1st Post (here) : ) My first project: Boozhound Amp

[John Bartley]

Originally posted by ray_moth

Avoid the dreaded hum, the enemy of most of us at one time or another.

Ensure all AC-bearing wire pairs are twisted, especially the heater leads, which cannot be kept away from the vicinity of signal-bearing leads and components.

Any reason why a person couldn't run AC bearing wires (still twisted) inside a shield? I'm thinking of something like braided co-axial wire shield stripped off the coax wire and slid over the heater wires with the ends of the shield soldered to the chassis.

[ray_moth]

I like how the old industrial tube stuff had a 16 or 14 guage solid gore ground - thingy from one end of the chaasis to the other. I parted out an old variable power supply for caps / variac / etc and still have the tank of a chassis. Icould probably try and duplicate that wiring.

You mean a bus-bar. A ground bus-bar is OK, provided you don't connect things to it 'out of sequence.' You want to avoid mixing ground-currents from different stages.

The best way is to run the bus-bar from the input socket at one end (which should also be its only connection to the chassis), to the negative terminal of the power supply's reservoir capacitor at the other end. In between, there should be a series of tightly-grouped grounding connections for each stage of the amplifier.

Any reason why a person couldn't run AC bearing wires (still twisted) inside a shield? I'm thinking of something like braided co-axial wire shield stripped off the coax wire and slid over the heater wires with the ends of the shield soldered to the chassis.

No reason at all not to shield the AC-bearing leads as you suggest, and that's what some people do. The only snag is that it might not be very practical with short leads, such as the leads going from one heater to the next, but with long leads it's a good idea.

[jsn]

Hey guys.

Thanks for all the interest in that site. I'm psyched.

I'm currently in Seattle for a show in some friends' space. I am giving them this amp. So it is a cool coincidence.

http://designcommission.com/pedalreloaded/

Anyway, it has been a while since I built this thing, but I am totally happy to help. I'll sub to this thread to keep in touch.

My one piece of advice would be to use a beefier power transformer. The Hammond gets pretty warm.

jsn

[bottom_feeder]

hey JSN - nice to meet Mr. Boozhound

I'm planning on using the iron from an old RCA 6v6 console, and since it's only running the amp, and not a whole tuner / preamp / amp setup, I *think* it'll sound decent with the first iteration. Later on, I'll swap in different transformers to mess with (fix) voltage, impedence, and FR if need be.

BUS-BAR - that's the ticket. I might even just cut it out and transplant right into "Franken-Booze" v1.0

Just waiting on the Hammond choke spec'ed in the recipe - BTW - could I use a different value choke (on-hand), and expect big variations in performance?

[EvilGenius]

Awesome!

I'm assuming you meant the primary power transformer for the 120V wall supply. Any suggestions?

What about my earlier post on the OPT's?

[jsn]

Power transformer and choke: I don't recall off hand what the B+ voltage was for that amp, but if you have a power transformer from a console using 6v6 tues, it should be close enough. There are a couple tricks you can use to get different voltages out of the same transformer. choke-input, cap input, and using a small first cap in the power supply. The choke can be pretty much anything, as long at it is rated for enough current. More henries means more filtering, and less resistance means less voltage drop, but it isn't critical.

Output transformers: You can use pretty much anything with a primary impedance of around 5k. If you are shopping, I would recommend the Magnequest Robin Hood series.

I'm travelling, but when I get home I will get familar with the schematic again, to be able to answer questions and talk in voltages and stuff rather than generalities.

jsn

[jsn]

My suggestion for grounding, noise, etc. is not to worry too much about shielding stuff. This is a low gain power amp, not a phono stage or something, so noise is not *that* much of an issue.

I have been building mic preamps using a bus bar and I really like it. Very clean, and easy to do. And of course sounds fine - very quiet. Have a look at the project for the aikido mic pre for photos.

jsn

[EvilGenius]

I'm going to trust you that the Magnequest RH OPT's will work with the 6V6's in your plan, or would a replacement with the 300B's (recommended on the site) yield better results, though at much higher cost? Or at the nominal ~15W power output, and all the characteristics of your planned amp, are the 6V6's just fine for a first timer?

Given the DIY nature of this hobby, it shouldn't be an issue to start with the 6V6 model (basically what you built) with either the Robin Hood OPT's or the cheaper Hammond P-t 1615 or P-T 1620 OPT's, and recycle parts for future project, right? Given that, perhaps the RH is a better investment? Do you think the RH series will provide a vastly cleaner sound from the 6V6 over the Hammond units? We're looking at about $200 vs. $80-$90 for the pairs.

I know, lot's of n00b questions...sorry about that.

[jsn]

Well the Hammonds are definitely more versatile, and darn good for what they cost. I just like the price of the RHs and the specs are right. The seem like the best bang for the buck - even if they cost more bucks. You want the 60mA version, btw.

But you will have fun and enjoy the results either way. Maybe using the Hammonds will give you an upgrade path for the future. Hey man, it's your amp, so you should use whatever parts you want!

jsn

[EvilGenius]

Well, yeah...but that doesn't mean I know what I'm doing!

I'd prefer not to blow myself up.