this is an older build now, but i wanted to post it while i’ve been on the subject to record the process. believe it or not, i still have some work to do on this one. i used a TL082 as a buffer for the mixing circuit. getting the gain set to my taste has been the toughest part. this one (unlike the last) is a bit low. it will all come in due time though. i’ve produced two solid builds this week (though really just debugging this one and one from scratch), and i’ll consider that a productive week.
ever wanted to see how that 2N2222 might hold up as a linear RF amplifier? here’s a handy feature of ngSpice that i found recently. i’m rather new to ngSpice and at first was somewhat frustrated by its differences from other SPICE variants. however, i’ve earned a deep appreciation for it and its integration with the gEDA suite.
This little guy is currently on eBay. I always thought that this tremolo wasn’t bad, but the volume drop was insatiable and drove me nuts sometimes. I thought I would try modding this one by cutting out the C4 cap (a 0.1uF bypass cap) which is the alleged cause of the gain loss. It is, but not without good reason. It does keep the effect sounding smooth and really clean. Removing the cap also opens up those capped frequencies which some people report a more warm and/or harsh tremolo tone. I enjoyed the more dramatic effect of the pedal myself, and decided to make it even more so by substituting the 10k ohm resistor before the non-inverting terminal of the first opamp for a 4.7k. This added a nice volume boost which gives the tremolo more cut especially when combined with heavy reverb or a washy delay. We’ll see if anyone decides to buy it. I think it’s a huge upgrade from the original sound.
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I’m hoping this will clear things up for the night. Practical matters have brought about the decision to build a tube amplifier. In this case, I’m going to get a WeberVST kit as not to go it solo on the first attempt. The winner of much debate as to which circuit to start with is the ever popular 5E3, a Fender ’57 Tweed Deluxe circuit.
Unfortunately, this circuit isn’t quite ideal. The goal for our prototype is going to be about balancing loudness with clarity and transforming its bluesy rock tone into something a little smoother and less aggressive. We’re going to attempt lowering the gain in the preamp by using tubes with a lower gain factor and increasing wattage in the output stage which will include substituting some 6L6 variety for the standard 6V6s. The use of two separate volume controls seems to be pointless for our purposes as well. I think I’ll probably wind up setting up a treble and bass tone stack by dumping one of the volume pots.
She’s big and bulky, but you can’t ask for too much when you’re dealing with pre-printed PC boards. The 22k resistor in the gain path makes for extremely high output (in terms of headphones). The 100k stereo potentiometer on the output side should make the noise floor a lot lower unless the knob is cranked. That’s what I was going for hear since the application of this device will be mainly for when other loud instruments are being played in the room. A short trip to the electronics store should yield three more of these guys. After that, it’s onto the chassis.
This was my first attempt at building the circuit on the PC board. Unfortunately, I think I’m going to have to get a different board since this one isn’t quite big enough with two opamps. Soldering it is also a bitch considering it’s tiny and my iron tip isn’t as small as it should be.
The 1/8″ plug is the output soon to have a pot attached to it for volume control. I’ve been thinking about attaching an light meter to each channel, but I still need to know what the dimensions of the chassis will be before I jump that far into it.
Double the circuit for stereo. This is a breadboard representation of a single “channel.” Each channel will have its separate PCB with controls. This one lacks a volume pot, but the output was more than enough. 750mW after hooking up the gain path resulted in ripping the ear buds out of my ears in order to avoid total deafness. Sadly to say, I have about as much luck avoiding electrocution as I do cutting myself with knives. I’ll keep to the low voltages for a little while longer.
Abram Morphew is a musician, composer, inventor, theorist, technologist, self-taught engineer, and amateur scientist who lives in a '96 Jeep Cherokee with his wife traveling from place to place as the binary marketing show. This blog is a catalog of stuff that I make or bits of information that I think could prove useful later on when memory fails me. I currently hold an Extra Class Amateur Radio Operator license and transmit on the air as K2NXF.
