Effects loop & 1 tube reverb SUCCESS!

[tubenit]

Guys,  it occured to me IF I go the outboard effects loop route ...........

Why not just build a one tube reverb into the unit also?  This would be for the TOS which currently has passive effects loop in it.

I haven't seen an active effects loop with tube reverb outboard unit, but I like the idea of it.

I don't know if this would end up with ground loops, but if other outboard effects loops don't have grounding and hum issues then it would seem possible to build this & have it work out OK.

I was thinking of the idea of making a small head with a 9" reverb pan.

Thoughts & comments?  



With respect, Tubenit

[rzenc]

Hi Jeff. I know you said one tube reverb, but why not Tore T 6G15? Verb + trem
http://www.el34world.com/Hoffman/images/revibeschematicToreT.gif

With Respect,
Best Regards

Rzenc

[tubenit]

Why not Tore T 6G15? Verb + trem

1)  I want an active effects loop (which is the center piece of the idea)

2)  I don't want tremolo (especially in the front end)

3)  I want reverb insertion after the preamp and before the LTIP & not before the
     preamp

4)  I like the tone of the 1 tube reverb better than a fender reverb tone (not
     saying it's better, but I prefer it)

5)  This is less labor intensive and less expensive

6)  It hasn't already been done, and I like new ideas

7)   I think the 6G15 sounds great with amps like a tweed bassman but I don't
      know how good it would sound with a high gain amp

8)   This idea incorporates an effects loop and one tube reverb that I already
      have tried and liked with a Tweed Overdrive

With respect, Tubenit

[67polara]

Sounds like a solid idea.  Go for it let us hear some clips when you are done.  Can't wait.  Only question I have is do you think you will get the same sound with a short tank?

Tony

[topbrent]

Tubenit, take a look at this RedPlate Amps 2 tube reverb + loop.  I know you are looking to do a 1 tube design, but the schematic, packaging and implementation might be a good place to look for ideas.  Henry has a gift for packaging fully featured designs into tiny spaces.  His stuff sounds awesome also.
Full page of info: http://ampgarage.com/forum/viewtopic.php?t=3031&highlight=reverb

HeistHL:
- 5 x 7 Hammond box, no compromise tank reverb and loop using a Fender stand alone reverb power transformer and tank transformer.
- This goes from preamp out to poweramp in. The build I'm working on right now to use with this box has 2 DPDT front panel switches labeled "Reverb" and "FX". These swiches are chained together so when both are off the signal stays in the amp. When both switches are on the preout feeds the loop in and the loop out returns to the amps "Reverb" switch which then routes the signal to the reverb in and the reverb out comes back to the poweramp in. This method puts tank reveb on the FX, but if you wanted reverb first you could switch the connections (the switches would be labeled wrong).

[topbrent]

Chassis wiring

[topbrent]

Layout

[tubenit]

Topbrent,

THANKS for posting that & I'll take a look.  I got something of a chuckle out of seeing all of that, because everytime I think I have come up with something original .......... I find someone else has already done it 98% of the time.
 

Appreciate the info.   With respect, Tubenit

[Geezer]

I got something of a chuckle out of seeing all of that, because everytime I think I have come up with something original .......... I find someone else has already done it 98% of the time.
 

Yeah, but when you hit that other 2%.....man, oh man!  :icon_sunny: 

G

[mat]

I am too considering of building an outboard loop + 2 tube reverb. Very interesting topic ! I think I'll use a PC power unit as chassis.

[gar13]

This thread over at AG might be helpful, schematic and layout there too. The builder uses the fender type reverb. In a post further down the page, he explains that he uses switches to take the loop and reverb in and out of the amp, with the reverb after the loop.

http://ampgarage.com/forum/viewtopic.php?t=3031&start=0&postdays=0&postorder=asc&highlight=reverb+power

[TIMBO]

Hi guys,I found Mesa's active loop in their DR and they have a couple options.Would the tried method of having the reverb before the FX loop would be the way to go? Thanks

[mat]

Great looking schem and layout Tubenit ! These will be great help when I start building my version, Thanks !!

[tubenit]

OK, I got it up and running.  It all works.  Reverb sound very good to me. The FX sounds good also (w/exception below noted).

All pots, switches etc.......... are working.

However, I have a buzz/hum that seems to be connected to the recovery pot of the FX side? This would the type of buzz one would hear when a input jack is not properly shorted. It's obnoxious.

Figuring a dial of 1-10 ..................  IF I put the pot on "1" it's noisey with a buzz.  IF I put the pot between "1.5 to 2"
then it's pretty quiet but I don't have the volume that I want. If I put the pot above "2" it is also pretty noisey.

The reverb side is pretty quiet when the FX side is bypassed.

What would you guys consider looking at first. I ran out of time today but I'll pick it back up tomorrow hopefully.

With respect, Tubenit

[VMS]

Hi,

try rewiring the recovery pot so that wiper goes to output aka bypass switch.

[VMS]

...and here is the picture.

If the pot is wired like it is in your schematic & layout then it also changes the gain of the triode before the pot.

You could try the same thing on the reverb pot.

 

[VMS]

I don't know what is the purpose with those extra wires on parallel/series switch. But if you encounter problems, here is a simpler way to wire that switch.

[tubenit]

Guys,

4 hrs later and NO success getting rid of the buzz. The reverb is very quiet now & has about the same noise level as an onboard reverb so I am very happy with it.

The bypass switch on "bypass" & the outboard FX and reverb unit is quiet.

The FX loop works great and the tone is excellent .......... however there is a constant buzz that does not really increase to any signficant degree even with the send and return pots on "10".  In other words, whatever those pots are dialed to between zero and 10 does NOT eliminate the buzz.

The buzz seems to be totally connected to the recovery pot. I already replace the .047 cap (which was brand new) to that pot. The pot itself is also brand new to this build. I have reflowed all the solder joints repeatedly.

I removed the local negative feedback. No buzz improvement but I like the effects tone better without it.

All switches are working including  reverb bypass, FX bypass and parallel-series switch.

For those of you who are following this build, I toasted the PT last wkend but have installed a new one.  I am thinking when that PT fried that something else got damaged but I don't know what it was or is ????

So what I am going to try next is the follow:

1)  bypass the recovery pot with a 220k resistor to ground

2)  clip a new filter cap in at node C and node D   ( the filter caps look fine but I am suspicious that is the problem?)

3)  bypass the "bypass switch"   This is in case the voltage fried something in the bypass switch.

Not sure what else it could be?

Given the reverb is quiet I am thinking nodes A & B are OK?  Does that sound like a reasonable conclusion?

I am open to any additional thoughts of what to try?

With respect, Tubenit

[sluckey]

Can you try a 12AU7 in the effects tube socket?

[tubenit]

Sure, I have some 12AU7's.  I'll try that in the next couple of days and report back.

I am not confidant that will resolve the buzz though.

It sounds like a guitar cord plugged into the input jack without being plugged into the guitar. Increasing the volume on the recovery pot greatly increases the buzz.

With respect, Tubenit

[VMS]

Did you try my simpler way of wiring that series/parallel switch?

[tubenit]

Did you try my simpler way of wiring that series/parallel switch?

No, I haven't but it made no difference whether it was in series or parallel mode at all.

Having said that, I can just disconnect the switch entirely to eliminate that as a factor.

While they both sound decent, I prefer the series FX loop.

With respect, Tubenit

[DummyLoad]

buzz is likely coming from PS, more to the point, inadequate filtering for SE amp - try moving everything down one RC stage and add another RC network. radial lead caps are more compact and IMHO layout easier in this type of ckt. take a gander at fender reverb ckt - PS tap for reverb driver is usually node "B" and that's usually an LC filter network. i don't believe single C network is going to cut the mustard for SE driver.

you're using SS recto - don't be shy with the filtering...  

<recto>100uF<1K>100uF<A><2K2>22uF<B><2K2>22uF<C>2K2>

PS taps C&D could be same tap point - if you keep the 4 PS nodes, make "C" tap the "send" amp and "D" tap the "return" amp.

your schematic says CT for 6.3V is inside tranny - looking at cut sheet, i believe that is incorrect - if there is indeed no 6.3V CT then ground one side of the filament ckt. better yet, since this is all line level signal stuff - make DC for filaments w/ 6.3V winding & volt reg.


PSU sim of as-built PS...  red line is your node "A"...



PSU sim of recommended changes... red line is not used - green line is now node "A"   aaaahhhh...much quieter. :-)



respectfully,

--ISO

[tubenit]

buzz is likely coming from PS, more to the point, inadequate filtering for SE amp

I am thinking that you're probably correct with this?  

What throws me off is that node A and node B feed the reverb.  And the reverb is very quiet with no more noise than an onboard reverb. In other words, if I bypass the FX and just have the reverb involved ......... it's quiet.

It is just the FX loop that is noisey.  Specifically it seems to be the recovery pot area as the send and return pots seem to have NO effect on the buzz while the recovery pot increased ......... also increases the buzz.

So, I am wondering if the FX nodes filtering is inadequate & I should concentrate on beefing nodes C & D up? I don't have any 100uf filter caps but have 20uf ones that I could parallel if needed. I can order a 100uf or two if needed.

The other thing I am wondering is when I wired the first PT wrong and burned it up (like within a minute) that I ran node D straight to ground on the hot side.
Perhaps that destroyed the filter cap even though visually it looks OK?

your schematic says CT for 6.3V is inside tranny

I honestly do not have a CT for the 6.3v and I am reading 6.2v for the heater voltage.  In addition, the box the trannie came in does not show a heater CT but does list a CT for the secondary HV wiring.

I am thinking the 6.3v is not a problem since with the FX bypassed and the reverb engaged the FX-Reverb is quiet.

Again, the noise sounds just like a guitar cord plugged into the input jack but not plugged into the guitar. And that noise increases when the recovery pot is dialed up.

I'll keep working on this as I have time and report back.

THANKs for the input and suggestions. They are appreciated.

With respect, Tubenit

[tubenit]

Heisthl on the AmpGarage did one of these successfully. Here is a comparison of his PS and the one I am using.

With respect, Tubenit

[sluckey]

however there is a constant buzz that does not really increase to any signficant degree even with the send and return pots on "10".  In other words, whatever those pots are dialed to between zero and 10 does NOT eliminate the buzz.

That indicates (to me) that the buzz is in the V1b circuit. Use a gator clip lead to ground V1b pin 7 directly at the tube socket. Does that kill the buzz?

I don't think your PT failure caused any damage to the node d cap since you placed a short across the cap and the cap was never exposed to any voltage. I still think you can benefit with bigger caps and bigger dropping resistors for nodes C and D. There's such little current flowing thru those resistors that increasing both from 2.2K to about 10K will not drop the voltage very much, but the decoupling between nodes and the actual filtering will be improved a lot.

Since the filament winding has no CT you really need to connect two 100 ohm resistors as an artificial center tap.

[tubenit]

I will definitely do the shorting the V1-7 to ground.  I actually had thought of that driving to work today to help pinpoint the area.

I will also increase the dropping resistors and capacitance.

I'll bump the dropping resistor from B to C to 10k and from C to D to 5.1k. And I have two reasonably small 10uf/450v caps I can parallel with the 22uf and 16uf.

(The schematic doesn't show it but currently I have 5.1k between A to B ...... and 3.3k between B to C.)

Since the filament winding has no CT you really need to connect two 100 ohm resistors as an artificial center tap.

I am confused by this??  I am getting 6.2v on the heaters when I put the voltmeter across  4/5  &  9 of the 12AX7's. So I presumed the PT has an internal CT that would give me that voltage?? Sounds like I am making an improper assumption?

Just to make sure ............ you're stating even though I am getting the 6.2vac
to still do the 100ohm resistors to ground as an artificial tap?  That won't lower the heater voltage?   Correct?        (I am remembering from Hoffman's Library of Info to not use both a CT and an artificial CT).

With respect, Tubenit

[VMS]

Merlin has great info about the heater supplies:

http://www.freewebs.com/valvewizard/heater.html


I was thinking that this feedback loop might be the cause for the buzz.

[sluckey]

I am confused by this??  I am getting 6.2v on the heaters when I put the voltmeter across  4/5  &  9 of the 12AX7's. So I presumed the PT has an internal CT that would give me that voltage?? Sounds like I am making an improper assumption?

Right, that's a wrong assumption. I have that same PT in a recent project. Well actually, I have the 269JX. The 269 series has no center tap on the filament winding. You can verify there is no 'internal' ct on an unknown PT by checking resistance from either filament lead to the case of the PT (or chassis). No continuity means no center tap. But you don't have to do that on that Hammond 269EX. Trust me, there ain't one.

Adding the 100 ohm resistors artificial center tap will not affect the filament voltage. What it will do is provide a ground reference for that 6.3VAC filament which will reduce hum in your amp. It may not fix your buzz, but you still need to do this as a matter of good  building practice. You need a real CT or an artificial CT.

Did you notice that Heisthl used 22K dropping resistors for his node C and D? He also used a 1/2 wave rectifier which is much harder to filter out the 60hz ripple, so that could be a factor in the larger resistors. Still, larger resistors will give better decoupling between nodes and will reduce B+ ripple (hum).

[tubenit]

Sluckey, thank you for the clarity about the heater wiring and no CT.

OK, I have got a plan ...............

Create artificial CT for heater.

Disconnect  series/parallel switch to rule that out as a factor.

Increase dropping resistors to 10k between B to C & C to D  and parallel
10uf caps on the 22uf & 16uf.

Try it ............ & if there is still hum, then I'll short V1-7 to ground.

With respect, Tubenit

[Geezer]

OK, I have got a plan ...............

Create artificial CT for heater.

Disconnect  series/parallel switch to rule that out as a factor.

Increase dropping resistors to 10k between B to C & C to D  and parallel
10uf caps on the 22uf & 16uf.

Try it ............ & if there is still hum, then I'll short V1-7 to ground.

Hey T, I would do it like this>>>

Create artificial CT for heater.

Try it, & if there is still hum, then:

Increase dropping resistors to 10k between B to C & C to D  and parallel
10uf caps on the 22uf & 16uf.

Try it, & if there is still hum, then:

Disconnect  series/parallel switch to rule that out as a factor.

Try it ............ & if there is still hum, then I'll short V1-7 to ground.

Hopefully you won't have to do them all before you find the culprit!   

G

[sluckey]

Check your B+ node voltages before and after changing the resistors.

[tubenit]

Great advice Geezer and Sluckey!  I'll do it that way.

Last hum problem I got resolved (that I was posting about), I did stuff one at a time to pinpoint the problem for a lengthy period......... and then at the end did about 4 things at once that resolved the problem (due to being impatient).  And now I actually don't know for sure what resolved it?
 

I will definitely check voltages before and after. 

Thanks, Tubenit

[tubenit]

Well guys ......... it was the lack of an artificial heater center tap!!!!

Not only does it resolve the buzz/noise. The amp is honestly so dog gone quiet that it's one of those where you have to look and listen to the speaker to see if the amp is working because it is so quiet.

  :icon_compress: :icon_thumleft: :icon_thumright:

With the FX-Reverb set at the same volume as the amp with the unit unplugged ............. there is less noise using the unit then not using the unit!  This project has exceeded my expectations for success.

The FX-Reverb adds ZERO noise to the amp and the reverb is very lush and the effects pedal (a boss digital delay) has an incredible tone and sounds incredibly rich and spacious.  When I hear guys like Joe Bonamassa get this
gigantic rich tone .......... the TOS with this unit has that type of tone, IMO.

I'm not just happy with the unit, I am estatic!!  I had resolved myself before building this that I'd have some added noise, but that is NOT the case. It has less noise. When I was having the buzz problem, I presumed I'd never get rid of it completely but it is totally completely gone. No buzz at all. Nada!

With the unit FX on bypass and the reverb on bypass ......... there is actually more noise (the TOS being a high gain amp).  But with the unit on ......... less noise and a richer tone. Amazing to me that it works that way.

Guys, I am VERY VERY appreciative of the help on this one!!!!  You guys made this a big success for me. I love the unit and plan to build a nice custom wood case for it as soon as I can find the time.

It was worth burning up a PT, and spending 6 or 7 hrs putting in a new PT and trouble shooting to get this kind of tone.

And I apologize to Isotone and others for suggesting the heater CT was inside the PT. It wasn't. You guys were correct and I was wrong in my assumption.

It was resolved prior to this, but I did increase the dropping resistors between B & C and C & D. As Sluckey suggested, it made very little difference in voltage drop. Only a few volts drop increasing  to 10k/3w.

I tried both a 5751 in the effects loop and it was still quiet (meaning no noise) but I liked the clarity of the 12AU7 tube in the FX loop so it will stay in there.

My appreciation and respect, Tubenit

[nateflanigan]

You're hitting it out of the park tubenit, is there a Nobel prize for tone?

I'm maybe 1/3 of the way into the TOS, can't wait to hear these guys together, 2011 is looking very promising.

What reverb tank are you using?

[Willabe]

tubenit,

I've been following your build and this is great news! I'm glad to hear you won!

I got to hand it to you, it seems when you put your hand and mind to something you dont give up or give in!

I'll be the 1st to say that I dont know very much compaired to you and many others here, so please dont get me wrong. I'm just glad for you.

I do have 1 ? tho, why do you think the buzz seemed to be coming from only one part of the (FX) and not showing up every where? 

Thanks for sharing your build with all of us. Got a feeling because of you, there's gonna be more of these built. Just might build one myself.


         Thanks,    Brad            

[tubenit]

I do have 1 ? tho, why do you think the buzz seemed to be coming from only one part of the (FX) and not showing up every where?  

I have NO explanation for that at all. I couldn't hear a buzz on the reverb side?  And because I didn't, I was convinced that it was not the 6.3v wiring needing a CT but that it was the power supply.

But the ONLY thing I changed was making an artifical center tap using the 100R resistors. That's all ....... & the noise and buzz was gone completely and it was super quiet.

I went ahead and added the 10k dropping resistors per Sluckey's suggestion. It didn't make super quiet any quieter.

Here are the final schematic and layout (minus voltages which I will post later).

With respect, Tubenit

[Geezer]

Alright!!  :icon_thumright: :icon_salut:

Rock on! 

[topbrent]

Way to go!   

I will have to put this one on my must-build list!

[stingray_65]

Now that my TOS is FINALLY up and running , I think I have a winter project!

Thanks Jeff !

Ray

[Willabe]

That's  -  3   -   do I hear 4 ?

        


  Brad

[DummyLoad]

And I apologize to Isotone

not necessary at all... for making an assumption? we all make assumptions at one time or another - i say this respectfully: no apology needed. 

happy to lend a hand (not much of one at that) and so glad you got things worked out. sorry about the tranny blow up - it happens. ALL of us make mistakes at some time or another.

kudos to sluckey and all the others who chimed in with the fix.

--ISO

[tubenit]

OK, I tried the local negative feedback loop again & still don't like it. It gives the amp a more compressed tone and I think playing loses some touch sensitivity.

I did try a 180p instead of 500p paralleling the 220k grid resistor to ground on the reverb return. I like the 180p better. The reverb is pretty cool and I think you could surf with this one IF one wanted to.

I took voltages and posted them on the schematic along with some grounding scheme tips.

THANKS again to ALL of you for helping me!  This would have not worked out without the great help and advice you guys so generously offered. You have my respect and appreciation.

The SCH schematic, layout and some photos and info are here:

http://www.el34world.com/Forum/index.php?topic=10624.new#new

With respect, Tubenit

[theundeadelvis]

This may be a silly question, but I've never really messed with effects loops at all, with an external active effects loop, do you run it in your already existing passive loop? What does it add? I'm prepping a build for a TOS, and now you have me wondering if I need to insert a passive loop and then build an standalone active loop like yours?

[tubenit]

The FX-Reverb just simply plugs into the passive effects loop jacks. 

At least with the digital delay I use, I can not get the same warmth rich tone using a passive effects loop as I can using an active one.

With respect, Tubenit

[theundeadelvis]

Thanks! Any sound samples coming?

[tubenit]

Just a couple of pics of the cab for the FX Reverb unit.

With respect, Tubenit

[Willabe]

tubenit,            Sa'wweeeett.....

Curly & flame maple, mahogany,and crotch black walnut?

Very nice!

      Brad      

[sluckey]

Very nice! That's what I call real eye candy.

[Fresh_Start]

That cab is S-C-H-W-EEEET ! ! !

tubenit - has anyone ever mentioned that you are persistent?

Cheers,

Chip