As some of you know, I’ve been building some basses of late. I recently posted a diagram for a passive treble bass harness for a bass with concentric blend and concentric volume/midrange. I finally got this harness up and running in a bass and it is impressive! But the real reason I’m posting is to talk about one of my fav subjects - midrange controls. The midrange controls I do - use audio signal transformers (AST’s - another favorite topic of mine) but most AST’s are too large for small bass cavities, like P basses and others. I found some time ago an SMD AST that can be used in guitar or bass that is a true space saver (and wonder). These little transformers are tiny yet produce on average 1.6H. So, they fit right in with the Henries needed for a Rothstein style midrange control. They are manufactured by Liroiodo (Chinese) and cost $2.91 a piece shipped (from Ali Express). Here is their size.
Here I have the aforementioned bass harness with 3 concentrics. With using these transformers, the fit is easy and clean in a small bass cavity.
Again, this harness provides a full passive treble bass (47nF, 4.7nF), a Pickup Blend and the Volume/Midrange Control. In this photo, I have two of these AST’s in Series to provide the Bass with a midrange control that pushes 3.2H.
My case in point to this whole post is 1., I’m terribly excited about this 3 concentric bass harness; and, 2. to share a “Tip” that if you want to do a midrange control, you don’t need the clunky large Mouser Xicon cubes, you can use one of these in its place in a guitar and save considerable space.
This is the last time I’ll talk about midrange controls. Weeeee!!
It's rated a 1.2H but many of them actually test out to 1.7H according to buyer comments.
keep in mind that the measured inductance varies by the frequency it is measured at, so if the manufacturer measures at 60hz and the lcr measures at 1khz, the lcr meter will measure a higher inductance value. do our uses for it require a high degree of precision when the stage lights are shining and the monkey of a drummer kicks in? probably not.
The size of inductor and capacitor are interactive. Attached spreadsheet will give you the target frequency of the mid cut. Just change the values highlighted. in blue to get different results. I can send the LTSpice model and GuitarFreaks model for this also if you want.
You can experiment with an equalizer to see what frequency you want to cut - I recorded my guitar and then played it back thru logic with an equalizer plugin and tweaked the frequency cut.
Some personal prefs IMHO:
1) I like to cut around 300Hz to take the "mud" out of neck pickups 2) I like a deeper/sharper (high Q) cut so I don't take out as much of the surrounding frequencies 3) I like a higher inductance (and lower resistance) inductor to get I higher Q and lower frequency cut 4) Least fav frequencies 300 Hz (mud) and 3000Hz (harsh) - try cutting these in a recording for clarity 5) Fav frequencies 730 Hz is mid boost tube screamer territory, 150 Hz is palm mute territory
I’ve wired one up for you to see. I hope you can make it out. There is a little rectangular “hump” on one side. This is where I make my connections.
Here’s an example of one connected to a volume/midrange push pull.
Now on a bass, I usually put 2 in series. Or, I use a Mouser Xicon 42TL018 7K Ohms 2.6 Henry.
Here are the smd AST’s on a dual concentric bass harness. It’s actually a PTBM (Midrange) for Bass. I think I diagrammed this one out for you. If not, It’s a Volume/Midrange, a Treble Cut/Bass Cut and a Bridge/Neck blender. I put it on this lucite plate for the pic so you can see the little AST’s seriesed together on the right.
They are kinda delicate, their prongs can break off easily. I hope this helps.
As far as a 1.5H on a bass, I alwaysl go higher with one between 2-3H. But I really think you’d be fine with one on a bass Varitone or a tone pot.
I just took a pic of a Varitone with the 2.6H on it.
If you’re going to do a Varitone, you’d have plenty of room to position the mini transformers. Notice how I clip the lugs in order to glue down the transformer, you could series two of the little one, shrink wrap them and glue them down right on the switch!
Post by ssstonelover on Mar 31, 2021 18:18:26 GMT -5
Hi Frets, Thanks for the always informative and very useful information. For the bass project I'll use the Xicon for convenience but the SMD AST will work well for the moment I resurface for my usual guitar projects
I'll be sending another message for the bass project (your post titled "Revised Passive Treble Bass Midrange (PTB-M) for HH". Fortunately for that I hugged out the cavity so that is lots of room for all the ideas.