The "Forum Amp" design thread

[JKowalski]

You are correct in your assumption! Thank you for the tip, and I've now located a whole assembly with mica spacer, bushing, etc.

BTW, googling "bush screw" does not turn up electronic info. 

I can only guess that whatever you get when you google "bush screw" is not "family friendly" 

Ahahaha, I can see how that might cause erroneous results....

The correct form "bushing" might help a little 

[Taylor]

Neat! I've been looking into little power amps, this one looks great!

Now I just need a more powerful one to replace my clunky Crate Powerblock for gigging situations.

I have looked into the issue of bigger power (in the 150 w range), speaking to a guy I know who really knows his stuff (designed class D amps for use as camera stabilization mounts or something, in addition to knowing guitar tech well). I would say that it's unlikely to be possible to make anything in that power range feasible as a DIY project, and it wouldn't be appreciably smaller than the power block even if we could do it.

The problem is the power supply. As noted to me in the threads that preceded this one, power out is equal to power in, minus losses. Even though class D is very efficient, there will still be something like 25% lost. So to get 150 watts out, we need something like 200 watts in. A power supply like this ain't cheap. Looks like $70 for an internal supply, which would not be safe for noobs to mess with. An external one like that is around $100. You can buy a Power Block for $100 if you look. And it would be unlikely to be any smaller than the PB. So as much as I wanted this to happen, I don't think it will.

With that said, 2 of these PCBs would be 40 watts into two 4 ohm speakers. That's loud. 40 watts is only half as loud as 400 watts. So for all the cost and complexity of 150w, you wouldn't really gain that much. To put that another way, 2 of these PCBs in one box is only barely quieter than a Powerblock. 

[Brymus]

Well, fellas. Here we have a complete 20 watt clean instrument amplifier (clean preamp and power amp) in a 1590A box.

Thats incredibly nice.
Much more compact than I had imagined.
Well done Taylor!

[askwho69]

any mp3 on this? sound testing? this is nice project!  

[Taylor]

Since it's a completely clean amp, it would be difficult to make a sound clip that would really show anything meaningful. You'd mostly be hearing my instrument (an 8-string bass), my speaker (a vintage Electro Voice 15"), my cheap microphone, etc. It wouldn't really tell you anything. It sounds like what you put into it, but louder.

[zambo]

so for the volume challenged among us, is it possible to bridge two of these and run 40 watts into one speaker? ( i am ok with 20 but i know a lot of bass players and they always want more headroom....)

[Taylor]

This amp is itself already a bridged amp, so I kind of don't think it's possible to bridge 2 bridged amps into one speaker, but I will investigate this.

[JKowalski]

Can't double bridge them. The only reason you can bridge amplifiers is because they have a ground connection that is fixed and an amplifier that outputs a signal around ground. When bridging, you replace this ground with another of the same amplifier. Already bridged amps don't have a fixed ground, they need connections to both ends of the speaker to work.

Unless you use some sort of output transformer to arrange it all.

[bassmannate]

so for the volume challenged among us, is it possible to bridge two of these and run 40 watts into one speaker? ( i am ok with 20 but i know a lot of bass players and they always want more headroom....)

I'm a bass player and I never really understood the power fascination. I have a little 120w combo 1x10 and I rarely ever get it up past half way. I don't normally need to, but if I ever have a need for more volume, the venue is usually big enough to have a PA that I can mic the amp with. Just don't get it. 20-40w would be plenty for me!

[deadastronaut]

yep 20 watts of a nice clean amp would suffice...i'll dirt it up later on..nice work taylor.

i'm just waiting for the eq version...

[slacker]

Nice work Taylor, looking forward to the PCBs.

[azrael]

I have looked into the issue of bigger power (in the 150 w range), speaking to a guy I know who really knows his stuff (designed class D amps for use as camera stabilization mounts or something, in addition to knowing guitar tech well). I would say that it's unlikely to be possible to make anything in that power range feasible as a DIY project, and it wouldn't be appreciably smaller than the power block even if we could do it.

The problem is the power supply. As noted to me in the threads that preceded this one, power out is equal to power in, minus losses. Even though class D is very efficient, there will still be something like 25% lost. So to get 150 watts out, we need something like 200 watts in. A power supply like this ain't cheap. Looks like $70 for an internal supply, which would not be safe for noobs to mess with. An external one like that is around $100. You can buy a Power Block for $100 if you look. And it would be unlikely to be any smaller than the PB. So as much as I wanted this to happen, I don't think it will.

With that said, 2 of these PCBs would be 40 watts into two 4 ohm speakers. That's loud. 40 watts is only half as loud as 400 watts. So for all the cost and complexity of 150w, you wouldn't really gain that much. To put that another way, 2 of these PCBs in one box is only barely quieter than a Powerblock. 

Oh, I know, I'm not looking to get a 150W amp. One that would work to get over drums would be cool, though.

This amp is itself already a bridged amp, so I kind of don't think it's possible to bridge 2 bridged amps into one speaker, but I will investigate this.

awesome!

Regardless of what happens, looking forward to grabbing one.

[Ben N]

I'm working on a gyrator-based mid section, with Baxandall bass and treble.

An Ampeg man, eh? Nice choice.

Actually, I hadn't really looked at any Ampeg amps for inspiration - I mostly just played with the various tone stack calculators and concluded that not having a mid boost is really limiting. What Ampeg amps use this kind of setup? I'd definitely be interested to see how some other designs have implemented this combination.

Sorry I didn't get back sooner. Here's are a few examples: http://www.unofficialampeg.com/schematics/v4preamp.gif, http://www.unofficialampeg.com/schematics/v9preamp.gif, http://www.unofficialampeg.com/schematics/svtpream.gif. My memory failed slightly, as these are all inductor based, but (with apologies to Clausewitz) what is a gyrator if not an inductor by other means, right?

[puretube]

Upgrade
yer
AMPs...

 

[bassmannate]

Upgrade
yer
AMPs...

 

The problem with some of those chips is that they're not nearly simple enough for noobs like me. surface mount and 64 pins just doesn't sound like a fun soldering day to me.

[arawn]

surface mount isn't bad if you work carefully. but 64 pins ick

[andersom]

Nice stuff Taylor

[therecordingart]

Taylor...how is everything coming along?

[Taylor]

Second round of prototypes check out just fine, so I've ordered the actual run. Normally this takes about 2.5 weeks, not sure how much this will be effected by Christmas.

[therecordingart]

Second round of prototypes check out just fine, so I've ordered the actual run. Normally this takes about 2.5 weeks, not sure how much this will be effected by Christmas.

Nice. I'm really excited! Any idea on costs yet?