OD pedal?

18watt-specific Tech Talk - Building, Fixing, Parts, Mods...

Moderators: CurtissRobin, colossal, zaphod_phil, Daviedawg, Graydon

sruffinc
Newbie
Newbie
Posts: 40
Joined: Sun 09/24/17 3:40 pm

Re: OD pedal?

Post by sruffinc »

Josh,

Attached is a sound file. No guitar input and turning up volume pots. First Normal channel then TMB. TMB side is noisier. Can't tell if I'm hearing a slight high pitched ringing?
You do not have the required permissions to view the files attached to this post.
0 x

sruffinc
Newbie
Newbie
Posts: 40
Joined: Sun 09/24/17 3:40 pm

Re: OD pedal?

Post by sruffinc »

Here a few samples with guitar into TMB channel. Low output bedroom level. And with JJ EL 84s. One without pedals, then with a tube screamer and a second one with an OCD. The OCD doesn't sound quite as bad as it did at first, but it still has a harsh bluntness to my ears. Maybe that is the way it should sound through my amp?
You do not have the required permissions to view the files attached to this post.
0 x

sruffinc
Newbie
Newbie
Posts: 40
Joined: Sun 09/24/17 3:40 pm

Re: OD pedal?

Post by sruffinc »

Just watched the soldering technique video. Wow! I had not idea I was so far off. Surprised my the two amps I built work as well as they do. I'm going to re-wire them. Is it best to use stranded wire?
1 x

User avatar
JMPGuitars
Super Duper Admin
Super Duper Admin
Posts: 1981
Joined: Tue 09/18/12 8:00 pm
Location: South Central, MA
Contact:

Re: OD pedal?

Post by JMPGuitars »

sruffinc wrote:
Thu 04/23/20 12:59 pm
Just watched the soldering technique video. Wow! I had not idea I was so far off. Surprised my the two amps I built work as well as they do. I'm going to re-wire them. Is it best to use stranded wire?
For the most part I use 20AWG pre-tinned stranded wire. If you can find good pre-tinned & bonded wire, even better.

I use 18AWG pre-tinned stranded wire only for the mains, IEC ground, and PT power switch. I use pre-tinned 18AWG solid core for the ground buss. Some people go heavier for the buss wire.

The noise I heard in the demos sounds fairly consistent with your build photos. But the tone was a little off. It could be the JJ EL84s, the speaker, or something else causing that. I'm not a fan of JJ EL84s. I would use them as the "test tubes" for your rebuild, and then replace them with better tubes when you're past all the troubleshooting and doing your final tweaking.
0 x
'I installed a skylight in my apartment yesterday... The people who live above me are furious.' - Steven Wright
Web Design: DolceVittoria.com
Guitars / Amps / Effects: JMPGuitars.com
(anti)Social: Facebook · Instagram
Items for Sale

sruffinc
Newbie
Newbie
Posts: 40
Joined: Sun 09/24/17 3:40 pm

Re: OD pedal?

Post by sruffinc »

Thanks again. I'm encouraged that the amp sounded a little better today after making a few of the changes suggested. I'll follow up after I rebuild.

-Ruffin
1 x

sruffinc
Newbie
Newbie
Posts: 40
Joined: Sun 09/24/17 3:40 pm

Re: OD pedal?

Post by sruffinc »

Josh,

I rewired my amp and it seems much better. Voltage chart attached.
TMB_Voltage_Test_Chart - 6.1.20.pdf
Sounds good, less noise, but seems to have more bass than before. I used a 1000uf cathode bias cap with a 150ohm cathode resistor on the power tubes. I'm going to try a 2200uf and 180ohm combination to see how that does. Any thoughts on my voltages. See anything that looks off?
You do not have the required permissions to view the files attached to this post.
0 x

sruffinc
Newbie
Newbie
Posts: 40
Joined: Sun 09/24/17 3:40 pm

Re: OD pedal?

Post by sruffinc »

Might be hearing the fizzy distortion I've read about.
0 x

User avatar
JMPGuitars
Super Duper Admin
Super Duper Admin
Posts: 1981
Joined: Tue 09/18/12 8:00 pm
Location: South Central, MA
Contact:

Re: OD pedal?

Post by JMPGuitars »

sruffinc wrote:
Mon 06/01/20 1:37 pm
Might be hearing the fizzy distortion I've read about.
You've got a few things going on there. But first...

Your voltages, including your B+ are too low. Pin 3 of the rectifier is your B+. Do you have a different rectifier you can test? It doesn't make sense for you to be only getting 334VDC at pin 3 with pins 1 and 7 VAC so high.

Also fill the bottom box on the sheet. Those numbers are important too. A and B are the two halves of the first filter can, A being the higher voltage where the standby switch connects to the cap. C is the point on the board that feeds the PI plate resistors. You can just measure that at the point where the PI plate resistors usually share a turret.

B+ ideally should be 345VDC +/- 5V. Under 340VDC usually sounds muddier, with lower headroom.

Oh yeah, definitely go up to 180R and 2200uF on the cathode. You're currently biased too hot.

Thanks,
Josh
0 x
'I installed a skylight in my apartment yesterday... The people who live above me are furious.' - Steven Wright
Web Design: DolceVittoria.com
Guitars / Amps / Effects: JMPGuitars.com
(anti)Social: Facebook · Instagram
Items for Sale

User avatar
Bieworm
Occasional poster
Occasional poster
Posts: 457
Joined: Mon 02/10/20 8:24 am

Re: OD pedal?

Post by Bieworm »

Try a SS rectifier?
0 x
"THIS should be played at high volume..preferably in a residential area"

sruffinc
Newbie
Newbie
Posts: 40
Joined: Sun 09/24/17 3:40 pm

Re: OD pedal?

Post by sruffinc »

TMB_Voltage_Test_Chart - 6.1.20.pdf
Added the ABC readings to the chart.

No I don't have another rectifier tube. What I'm using is an old stock German made ez-81. Perhaps I need to get a new one. I need to replace the JJ EL-84s anyway.

Just noticed it does sound a little dull. That nice crispy top end that it had previously is not there.
You do not have the required permissions to view the files attached to this post.
0 x

User avatar
Bieworm
Occasional poster
Occasional poster
Posts: 457
Joined: Mon 02/10/20 8:24 am

Re: OD pedal?

Post by Bieworm »

sruffinc wrote:
Mon 06/01/20 2:00 pm
TMB_Voltage_Test_Chart - 6.1.20.pdf

Added the ABC readings to the chart.

No I don't have another rectifier tube. What I'm using is an old stock German made ez-81. Perhaps I need to get a new one. I need to replace the JJ EL-84s anyway.

Just noticed it does sound a little dull. That nice crispy top end that it had previously is not there.
There is something wrong on your chart .. A is right after the rectifier and B is after the filter cap. I think you swapped your values...
Trying a solid state rectifier is easy. Just a couple of 1N4007 diodes and perhaps a 100R resistor ... at least then you're sure your voltages are more in the right ballpark
0 x
"THIS should be played at high volume..preferably in a residential area"

sruffinc
Newbie
Newbie
Posts: 40
Joined: Sun 09/24/17 3:40 pm

Re: OD pedal?

Post by sruffinc »

I'll try that.
0 x

User avatar
JMPGuitars
Super Duper Admin
Super Duper Admin
Posts: 1981
Joined: Tue 09/18/12 8:00 pm
Location: South Central, MA
Contact:

Re: OD pedal?

Post by JMPGuitars »

sruffinc wrote:
Mon 06/01/20 2:00 pm
TMB_Voltage_Test_Chart - 6.1.20.pdf

Added the ABC readings to the chart.

No I don't have another rectifier tube. What I'm using is an old stock German made ez-81. Perhaps I need to get a new one. I need to replace the JJ EL-84s anyway.

Just noticed it does sound a little dull. That nice crispy top end that it had previously is not there.
JJ EZ81 tubes have been fine, and not expensive. Get a couple. I think your old stock is too old.

Bieworm is correct, your voltages don't make sense. If you don't have a dropping resistor or zener diode between Pin 3 of the rectifier, and "A" (the first filter cap), then the voltage should be exactly the same. There's a resistor between A and B, so B should be lower than A.

In addition to getting new tubes, I would also highlighter verify your build.
Bieworm wrote:
Mon 06/01/20 2:28 pm
Trying a solid state rectifier is easy. Just a couple of 1N4007 diodes and perhaps a 100R resistor ...
Solid state rectifiers are cool, but UF4007 is superior to 1N4007. They're better/faster diodes with less noise. The SS rectifier should have 4 of the diodes either way.
0 x
'I installed a skylight in my apartment yesterday... The people who live above me are furious.' - Steven Wright
Web Design: DolceVittoria.com
Guitars / Amps / Effects: JMPGuitars.com
(anti)Social: Facebook · Instagram
Items for Sale

sruffinc
Newbie
Newbie
Posts: 40
Joined: Sun 09/24/17 3:40 pm

Re: OD pedal?

Post by sruffinc »

I'll try all of that. If I can't get it on this try I may have to admit defeat and turn it over to a pro. I'm getting tired of spinning my wheels. I do appreciate all of the help.
0 x

User avatar
Bieworm
Occasional poster
Occasional poster
Posts: 457
Joined: Mon 02/10/20 8:24 am

Re: OD pedal?

Post by Bieworm »

sruffinc wrote:
Mon 06/01/20 4:19 pm
I'll try all of that. If I can't get it on this try I may have to admit defeat and turn it over to a pro. I'm getting tired of spinning my wheels. I do appreciate all of the help.
Patience, soldier!!! Don't give up on it yet...
We'll get this fixed, don't sweat
😃😃😃
1 x
"THIS should be played at high volume..preferably in a residential area"

Post Reply