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Projects => Build Reports => Topic started by: add4 on March 09, 2017, 12:06:06 PM

Title: Polytone preamp
Post by: add4 on March 09, 2017, 12:06:06 PM
As i have a passion for jazz, I also love the jazz sounds and a few of these are linked to the polytone mini brute amps.
I have one myself and it literally kicked out all my other amps of the house when I needed space because of the babies.

I thought of putting the polytone mini brute preamp in a pedal to get closer to that very specific sound even in a normal amp at a gig or jam session.

It's basically an OpAmp clean boost stage followed by a bass/mids/treble bandaxall. The voice switch controls the freq response of the boost stage with different switchable RC network to ground and goes from Wes Montgomery to fusion/rock sounds (hence the name "multitones") and I added the LEC (Low End Control) switch as a request for some people who wanted to control the "boominess" when used with an archtop.

It's actually a project for some jazz guys in a forum who would order me a few of these so wish me good luck

(https://uploads.tapatalk-cdn.com/20170309/a56f890b999b7993c7293c4893a77efd.jpg)

(https://uploads.tapatalk-cdn.com/20170309/8b03dad5de40389b6862702cdd3f293b.jpg)

(https://uploads.tapatalk-cdn.com/20170309/30678d1e93538cd29fa3159fd3f8c4bd.jpg)


 


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Title: Re: Polytone preamp
Post by: Aleph Null on March 09, 2017, 02:21:06 PM
Is that a silk screened enclosure? Did you do it yourself?

Also, show us the guts!
Title: Re: Polytone preamp
Post by: crashguitar on March 09, 2017, 04:43:25 PM
Looks cool!

Any chance you would share the project files?

Chad
Title: Re: Polytone preamp
Post by: add4 on March 09, 2017, 04:48:28 PM
Is that a silk screened enclosure? Did you do it yourself?

Also, show us the guts!

A local guy is doing UV printing so it's getting very easy to have this kind of finish . Which is the only reason why I accepted to do a small run of these for people. Haha.

Gut shots are coming


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Title: Re: Polytone preamp
Post by: add4 on March 09, 2017, 04:53:57 PM
Looks cool!

Any chance you would share the project files?

Chad

I can point you to the original polytone schematic which is publicly available but I'm not confortable with sharing the files since I'm making a few for some people.
I have no problem to provide you a board and BOM however, but this version of the PCB still has errors and I had to do off board wiring to actually make it do what I wanted (actually it's a change of the way the LEC switch works ... I didn't like my first way of making it work).
If some of you are interested I could make a few more for madbean people when the boards are correct and provide a doc how does that sound?


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Title: Re: Polytone preamp
Post by: add4 on March 09, 2017, 04:59:21 PM
Is that a silk screened enclosure? Did you do it yourself?

Also, show us the guts!

Guts as requested there are a few cuts and offboard wiring on the pcbs as my boards are still not mature

(https://uploads.tapatalk-cdn.com/20170309/8543976dda4c40ef6290b599017d973b.jpg)

(https://uploads.tapatalk-cdn.com/20170309/8ba456352bfef2df9700cd7bcda55ede.jpg)


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Title: Re: Polytone preamp
Post by: nzCdog on March 09, 2017, 05:37:02 PM
hotness! 8)
Title: Re: Polytone preamp
Post by: Leevibe on March 10, 2017, 08:08:27 AM
Shnazzy!!
Title: Re: Polytone preamp
Post by: Marshall Arts on March 10, 2017, 01:05:14 PM

If some of you are interested I could make a few more for madbean people when the boards are correct and provide a doc how does that sound?


Fair enough. Count me in!
Title: Re: Polytone preamp
Post by: Droogie on March 10, 2017, 01:37:40 PM

If some of you are interested I could make a few more for madbean people when the boards are correct and provide a doc how does that sound?


Would buy!
Title: Re: Polytone preamp
Post by: stringsthings on March 12, 2017, 05:02:51 AM

If some of you are interested I could make a few more for madbean people when the boards are correct and provide a doc how does that sound?


Also interested!
Title: Re: Polytone preamp
Post by: jubal81 on March 12, 2017, 04:54:15 PM
Top notch, bud. Great work!
Title: Polytone preamp
Post by: add4 on March 13, 2017, 03:48:16 AM
Thanks to everyone for your kind words and your interest! I more or less learned a majority of the few things i know here, because of you, and the madbean projects (and the other great forums, and sites that some great people maintain, but here is where the heart is).

For those interested in a PCB, are you ok with some minor mistakes? With this version of the PCB we need to lift one leg of 2 different capacitors and run a wire from both of these floating legs to the leg of a pot. it's a bit messy, but i've seen that on some madbean projects (egodriver :) ). Actually the PCB also works without the mod, but it's not doing what i wanted it to do .. so you cna even try without the correction and with them and keep what you prefer..
The correction removes bass from the signal with a switch (it's just adding  caps in // to the very small one decoupling cap I put really... the values I propose should probably be tweaked, especially for bass..) , without correction, the switch adds mids/highs by adding/tweaking a rc network in the feedback loop of the amplification stage. which also sounds cool.. but it keeps too much bass actually be useful to prevent feedback on jazz guitars .. which is the goal here
if you are ok with it, i have some boards ready right now, they are verified.
I can provide the BOM with the notes for the error correction on PDF, but i don't have a fancier doc ready yet, even if it would be fun to make one..

How does that sound?
Whats the usual price for something like this ? :D
Title: Re: Polytone preamp
Post by: Droogie on March 13, 2017, 08:17:04 AM
Seems fine to me! Let t rip!
Title: Re: Polytone preamp
Post by: Marshall Arts on March 13, 2017, 11:31:12 AM
Fine for me as well. Take madbean's prices as a guidance and deduct some money for missing documentation and the bugs you wrote about.
Title: Re: Polytone preamp
Post by: diablochris6 on March 14, 2017, 08:56:39 AM
Looks neat. What is your rail to rail voltage? I only glanced at the original schematic, but it looks like the circuit goes from -15V to +15V. Are you using a charge pump?
Title: Re: Polytone preamp
Post by: add4 on March 14, 2017, 08:57:44 AM
Looks neat. What is your rail to rail voltage? I only glanced at the original schematic, but it looks like the circuit goes from -15V to +15V. Are you using a charge pump?


Yes. I used -9v/+9v


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