TBM clean only with active fx

[Bugman3183]

Good morning all.   As the title states I'm going to attempt to build a Tbm With clean channel only with the active fx loop only using parts I already have on hand.  it won't be exact but hopefully close enough. I've been studying the layout and schematic and for the life of me (possibly due to all of the switches and such) I can't wrap my head around where to connect the. 01 capacitor coming off of v1 b plate (pin 6) in order to eliminate the overdrive channel.   Looks to me like it should connect directly to the grid of v3 a (pin 2)  where there is a .047 cap there already.  If that's the case, do I combine the value of the two caps by running them parallel or is the value not critical in this position?  Or maybe I'm on the wrong track all together.   Any clarification on this matter would be greatly appreciated.   Thanks.

[sluckey]

What is a TBM? Got a schematic?

[Bugman3183]

Sorry about that.  Tweed bluesmeister . Not sure how to post schematic or if I even can with cellphone, but schematic is located on this forum under schematics and diagrams/pc express and jschem.

[Bugman3183]

 hopefully this will be the schematic ands layout I've been studying.

[Bugman3183]

Ok, here's layout.  Thanks.

[sluckey]

You need the .01 and the .047 caps. Here's how I would do it...

[Bugman3183]

Thank you very much.  I feel very silly that I spent do much time looking at those drawings and couldn't figure that out. I somehow thought the master volume was out of the equation without the overdrive channel.   Thanks again.

[pdf64]

You don't have to keep the master volume; there won't be enough preamp gain to get much preamp overdrive (unless a booster etc stompbox is used).

Why does the fx loop have a 250k pot for the send level?
The low output impedance of the CF stage (~1k) will then be raised up to a max of 125k.
Which makes the CF stage seem kinda pointless?
Is it a typo? A 25k pot would be a way better choice.

[tubenit]

I built a Tweed BluezMeister for a friend with just the clean channel and active FX.   Beautiful sounding amp, IMO.  He is using with an Emminence  Cannabis Rex speaker.  With the midboost and preamp boost (PAB), you can actually get some decent slightly overdriven tone with it.  Sounds great with a delay or reverb pedal in the FX.

My friend spec'd a  Hammond trannie that was 275-0-275 with enough ma to handle either 5881/6L6 or 6V6's (which he is currently using).

With respect, Tubenit

[tubenit]

He wanted a "tweed style" chassis.  This one was 20" x 6.5" x 2.5".

With respect, Tubenit

[Bugman3183]

Awesome looking build, and great info.   Exactly the amp I had in mind.   Thanks for sharing.

[sluckey]

Awesome looking build, and great info.   Exactly the amp I had in mind.   Thanks for sharing.

Did you notice this has a passive FX loop? You originally asked about an active FX loop. Sorry, it is an active FX loop.

[SILVERGUN]

Awesome looking build, and great info.   Exactly the amp I had in mind.   Thanks for sharing.

Did you notice this has a passive FX loop? You originally asked about an active FX loop.

I would see the schematic that T posted as having an active loop, even though it just appears to be part of the preamp circuit.

Why does the fx loop have a 250k pot for the send level?
The low output impedance of the CF stage (~1k) will then be raised up to a max of 125k.
Which makes the CF stage seem kinda pointless?
Is it a typo? A 25k pot would be a way better choice.

Great point and nice catch.
Thanks for pointing that out. There are some designs that have been adopted through cut and paste and we tend to just overlook some design details until someone knowledgeable and attentive corrects our "mistakes".

EDIT: I searched around on my computer trying to find another occurrence of a 250K send pot and found it on the Dumble-ator
So, I'm guessing that if it was either a misrepresentation on that schematic or a design mistake by The Great One

[sluckey]

I would see the schematic that T posted as having an active loop, even though it just appears to be part of the preamp circuit.

On second thought, I agree.

[2deaf]

Great point and nice catch.
Thanks for pointing that out. There are some designs that have been adopted through cut and paste and we tend to just overlook some design details until someone knowledgeable and attentive corrects our "mistakes".

It is not enough to be knowledgeable and attentive -- you need to be an authority.  I have commented numerous times on erroneous FX loop designs, but they are rarely acknowledged because I am not an authority (doesn't mean that they were always ignored, though).  I used to have a "Question Authority" bumper sticker on my Hippie van, so just being an authority isn't good enough for me.  Authorities can be useful for non-authorities like me, however, if I can get them to validate my point, but they are rarely willing to do that just out of the blue.  So I provoke authority and attempt to make my point and have it validated at the same time.

The other bumper sticker on my van said "I Know Jack Sh*t", which sort of detracted from the credence of the first sticker.       

[tubenit]

For the record,  I am neither knowledgeable nor an authority on amp design, reverb, FX loops, etc ...........    I simply do alot of trial and error and experiment and tweak til I like how something sounds. 

I freely admit that I "copy and paste" ideas.  Many of them don't work all that well so I desolder them and try something else & occasionally one turns out great and then I share it on the forum.

My guess is 80% of the guys on the forum know more about electronics then I do since I've not had a single hour of formal training.

Having said all that, if I like the way it sounds and it works OK for me & it's safe  .............. then I don't consider it a mistake.  Just my 2 cents.

With respect, Tubenit

[Bugman3183]

Hopefully this will be my final question on this build, but I was looking at the schematic and layout tubenit posted.  On the schematic,  the ppimv looks to be a 250k ganged pot with 2.2m resistors from wipers to ground, while the layout seems to show something a bit different.   I'm assuming the schematic would be the way to go, but i would also like verification that I'm seeing that properly please.   Thanks.   Btw.  Please excuse my ignorance but I'm still on a level where I have to study a schematic for quite a while before it starts to click.

[tubenit]

Go with the schematic typically when you see a discrepency between one of my schematics and a layout.   Yes, 250k dual gang pots and 2.2 M resister from wipers to ground.

Nothing to excuse on your part.  The error was mine and you were thorough enough to catch it. Good show.

with respect, Tubenit

[Bugman3183]

Thanks.   I really appreciate everyone that's so willing to donate their time and expertise in helping those of us who are less experienced.