Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on September 14, 2022, 06:00:06 am
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I met an issue to which I don't have a clear clarification.
I'm building a 6G15 stand alone reverb and have added a tremor-lator circuit after the mixer pot i.e. on the output.The tremolo is using LND150 Mosfet oscillator.
Tremolo works fine with both dry and reverb signal when the mixer pot has been opened a bit.But if I set the mixer fully for the dry signal tremolo stops to work. It seems that some serial resistor is needed
which is created when you turn the mixer pot. Has the cathode follower something to do with this issue?
https://el34world.com/charts/Schematics/files/Fender/Fender_reverb_6g15.pdf
/Leevi
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We need a schematic that shows exactly how you connected the tremolo to the 6G15.
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Here are the schematics (6G15 and Tremolo):
6V6 is used instead of 6K6 and full-wave rectifier instead of half-wave rectifier.
/Leevi
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You probably need a series resistor, or 250K pot, or rewiring the intensity pot, or maybe even a combination of these suggestions. Look on my website for several examples of how others have had to adapt the TON to their different circuits.
http://sluckeyamps.com/trem/trem.htm
Good idea. I think you'll get it sorted with a little experimenting. Be sure to post your final schematic. I'll add it to my TON page if you don't mind.
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Thanks, I'll come back.
/Leevi
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You probably need a series resistor
I used 22K resistor on the dry signal side which helped, even 10K might have been enough but was on the limit.
Below drawn schematic and give you free hands for it.
/Leevi
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I think it’d be better to aim for a better impedance bridge there. Feeding a 50k load via the 250k mixer pot seems like it may reduce the signal level.
It could be as simple as removing the 0V common connection to the trem depth pot.
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Good idea, have to test. I tried the tremolo with a 250K RA intensity pot but it was not any better.
/Leevi
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It could be as simple as removing the 0V common connection to the trem depth pot
Signal level increases but the effect of the pot is minimal i.e. in practise there is only speed control left.Furthermore the tremolo does not stop even if it is turned off.
I tried the similar idea with the 150K RA and 250 RA pots. With the 250K the tremolo almost stops when turned off
but the effective area begins from 11 o'clock.
The selection must be done between tremolo effect and signal level.
I think maybe the best option is to use the 250K RA and connect as grounded.
/Leevi
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Oh yeah, the trem on/off doesn’t actually turn the modulation oscillator off.
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Your latest schematic shows the footswitch grounded on both sides! That can't be right. The footswitch needs to be connected to the LED side of the optocoupler. Your hand drawn schematic had it correct.
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Your latest schematic shows the footswitch grounded on both sides! That can't be right.
Yes indeed, I corrected it in the attached schematic. Furthermore there are some other changes like the tremolo intensity pot value and some component names added.
/Leevi
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Are you satisfied with the latest changes? Any more tweaks anticipated?
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Are you satisfied with the latest changes?
Yes, I'm quite satisfied with the changes. The signal level is now higher and the tremolo works.Actually the effect of the tremolo is very similar to what it was with 50K pot but the signal level is much higher.
Any more tweaks anticipated?
Not for the moment. I'm very happy with the ground lift switch that works well.Caused a little extra work when everything had to be isolated.
/Leevi
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Well done! Very good idea. :worthy1:
Can we see some pics of your build?
I've added your project to my Trem-O-Nator (http://sluckeyamps.com/trem/trem.htm) web page.
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So to go back to the original query, the issue was due to trying to use the LDR to modulate the signal output of the cathode follower.
That method relies on the source impedance being much higher than the ON resistance of the LDR, eg as per the common cathode stage whose output gets modulated in a Twin Reverb etc.
Whereas the source impedance of a cathode follower is probably similar to, or lower than, the ON resistance of the LDR. So the depth of signal modulation with the reverb mix set to totally dry was minimal.
Hence the 22k ‘build out’ series resistor fixing that issue.
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Has the cathode follower something to do with this issue?
Got a good explanation, thank you pdf64!
/Leevi
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Can we see some pics of your build?
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Did you end up removing the "0volt common connection" (ground) per PDF64? I find that leaving the third terminal unconnected on the intensity pot is essential for proper working of Sluckey's circuit when adapting it to non-blackface amps.
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Where is the tank
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Where is the tank
The tank is planned to be placed outside. The unit will be used with a high gain amp and head transformers cause buzz if the tank is in the same stack. Tested.
/Leevi
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Did you end up removing the "0volt common connection" (ground) per PDF64? I find that leaving the third terminal unconnected on the intensity pot is essential for proper working of Sluckey's circuit when adapting it to non-blackface amps.
No, I used ground connection but a bigger pot 250K RA.
/Leevi
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Grounding the intensity pot puts a minimum 250k load on the output of your unit. That load was not part of Fender stand alone reverbs. I suggest lifting that third terminal to achieve the output level that the nontrem circuit originally had. The trem should work as well or better than it does now.
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Grounding the intensity pot puts a minimum 250k load on the output of your unit. That load was not part of Fender stand alone reverbs. I suggest lifting that third terminal to achieve the output level that the nontrem circuit originally had. The trem should work as well or better than it does now.
I had always wanted to ask you a question about your TON project but lost that thought until now. I know that wiring the INT pot as you suggest works but my question is this... Does The INT pot take the tremolo down to zero effect when the pot is turned max CCW?
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Grounding the intensity pot puts a minimum 250k load on the output of your unit. That load was not part of Fender stand alone reverbs. I suggest lifting that third terminal to achieve the output level that the nontrem circuit originally had. The trem should work as well or better than it does now
I made different tests with 50K, 150K and 250K pots. When lifting ground of these pots no one did not stop the tremolo at zero position.I even tested the signal levels and with a 250K pot it was difficult to hear any difference regardless if it was grounded or not. That's why I ended up to the 250K grounded pot.
DEMO:
https://rikstone.fi/ReverbTremoloTelecaster.mp3 (https://rikstone.fi/ReverbTremoloTelecaster.mp3)
/Leevi
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That's a lotta trem!
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Yes Sluckey, I get no trem at the minimum setting (as desired). Trem intensity gradually increases to swampy at the maximum setting. Lotsa spearmenting found that a 250ka pot with no grounding (variable resistor) was about perfect when inserted at the intersection of the coupling cap and the 1 meg volume pot in a plexish circuit. When I grounded one pot terminal, it reduced the trem intensity and also reduced the tone quality and volume level. The reduction happened whether the trem was switched on or off. Leevi's results suggest that my experience may not apply in the stand-alone fender reverb unit.