Hi All,
If you own one of these, you probably are in the same love-hate relationship as I am.
I love the way this amp sounds, but the noise level is simply unbearable.
I am on my second WT-1205. The first one was one of the better ones. I owned and used it regularly for a decade. The noise floor was bad, but workable on gigs. Eventually I reached the point where I could no longer stand the noise (and the input jack pop and the semi-parametric EQ that went from 40Hz-11kHz and not the 250Hz-2.5kHz it said on the dial) and I sold it.
Not long after I regretted that decision. I wished I had kept it and made the effort to figure out why this amp was so damn noisy. I subsequently acquired another WT-1205 after finding a deal that was too good to pass on. Unfortunately, my second WT-1205 was even noisier than my first. It was so bad that I put it away in a closet and closed the door in disgust....ugh...
So COVID-19 shows up and I'm not gigging on weekends. So with my free time, I decided to get to the bottom of the infamous Eden WT-1205 noise issue.
I won't bore you with the details of how I figured it out, the source of the problem is the transformer. This is likely the reason why some WT-1205's are better than others. Induction hum is a huge issue in the WT-1205. The ideal solution would be to enclose the transformer in some sort of shielding cage, but this is not practical. USM era Eden claimed that moving the DI cable to another location in the amp solves the noise issue (at least on the DI output) This may reduce the noise a little for some amps, but it solved nothing in my case.
The transformer induction hum enters the input of the THAT4301 chip (the first amplifcation stage) on both channels. The level of the noise from the transformer is comparable to your bass signal. Thus, both get amplified to the same extent. Things get even worse if you boost the midrange and treble frequencies on the EQ. As illustrated in the schematics below, the induction hum enters the first amplification stage via the cables leading to the pre-EQ DI and the tuner out signal path.
The solution to the noise issue is to disconnect the pre-EQ DI and tuner out from the input of the THAT4301 chips. This is accomplished by removing R111, C109, R211, C209 and U100 (TL072 op amp) from the lower board. BTW, you do not need to take the lower board out to perform this mod. The op amp is in a socket and the caps and resistors can physically be cut off the board.
After doing this, there is still induction noise on Channel 1 via Pin 1 of the cable leading from the lower board to the upper board. To get around this you have to insert a patch cable between the Channel 2 Pre-EQ effects send and Channel 1 Pre-EQ effects Return jacks and turn the gain control and compressor control on Channel 1 to zero.
Now if you plug into the main input and raise the master volume above 9 O'clock the noise will be gone from Channel 2 and barely noticeable on Channel 1 - even with extreme EQ adjustments. There will still be noise when the master volume is set at zero, but that is kind of irrelevant eh?
if you prefer a schematic representation of all of that, follow the blue arrows in the before and after pics below....
All of the switching functions of the amp are still usable after the mod. The only things you have to give up are the tuner out, Pre-EQ DI and the pre-EQ effects loop. The post-EQ DI will still be noisy after the mod. I always used a direct-box anyway but I digress....
OK, on to the other arrows in the diagrams above....
Input jack pop noise solution (red arrows in schematics):
NOTE: You have to remove the lower board to perform this mod.
The red arrows in the schematics above indicate where to install a couple of 2.2M pull down resistors on the input jacks of each channel.
The resistor is connected between the tip and sleeve of the input jacks on the underside of the board.
Now when you plug your bass in, you will not generate a loud annoying pop if you forgot to mute the amp before doing so.
Enhance control Mod (green arrow in schematics):
The mid-scoop for the enhance control is at 550Hz on both channels of the WT-1205 vs 200Hz for the original WT-series of amps.
I thought: 'hey, why not have both versions in the same amp?' So that's what I did. If you change C123 on the upper board from 820pf to 4.7nf, you convert the enhance control into the version found in the WT-800. The enahnce control on channel 2 (also can be modified in a similar way) is unaffected by this change.
Channel 2 Semi-parametric EQ Frequency Range Mod (yellow arrows in schematics):
For the life of me I do not know why the stock configuration of this control has a range from 40Hz to 11kHz! It is advertised as adjustable from 250Hz to 2.5kHz. Here are the changes you have to implement in order make it work as specfied on the front panel:
Change:
R253,R254 from 68K to 22K
R252,R255 from 330R to 10K
C225 from 68nf to 12nF
C226 from 22nF to 4.7nF
Diregard the missing pot in the picture below. It was worn out and needed to be replaced.
Well, if you read all that and reached the end, thanks for hanging in.
I hope this information proves to be useful to all current and future Eden WT-1205 owners.
All the best,
Sheldon
PS One more thing....low preamp gain with passive basses was also an issue for these amps. The THAT chip gain trimpots are set around 75% from the factory. it was likely not set higher than this due to the noise issues discussed at the top of this thread. Post-low noise modification you should be able to bring the lower board trimpot (VR201) up to the maximum setting. If you have a low output passive bass and have trouble getting the compressor or clip light to function, increasing the setting of this pot should also fix this issue.
Disclaimer: all of the mods described in this thread are done at your own risk. I accept no responsibility for any misfortune experienced by anyone who decides to try this stuff out on their own amp.
If you own one of these, you probably are in the same love-hate relationship as I am.
I love the way this amp sounds, but the noise level is simply unbearable.
I am on my second WT-1205. The first one was one of the better ones. I owned and used it regularly for a decade. The noise floor was bad, but workable on gigs. Eventually I reached the point where I could no longer stand the noise (and the input jack pop and the semi-parametric EQ that went from 40Hz-11kHz and not the 250Hz-2.5kHz it said on the dial) and I sold it.
Not long after I regretted that decision. I wished I had kept it and made the effort to figure out why this amp was so damn noisy. I subsequently acquired another WT-1205 after finding a deal that was too good to pass on. Unfortunately, my second WT-1205 was even noisier than my first. It was so bad that I put it away in a closet and closed the door in disgust....ugh...
So COVID-19 shows up and I'm not gigging on weekends. So with my free time, I decided to get to the bottom of the infamous Eden WT-1205 noise issue.
I won't bore you with the details of how I figured it out, the source of the problem is the transformer. This is likely the reason why some WT-1205's are better than others. Induction hum is a huge issue in the WT-1205. The ideal solution would be to enclose the transformer in some sort of shielding cage, but this is not practical. USM era Eden claimed that moving the DI cable to another location in the amp solves the noise issue (at least on the DI output) This may reduce the noise a little for some amps, but it solved nothing in my case.
The transformer induction hum enters the input of the THAT4301 chip (the first amplifcation stage) on both channels. The level of the noise from the transformer is comparable to your bass signal. Thus, both get amplified to the same extent. Things get even worse if you boost the midrange and treble frequencies on the EQ. As illustrated in the schematics below, the induction hum enters the first amplification stage via the cables leading to the pre-EQ DI and the tuner out signal path.
The solution to the noise issue is to disconnect the pre-EQ DI and tuner out from the input of the THAT4301 chips. This is accomplished by removing R111, C109, R211, C209 and U100 (TL072 op amp) from the lower board. BTW, you do not need to take the lower board out to perform this mod. The op amp is in a socket and the caps and resistors can physically be cut off the board.
After doing this, there is still induction noise on Channel 1 via Pin 1 of the cable leading from the lower board to the upper board. To get around this you have to insert a patch cable between the Channel 2 Pre-EQ effects send and Channel 1 Pre-EQ effects Return jacks and turn the gain control and compressor control on Channel 1 to zero.
Now if you plug into the main input and raise the master volume above 9 O'clock the noise will be gone from Channel 2 and barely noticeable on Channel 1 - even with extreme EQ adjustments. There will still be noise when the master volume is set at zero, but that is kind of irrelevant eh?
if you prefer a schematic representation of all of that, follow the blue arrows in the before and after pics below....
All of the switching functions of the amp are still usable after the mod. The only things you have to give up are the tuner out, Pre-EQ DI and the pre-EQ effects loop. The post-EQ DI will still be noisy after the mod. I always used a direct-box anyway but I digress....
OK, on to the other arrows in the diagrams above....
Input jack pop noise solution (red arrows in schematics):
NOTE: You have to remove the lower board to perform this mod.
The red arrows in the schematics above indicate where to install a couple of 2.2M pull down resistors on the input jacks of each channel.
The resistor is connected between the tip and sleeve of the input jacks on the underside of the board.
Now when you plug your bass in, you will not generate a loud annoying pop if you forgot to mute the amp before doing so.
Enhance control Mod (green arrow in schematics):
The mid-scoop for the enhance control is at 550Hz on both channels of the WT-1205 vs 200Hz for the original WT-series of amps.
I thought: 'hey, why not have both versions in the same amp?' So that's what I did. If you change C123 on the upper board from 820pf to 4.7nf, you convert the enhance control into the version found in the WT-800. The enahnce control on channel 2 (also can be modified in a similar way) is unaffected by this change.
Channel 2 Semi-parametric EQ Frequency Range Mod (yellow arrows in schematics):
For the life of me I do not know why the stock configuration of this control has a range from 40Hz to 11kHz! It is advertised as adjustable from 250Hz to 2.5kHz. Here are the changes you have to implement in order make it work as specfied on the front panel:
Change:
R253,R254 from 68K to 22K
R252,R255 from 330R to 10K
C225 from 68nf to 12nF
C226 from 22nF to 4.7nF
Diregard the missing pot in the picture below. It was worn out and needed to be replaced.
Well, if you read all that and reached the end, thanks for hanging in.
I hope this information proves to be useful to all current and future Eden WT-1205 owners.
All the best,
Sheldon
PS One more thing....low preamp gain with passive basses was also an issue for these amps. The THAT chip gain trimpots are set around 75% from the factory. it was likely not set higher than this due to the noise issues discussed at the top of this thread. Post-low noise modification you should be able to bring the lower board trimpot (VR201) up to the maximum setting. If you have a low output passive bass and have trouble getting the compressor or clip light to function, increasing the setting of this pot should also fix this issue.
Disclaimer: all of the mods described in this thread are done at your own risk. I accept no responsibility for any misfortune experienced by anyone who decides to try this stuff out on their own amp.
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