool Tube" (TM) preamp. This particular guitar does in fact have very little piezo "quack" or harshness. Whether this is because of the 12AU7, or simply because of good piezo pickup design, I don't know.

Takamine designed both the Palathetic (TM) piezo pickup and the tube preamp. This piezo pickup is used in many Takamine guitars, but the tube preamp is only used in a few premium models. Of course Takamine claims that while the pickup is good, the Cool Tube preamp is the cherry on the cake, making it even better. Could be true, could be the usual advertising lies, I don't know.


-Gnobuddy
 
But, trying to keep an open mind, I think there is some chance that the nonlinearity of a valve preamp might help to tame (compress) those harsh piezo transients that some acoustic-electric guitars put out, and which sound particularly nasty when turned up loud.
At this point I, once again :), drag out Hamm, R.O. 1973 21(4) JAES "Tubes Versus Transistors-is there an Audible Difference" to remind us what most of the posters here have shown over and over again: it's a whole lot easier to build a preamp that overloads euphonically with a valve (or a FETzer) than an op-amp.

(Not that it stops us trying: right now I've a breadboard on the bench to try and improve on the Red LED pair for the Vox Pathfinder 15R )
 
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.