Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: FranciscoPerez on March 13, 2017, 07:58:55 am
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Hi,
Started a thread a few days back because I wanted to add a ppimv to an Orange Rockerverb 50 MKII.
With a couple of minor changes the amp sounds very nice overall, good modern tones, the ppimv is a great addition to the amp as well.
Everything's fine but the reverb!!
The reverb pot is barely usable, it goes from no reverb to a highly noticeable reverb in a fracition of a turn.
At the same time, seems like there's too much reverb effect regardless of the pot setting.
I'm thinking about increasing R64 to say 470K or higher, to have a finer control of reverb level.
On the other hand, would adding a voltage divider before V6-A input grid be a good idea to reduce the amount of reverb?
What do you think?? I'm not very used to reverb circuits, and trial and error on this amp is a pain, being PCB and all...
Attached is the reverb circuit.
It uses a short 3-spring reverb can.
Input impedance/DC resistance 800 ohms/58 ohms.
Output impedance/DC resistance 2575 ohms/200 ohms
And the entire preamp schem:
http://www.orangefieldguide.com/OFG_SCHEM/RV50C_sheet1.jpg (http://www.orangefieldguide.com/OFG_SCHEM/RV50C_sheet1.jpg)
Thank you!!!
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Is this something that started happening after the installation of the PPIMV, or has it always been like this? Is the problem worse with the PPIMV turned down and the preamp turned up?
There is nothing wrong with the circuit as drawn and I would strongly discourage you from changing out parts. It shouldn't act in the manner described, or at least in the manner that I interpret your words to mean.
An 8E tank is an odd choice to use with a transformer, but that doesn't mean Orange wouldn't do it. Is there any reason to believe that an 8E tank is the correct tank for this amp?
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It's always been like this.
The tank is stock 100%, no doubt. Tank and PPIMV pics attached.
Maybe now it's a little more noticeable, with high preamp settings and low ppimv, but I might be seeing things. How could this PPIMV alter the reverb effect? Anyway, it had this problem before as well.
or at least in the manner that I interpret your words to mean.
Sorry :) I wrote it too fast, I'll try to explain things better this time.
It feels like you are playing in a huge empty hall regardless of the reverb knob setting, the decay or dwell is way too much, feels unnatural, exaggerated. That's the main problem. The reverb knob doesn't change that, just alters the reverb level as expected, but it is of no use, since decay is always too long.
Maybe as you suggest, it's not a circuit problem, but the tank itself is not well suited.
According to the model number it's medium delay and horizontal plane mounting with open side down. The tank is mounted with open side up inside the head cab, however.
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I would temporarily add a dwell pot to control the level of reverb drive going into the spring assembly. Use the 6G15 as a guide to replace R21 with a 250KA dwell pot. I would leave R23 in place. This will go a long way toward taming the reverb. If you like it, figure out a way to make it permanent.
http://el34world.com/charts/Schematics/files/fender/Fender_reverb_6g15_schem.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_reverb_6g15_schem.pdf)
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Great thanks! Will try that.
You mean this, right? And then adjust to taste and replace the pot with fixed resistors.
Should be easy to make,definitely worth the try.
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In the OP you said the input was 800 ohms with three springs which would be an 8E tank. But in the picture you have a Ruby (re-labeled Belton) 3A tank which I believe is the equivalent to an 8A tank with a 10 ohm input. Since it is re-labeled, it may be also be mis-labeled as medium decay when it is really long decay.
If you overdrive the PI, the larger signals stop rising at overdrive while the smaller signals continue to rise toward the overdrive point. The result is that the smaller signals have a larger magnitude relative to the larger signals than they would have without overdrive. Reverb would be brought up with overdrive as well as the decay. But if it was problematic before the PPIMV installation, this wouldn't seem to apply.
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You mean this, right? And then adjust to taste and replace the pot with fixed resistors.
Yes, like that. I bet you'll like the dwell control enough to want to keep it, rather than replace with fixed resistors.
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Great sluckey! I'll try first and ask the owner in case he's happy to add an extra pot.
2deaf, thanks! I got those specs somewhere, but it was not really a reliable source, so you might be right and it might well be equivalent to a 8A. It'd make sense to have been mislabelled , since this reverb has most probably long delay.