Someone in LA area want to help me?

[Lindz]

I've posted a few times here and have now made 3 amps - 2 different 18 watt builds and a Weber Java. All work well and sound great but I am having trouble getting rid of buzz/hum on the two 18 watters (the Java is pretty quiet by comparison in spite of the weird layout).

The grounding is more or less verbatim what Trinity, Ceriatone and other 18 watt builds use with the bus bar etc., yet both amps are quite noisy in terms of hum/buzz. I am sure that my mods contribute to the noise as does the power in my condo but other amps I own and the Java are much quieter - both have a bit of extra gain vs stock, one has power scaling, one has channel switching, etc. so there is a bit more to them than completely stock 18 watters and I am sure my mods and lead dress are contributing to the noise

I have played with all sorts of variations over the past month or so trying to kill the noise but I am at the end of my ablility and tired of getting nowhere with this.

I'm interested in having an experienced builder/repair guy in the Los Angeles area go over my 2 amps with me so I can learn how to troubleshoot noise, lead dress etc better than I have been able to on my own, and critique my builds so I can tweak these so they are quieter and do better with future amps.

I'd also be interested in learning how to use a scope etc. so I am not so helpless with problems in the future. I'm not really interested in just having them repaired - I want to participate and learn. I'm green but learning fast

Anyone interested in helping me out? I'm in Sun Valley near the Burbank airport but will gladly travel a bit if someone would be interested. I'll pay a reasonable fee.

Thanks!

[selloutrr]

I'm in Palm Springs. I should have a weekend free in about 6 weeks.

[M Fowler]

Wow Burbank and Palm Springs both bring back memories!

Wish I was back in the area, especially today 5 above Zero

[selloutrr]

Mid 70's clear blue skies

[dansamp]

I can help if you'd like
I am near LAX
I am available evenings or weekend afternoon, early evening

Dan.

[dansamp]

OH,
wait,
I don't have a scope

but I can help either way

[Diablo1]

Why don't you just post up some pictures of your layout and the schematic/mods incorporated. Folks may be able to steer you in the right direction to quiet them down. Post 'em here as well as on the music electronics forum.

[Lindz]

Selloutrr - I may take you up on that if I can't figure out something closer to home - thanks for the offer. My GF's folks have a place in Palm Springs so it may work out to go visit them and do some amp work while I am there

Diablo1 - I get that I could post pics and info for help - I have done so with other issues and people here and elsewhere have been very helpful

But that is not the same as working in person with someone who really knows their ABC's. I'd like to accelerate my learning and nothing beats seeing things in person and being able to ask a million questions.

[LOUDthud]

The grounding is more or less verbatim what Trinity, Ceriatone and other 18 watt builds use with the bus bar etc., yet both amps are quite noisy in terms of hum/buzz.

Let me guess. A transformer bolt is used to ground the center tap for the B+ winding. Are you using a multi section cap with a common ground pin? Are you using some poor implementation of a star ground? Chassis grounded input and speaker jacks? Does the hum go silent immediately when the standby switch is moved from play mode to standby?

[Lindz]

yes - b+ center tap is grounded to lug bolted to chassis near transformer bolt

"Are you using a multi section cap with a common ground pin?" If you mean am I using a cap can for the first cap .. yes, and it is grounded at same point as the center tap as per Ceriatone, Trinity and other 18 watt layouts

"Are you using some poor implementation of a star ground?" No I am using a bus ground as per those layouts, more or less verbatim - as for the implementation being poor I am not qualified to say - I believe they are based off the 18watt.com layouts which I think are pretty decent if not absolutely ideal. I don't have the chops to improve on what the folks at 18watt.com, Ceriatone and Trinity did. If there are obvious problems with those grounding implementations by all means let me know what changes you suggest.. Please be specific as I am not an experienced builder who can take a comment like "Are you using some poor implementation of a star ground?" and magically improve my layout. If I knew I was using a poor implementation I don't think I would need to post

The whole point of my post is that I have followed these fairly well established grounding layouts for my 18 watt builds and yet they are pretty noisy. I've read Aiken, Valvewizard etc., tried a few things but I am green and so far I am getting nowhere. Its beyond my ability to troubleshoot and I was hoping someone would be interested in helping me go over and improve them

[M Fowler]

Use the Larry grounding and your problems will be over.

[Lindz]

OK - I'll bite. I've looked with interest at the various Larry grounding threads - thanks for the heads up guys.

My 18 watt head has a few mods so I have inserted a few questions below.

If I apply the 45watt concept to my amp I am guessing I would do the following - please correct me if I am wrong

1. inputs, v1a & v1b cathodes, heater ct - in yellow on my pic

2. volume pots, v2a & v2b cathodes, preamp filter and as I have a footswitch relay to switch between the normal and tmb channels inserted here in the circuit I am guessing I should ground the shunted channel signals here as well?? Footswitch relay is a Skipz circuits jack (2 opto-fet form c relays) on the back of the chassis.

relay configured as follows: 1NC taps the normal channel volume wiper, 1 common connects after the coupling cap on v1b and has 1 meg resistor to ground, 1 NO to ground, 2NC to ground, 2 Common inserted after coupling cap on V1a, 2 NC to volume pot on TMB channel also 1 meg resistor to ground

I used shielded cable for all the signal runs to and from the relay board with the shields grounded only at one end for each cable - at the pots for those 2 connections and on the bus bar by those 2 connections - I'm thinking this shield grounding may be a weak link?

This setup switches channels fine, but does have a small amount of relay pop. It is also noisier than the amp was stock, but the amp had some hum before I installed the relay so not all the noise can be attributed to the relay. My other 18 watt combo is laid out the same but has no channel switching and still is quite a bit noisier than other amps I own so I assume I am still doing other things less than optimally for hum and buzz reduction.

I would appreciate any ideas on how to improve this switching setup too - It works but I am a noob so probably far from ideal. I was pretty stoked to even get it working as well as it is

3. Tone pots, PI Filter, 56k tail resistor, grid leaks for el 84's, OT common

4. I assume I can ignore the bias ground as I have no bias circuit per se
- my amp is cathode biased (sort of - astute eyes will see it also has a diode clamp across the cathode resistor and ruby mod to help squash crossover distortion)

5. Cap can ground (first filter cap), HV CT, Cathode resistor ground. Again astute eyes will notice that the HV center tap has a string of zeners to drop the voltage because of the voltage bump from the solid state rectifier.

6. mains ground from plug

Thanks for any input guys and gals... !

[M Fowler]

What is your HT center tap red/yellow wire connected to? Circled in red.

Looks like a series of dropping resistors?

[Lindz]

If you look closely it connects to a string of dropping zeners grounded at the star below the cap can.

Its not really properly secured at this point as I am still messing with the amp. Will be better secured once I figure the final layout - I may move the dropping zeners elsewhere as I have been told that the CT is not the ideal place to drop b+ -

[M Fowler]

Does the noise improve when removing those zeners?

So the Trinity PT is 300v-0-300v I take it? I would put in a tube socket and use the EZ81 rectifier tube which will drop the B+ voltage down.