Echomatic attempt - progress report

[KarenColumbo]

Can't contribute to this at all but thinking this is awesome!

[Passaloutre]

I should mention that I built my mostly according to the original design, with a few of my own tweaks. My mods (referencing Boscorelli's schematic):

"Lo-cut" switch is just a 202 cap in series with C4 going to the tape input. Likewise the "Hi-cut" switch is a 203 cap from that same point to ground. As you can hear in the video the Hi-cut has no effect, so that cap value could probably be increased. I guess you'd have to tune it to R5.

I also changed the "Mix" knob from a "wet level" to a true mix between dry and wet sounds, allowing for 100% wet or 100% dry. I accomplished this by removing R14 (again, referencing the original schematic here: http://imgur.com/a/NHRjW) and connecting the pin 8 of the opamp to the bottom of the "Mix" pot (R11). Of course, I disconnected this pot from ground, so it simply pans between full wet at pin 1 and full dry at pin 8. I used a linear taper pot for this, to achieve a 50/50 mix at halfway.

The speed control was taken directly from this page: http://proto-schlock.blogspot.com/2015/04/echo-matic-diy-tape-delay.html , which seems to be a much easier way than dealing with cutting traces, etc. It's completely reversible, as it just replaces a resistor with a pot.

[Passaloutre]

I recorded some better quality demos tonight. Hopefully these demonstrate some of the breadth of this effect. All were recorded with my Gretsch 6120 into my Silvertone 1484, no other effects. I recommend listening with headphones

https://soundcloud.com/passaloutre/sets/tape-echo

I changed the caps on both switches tonight too. The "LoCut" is now a 103 and "HiCut" is a 105 (still fairly useless).

Edit: guts:

[Passaloutre]

Since my idea for a high cut switch didn't turn out to be terribly useful, I'm already starting to wonder what might be a worthwhile feature to put in its place. Most of the really interesting mods would involve changes to the tape player rather than the mixer circuit, so I'm left with the usual candidates of putting clipping dudes in the feedback loop of the first opamp stage (and simultaneously adding gain) or misbiasing the Vref, but I have no idea what that would sound like.

Anybody else have some clever suggestions?

[Strategy]

Great work Passaloutre -- I am so glad someone found an easier way to mod tape deck for pitch control!!!
And I also will try your wet/dry mod. I used a toggle switch and get some dry signal leak that's not nice. At this point it might even be easier to build a 2nd echomatic than to modify mine, which already has a lot of hacks and I will probably damage if I try to extract the circuitry from the deck battery compartment. 

[Passaloutre]

I'll post my modified schematic. I think the mix mod and the low cut are very useful. I wouldn't bother with the high cut (maybe it would be useful if you used a reel-to-reel, which actually has some treble content).

[Passaloutre]

Here is mine as-built (minus the high-cut). The nice thing is this requires no changes to the PCB, as all the changes involve off-board wiring (and omitting R14).



You don't need a DPDT for the Lo-Cut, but I used one because it gave me somewhere to mount the cap. If you want to try the Hi-Cut, send another (switchable) cap to ground from the left-hand node of that switch. Calculate your cutoff frequency using the value of R5 resistor.

[Passaloutre]

Ok, so I have found a problem. I'm running a Tubescreamer before this circuit, and funding that when I engage the echo I lose quite a bit of the volume boost that the Tubescreamer was giving me. Can anyone tell me, based on the circuit as drawn above, why that might be? Is it possible I'm loading down my dry signal by connecting it to the mix pot that way? Do I need a cap between Pin 8 and the mix pot? That pin wouldn't normally have a DC path to ground, but I see now that it does after my modification. For that matter, wouldn't Pin 1 need a cap somewhere?

Pretty much any time I don't understand what's going on in a circuit, the answer involves the word "impedance".

[Passaloutre]

It looks like putting a cap in series with R9 would decouple both opamps from the ground. Can anybody confirm this is the right thing to do? Would that have anything to do with my volume loss when driving this circuit hard?

[PRR]

Cap at R9 is the right thing to do. It reduces pot scratch. I don't think it has anything to do with your overdrive problem; that first stage may just be too much gain.

[Passaloutre]

Hmm, that sounds reasonable, but I'm not convinced it's a headroom issue--if I crank up the TS all the way I get plenty of volume boost. The volume loss happens if the TS is up less than, say, 3:00, which is still well above unity without the delay. Could that possibly make sense?

[Passaloutre]

I finally got a hold of some Type IV Metal tapes today (Sony XR), and the difference is remarkable. Now I can really hear the effect of my HiCut switch!

[Passaloutre]

Playing around with this circuit again last night, and I was finding that it cuts a lot if the treble out of my dry guitar signal. I notice that it has a very low input impedance, could this be the culprit? I also certainly don't need the factor of 10 gain from the first stage. Would it work to bump up the two resistors on that first opamp to 1M in order to increase the impedance and decrease the gain? Would this have any negative effects like adding noise, etc.?

[fair.child]

I wonder how this guy did the mod though makes me inspired to build my own now.

[fair.child]

Are there any other mods that haven't been documented?

[fair.child]

Does anyone know the link for the veroboard or perfboard for the PCB?

[Piamp]

Hello !
First post here
I'm trying this project too
Could'nt etch q pcb so i went the veroboard route. It's working
Now i have to work on the tape deck. I use a marantz superscope c205 modified to be able to reduce motor speed.
As everybody i get a lot or warble at low speed, and some oscillations, but the c205 already has a hpf so it's quite usefull.
Still work tondo though


Envoyé de mon Redmi 4X en utilisant Tapatalk

[Piamp]

Sorry, don't know of to delete posts here...

[Piamp]

[Piamp]

almost done :