Maxon - AD900 Analog Delay

vaccastracca · Post by **vaccastracca** » 15 Jun 2015, 07:43

No, as i said, i put all the trimmers back like they were.
The repeats are as dirty as when i tried the pedal out of the box.

Dirk_Hendrik · Post by **Dirk_Hendrik** » 15 Jun 2015, 10:36

You cannot place em back as they were by eye.

Regarding those tails,
my experience is a yes. The 4 chip version is somewhat grittier than the 2 chip. Same applies for the EHX DMM's

vaccastracca · Post by **vaccastracca** » 15 Jun 2015, 12:10

Yes, i agree that placing them back by eye cannot be precise, even if aided by ear.
But i can assure you the pedal sounds exactly like before!
Maybe the differences are so tiny that there is no significant changes in sound.
If you confirm that the 4 chip is grittier, that could be it, and the pedal should be just ok, so i could stop worrying that it has something weird going on!

Just to be 100% sure, i did a video of the pedal, I'll upload it on youtube and link it here as soon as I it's ready.

Dirk_Hendrik · Post by **Dirk_Hendrik** » 15 Jun 2015, 12:33

If you have the guts to do so;

Adding a capacitor (1uF or larger is fine) between the last balance trimmer and the input of the post-BBD filter, as well as a pullup resistor to half Vcc at the junction of the new cap and the resistor at the input of the filter (that used to go to the trimmer) your delayed audio will be way less grittier.

vaccastracca · Post by **vaccastracca** » 15 Jun 2015, 13:33

Dirk_Hendrik wrote:If you have the guts to do so;

Adding a capacitor (1uF or larger is fine) between the last balance trimmer and the input of the post-BBD filter, as well as a pullup resistor to half Vcc at the junction of the new cap and the resistor at the input of the filter (that used to go to the trimmer) your delayed audio will be way less grittier.

Very nice tip, thank you so much!!!

I don't have any technical/electronic knowledge, so i couldn't perform this myself, but I can talk about it with someone who could!

vaccastracca · Post by **vaccastracca** » 15 Jun 2015, 15:41

So, here is the video:

Pardon the crap playing but i just wanted to let the repeats be heard so i didn't actually play anything meaningful!

With the les paul the repeats are slightly dirtier than with the strat.

P.S. I hope the video works....I was not sure how to link it here...

armdnrdy1 · Post by **armdnrdy1** » 15 Jun 2015, 15:54

So...that's what it sounds like after you messed with the trimmers?
You were warned!

vaccastracca · Post by **vaccastracca** » 15 Jun 2015, 16:08

armdnrdy1 wrote:So...that's what it sounds like after you messed with the trimmers?
You were warned!

It sounded like this also before.

Dirk_Hendrik · Post by **Dirk_Hendrik** » 15 Jun 2015, 18:16

Sounds pretty normal. Having the repeats on max will always result in the repeats turning grainy eventually.

Thinking about it it's rather surprising how long the pitch information remains intact.

vaccastracca · Post by **vaccastracca** » 15 Jun 2015, 18:49

Dirk_Hendrik wrote:Sounds pretty normal. Having the repeats on max will always result in the repeats turning grainy eventually.

Thinking about it it's rather surprising how long the pitch information remains intact.

That's VERY reassuring!
So it IS the character of this pedal after all!

masewal · Post by **masewal** » 25 Jul 2018, 15:24

soulsonic wrote: Now, this is how I did the bypass mod:
- Remove the Brown and Light Blue wires that are connected between Pads 13 & 14 and the bypass switch.
- Jumper Pad 13 and 14 together.
- Break the connection between Pin1 of IC1a and C5.
- Connect wires from the bypass switch to the spot that was just broken. The bypass switch now makes that connection when the effect is engaged.
- Put a large resistor (I used 10M) between the two lugs of the bypass switch that the wires attach to, this prevents pops from happening.
- Done!

I'm not an expert so I have some questions about this mod.

STEP 1 “Remove the Brown and Light Blue wires that are connected between Pads 13 & 14 and the bypass switch.”

Just to clarify, remove the Brown from the Delay time pot. Is that correct? And then, remove the light blue on the board or the part that connects to the switch?

STEP 2 Jumper Pad 13 and 14 together.

Jumper 13 and 14, do I keep the green cable connected to the switch?

STEP 3 Break the connection between Pin1 of IC1a and C5.

lift leg on C5?

STEP 4 Connect wires from the bypass switch to the spot that was just broken. The bypass switch now makes that connection when the effect is engaged.

when you say connect wires from the bypass switch to the spot that was just broken, you mean both, the light blue one and the brown?

- STEP 5 Put a large resistor (I used 10M) between the two lugs of the bypass switch that the wires attach to, this prevents pops from happening.

in between the green and blue cables?

I know it's been here a while but thanks for sharing this mod!

miketbass · Post by **miketbass** » 26 Jul 2018, 07:43

Sorry to bump a necro thread, but instead of creating a new one I figured I'd post here. I am looking for the calibration procedure for the AD 900 and it appears it may have been uploaded to Dropbox at one time. Does anyone have the calibration for this unit they could share?

Post by **modman** » 07 May 2020, 14:34

miketbass wrote:Sorry to bump a necro thread, but instead of creating a new one I figured I'd post here. I am looking for the calibration procedure for the AD 900 and it appears it may have been uploaded to Dropbox at one time. Does anyone have the calibration for this unit they could share?

I restored the dead links - this was since and due to the switch to a secure server https

Angelp · Post by **Angelp** » 14 May 2020, 00:51

Hi there Maybe this is a dum question but who here in the group has a veroboard layout of this circuit I would to build one Thank you in advance

soulsonic · Post by **soulsonic** » 14 May 2020, 01:57

Angelp wrote: ↑14 May 2020, 00:51 Hi there Maybe this is a dum question but who here in the group has a veroboard layout of this circuit I would to build one Thank you in advance

It's not a dumb question, but have you noticed how complex this circuit is? I would never recommend trying to build this on veroboard, you'd go crazy trying to hunt down the problem if it didn't work.

soulsonic · Post by **soulsonic** » 14 May 2020, 02:22

Also, this is the kind of pedal where it's probably a better deal to buy a used one and fix it up or modify it to taste. I just did a search on Reverb, and used AD-900 can be had for around $150. If you wanted to build one from scratch using either MN3005 or MN3008, you'd be spending at least $40 - $80, JUST FOR THE BBD CHIPS ALONE. So building a thing like this from scratch is by no means cost effective. The value of the information here is for people who want to repair or modify. I think there's good reason why in the 10 years this info has been up here, no one has published an AD-900 clone PCB.

dfx_pcbs · Post by **dfx_pcbs** » 18 May 2020, 22:05

Madbean has one https://www.madbeanpedals.com/projects/ ... anOWar.pdf

luuri · Post by **luuri** » 12 May 2021, 14:00

Hi all, I'm new to this site, an AD900 led me here =D i recently got it for a really good price. Anyway, sorry for repeating what has been asked before but I need some guidance with the trimpots, the dropbox ling in this thread says 404... Any help is greatly appreciated.

EDIT: So I did what others and wrote to Godlyke, they gave me the document, awesome people.

Maxon - AD900 Analog Delay [schematic]