Bass PreAmp

[tubenit]

Anyone have any knowledge of building a bass preamp?   I have seen this:


Jule Monique All Tube Bass Preamplifier by Jake Wolf


From what I can gather, it has a tube rectifier, one 6SL7 and one 12AU7  and a Baxandall (maybe James?) tone stack?


I'm wondering if this is somewhat built (loosely) around the idea of a preamp of a Ampeg Heritage B-15 with a built in direct box?


Anyone have any schematics or personal experience building a tube bass preamp?


With respect, Tubenit

[kagliostro]

https://www.frontiernet.net/~jff/SonOfAlembic/SonOfAlembicF2B.html

https://www.thallenbeck.com/blog/posts/d-i-y-ampeg-b15n-fliptop-clone/




Franco

[tubeswell]

That Alembic preamp looks good but getting the Toroidal PT to fit in the 1U rack case without creating a short looks like a tight squeeze

[kagliostro]

Missing an adequate Antek AN-05T280 toroidal power transformer or similar spec, use an U2 Rack or higher

----

Antek AS-05T280 >>> https://www.antekinc.com/as-05t280-50va-280v-transformer/

http://www.frontiernet.net/~jff/SonOfSVPCL/DIYSVTBassPreamplifierPowerSupplies.html

Look also to this project

http://www.frontiernet.net/~jff/SonOfSVPCL/DIYSVTBassPreamplifier.html

Note This: http://www.frontiernet.net/~jff/SonOfSVPCL/DIYSVTBassPreampInductor.html

Also here you can find something interesting, look to the different arrangemet on channels Tone Control position

https://ctgelectronics.weebly.com/custom-amplifier---fcn-51-b.html

https://ctgelectronics.weebly.com/custom-amplifier---fcbn-51b.html

Franco

[tubenit]

This is all very helpful information!  Thank you for taking the time to share this all. 


With respect, Tubenit

[kagliostro]

Glad to know you appreciate It

Franco

[glass54]

Hi TubeNit;
Built a Bass Preamp for a friend (around 2004, on PCB with chassis mounted Tube Sockets) and it still is going strong 
Two Tx's used for compacted an availability issues in Aussie and used a DC supply for heaters.
I have attached the Sch and have Audio Precision FR responses, etc. You could easily change TCs to other topologies.
If you want, I could do a PM with more info.
Kind regards
Mirek

[Lekky]

I built a near-clone of Arkham's Oracle preamp a few years ago. There are many gut shots of the Arkham preamps around, so it was easy to figure out the Ampeg-inspired circuit. Schematic is attached.

EDIT: I added an output transformer and XLR output after the schematic was made.

[tubenit]

Mirek and Lekky,


This is fantastic information and also very helpful!  Thank you also!


I noticed you both chose to use 12v filaments instead of 6.3v?  Is there any reason that 6.3v filaments wouldn't work? Does it need 12v filaments .......... or is that something you choose because of the power transformers you used?


I'd likely use a Hammond PT with tube rectification and 6.3v winding.


With respect, Tubenit

[Lekky]

I used 12V heater voltage for simplicity, as I use a standard 12V switching wall wart which powers both the heater and the VPump converter. Tube pedal maker Sushi Box uses the same arrangement in his pedals.

I *could* wire the tube socket for 6.3V heater voltage, but that would require wasting power and generating heat through a regulator and/or dropping resistor. It's more practical to use 6.3V if the transformer has a 6.3V heater winding.

[tubenit]

Thanks Lekky!  I appreciate the response and it's helpful.


With respect, Tubenit

[glass54]

Sorry about the transformer confusion.
I used a (T1)15VA 240:12V Tx for Heaters and powering a (T2) 5VA 12:240V Tx for generating HT due to limitations and cost of suitable 1RU transformers in Aussie.
You can certainly use 6.3V AC for heaters or if you could be bothered use a minimum 2A Bridge rectifier and 4,700u 25V (or up to 10,000uF) electro as DC filter, but you may have to fit a small build-out resistor to bring the heaters back to 6.3V DC (6.3x1.4 minus 2 diode drops gives about 7.6V DC therefore requires approx 1.3V DC drop  )
I used a 12V 3 Terminal regulator (LM7812 or similar) offset with a diode (D_P1) on groundpin which gave me +12.55DC (ideal for series heaters)
Taking up Lekky's idea, I have no problems using a DC-DC inverter for PS as long as inverter runs >100kHz and additional RF protection is used. I could demonstrate RF rubbish on PS rails with my APx525 audio analyser 
Advantage of such PS topology is reduced size of filter capacitors BUT if you already have a simpler solution, go for it.
Regards
Mirek

[tubenit]

OK, here's what I've got so far in the idea. I've built 2 amps that use a H&K Red Box that I'm very pleased with.  So, my thinking is to "keep this simple" and within what I am already familiar with.


My thinking is some of the schematics shared incorporate internal either solid state or tube functions similar to a direct box?  I'd rather just use a direct box mounted on the back of the amp head cab instead IF that is the case?


Anyone see any major flaws in this design? 


With respect, Tubenit

[tubenit]

Here is an example of what I've done in the past that I've found successful and has been used for a zero volume stage. I've had quite a few guitarists play thru this and they've been very favorable to the design.


I'm understanding the bass preamp would NOT need a dummy load resistor. So, the same idea with a direct box without the dummy load. 


Amazon.com: Radial Pro DI Passive Direct Box : Musical Instruments


or    Amazon.com: Pyle Premium Direct Injection Audio Box - 2.36" x 4.09" Passive DI Unit Hum Eliminator w/ Input Attenuator to Connect Guitar & Bass, 1/4'' Impedance Transformer Connector to Balanced & Unbalanced XLR : Musical Instruments

The guy I'm thinking about building the bass preamp for ........... owns the one attached.



With respect, Tubenit

[tubenit]

I'm wondering if a cathode follower would work well with this design?  Perhaps it may add a dab more compression to the tone?


With respect,  Tubenit

[shooter]

not totally sure but I believe the 820 is acting as a CF

[tubeswell]

Yes the IRF820 is the buffer for the TS load.


But another low impedance buffer just before the preamp output would probably help with pushing the output signal along to the next/main amplifier/whatever.

[shooter]

agree but the TS will eat up signal, attenuate, so without knowing what's coming out 1st, it'll be hard to guess at just another CF/impedance-match or gain +CF

[kagliostro]

Also you can consider the use of something like this

https://www.tubetown.net/ttstore/en/audio-transformer-1-1-2-1-for-line-signals-ltr-110.html

It will allow also a Balanced Output (600 ohm with CT secondary)

Franco

[kagliostro]

There was an italian guy who had a certain celebrity, Gianni Cornara

now if I try to find his web pages the link I find with Google didn't work and if I click on it an error appair

here a pair of his Bass Amp projects
(that were build with satisfaction few years ago but at the moment I didn't find the  soundclips)

For those who can be interested, save the schematics on your computer, this copies comes from my archive because the original web pages of the author don't exist more

300W Tube Bass Amp (note the way he obtain a balanced output from the preamp)







15W Tube Bass Amp





Here you can read a bit about who is the author

He has a degree in physics and is passionate about audio circuits

https://www.audioplay.it/gianni-cornara

https://www.audioplay.it/author/giannicornara

Franco


p.s.: Try if this links works, I found it using Google Lens


http://www.giannicornara.net/pages/page_guitaramp-i.htm

http://www.giannicornara.net/pages/page_stbassamp.htm

[tubenit]

THANK you again!  All useful information.


With respect, Tubenit

[kagliostro]

If you build this Preamp



You can omit the Balanced Output and connect a Red Box H & K to the Power amp exit, if you need you can play with the resistors at the exit to achieve the right level to the Red Box

That Preamp is really High Quality

Franco

[Lekky]

Another nice bass preamp design is the Nobelium by C2C Electronics, which is a clone of the coveted Noble preamp. Schematic is in the build document.

[tubenit]

All great info!  Thanks!  I'll meet with the guy that's interested in this in a few weeks and then make a decision. I've got a stack of schematics & options to consider at this point.


With respect, Tubenit

[kagliostro]

Interesting, there are also kit of that Preamp clone

https://www.musikding.de/Nobelium-kit

https://en.uraltone.com/c2c-electronics-nobelium-pcb-set.html

https://c2celectronics.com/product/nobelium-pcb-set/?utm_source=chatgpt.com

Franco

[Wardy]

Seems I'm on the same quest. Trying to put together a bass preamp with built in compressor and variable HPF.

I built the attached stomp version from Tubetown and I can verify it works well. have gigged with it a couple of times. I'm thinking of using this as base and adding in the other stuff plus a footswitch and let it sit on my stack.

[kagliostro]

May be you are interestednon this


COMPRESSOR - EXPANDER with ECH84
If diode D is inverted, it functions as an expander. The top potentiometer adjusts the gain.
The bottom potentiometer adjusts the compression.
The 100-500k trimmer adjusts the delay



Franco

[Wardy]

Many Thanks Franco,

I must admit I am struggling to read that schematic. I'll have to print it and enlarge and rewrite so I'm sure what all teh values are. I also found this that you recommended in another thread.https://www.audiovalvole.it/progetto_preamplificatore_compressore_chitarra_basso_elettrico.html

It looks like it could be what I'm looking for but its still confusing. It discusses using a ECC91 and then goes on to specify a 12au7 in the BOM.
I defo don't want to use the ECC91 as I want to use 12vdc for the heater.
Also there is a level control but no ratio.

best
Steve

[kagliostro]

Ciao Wardy

I've that schematic in my archive since a lot of time, It was part of a DIY amp relized on the East Europe, but I've Lost the link to the web page

---

Unfortunately the author of the Audiovalvole project deleted his e-mail contact and for those that want to try to ask something he say to try to theyr's Facebook page, but I've no Facebook registration (and don't want to have one)

Franco