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**Twin** · 02-17-2012, 04:35 AM

Alan,

The kit that I purchased was a "small parts kit" from Mojotone(I think I posted a link earlier in this thread). The cab, chassis, speakers, grill, etc. I bought off a seller on ebay for an amazing price & the transformers & choke I bought from Mercury Magnetics. This was not the easiest way to put a kit together BUT it is very "period correct" visually & most importantly it sounds great!!!

**Twin** · 02-17-2012, 04:40 AM

txstrat - Sure, I'll take some pics of the finished product here in the next couple of days.
Also, Alan is right. I eventually just copied Fender's grounding scheme so that I would avoid the trouble of chasing elusive hums...

Alan - Thanks again on the copper tape tip, works wonders!!!!

**Steve Conner** · 02-17-2012, 08:52 AM

I agree with Alan, star grounding is an "easy" fix for people who don't understand, or don't want to think about, what the ground current actually does.

If you think star grounding is a panacea, just try adding the rectifier's negative output and the first filter cap's negative terminal to your stack of solder tags. Preferably one at the top and the other at the bottom.

Suddenly the amp starts to buzz nastily, and the only way to fix it is to modify the ground scheme so it's not a true star ground any more. (The rectifier should connect straight to the first filter cap, and then another wire should come from the filter cap to the rest of the ground system.)

At audio frequencies, the guided waves are tens of miles long, far bigger than the circuit itself. So the "EM wave" point of view isn't terribly helpful either.

**Greenmachine** · 02-17-2012, 02:37 PM

Originally posted by Steve Conner View Post

I agree with Alan, star grounding is an "easy" fix for people who don't understand, or don't want to think about, what the ground current actually does.

If you think star grounding is a panacea, just try adding the rectifier's negative output and the first filter cap's negative terminal to your stack of solder tags. Preferably one at the top and the other at the bottom.

Suddenly the amp starts to buzz nastily, and the only way to fix it is to modify the ground scheme so it's not a true star ground any more. (The rectifier should connect straight to the first filter cap, and then another wire should come from the filter cap to the rest of the ground system.)

At audio frequencies, the guided waves are tens of miles long, far bigger than the circuit itself. So the "EM wave" point of view isn't terribly helpful either.

Let me start by saying 1) both methods work, and 2) both methods can be done improperly (as demonstrated in this thread).

What's developing in this thread is just more of what I see all over the internet, which is each side convinced of the other's flaws and doing their best to prove this (which I'm sure is grounded - no pun intended - in both the theory and experience).

I really can't engage at the level of theory you two have - all I can say is, here's a picture of my BFDR with star grounding that works beautifully. It's one of three amps I've done the same scheme with. I was taught to do this by a guy with a 4-year electronics degree from a North American University and some 25 years of building studios, designing and repairing amps and pedals (for a living) and so forth.

Alan seems to think star-grounding can work if done properly - I'm interested to hear how this is done. What are some common errors of star-grounding that you've seen? Perhaps I'm just 3/3 lucky? What might I have done wrong to get that buzzing you describe? - my filter caps all have direct and separate leads to star ground.

And yes, you're right about the rectifier going to the first filter cap - I've done that, you can see it heading from the SB switch to the front of the amp, where the filter caps are lined up in series between the board and front of the amp.

**Alan0354** · 02-17-2012, 03:18 PM

Originally posted by Steve Conner View Post

I agree with Alan, star grounding is an "easy" fix for people who don't understand, or don't want to think about, what the ground current actually does.

If you think star grounding is a panacea, just try adding the rectifier's negative output and the first filter cap's negative terminal to your stack of solder tags. Preferably one at the top and the other at the bottom.

Suddenly the amp starts to buzz nastily, and the only way to fix it is to modify the ground scheme so it's not a true star ground any more. (The rectifier should connect straight to the first filter cap, and then another wire should come from the filter cap to the rest of the ground system.)

At audio frequencies, the guided waves are tens of miles long, far bigger than the circuit itself. So the "EM wave" point of view isn't terribly helpful either.

Actually I don't agree with star ground. I always use ground plane( in this case is the chassis) from grounding.

A guided wave don't have to be high freq that the wave length is close to the side of the structure. TEM wave travel in coax is guided wave regardless of frequency as it is following the coax however which way the coax is bended. Two parallel wires that carry the signal and it's return form a guided structure and the EM wave that travel in it is a guided wave. In this low frequency, it is all TEM wave.

**Alan0354** · 02-17-2012, 03:35 PM

Originally posted by Greenmachine View Post

[ATTACH=CONFIG]17409[/ATTACH][ATTACH=CONFIG]17409[/ATTACH]

Let me start by saying 1) both methods work, and 2) both methods can be done improperly (as demonstrated in this thread).

What's developing in this thread is just more of what I see all over the internet, which is each side convinced of the other's flaws and doing their best to prove this (which I'm sure is grounded - no pun intended - in both the theory and experience).

I really can't engage at the level of theory you two have - all I can say is, here's a picture of my BFDR with star grounding that works beautifully. It's one of three amps I've done the same scheme with. I was taught to do this by a guy with a 4-year electronics degree from a North American University and some 25 years of building studios, designing and repairing amps and pedals (for a living) and so forth.

Alan seems to think star-grounding can work if done properly - I'm interested to hear how this is done. What are some common errors of star-grounding that you've seen? Perhaps I'm just 3/3 lucky? What might I have done wrong to get that buzzing you describe? - my filter caps all have direct and separate leads to star ground.

And yes, you're right about the rectifier going to the first filter cap - I've done that, you can see it heading from the SB switch to the front of the amp, where the filter caps are lined up in series between the board and front of the amp.

I don't believe is star or one point ground. I believe in ground plane which in this discussion is the chassis.

Star ground usually are used in big systems that contain many rackful of electronics and there is not way to have a ground plane. Example of start ground gone wrong is having the return of the preamp connected to the ground point that carry heavy current of the output stage like this case here. And you can see it is hard to trouble shoot particularly if I can't look at the wiring directly, only looking at the picture. I have a strong suspicion it's ground problem way at the beginning the moment I saw the way the ground is connected.

I can tell you other than in audio field, all the more critical electronics gone to ground plane and multi point grounds to make it simpler and only concentrate on component placements to make sure critical signals don't cross. Guitar amp have relative fewer and big components, you can still use star ground and make it work. If you have small components on pcb and you have a huge circuit, you put a one point ground, how are you going to account for every signal?

**soundguruman** · 02-17-2012, 04:23 PM

Actually, you get less hum by grounding the power supply to one end of the chassis, and ground the preamp to the other side of the chassis. Builders have realized this for many decades.
There should actually be some resistance between the power supply ground and the preamp ground, the resistance of the chassis.
More modern designs actually install a resistor between the two. Yes it works better.

The concept of star ground would seem to be the best, but it does not work out that way. The ripple rejected by the capacitors when filtering, ends up being amplified by the preamp, and you get hum with a star ground.