Johnson EAD-2 Echo Analog Delay [schematic]

[raindog]

effectsdatabase: http://www.effectsdatabase.com/model/johnson/ead2

[Dirk_Hendrik]

Thanks!

Deemphasis but no preemphasis. Odd.
No evident BBD bias arrangement. Vary odd

[ilcaccillo]

Thanks!

Deemphasis but no preemphasis. Odd.
No evident BBD bias arrangement. Vary odd

I have this pedal, I dont mind the lack of longer delay times but I find the sound too muddy and bassy.

I would love to modify it to be more usable, Im not looking to take the chips out and rebuild a new pedal,
would just like some help in how to add the needed preemphasis (thats probably one of the main reasons it sound muddy) and also add the BBD bias arrangement.

Could you help me on this?

Thank you so much

[Dirk_Hendrik]

The deemphasis is around 3u2-A. The preemphasis should be the reverse of the deemphasis. Use an Ibanez analog Delay schematic like the CD10 to study how that looks.

[ilcaccillo]

The deemphasis is around 3u2-A. The preemphasis should be the reverse of the deemphasis. Use an Ibanez analog Delay schematic like the CD10 to study how that looks.

Thank s Dirk, I will check the CD10 schematic.

One thing that I'm not understanding, shouldn't the De-emphasis be a High Freq reduction (in the same amount as the High Freq Boost in the Pre-emphasis) only in the Delay signal and not affecting the dry signal?

In the EAD-2 Schematic is seems that the De-emphasis is after the Mix of Dry Signal and Delay signal, so it seems to affect both instead of just affecting the Delay.

[Dirk_Hendrik]

You are correct. It seems to me the absence of the preemphasis is a design error as result of a hasty design process. These Johnson pedals were cheap.

Naturally it would be best if the dry signal does not pass these filters. However it's easier to have one signal path in which a mixer stage in which the wet signal is just added to the total. Drawback is that the dry signal does pass these 2 filters. Frequencywise there's little loss. Phasewise the signal makes a few rollercoaster twists. I suspect this to be the main reason theres so much reference to "bad buffers" in Boss, Ibanez and many other chorusses and delays.

[Sir Fayzalot]

I have this pedal.

One weird thing about it is that you can get an almost all wet signal if you turn the mix knob all the way to the right, but it's not 100% wet, more like 90% or 95% wet.

Another thing is that the regeneration knob made it hard to get into feedback, so I modded it (7 years ago or something like that), probably by decreasing 3R13 to 47K or something like that. I can look inside if you guys are really interested.

Nice pedal, one of the few early Chinese analogue delays actually exported, other than the Daphon.

[ilcaccillo]

Thanks for the replies,
What does the Regeneration knob does exactly?

The pedal was cheap, but I kind of like it, the only think I dont like is that it's too muddy and dark,
now it makes sense, there is De-emphasis only so basically all the high end is lost.
Of course you exepct high end roll off in an analog delay pedal, but this one it's too much.

It would be really useful to me if the high end was recovered by using the correct pre-emphasis and then the High End Roll off could be just tuned to taste with the Quality knob, at the moment the delays are already so dark, that the Quality knob can't be used.
This would make this pedal interesting for sure. I'm sure with one or two more corrections to the circuit the pedal would be really useful.

[ilcaccillo]

I have some reading to do know, learning about Pre-emphasis and De-Emphasis in delay circuits.
attached is some info I've found.

If anyone has suggestions on how to implement a correct Pre-Emphasis circuit in the pedal, please let us know.
Also more suggestions are welcome.

Thanks

[Sir Fayzalot]

Thanks for the replies,
What does the Regeneration knob does exactly?

The pedal was cheap, but I kind of like it, the only think I dont like is that it's too muddy and dark,
now it makes sense, there is De-emphasis only so basically all the high end is lost.
Of course you exepct high end roll off in an analog delay pedal, but this one it's too much.

Regeneration is feedback/repeats.

I never bothered with the tape quality pot, just keep it all the way to the left.

[Sir Fayzalot]

Actually I think I meant right, I haven't used it in a while.

(btw, is there a way to edit the posts?)

[ilcaccillo]

I never bothered with the tape quality pot

Off course not, it's unusable at this point since the pedal is already exaggerated Dark.

If the pedal had the missing Pre-Emphasis, the high End would be restored, and then you could use the quality pot to make it darker to taste.