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6L6GB  Stereo Amp With Tone Stack
6L6GB  Stereo Amp With Tone Stack
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Old 6th May 2018, 07:37 AM   #1
rifraf50 is offline rifraf50
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Default 6L6GB Stereo Amp With Tone Stack

Hi good people of DIY ... I have just been surfing the net for a good 6l6gb stereo schem with a tone stack ......and I cant seem to find one

What I have is ecc88 6av6 6c4 6at6 12au7 12at7 in abundance so I want to go with these.

I have RCA 6l6gb's and RCA 7027A's and Sylvania 6l6GB's

Going for the bigger headroom and possible triode switch...maybe

I have used 6av6 in SE 6l6 guitar amps previously and had nice results , but it was all experimental ....the 6c4 , 6av6 , 6at6 are single triodes and easy to wire in a tidy fashion ....very quiet results

the unit I wish to build is for my ipod so I think 6av6 will be too aggressive so I am thinking 6c4 or ecc88 12au7

I have already built a stereo push/pull 6gk6 it sounds pretty good but made the mistake of trying to stuff too much into such a small enclosure that it has a slight hum which annoys me and if it wasn't for that I would stay with it . eventually I will rebuild it into a stereo SE unit ....maybe

But since I enjoy building amps perhaps there is someone who has done this and I could just build without experimenting too much from someone who already has a schem .....this I would appreciate

I have all the transformers I need but none are UL .....

If anyone has a schem I would be greatull......thankyou
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Old 6th May 2018, 12:09 PM   #2
kodabmx is offline kodabmx  Canada
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6L6GB  Stereo Amp With Tone Stack
Just kang two schematics together.


Here's a good place to start: Practical Tone Controls.
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Old 6th May 2018, 01:14 PM   #3
rifraf50 is offline rifraf50
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thanks Kodabmx , I was hoping more for a proven schem to pass my way ...

I know that with enough messing about I will achieve what I want but in this case I just want to get it done....I may resort to a previous build , a 6l6 + 6av6 SE build that had quite nice results (for guitar)...

I would use perhaps a 6c4 as cathodyne PI and perhaps ecc88 with tone stack between the two triodes, because the ipod already puts out plenty of gain .......trying to keep the noise floor down and volume right at the start...

I could use it like 2 monoblocks.... , but I want to keep it people friendly ....so others can enjoy it , just like what theyre already using

I'm sure someone has what I am looking for ....surely !!!
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Old 6th May 2018, 01:42 PM   #4
kodabmx is offline kodabmx  Canada
Affordable triode connected sweep tube amps.
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6L6GB  Stereo Amp With Tone Stack
I built this... It's a typical bass/treble control. It can be inserted between the preamp and the power stage.
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Old 6th May 2018, 03:30 PM   #5
Lingwendil is offline Lingwendil  United States
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6L6GB  Stereo Amp With Tone Stack
For hifi tone stacks, look at baxandall types. A quick Google search of this forum will show a bunch. It's pretty flat when in a neutral position.

The link kodabmx posted is a great resource, and I'll add this one-
Baxandall 2

And this one-
DIY Audio Projects Forum • Baxandall circuit

You can also download the tool from Duncan amps, that lets you play with different tone control schemes, and see the effects of different parts values. Good for figuring out how to use "parts on hand" or for limiting the range to areas you want to control. They also have the PSU designer tool, which every casual tube gear builder should try, it's really useful! Software

Personally, I haven't found tone controls to be of much merit for most builds, unless it's for a dedicated subwoofer amplifier, baffle step correction, or for some really weird room correction scenarios. When I build for people that want tone control, I use the baxandall. It's a pretty good circuit.

One last word from personal experience on the 6L6- unless you listen at pretty high power levels, you won't use that triode switch very often. When I've built similar amps I found that I usually preferred triode connection for all but party SPL! Triode mode rocks with the 6L6 types, especially with a smidge of GNFB to pull the damping factor in nice and tight.
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Last edited by Lingwendil; 6th May 2018 at 03:42 PM.
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Old 7th May 2018, 01:22 AM   #6
rifraf50 is offline rifraf50
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Hi , used the Duncan tone stack simulator tool to fine tune the 6gk6 (6bq5) stereo build and it works a treat when making adjustments because of transformer / component / tube nuances ....

The original build had too much vocal frequency coming through ,1-3 Khtz range and it just wasn't pleasant listening.....but the tone stack simulator was a blessing

The 6gk6 build incorporated a baxandall tone stack and worked well ... I used 12au7 instead of 6eu7 / 12ax7

Its looking more like I will use the same schem for the front end.... and another for the power tube section

Many thanks for the advice , I found the notion that 6l6 in triode mode has more than enough volume ....I listen to just about everything but like it loud ...especially jaz / rock fusion..

Still hoping someone has a schematic to offer though...
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Old 21st January 2019, 02:50 AM   #7
kissabout2002 is offline kissabout2002  Italy
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Hi to everybody here, I just finish to build a tone stack bass/mid/treble that can be add to any tube amp or solid state as well, I am using it with external solid state dual power 240VDC + 6.3 VCA, so the two channel are completely independent, the original schematic was suggested by a link from "Kodabmx", from the original schematic I just change the fist stage because I used in this project all 6N2P-EV instead of 12au7 and 12ax7. The result is very good and I really like it, I also make a simulation with LTSpice prior the building and was already impressive, compare to my previous tone stack following the RCA schematic this is much better, also because the adding of mid tone control, but what I really like is when the three pot are in the middle the frequency response is absolutely flat rather the RCA where I cannot have a really flat response, so I am posting here also the simulation and the real frequency response take with an rta, if somebody is interested I can also give the LTSpice .asc file of the project.
Best Regards to everybody.
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File Type: png Screen Shot 2019-01-21 at 11.06.31 AM.png (75.8 KB, 140 views)
File Type: png Screen Shot 2019-01-21 at 11.08.35 AM.png (58.0 KB, 141 views)
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Old 21st January 2019, 01:48 PM   #8
Kay Pirinha is offline Kay Pirinha  Germany
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Yers, active Baxandall, that's it! And for both of the passive schematics above I'd strongly recommend audio taper potentiometers to get rather flat response when they are set halfway between maximum and minimum.
Best regards!
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