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My K-20X

Started by joecool85, February 27, 2014, 12:17:45 PM

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joecool85

#15
I've finally done it.  I added reverb to the K-20X.  I chose to do a digital reverb based on the Accutronics/Belton "brick."  The PCB I chose to use is from 1776 Effects, the Rub-a-dub reverb.  All other parts were sourced from SmallBear and I used the short delay Belton brick.  I think next time I might use the mid or long though...or the model 3 so you can adjust length.  The decay is a little faster than I would like, but still sounds pretty good.

While in there I also added a speaker kill switch so that I can turn the amp on and off without pops or noises.  No gut shots, but the power for the brick comes from an LM7809 drawing power from the positive leg of the stock power section.  There aren't any holes for standoffs on the PCB, so it is attached to the enclosure with a zip tie and foam between the board and the enclosure for electrical insulation.

Also not shown (and happened after these two pictures), the line out and speaker out jack have been changed to insulated plastic type jacks as the reverb brought out an issue I had made back in 2005 when I added those two jacks - a ground loop!  All fixed now and working better than ever.  I honestly never noticed it before since it was so subtle, but the reverb made it pretty obnoxious.

I like that I put the knob on the back - hidden reverb   8|
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

galaxiex

That's pretty cool, Joe...  :cheesy:

Where in the amp circuit did you put the reverb?

I assume at the front end since it's a stompbox type circuit?

Gut shots would be great.  8)
If it ain't broke I'll fix it until it is.

joecool85

#17
Here it is.

Please bear in mind that this looks different now as this was a test fitment.  The wires in this picture were connected to either end of R11 (one end lifted).  I have since removed R11 and now connect on the bottom side of the PCB to help with noise.  I have also added star grounding and replaced the metal speaker and line out jacks with insulated plastic types.

The schematic attached to the first post in this thread shows were I connected in.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

galaxiex

Quote from: joecool85 on February 25, 2020, 08:49:31 AM
Here it is.

Please bear in mind that this looks different now as this was a test fitment.  The wires in this picture were connected to either end of R11 (one end lifted).  I have since removed R11 and now connect on the bottom side of the PCB to help with noise.  I have also added star grounding and replaced the metal speaker and line out jacks with insulated plastic types.

The schematic attached to the first post in this thread shows were I connected in.

Thanks for the gut shot, but I don't see the schematic attachment?
If it ain't broke I'll fix it until it is.

joecool85

Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

galaxiex

Ohhh, DUH!

I didn't see we are on the second page!  ::)
If it ain't broke I'll fix it until it is.

Bill Moore

Now I'll have to try that!
I gave my first little amp away, but last year a fellow wanted to trade a "practice amp" for a pedal I had. I was surprised when he showed up with another Dean Markley. One of the pots had the shaft pulled loose, and after searching for a replacement. I ended up repairing the original. Speaker is a little rough, but at low volume it isn't noticeable.
Now reverb?

joecool85

Quote from: Bill Moore on March 02, 2020, 05:46:19 PM
Now I'll have to try that!
I gave my first little amp away, but last year a fellow wanted to trade a "practice amp" for a pedal I had. I was surprised when he showed up with another Dean Markley. One of the pots had the shaft pulled loose, and after searching for a replacement. I ended up repairing the original. Speaker is a little rough, but at low volume it isn't noticeable.
Now reverb?

I love it, well worth the time and money.  I think it was $45 or so in parts.  At first I wasn't sure I was sold on the "short" Belton brick, but I really jive with it now.  That said, I've heard clips of the medium and long bricks and they sound great too.  Others have said that the difference between the three is pretty small anyway.  Or, of course, you could go with the "3H" version using the Rub-a-dub Deluxe PCB.  It's an extra $2 and would require 2 more pots.  Other than that it's the same basically and would allow you to control the decay length, and tone of the reverb as well as the normal mix amount.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

linty

Hoping JoeCool85 is still around for me to necro this thread.  Would you be able to elaborate on the difference (if any) between the line out and the headphone out?  I'm having weird issues with using a K30RX to add reverb and pass the signal along to a mixer and am wondering if maybe this could be a better option than using the ph out.

Thanks!
Steve

Enzo

LIne out is a signal that is suitable for a mixer or another amp or some line level effect unit.  Headphones out is...tada.... for headphones.

willpirkle

In addition, a line out is designed to drive a high impedance load (>10k, such as the unbalanced input to a mixer, FX return, etc...) while the HP out is designed for very low impedances (8-32 ohms, speakers). A more important difference is that line out on an RCA or 1/4" jack, is designed (by spec) to deliver a specific nominal value of -10dBV, or ~316 mVRMS into that load. There is no formal spec for headphone outputs, so you never know what you're going to get, which is why some headphone outs are really loud and others are quiet, when driving the same load. Headphone outs are typically noisier as they usually use headphone (low power) IC amps, rather than op-amps but in many cases you can't really tell the difference (high gain guitar preamps, etc...).

linty

Thanks will, that makes sense.  From what I see in the modded circuit diagram at the start of this thread, it seems like line out volume would follow speaker volume.  If I wanted to silence the speaker when using line out would I just need to add an spdt to switch between the speaker and a 4 ohm power resistor?

Enzo

That solid state amp does not require a load, you can simply turn off the speaker with a switch.

What I would do is connect the line out 10k resistor to the phones jack tip connection instead of the speaker.  Now the line out works when you are on speaker or when on phones.  Now the phones still work, but you can use the phones jack to kill the speaker.   Just plug an unwired plug into the phones jack, and that opens the speaker connection.But a switch works fine too.

joecool85

Quote from: Enzo on July 21, 2021, 01:37:52 PM
That solid state amp does not require a load, you can simply turn off the speaker with a switch.

What I would do is connect the line out 10k resistor to the phones jack tip connection instead of the speaker.  Now the line out works when you are on speaker or when on phones.  Now the phones still work, but you can use the phones jack to kill the speaker.   Just plug an unwired plug into the phones jack, and that opens the speaker connection.But a switch works fine too.

Enzo, that's a pretty slick idea! I'm not going to re-wire mine since I rarely use the line out now anyway, but if I ever did another I would probably do it this way.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

flester

Great to read stories of people modifying gear like this, and also handing it on to a younger generation. My kids showing no interest in guitar gear yet, sadly. I'm holding out for their  kids.