Hi,
Since there were no schematics available, I've traced most of my Orange TH30 amp (preamp, loop driver, PI, power stage).
For reminder, it's a 2-channel preamp with a quad-EL84 power stage.
I can post my crappy drawings here if anyone's interested, however this amp looks like an EL84-driven Rockerverb 50 MK1 (its schematics can be found online):
- Clean channel: almost identical to RV50
- Dirty Channel: identical to RV50 (except one cathode bias resistor)
- Dirty Shape Control: identical to Dark Terror
- Loop Driver: identical to OR15
- Phase Inverter: identical to OR15
However, I noticed 2 weird things:
- The bass pot (in the Clean Channel tone stack) is a linear 250k pot, whereas it's a logarithmic pot in all the Orange tone stacks I've seen yet
>>> could that be an error made at the plant ? I already noticed that the bass control was not very "responsive"...
- For each EL84 valve, there's a 2k2 input resistor coming from the Phase Inverter into the valve grid (pin 2)... except for one valve, where this input resistor is only 1k !
>>> here, I'm kind of lost, why change this on only one of the 4 valves ? Crappy biasing for bad factory valves ?
Any advice would be very appreciated, thanks
Since there were no schematics available, I've traced most of my Orange TH30 amp (preamp, loop driver, PI, power stage).
For reminder, it's a 2-channel preamp with a quad-EL84 power stage.
I can post my crappy drawings here if anyone's interested, however this amp looks like an EL84-driven Rockerverb 50 MK1 (its schematics can be found online):
- Clean channel: almost identical to RV50
- Dirty Channel: identical to RV50 (except one cathode bias resistor)
- Dirty Shape Control: identical to Dark Terror
- Loop Driver: identical to OR15
- Phase Inverter: identical to OR15
However, I noticed 2 weird things:
- The bass pot (in the Clean Channel tone stack) is a linear 250k pot, whereas it's a logarithmic pot in all the Orange tone stacks I've seen yet
>>> could that be an error made at the plant ? I already noticed that the bass control was not very "responsive"...
- For each EL84 valve, there's a 2k2 input resistor coming from the Phase Inverter into the valve grid (pin 2)... except for one valve, where this input resistor is only 1k !
>>> here, I'm kind of lost, why change this on only one of the 4 valves ? Crappy biasing for bad factory valves ?
Any advice would be very appreciated, thanks
This should be in the instrument amps section.
The grid stopper value is not critical, anything between 100 ohms to 100k is ok in an instrument amp. Some high gain amps need a bigger one, like 10k, but most are ok with just a perfunctory 1k.
Strange though that only one is different. Factory mistake probably.
The pot looks like a mistake as well.
The grid stopper value is not critical, anything between 100 ohms to 100k is ok in an instrument amp. Some high gain amps need a bigger one, like 10k, but most are ok with just a perfunctory 1k.
Strange though that only one is different. Factory mistake probably.
The pot looks like a mistake as well.
Hey, here's what I did following your advice:
- Replaced the bass pot from B250K to A250K (treble pot was the right value, ie. B250K). The bass control now works way better, the clean channel had way too much bass response before this fix. Great !
- Replaced the 1K grid stopper with the 2K2, like its sisters, for the sake of symmetry. Doesn't seem to change anything (as expected).
- Also, I replaced R21 from 1K5 to 2K2 (dirty channel's 3rd stage cathode resistor) to exactly match the Rockerverb preamp. The sound seems fuller, chunkier to me - gonna keep it like that !
Last thing I have to mention: the soldering quality on this amp's PCB was terrible. Cold joints, flux residues, a capacitor had its pins way too long... the 4th gain stage plate pin wasn't event fully soldered, the amp was luckily working due to a bad contact. Has to re-solder about 10 points. So I guess a very poor quality control occurred at the factory. Quite shameful for a 900€ amp.
...and thanks for moving the thread
- Replaced the bass pot from B250K to A250K (treble pot was the right value, ie. B250K). The bass control now works way better, the clean channel had way too much bass response before this fix. Great !
- Replaced the 1K grid stopper with the 2K2, like its sisters, for the sake of symmetry. Doesn't seem to change anything (as expected).
- Also, I replaced R21 from 1K5 to 2K2 (dirty channel's 3rd stage cathode resistor) to exactly match the Rockerverb preamp. The sound seems fuller, chunkier to me - gonna keep it like that !
Last thing I have to mention: the soldering quality on this amp's PCB was terrible. Cold joints, flux residues, a capacitor had its pins way too long... the 4th gain stage plate pin wasn't event fully soldered, the amp was luckily working due to a bad contact. Has to re-solder about 10 points. So I guess a very poor quality control occurred at the factory. Quite shameful for a 900€ amp.
...and thanks for moving the thread
Hi,
I have a problem with my TH30 that the clean channel sometimes can become very loud and the clean volume pot has no function. Dirty channel is fine! I would like to see if I could solve the problem by replacing the clean volume pot. Do you know what value I should use? If I look at the RV50 shematic it's looks like it should be a 500 kohm logarithmic. Do you think that's correct? Or could it be something else that's wrong?
It would be great if anyone can inform me what to buy? Manufacturer and part number?
Any advice would be very appreciated! Thanks!
I have a problem with my TH30 that the clean channel sometimes can become very loud and the clean volume pot has no function. Dirty channel is fine!
I would like to see if I could solve the problem by replacing the clean volume pot. Do you know what value I should use? If I look at the RV50 shematic it's looks like it should be a 500 kohm logarithmic. Do you think that's correct? Or could it be something else that's wrong?It would be great if anyone can inform me what to buy? Manufacturer and part number?
Any advice would be very appreciated! Thanks!
If you really suspect the pot, clean it first.
Verify. Monitor signal level entering teh pot, is that stable. if the signal leaving teh pot is not stable but that coming in is stable, then the pot is suspect. but if the incoming signal is already unstable, replacing the pot does nothing.
And check out the solder work, problems are not always due to a bad part.
Verify. Monitor signal level entering teh pot, is that stable. if the signal leaving teh pot is not stable but that coming in is stable, then the pot is suspect. but if the incoming signal is already unstable, replacing the pot does nothing.
And check out the solder work, problems are not always due to a bad part.
These symptoms can be caused by a bad ground connection on the volume pot, or a bad pot.
I had an old Traynor EL84 amp head maybe 30 years ago. It would suddenly go to full throttle whenever it felt like it. A good smack, or lifting one corner up about an inch and dropping it, would return it to normal, often for weeks, then full crank again. Autopsy revealed that the wire connecting the ground side of the volume pot had been looped through the lug on the pot, but never soldered. Ten years of south Florida humidity, a little oxidation, some corrosion, a lot of vibration and an intermittent contact happens.
Hi,Hi,
Since there were no schematics available, I've traced most of my Orange TH30 amp (preamp, loop driver, PI, power stage).
For reminder, it's a 2-channel preamp with a quad-EL84 power stage.
I can post my crappy drawings here if anyone's interested, however this amp looks like an EL84-driven Rockerverb 50 MK1 (its schematics can be found online):
- Clean channel: almost identical to RV50
- Dirty Channel: identical to RV50 (except one cathode bias resistor)
- Dirty Shape Control: identical to Dark Terror
- Loop Driver: identical to OR15
- Phase Inverter: identical to OR15
However, I noticed 2 weird things:
- The bass pot (in the Clean Channel tone stack) is a linear 250k pot, whereas it's a logarithmic pot in all the Orange tone stacks I've seen yet
>>> could that be an error made at the plant ? I already noticed that the bass control was not very "responsive"...
- For each EL84 valve, there's a 2k2 input resistor coming from the Phase Inverter into the valve grid (pin 2)... except for one valve, where this input resistor is only 1k !
>>> here, I'm kind of lost, why change this on only one of the 4 valves ? Crappy biasing for bad factory valves ?
Any advice would be very appreciated, thanks
I'm looking for the schematic of the TH30. I read that you already did a lot of work to get it out of your amp. You'd be kind enough to share your work.
Thanks in advance..
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