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Building your own stompbox / Aion Andromeda - works but small issues
« Last post by stevengkeezer on Yesterday at 08:00:58 PM »
I recently built an Aion Andromeda odr-1 clone and it's functioning well, delivering great sound. However, I encountered two minor issues that have been bothering me.

Firstly, I don't hear any increase in volume when I turn the volume knob past 12 o'clock. I'm unsure if there is a limit to how much volume the device can produce, but it's not a big problem since the volume at 12 o'clock is sufficient. I'm not sure if this is a design feature or if I made an error during the build.

Secondly, when I turn the gain knob on and off, it produces a popping sound. Additionally, there are some noises that resemble those from a dirty pot when I turn the gain knob from 0 to 12 o'clock. However, the behavior smoothens out above 12 o'clock. I tried using contact cleaner to clean the pot and touched up the solder points on the pot, but the issue remained unresolved.

I don't really mess with the gain knob when I am recording so I can live with it, just wanted to see if anyone smarter than me had any insight into possible causes.
Building your own stompbox / Re: 3 position tele-style switch, what kind?
« Last post by ashcat_lt on Yesterday at 07:40:13 PM »
…with position 2 linked to 1 or 3 for both on in the middle…
There’s no link intrinsic to the switch itself.  In standard tele wiring, we usually tie position 1 to 2 on one pole and 2 to 3 on the other, then connect the two poles together to get the “both in parallel” in the center position.  It is not “on-on-on” in the sense we would normally talk about a dpdt, but an actual discrete 2p3t.
I wouldn't know where to begin for a Strat 5 way.
They’re the same basic switch.  PRR said “shorting”, but I think “make-before-break” is more fitting.  As you’re flipping the tele switch, there’s a spot in between two positions where both contacts are connected to the pole.  Early Strat players found they could wedge the things just right to get those in between (n+m, b+m) sounds, and Fender started modifying the switches to have actual detents so you could do it on purpose.  It’s still a 2P3T at heart, but with some in-between positions.

Some import versions of these switches - especially 5-way “Strat” switches - will have the two commons internally tied and present just the one because standard Strat switching uses the second pole for T pot switching, so both commons want to go to the same place anyway.
Building your own stompbox / Re: Tube Amp Tremolo Thumping
« Last post by Rob Strand on Yesterday at 06:08:09 PM »
One last dumb question: would a speaker impedance mismatch matter here? I discovered after measuring the OT that I apparently have an 8 ohm speaker connected to what appears to be a 4 ohm OT - primary measured 2.5K-5H/2.5K-5H and the secondary measured 3.1 ohms/8.3mH. Just wondering if an impedance mismatch could contribute to the situation. I don't intend to change the speaker as the 8 ohm OEM alnico Matchless speaker that came with the amp sounds really good and it has never been a problem, but it would be good info to know.
To the ear, what I've found is the opposite connecting an 8 ohm speaker to an amp set to 16 ohm produces a little more bass.

Your best hope is to get everything balanced as much as possible.   

You could even try a DC bias tweak by feeding DC a little DC into the grids vias large valued resistors.   Some amps have these schemes so the DC bias currents of the two output tubes can be balanced.    As a starting point you can measure the voltages across you cathode resistors - that only goes so far as the cathode resistors themselves are not exactly equal.  You can do better if you measure the resistor values and calculate the current.    Keep the amount of adjustment small and don't allow the tube currents to be adjusted with large bias differences in the bias currents.

It's important not to using the bias adjustment as a fix-all.  You want to balanced the LFO level feeding the grids first *then after that * use the bias balancing as a fine tweak.
The output is still differential, it doesn't matter which side of the transformer the pot is on. Putting it on the secondary has the advantage of keeping the drive impedance to the transformer low (or at least constant).
It's not technically full differential.  Bill Whitlock (from Jensen) has written about it  number of times.  See pages 38, 39.  You want to have balance impedances to ground at every point - looking forward or backward.   Looking back into the terminals the simple divider isn't 100% compliant.

That's not to say a simple divider isn't OK.    On page 2, figure 2.2 vs figure 2.3.

It's just that if you want high CMRR over the widest frequency range the "true different" is better.  Something in-between figures 2.2 and figure 2.3 is a U-pad attenuator, which maintains the impedances.
A variable U-pad divider would replace R2 with a pot that opens and shorts.

To gain all the benefits you need a transformer with balanced capacitances feeding a a differential input. If you connect to a single-ended input or uses transformers that aren't really balanced then it all fall in a heap.

All I'm saying here is there is a fully differential version.   The simplified case like figure 2.2 is usually fine.

Not sure what you mean by that. Cheap or not, the source impedance should be as low as possible for best audio performance. It's the secondary loading that is important for matching, not the source impedance.
No doubt about it.

All I was implying is good transformers will have a good response with a drive impedance equal to the rated impedance (that's usually how they are spec'd) but the small transformer could probably need some help from a low-impedance.    Your 100R divider is good.  Whereas the ESP circuit with 1k pot might not be so great for those small transformers.

With posts like this it's hard to know where to set the quality bar.   I suspect Jensen transformers would be out but it's also possible those small Xircon's are pushing their luck as well.

There are some serious errors of understanding on that page :icon_eek: He shows the amplifier plugged into >100k impedance (totally unecessary), the guitar plugged into <1k impedance (good luck), and a grounded centre tap which destroys the benefits of a balanced output. Yikes!
Good catch, I didn't read it all.  I was only hunting down a commercial example with a schematic.
[FYI: one of the pic does show Speaker or Dummy Load]
previous post

its been awhile, but i finally finished making a new PCB for my "tube booster" (its basically a tube screamer modified to be strictly a clean boost/eq pedal). all of the signal traces are .012", and most of the power traces are .016", and there are 2 ground planes; 1 on top, and 1 on the bottom.

are there any issues with the layout?


schematic (for some reason it wouldnt let me upload the schematic on here)
Building your own stompbox / Re: i'm new to pedals, any advice for me?
« Last post by Kipper4 on Yesterday at 05:34:25 PM »
 :icon_mrgreen: Advice…..
Buckle up and welcome to the Hotel California of forums.
Hope you enjoy your journey. Welcome and have fun.
Building your own stompbox / Re: Prescription Electronics COB Question
« Last post by antonis on Yesterday at 05:24:32 PM »
If we're talking about C5 here:, it's just a NFB cap (it would have the same effect as if it was wired between Q3 Collector & Base) and, IMHO, it's tolerance is irelevant..
Building your own stompbox / Re: Tonewoodamp
« Last post by DrAlx on Yesterday at 05:14:57 PM »
The download link doesn't appear to be working. Do you have a new one?

Here you go...!AvrH61utWEtEiz97o2-i-hpundLe?e=F6bDuy

Building your own stompbox / Re: Prescription Electronics COB Question
« Last post by pedalbob on Yesterday at 04:56:28 PM »
 Thank-you so much for all of the replies.  As always I learn something from the experts when I post a question here.  Hoping I can reciprocate somehow eventually but I am still a humble neophyte at the DIY pedals ... but I became addicted as something to do during covid ...
Thanks for the schematic too !  I had found some tagboard/vero board layouts but none were exact looking at the real thing ... this will save me a bunch of time ...
Thanks again guys !!

PS. I did identify a couple of components that have slightly different values than the schematic online  ... one of the film capacitors is .047mfd not .1 mfd like the other 2.  Transistors in this one are actually MPSA05 which shouldn't matter vs. 2N3904.  If I find anything else I will post an update.

The PCB is old school single layer bare copper and almost looks hand drawn.  I definitely am going to build one and may make the PCB too.

Why would they use the styrene cap over a more conventional film or ceramic disk ?  Is it just a boutique mystique thing or will the tighter tolerance have an impact on that circuit ?   

Building your own stompbox / Re: Med-high voltage Valvecaster/Tube preamp project
« Last post by momo on Yesterday at 04:55:21 PM »
Sometimes you never know how deep the iceberg goes.
So I think I had faulty plastic audio jacks, the input was shorting a few electrons I think.
I noticed right away a difference in audio levels which got higher. That is,  no dc present, just circuit bleed.
Anyhow, now I measured current on pin 5 heater, it's a very very efficient heater lets say.
I get 140mA @ 3.5v psu....
No shorts and infinity resistance now when I plug the meter on the dc input without power.
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