Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tubenit on August 19, 2012, 02:55:38 pm
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Built another tube FX loop. I did a few yrs ago with FX loop plus reverb.
This one is quieter. NO hum or noise at all added that I can tell. It sounds GREAT!
I've been using it with the D'Mars OD Special. The D'Mars does not need an active FX loop to use a delay pedal. Digital or analog delay sounds good in the passive D'Mars effects loop.
So what advantage is there in having one? The FX loop seems to add slight additional warmth and harmonics, IMO.
However, the better reason is that the D'Mars can be dialed to this really clean transparent overdrive tone. Well, with the FX loop ......... I can increase the sustain and the blooming while maintaining that clean transparent OD. Works excellent in that regard.
Chassis is 12" x 2.5" x 6.5". I tried a bunch of different 12A_7 tubes and liked a 12AT7 NOS the best. A 12AY7 and 12AV7 sounded good to me also.
With respect, Tubenit
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I will try to record the D'Mars with the FX and post later.
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Looks real nice! :icon_biggrin:
Where'd you come up with the values for the FB loop on the recovery stage? Trial and error?
Brad :bravo1:
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Where'd you come up with the values for the FB loop on the recovery stage? Trial and error?
Oh, it's really a modification of what the Dumblish guys use on their D'lators. A couple of yrs ago, I tried different values and they just sounded different. I couldn't pick one as necessarily "better".
With respect, Tubenit
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Ok, thanks.
Someday I'd like to build 1, it's on my list.
Brad :laugh:
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Built Tubenit's active effects loop this weekend.
He kept "insisting" that I needed to build one, and boy was he right! MUCH better tone than the SS Kleinulator I have been using.
The tone stays absolutely the same as I turn down the "recovery" pot....best Master Volume I've ever used.
I used a 12AY7 (didn't have an 12AV7) & had to tweak the B+ dropping resistors a bit, since I used a different PT pulled from an old piece of 60's Military gear.
Anyway, this is a worthwhile build & I see it becoming a vital part of my rig!
Geezer
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Hooray! Glad you like it! Cool. :thumbsup:
With respect, Tubenit
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Is this an external effects loop that you can use with any amp that does not have one built in?
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Is this an external effects loop that you can use with any amp that does not have one built in?
That is correct and it plugs into a passive effects loop making it an active loop.
With respect, Tubenit
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Shortfuse,
Just for clarity, the active FX loop does NOT plug into the front end of the amp. It goes into the passive effects loop between
the preamp/OD & LTPI.
With respect, Tubenit
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Tubnit Ive used several loops but this one has something i havnt seen before what does the recovery do.
Thanks Bill
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what does the recovery do
Just another volume control. However, it's pretty much the only one that I adjust. I tend to just "set & forget" send and return.
It functions as a great master volume for the amp.
with respect, Tubenit
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It functions as a great master volume for the amp.
Indeed it does.....since most of my distortion is generated in the preamp, I can turn it down to a whisper on my loop without any change in tone, so much so that my hollowbody is louder acoustically than the amp, but the tone is still exactly the same thru the speaker.
I set the send just to where it doesn't clip the effects unit, set the return for the best tone (usually 50 to 75%) then use the recovery to adjust the overall volume without affecting the tone whatsoever.
G
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Cool guys .
Thanks Bill
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Jeff
I was busy all last week and did not see your post. Thank you for the explanation I do understand now.
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I'm building this active fx loop and am confused by the schematic. The power string is labeled A B C and the connections to the board are labeled C and D. Thanks for your help.
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Yes, I think that was a "cut and paste" error.
"A" is not used, "C" board connection is actually the second node (B) , and "D" board connect is the third node (C).......at least that worked for me.
HTH, G
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Sorry Geezer, I don't think so, the error (if there is one) to me seems to be one other
In the schematic you can see V1a is at 262v and V1b is at 196v
so no accordance with the voltage on the A - B - C points
A = 367v (I agree with you that this isn't used)
B = 295v
C = 262v
So if C = 262v is connected to V1a, to have 196v to be connected to V1b you must have a further "D" point on the supply (that actually is missing)
That only if the voltage reported on V1a & V1b are corrected
here a pair of similar circuits with voltage indications
(http://lh3.ggpht.com/_MHnI-B0pJ8k/TSHnC0EmElI/AAAAAAAAAVQ/_nQ4kcTN4QQ/s800/BEST!%20DumblelatorSchematic-1.jpg)
(http://lh6.ggpht.com/_MHnI-B0pJ8k/TSHnDEAo76I/AAAAAAAAAVU/BUVmJSmzU2Y/s800/Final%20Schematic%20of%20D'Lator%20with%20Reverb%20PT.JPG)
K
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I'm looking at tubenits gutshot and it appears to be as geezer said . Will wait for tubenit to verify. Thanks
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I agree with you, the only person that can clarify this thing is of course Tubenit
K
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The 196v is NOT @ node "C"....it is @ pin 6 (after the 82k plate resistor)
G
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The 196v is NOT @ node "C"....it is @ pin 6 (after the 82k plate resistor)
OK that has sense
Thanks Geezer
K
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bump'n this up hoping tubenit will respond,thanks
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Geezer's reply 16 is correct. with respect, Tubenit
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Thanks
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I built one of these over the weekend and I thought I'd share. The same "Dumbleator" schematic, but with an added "Parallel" switch to select between parallel and series operation.
So far I've used it primarily with a three channel head I built that has a high gain channel with lots of preamp gain, so it's very useful with that. In the loop I'm using a Line 6 M13 stompbox modeler. I think I prefer parallel mode with this setup, but the effects need to be set up differently for parallel mode with a much higher "mix" setting.
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Boots nice job, looks real good!
But no vent for heat from the tubes filament? I might worrie too much but I wouldn't trust it without some kind of vent.
Brad :icon_biggrin:
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Where did you get the little PT?
Brad :think1:
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Yeah, I debated about the venting and ended up putting a 1" hole in the lid (floor) with a screen over it. You can't see it in the pix. It doesn't get very hot at all so hopefully that will suffice.
The transformer is from AllenAmps, part number TP2X
-John
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Man, you did a fantastic job with that! Looks great.
I appreciate the comment about the parallel mode being useful to you with that device. Good to know.
With respect, Tubenit
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Yeah, I debated about the venting and ended up putting a 1" hole in the lid (floor) with a screen over it.
Heat rises and fresh cooler air needs a place to come in and go out.
IIWM, I'd put a 2'nd hole with screen right above the tube in the top/face on the chassis box. Then as the heat rises up through the 2'nd/new hole it will pull fresh cooler air in through the 1'st hole in the bottom.
The transformer is from AllenAmps, part number TP2X
I thought I'd seen that PT before, thanks.
Brad :icon_biggrin:
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Thought would bump this up.
Thanks Bill
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Hey Boots, Could you supply me with more info/schem on the parallel swithcing. Is it worth adding to T's active loop???? Thanks
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Hi TIMBO
are you looking for something like this ? (look to reply #9)
http://www.el34world.com/Forum/index.php?topic=10208.msg93531#msg93531 (http://www.el34world.com/Forum/index.php?topic=10208.msg93531#msg93531)
(http://www.el34world.com/Forum/index.php?action=dlattach;topic=10208.0;attach=19354;image)
(http://www.el34world.com/Forum/index.php?action=dlattach;topic=10208.0;attach=19358;image)
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Hi Boots
is this the way you have do it ?
K
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Yup, that's the schematic I followed. The only difference is that I added the recovery pot, as tubenit did.
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Thanks for the info Boots Deville
effectively in the schematic the recovery pot is missing, but in the layout is present
Thanks again
K