Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Wonder2121 on October 04, 2024, 07:54:21 pm
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Wintertimes coming, that means the irons coming out.
Natural progression since building Slucks dual-lites led me to Geezer/Tubesnits HoSo56/SoLow
Updating thread as build progresses.
Ef86 - CF - TS - FX - PI - Cut - Type 2 MV - EL84
Elevated Heaters
6800 Ohm OT (only one I got but should yeild some interesting tonality)
FX loops are new to me, so learning experience ahead. Added one to schematic but unsure if passive or series would be best in this design, or whether signal needs boosting from send (seems waste using only half a tube) totally out the loop on this (no pun intended) I don't want the mix pot acting as pre PI volume control...
First time building cathode follower, done some research! Suppose I'll be A/B-ing tweeking as I go..Its a bit of a hodge-bodge this build as I'm using donor parts from whats at hand...
Concerned about gain from the Ef86, I might A/B different pentode tubes 5879s, think it might benefit voltage divider maybe..Thats why I've gone for a 47k Ra + 500k vol pot also debating the cut control, will it be needed?....As with CF tube, opted for AY7 just to drop some signal.
Plenty space on chassis for switches if mids need a boost or switching Cks...
All advice/ideas considered!!
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Look at this attached example of using a mosfet in the CF position. If you do this then you can use fewer tubes and not have a "left over" unused triode using 12A_7 tubes.
I honestly hear NO difference between a tube triode vs. mosfet cathode follower in tone.
geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm (http://www.geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm)
The layout I attached showing the wiring I used on parallel turrets is not using accurate mosfet nomenclature. I labeled the mosfet plate, grid and cathode simply because that is how I think of the mosfet structure.
Just a thought to consider.
With respect, Tubenit
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This being my first cathode follower, opting for the traditional set-up for now @Tubenit. I can experiment that way you see..
Modified my first schematic pic above
Question.
1. Do you think the FX send/return pots here will act as a pre PI volume? Dont really want to be adjusting all the time.
2. Do I even need a send pot considering its coming after the CF?
If anyone can provide a workable FX loop for this design, tried/tested much appreciated.
Only using true/bypass delay and reverb through it.
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In my opinion, 1) yes and 2) yes. My send pot is on the back of the chassis and is a "set and forget"
Lots of examples here: tube effects loop on board (el34world.com) (https://el34world.com/Forum/index.php?topic=10208.0)
I just provided you a tried and true one using a mosfet. :icon_biggrin:
With respect, Tubenit
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Getting hiss noise when pedal is activated through loop...Any suggestions??
I used whats known as Merlins FX loop on other forums..
I changed R2/R1 to 1M/4.7K. I have a feeling its something to do with source impedance which I have no knowledge about...The amp sounds great, latest schematic is posted in first post..
(https://el34world.com/Forum/index.php?action=dlattach;topic=32122.0;attach=117084;image)
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Your send jack wiring will not work the way you have indicated on the schematic. Typo?
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What makes you say that? Tip goes to wiper, sleeve to ground...Sends none switching, returns switching jack...
Problems when delays activated in loop creates a hiss through pedal, I'm using mxr carbon copy delay..
Tried with reverb pedal same thing, tried powering with 9v battery same hiss...Is this just the nature of tube fx loops?
My cables are good mogami so not that...
Tried with good working 12ax7, 12ay7 none microphonic valves...I'm at stage where the irons going to have to come out and fiddle with the input voltage divider...
From what I'm reading it might be an impedance thing..
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What makes you say that? Tip goes to wiper, sleeve to ground...Sends none switching
But you drew a switching jack with a jumper between the switch and the sleeve. Works fine if something is plugged into the send jack. But with nothing plugged in, your FX trim behaves like a volume control. Remove that jumper if you want the circuit to act like Merlin's circuit.
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On the Merlin Loop in the book as opposed to the website, the input has a 22k for R1 and for R2 a 1meg resistor for the input attenuation, to get around x46 attenuation before the cathode follower, so the return stage should bring that back up by around x50
Would the 4k7 resistor attenuate a lot more? Nearly x200 ish? Could that be a factor?
There is a 100pf capacitor added to the return gain stage grid to ground to help with miller capacitance, would that affect noise in certain situations or layout?
Would a coupling cap help on the way in?
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But you drew a switching jack with a jumper between the switch and the sleeve. Works fine if something is plugged into the send jack. But with nothing plugged in, your FX trim behaves like a volume control. Remove that jumper if you want the circuit to act like Merlin's circuit.
Ah ok, you mean something like this
(https://el34world.com/Forum/index.php?action=dlattach;topic=32122.0;attach=117118;image)
Wouldnt this stop signal passing when no jacks are inserted, isn't this the point in the jumper?..The FX pot right now is acting like a pre phase inverter MV. Turned all the way down no sound at all to speaker. Thought was bit strange because I thought it would act as a volume for the effects only...
the input has a 22k for R1 and for R2 a 1meg resistor for the input attenuation, to get around x46 attenuation before the cathode follower, so the return stage should bring that back up by around x50
Would the 4k7 resistor attenuate a lot more? Nearly x200 ish? Could that be a factor?
There is a 100pf capacitor added to the return gain stage grid to ground to help with miller capacitance, would that affect noise in certain situations or layout?
Would a coupling cap help on the way in?
Yes Im using 4.7k to bring the signal down to give more use from volume pot...I've experimented with different R1 values all the way to up to 64k the hiss is still present...
Tried coupling cap before 1M/22k divider hiss still present...Will give the 100pf cap to ground a try tmro...
Hiss only starts when pedals activated through loop
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Remove that jumper if you want the circuit to act like Merlin's circuit.
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Ok I've just removed the jumper, guess what happened...No signal when jacks are unplugged...
Where are you getting the idea jumper needs removing? I have like 3 different schematics of Merlins loop all showing jumper...Its present for when jacks are unplugged...Am I missing something here..
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Ok I've just removed the jumper, guess what happened...No signal when jacks are unplugged...
Where are you getting the idea jumper needs removing? I have like 3 different schematics of Merlins loop all showing jumper...Its present for when jacks are unplugged...Am I missing something here..
You did not follow my directions! Removing that jumper will not kill the signal. You still have a signal path. See attached pic.
BTW, the pic of Merlin's FX loop in reply #4 has no switch lug on the send jack, so it can't have a jumper between the switch and sleeve lugs.
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Thats the shield, drawing error, I'll fix schem...
After a bit of research, hiss problem seems to be a common occurrence in some loops with certain pedals...
Now considering stripping it out and installing a Dumbelator type..
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FWIW, every delay (3), reverb (2), and phase pedal I've tried in my loop has worked just fine for me with no issues.
You could simply use a triode instead of a mosfet for the cathode follower. See the schematic in my first reply in this thread. Look at the component values and topology compared to Merlin's FX loop.
You could also try the one I used in the D'Mars (attached)
With respect, Tubenit
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Installed the D'Mars loop attached above....This loop has no hiss issue :headbang:, plus it sounds just like Merlins one...Great news!
However heres the problem, the volume levels are way to loud, if send or level are dialed anything past 1. Volumes heading into blowing speaker territory..This is when the MV is full up and pre-amps just over 1. Turning pre-amp up sends volume way to loud...Ive followed the schem to full...
Its almost like its great set-up with send 1, level 2..Pre 1, MV full...Anything turned makes for a huge jump in volume..
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I'm assuming your using audio taper and not linear correct?
I'm assuming you followed the D'Mars FX loop exactly, correct? In other words, after the return jack you have an 82k resistor to ground and not a 1M resistor to ground? Right?
For illustration purposes .............. let's say when the FX send pot is at "1", it's 18k to ground.
So instead of a 250k pot, use a 220k resistor going into a 25ka pot and now you might be able to put the send pot at 5 or around that?
Do something for FX level pot IF you need to.
Hope that makes sense to you?
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I'm assuming your using audio taper and not linear correct?
I'm assuming you followed the D'Mars FX loop exactly, correct? In other words, after the return jack you have an 82k resistor to ground and not a 1M resistor to ground? Right?
For illustration purposes .............. let's say when the FX send pot is at "1", it's 18k to ground.
So instead of a 250k pot, use a 220k resistor going into a 25ka pot and now you might be able to put the send pot at 5 or around that?
Do something for FX level pot IF you need to.
Hope that makes sense to you?
With respect, tubenit.
:icon_biggrin:
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Alright, full day playing round an learning..
That 82k (return tip to gound) doesn't seem to make any difference, tried clipping diff values, no change to volume levels in or out..
Heres wiring layout..All pots are 250kA.
(https://el34world.com/Forum/index.php?action=dlattach;topic=32122.0;attach=117222;image)
(https://el34world.com/Forum/index.php?action=dlattach;topic=32122.0;attach=117227;image)
Removed parrallel connection, couldnt hear any difference between either to justify extra wiring...
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Are you using a 12AY7 for the FX loop tube? You could also try a 12AU7
This is what I was referring to regarding FX send and level pots
With respect, Tubenit
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Using AY7, I don't own AU7, from what I've read they draw down B+ V because of high cathode current, but will give one a try when I get my hands on one..Actually thinking bout it, maybe a, forget name, 12ax7/au7 in same bottle might do the trick here...
Yes took your advice, been playing around with different pot/resistors combinations today...
What I found - The send pot doesnt seem to be the problem here,,,, it the level pot...
Sticking with schematics 250k send pot, no resistor & using 10K level pot with a 2.2M resistor seems ideal, I can turn both up without dramatic volume spike, no adverse effect on tone stack...But a 10k pot/2.2M res seems strange..
The 82k to grounds still baffling, not acting like a voltage divider for me. Is this just a grid leak for v2b? Noticed other schematics its replaced with a pot, not sure what you would call that pot, return level maybe...
Just cant understand why original layouts not acting like should, when you built the amp did you have similar volume problems?
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At DIYItalia, some time ago we modded a 5E3 project and also added an FX Loop, our choice was the FX used on Engl Fireball (explained on one of the Merlin's books)
The amp was build with succes, so, if you want to give a look to the FXLoop, here is the schematic
(http://i.imgur.com/lx0Onyg.jpg)
Franco
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Right...Went back to Merlins loop..Couldn't deal with Dumblator volume increases...
(https://el34world.com/Forum/index.php?action=dlattach;topic=32122.0;attach=117424;image)
Changed:
Recovery triodes now split plate resistor to knock down signal 64k/47k
Send triodes input dividers now 1M/20K
MV type2 stereo pot 1M down to 500K
5879 Volume pots down to 500K
Running water sounds still present once MVs dialed past 6 when pedals activated...A lot better than before...It seems the more signal I drop at recovery the less present...
If no more ideas I'll call this one done..
Amp sounds great, blooms, sustains, harmonics right up the neck, fat and in your face...
May add some smoothing caps, drop PI tail down to 27k
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Thank you for sharing your success! Congrats figuring out a good solution for yourself. IF it's convenient, I'd love to hear a soundclip of the your amp please.
With respect, Tubenit