Frog Tube Preamp Inspired by Alembic F2b

[mark.price]

Wouldn't it be nice to have a Fender Dual Showman amp with a low wattage output for bedroom/practice? It is coming closer to a possibility with my latest prototype PCB (see attached picture) I have sent out to fabrication. You can front end this 1 watt (approximate) output section PCB (I am calling the Bigmouth) with a Frog Tube Preamp PCB. You can use the B+ (high voltage) from the Frog Tube Preamp PCB and run the Frog Bigmouth output section PCB. I have kept a 6volt regulator onboard for the heater. This is more than theory, but I haven't tested this implementation yet until I get the prototype PCB back from fabrication. It is a hugely simple PCB to populate and quite compact in size, about 1.1 inches by 2.25 inches. It still has the option of using a standard 9 pin 12AU7, or Russian 6n1P with a heater switch or the Russian submini tube 6n16b. The 6n16 solderable socket has been "MillMaxed". Since this is an output push-pull configuration, you should only use the tubes mentioned above. Let me know what you think and if you have any questions. Thanks! http://frogpedals.com

[rbstep]

I think you are going to need an output circuit or transformer for speaker output..

[mark.price]

Thanks for the question. It is a good one. This is a push pull output circuit. The connector solder pads on the bottom left is where a output transformer would be connected as well as your B+ High voltage. It is a screw terminal connector. The output transformer I have used for this type of application is a 22k5 x 4,8 ohm 2VA output transformer. This is a link for the item I used from Musical Power Supplies in Missouri, USA. http://www.musicalpowersupplies.com/app ... WG_STD.pdf He actually made one specially for me as flat a possible with no outer shell with the same specifications at only 8 ohms output only. See picture below. The transformer is about 1.6 inches thick x 2 inches. I would like to install it inside a 2 inch deep enclosure. When I get the prototype Bigmouth PCB back, I will populate the board so all can see what it looks like and how it operates.

[rbstep]

Sounds great..

[mark.price]

With quite a few PCBs for the Frog Tube Preamp out across the world, has anyone begun their build? If so, how is it going? Have you had any issues, or suggestions (be nice!)?. I know, though how getting time is hard, I want to do more myself but will be hit or miss until Winter! I can't wait to see some build reports with pictures. I will start posting some information about my other projects on the http://frogpedals.com web site with a "coming soon" note. The list grows:
1. Frog Tube Preamp PCB without power supply - to be tested
2. separate SMPS (same as on the original 2.0 PCB) with same capabilities. It can be used for things other than a preamp like a Magic Eye, Nixie power supply, other small tube projects, etc... - tested, need to order for sale!
3. Frog Classic power supply for compact, but classic transformer/rectifier/cap/resistor/cap layout. It can run the Tube Preamp PCBs too. - to be tested
4. Frog Big Mouth 1 watt (approximate) tube output section. Can be used as an add-on to the Frog Tube Preamp PCBs. Run high voltage off of 2.0 version of tube preamp PCB, SMPS or Classic supply. - to be tested
5. Frog Jfet preamp 2.0 - based on Tillman J201 preamp - with mods - to be tested
6. Frog Stomp Bypass board 1.0. A stomp switch bypass board, has pads for 2 LEDs. I like to run one LED for stomp indicator and one for a light plate. So one can to point up and the other down. Will give you the true bypass capability. See attached picture - to be tested

[rbstep]

Just started populating my board. Love this project and thanks for sharing it.

[rbstep]

Forrest Cook designed a tube push-pull distortion circuit called "The Fuzznikator" that the Big Mouth is ideal for building. See that project at www.solorb.com/elect

[mark.price]

I have never seen anything like that. Would be an interesting experiment. The layout of the push pull would be a bit different.

[mark.price]

I received the new Frog Tube Preamp PCB 2.1 (no power supply) last week and am testing it now. It is the purple board in the pictures. It is a second channel and all the power is pulled off of the primary channel Frog Tube Preamp 2.0 (with power supply). So far it is working perfectly. I am going to continue burning it in. This configuration gives you the opportunity to have 2 channels like the Alembic F2b preamp without having to populate two boards with separate power supplies (which you still could do). All that would be needed to have the same configuration as the Alembic F2b is add a mixing 1/4 inch output jack. If you did that, then you could have two channels in and mono channel out. You could still use it as a "stereo" or dual channel instrument preamp. I need to find a drawing that shows how that "mixing" jack is configured. So, in a nutshell, the Frog Tube preamp PCB 2.1 (no power supply) could be used in the following manner (as far as my brain can grasp now):
1. Single preamp (would need the SMPS power supply) maybe smaller footprint than 2.0 with power supply
2. Multiple single preamps (would need adequate power supply depending on how many channels)
3. Add on channel to Frog Tube preamp 2.0 with power supply (as in attached pictures)
4. Preamp section to frontend the Frog Bigmouth output section (to be discussed in a later post) - Would need a power supply because the Frog Tube Preamp 2.1 and the Frog Bigmouth output section don't have a built in power supply (again, the stand alone SMPS power supply or the Frog Classic power supply would be used)
5. This preamp could be added into an existing tube amplifier as an extra preamp stage using the high voltage and low voltage (heater supply 6.3v) available within that amplifier. This would take a skilled Tube Amp technician
6. Preamp section to frontend a Hybrid amplifier with a solid state output section. Advantage? Power amp could be any size you want it to be and still have the guitar ----> tube preamp advantages. Also, no output transformer required!
http://frogpedals.com

[rbstep]

Keep the goodness coming. I was starting a 2 channel tube preamp build when you posted The Frog. Same circuit. Thank you..

[mark.price]

Keep the goodness coming. I was starting a 2 channel tube preamp build when you posted The Frog. Same circuit. Thank you..

Are you using the Frog Tube Preamp PCB or your own circuit? If you are using off-board pots, I may be able to help you out on the second channel.

Mark

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I will begin testing the prototype Frog Bigmouth 1 watt output section this weekend. I have the board populated, but not wired up to signal and power yet. It is a very simple board to populate with not too many components. I am very excited about this companion board to the Frog Tube Preamp PCBs. I will follow-up with some pictures from this weekends testing.

[rbstep]

I am using the Frog with off board pots for my pedal build and 2 channel preamp.

[theehman]

When will the expansion pcbs be available again?

[mark.price]

I have tested the PCB and am satisfied it works. I need to move the pots a bit before I can send to production. I can't set a date, but I believe I can get the add-on preamp channel to fabrication with the next week and it can take 2 to 3 weeks for fabrication, so probably early October. That is the reality of it.

[mark.price]

I was able to get the potentiometers moved on the add-on Frog Tube Preamp 2.1 (no power supply) to reflect the positioning of the original Frog Tube Preamp 2.0 with power supply. I felt it was important if you wanted to use the on-board pot arrangement and especially if you wanted to mount this in a 19 inch rack enclosure like the original Alembic F2b. I also added a few more test and connection pads for 6 volt heater supply and B+ high voltage supply. I was working on it late last night, so I will look it over tonight again and if everything looks good, I will get an order started this weekend for a quantity of this board for sale. I am re-thinking the cost but it will go for 8 dollars for at least the first 30 days of sale. I am assuming that it will be ready for sale by the first week of October. I'll keep you posted on progress.

In other news, I am testing the Frog Bigmouth tube output section prototype now (pictured below). I have some tweaking to do on the configuration, but it is working so far with my Frog Tube Preamp 2.0, just not the way I want it to yet!

I need suggestions about how to name the Frog Tube Preamp 2.1 because I am afraid the numbering will confuse people. Maybe just the Frog Tube Preamp 2nd Channel? Thoughts please, because 2.1 sounds like it is newer or better than the 2.0, but it isn't a replacement for the 2.0, just an additional channel.

http://frogpedals.com

[mark.price]

I have ordered the Frog Tube Preamp 2.1 with no power supply. It is the add-on preamp channel I have been testing. It will be black with white screen printing (the frog skeleton will look great!) and 2 ounce copper with Gold solder pads. Its going to look great! I still don't know yet what the delivery date will be. We are still in the process of setting up the fabrication. I am excited about this, because it is another addition to what is turning out to be a very high quality, really fun, and flexible tube preamp suite of products for the DIY world.

I am still working on the testing for the Frog Bigmouth 1-2 watt output section that you can add on to a Frog Tube Preamp and have you a little recording/bedroom amp with the front end of a Fender Dual Showman/Alembic F2b. That will be fun too. The thing I am having to work on is getting the power supply verses output balanced out.

[mark.price]

More news from the Frog pond... As I indicated earlier, the Frog Tube Preamp 2.1 add-on board is entering fabrication and it looks like a late September or early October arrival. I can't wait to see that black board with gold pads (with my frog skeleton logo)!

Below you will see a picture of the Frog Bigmouth output board with a 12bh7a tube in place running at about 1.2 watts. I am wanting to push it to about 1.5 watts which is well within the capabilities of any of the tubes I have mentioned. If you aren't familiar with the 12bh7a, it is much like the 12au7, but can handle a bit more current/output power and it taller.

I have tested the Bigmouth with a Russian 6n1P-b tube also and it works great too. The 6n1P-b is a Russian tube that is a pin for pin functional equivalent (approximately) of the 12au7 but requires 6vdc on the heaters. I have a 12au7 that I will test it with tonight. This board has my signature 6/12 volt tube heater switching included like on all my boards so far.

I will probably configure a board with a Russian subminiature tube 6n16b soon, but need to order some more MillMax 8 pin sockets (yes I have MillMax'ed this submini tube solder socket). At the right of the picture, you can see I am using my prototype Frog Classic power supply for this test. I am going to move testing to the Frog SMPS power supply prototype this weekend.

I have it hooked up to a cruddy little PA speaker and it doesn't sound too bad. I will hook it to my Celestion speaker this weekend. I will take some more detailed pictures and maybe some video this weekend to show you it working. By the way, this thing can whisper, like you would need it to in a bedroom, but it can get loud, especially with the Frog Tube Preamp 2.0 running into it. I will also demonstrate some other capabilities you might not of thought of also. http://frogpedals.com

[mark.price]

I forgot to add: A big thanks to Dmitry Nizhegorodov who helped me troubleshoot the Bigmouth board based on his original schematic! His website is: http://www.dmitrynizh.com. He has some neat projects on his site and has been very gracious in helping me figure this thing out.

[mark.price]

Update on the Frog Bigmouth output section. It works good with the Frog "Classic" power supply (see earlier thread for info on this), but when I powered it from my Frog SMPS (which is the little 20ma, preamp/nixie/magic eye type power supply), it couldn't keep up with the Bigmouth. In its current configuration, the Bigmouth draws a little too much power for the SMPS, so I still have some tuning to do.

It may end up that there will be a configuration of the Bigmouth for the little SMPS type supply, and a configuration for the "Classic" power supply. With the "Classic" power supply, that is about 3.9 inches by 2.1 inches, when finally tuned, I should get close to 1.5 watts output, with the SMPS, maybe .75 to .8 watts.

So, I am still working on tuning the configuration of it, it does work and I just need to make sure that it can be practically applied. Lets see how much progress I can make in the next week.''

In other news.....The second version of my stompswitch true bypass PCB came back and it looks good with the bigger pads and different switch solder lugs hole configuration. I will order some of these for sale soon. It would be a good add-on to an order of a preamp or other board. Any votes on what color I should order this in? Unfortunately can't order production quantities in purple, but I was thinking black. I could order in multiple colors though....

Thanks for tuning in! http://frogpedals.com