OD Reverb is done... maybe

jackson649 · Post by **jackson649** » Sat Nov 11, 2006 3:23 am

I completed my amp yesterday and played it yesterday and this morning. Sounds okay. Cleans have lots of bass and mids, but the highs seem shrill. OD channel also doesn't sound too hot either. I'm using 2x12 cab with Weber Ceramic Michigan. I'm going to play with this amp for the next month, give speakers a chance to break in and get use to this amp before I start tweekning it.

There is a link to my previous thread for this amp.

https://tubeamparchive.com/viewtopic.php?t=1347

dogears · Post by **dogears** » Sat Nov 11, 2006 3:41 am

Try removing the bright cap on the master. Also, disconnect the reverb and see how the straight amp tone is. WHat are the preamp voltages?

jackson649 wrote:I completed my amp yesterday and played it yesterday and this morning. Sounds okay. Cleans have lots of bass and mids, but the highs seem shrill. OD channel also doesn't sound too hot either. I'm using 2x12 cab with Weber Ceramic Michigan. I'm going to play with this amp for the next month, give speakers a chance to break in and get use to this amp before I start tweekning it.

There is a link to my previous thread for this amp.

https://tubeamparchive.com/viewtopic.php?t=1347

Bob-I · Post by **Bob-I** » Sat Nov 11, 2006 6:13 am

Not to be critical, but some of the lead runs are a tad sloppy, especally around the power supply board and tube sockets. I'd spend some time cleaning up these leads. Do this one at a time and shorten them to remove the snake like runs. The control runs look excellent, try to get the tube socket side to look like that. Remember that leads should not run parallel and should cross only at 90 degrees. I'd bet it'll sound better when that's done.

What value snubbers do you have on V2? What tubes are you using? What's the bias reading?

Otherwise looks like a good build. Everything works and that's the first step.

Normster · Post by **Normster** » Sat Nov 11, 2006 2:12 pm

First off, congrats on a successful build! Kind of a rush when you hear your creation for the first time, eh?

Second, now that it's working, take your time refining it. When I go through my amps I tend to do work in small batches so I don't screw up too much at a time.

Adding to what Bob said about lead dress, look closely at the pictures of #40 on acplink.com. You'll notice that Dumble drops his leads from the circuit board to the chassis and keeps them flat against it. This really does help keep the noise down since the chassis acts as a shield. Also, don't trust those crimp-on ground connections. Cut the plastic off of them and solder the connection. Bad grounds are a curse that all of us have had to deal with and they can cause some weird shit to happen.

jackson649 · Post by **jackson649** » Sun Nov 12, 2006 4:54 am

Hello again,

First off I was able to remove the 10pf capon the master and take some voltage readings.

B1 = 481V
B2 = 480V
B3 = 458V
B4 = 296.4V
B5 = 291.1V

V1 1=200V / 3=1.34V / 6=196V / 8=1.43V

V2 1=197V / 3=1.37V / 6=196V / 8=1.37V

V3 1=394V / 3=3.2V / 6=141V / 8=0.85V

V4 1=318V / 3=59.4V / 6=312V / 8=59.4V

V5 and V6 3=480V / 4=476V

Bias=51mV

Snubber Values on V2 are 300pf, using EH preamp tubes and Ruby output tubes.

Bob-I · Post by **Bob-I** » Sun Nov 12, 2006 10:36 pm

jackson649 wrote:Hello again,

V1 1=200V / 3=1.34V / 6=196V / 8=1.43V

V2 1=197V / 3=1.37V / 6=196V / 8=1.37V

Very strange. Your cathodes should be higher than this. Sounds like you're biased low on the preamp tubes. What values are you using on the plate load and cathodes?

Snubber Values on V2 are 300pf, using EH preamp tubes and Ruby output tubes.

The rest looks ok. I don't know the speaker you're using but it might be part of the cause of the shrillness. Dumbles are very sensitive to speakers. Break them in a bit and listen again. I like to break in my speakers by connecting them to the stereo and blasting them when I'm not home.

jackson649 · Post by **jackson649** » Tue Nov 14, 2006 8:58 pm

Hello, please excuse my ignorance but I'm not sure what you are refering to by values on the plate load and cathodes? Could someone help me with what I'm looking for.

Also, I posted an updated layout with current values I am using in my amp.

Bob-I · Post by **Bob-I** » Tue Nov 14, 2006 11:08 pm

jackson649 wrote:Hello, please excuse my ignorance but I'm not sure what you are refering to by values on the plate load and cathodes? Could someone help me with what I'm looking for.

Also, I posted an updated layout with current values I am using in my amp.

The plate loads are the 100K vishay resistors connected to pin 1 and 6 of V1 and V2. The cathode resistors are 1.5K's connected to pins 3 and 8 of V1 and V2.

I'm not sure why but you're cathode voltages seem low. I'd expected them to be closer to 2V, maybe 1.8 or so.

So have you had any progress with breaking in the speakers? I'd thing that it'll smooth out as they break in.

dogears · Post by **dogears** » Wed Nov 15, 2006 12:34 am

Here are some ideas.....

1) Add a .002 cap across the 220k reverb pan ground resistor. Sounds better to me.

2) Lower the 56K isolation resistor on between B+2 and the reverb tranny to a 24K. Add a 10uf-20uf cap to isolate further

3) Change mains to 2X100uf in series. Makes a big difference!

4) Try a 110K plate load on OD2. Like 124 has. Alternatively, scrap the 100k plate load setup and use 220/150 like most people. I prefer it fwiw.

5) Try lowering the CL1 and CL2 bypass caps to 10uf. Maybe clean out some buzz.

6) Try a 470 ohm shunt on the PI tail. Up from 390 ohm. You may like it

jackson649 · Post by **jackson649** » Wed Nov 15, 2006 5:49 am

Thanks for the suggestions dogears, I've made the changes to my layout, can someone please check for the changes to make sure I didn't miss anything.

Might be a while before I will be able to make these mods, but I'll make an update as soon as I'm able to. Thanks

Bob-I · Post by **Bob-I** » Wed Nov 15, 2006 4:56 pm

jackson649 wrote:Thanks for the suggestions dogears, I've made the changes to my layout, can someone please check for the changes to make sure I didn't miss anything.

I don't see anything you missed.

Normster · Post by **Normster** » Wed Nov 15, 2006 5:34 pm

Looks good. I'm not sure if it makes a difference, but the resistors on the first two filter caps go between the two filter caps, not end-to-end as you have them.

BTW, I think you've taken the right approach by drawing this out rather than rely on someone else's layout (including mine). It really helps you understand the circuit and helps visualize the build before you pick up a soldering iron.

heisthl · Post by **heisthl** » Wed Nov 15, 2006 10:12 pm

His resistors on the caps are drawn correctly it just looks confusing because of the diagonal interconnect. Each resistor is in parallel with its respective cap to provide balance between the 2 caps in series and bleed off for that leg of the P/S.

hipbluescat · Post by **hipbluescat** » Sat Nov 18, 2006 11:35 am

Hello

My name is Paul and I have built some Fender amps bit have the itch to build a Dumble ODS style amp !

Congregations for the successful build.

I am also starting on a similar project and am collecting information.

Does the clean channel sound like a typical Fender clean channel ?

Is the overdrive similar to what Robben Ford uses ?

What doe the internal trim pot do on the circuit board ?

Where did you get the chassis from ?

I have seen a guy in Thailand that does copies of Dumble amps chassis. Does anyone have his contact details?

What does the 9AB3CIB stand for ?

What does the Accent switch do ?

Next to the Preamp tubes V1 and V2 what does the little box with circles stand for. Is this suppose to be the three contact points on the drive pot and these other components should be added to these ?

Can you bias this amp with resistors that hang off the output tubes?

Can anyone explain why FET input has been used in some amps and what they achieve.

Can you post the corrected schematic by any chance ?

Thank you for any help you can give me.

Regards

Paul

Bob-I · Post by **Bob-I** » Sat Nov 18, 2006 2:30 pm

hipbluescat wrote:Hello

Hi, welcome to your next addiction, Dumble's

Does the clean channel sound like a typical Fender clean channel ?

No, it's fatter and more midrangy. Think Larry Carlton's intro on Steely Dan's Asia.

Is the overdrive similar to what Robben Ford uses ?

I think so, but Robbin has so many OD tones it's hard to say.

What doe the internal trim pot do on the circuit board ?

It adjusts the amount of drive going into the OD channel.

Where did you get the chassis from ?

Head over to the Dumble files section, and the for sale section. You'll find a complete chassis by funk, layouts, schematics etc.

What does the Accent switch do ?

It's like a presence control. I prefer the presence pot myself.

Next to the Preamp tubes V1 and V2 what does the little box with circles stand for. Is this suppose to be the three contact points on the drive pot and these other components should be added to these ?

The circles around the wires are indicating shielded wire. Use low capacitance RG174 only.

Can you bias this amp with resistors that hang off the output tubes?

Yep

Can you post the corrected schematic by any chance ?

Well, again check out the files section, but there's no one definitive schematic. You have to build, then let the amp speak to you and make adjustments. Every Dumble is unique.

Happy to help. Search through this forum and the files section, you'll get a ton of information.

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