My Dumb-oogie project - opinions?

[KGW]

Hi all,

A while back on the TW forum, I had this discussion:
http://ampgarage.com/forum/posting.php? ... iew&t=2120
concerning building an ODS into a Mesa/Boogie MkIII.

Anyway, having finally decided that I wanted to build a better amp in my Mesa Boogie MkIII chassis, I thought I would seek help/advice here.

First of all, I have only heard clips of the ODS. I love the clean sound. The overdrive sound reminds me of Holdsworth. So, the ODS sounds like a great Jazz/Fusion amp. As for the Mesa, I have always had problems with it (I'm the original owner), but I do like the lead channel for some sounds - like for more heavy metal-type sounds. Can the ODS get that much gain?

Here are my initial goals:

• (channel 1) Great clean sounds - jazz to funk

• (channel 2) The ODS overdrive sound

• (channel 3) The Mesa lead sound

• Non relay/LDR switching - probably JFETs and mute points

• Use the existing iron

I was going to use the "rhythm 2" switch for channel 2 and the lead switch for channel 3. I'll put the channel 2 level controls on the back where the direct level/out was.

Later goals:

• Nice tube reverb

• Parallel tube FX loop

Here are the main challenges that I can think of:

• The Mesa is a 3 tube preamp where the 1st and 2rd tubes are always used. The 3rd tube is the lead channel and goes between the 1st and second tube when switched in

• The ODS preamp used 2 tubes. The first is the clean channel and the second is the overdrive channel

• Using the first tube as the clean channel in the new amp should pose no problems

• Converting the Mesa "rhythm 2" channel into the ODS overdrive channel should be pretty easy as well

• Adding the new lead channel is the big quandary. Any ideas on this?

Thanks for your help. I'll post my progress as it progresses.

[Bob-I]

First of all, I have only heard clips of the ODS. I love the clean sound. The overdrive sound reminds me of Holdsworth. So, the ODS sounds like a great Jazz/Fusion amp. As for the Mesa, I have always had problems with it (I'm the original owner), but I do like the lead channel for some sounds - like for more heavy metal-type sounds. Can the ODS get that much gain?

It's not so much about the amount of gain but the structure. Dumble gets the tone you're describing by driving a narrower frequency through the gain structure. Boogie pretty much goes full bandwidth through all the gain stages.

Here are my initial goals:

• (channel 1) Great clean sounds - jazz to funk

• (channel 2) The ODS overdrive sound

• (channel 3) The Mesa lead sound

• Non relay/LDR switching - probably JFETs and mute points

• Use the existing iron

First off, the Dumble only has one real channel, but adds 2 additional gain stages between the clean side and the output for the ODS.

It's do-able but you'll be pretty much on your own on this one. I'd bet you'll need a true 2 channel amp, 2 12AX7's per channel. You could design it as Dumble on one side, Boogie on the other.

The switching of course is up to you. We tend to use relays because that's how the big man did it, and because there's 0 resistance or impedance when latched. An LDR can have some resistance that can couple with the tube's miller capacitance and change the tone. I've noticed quite a bit of this on the SLO I built.

Later goals:

• Nice tube reverb

• Parallel tube FX loop

Glaswerks has a nice single tube reverb schematic, I drew up and breadboarded a single tube parallel effect loop using a feedback amp mixer. The concern is for real estate is starting to show up.

Here are the main challenges that I can think of:

• The Mesa is a 3 tube preamp where the 1st and 2rd tubes are always used. The 3rd tube is the lead channel and goes between the 1st and second tube when switched in

• The ODS preamp used 2 tubes. The first is the clean channel and the second is the overdrive channel

• Using the first tube as the clean channel in the new amp should pose no problems

• Converting the Mesa "rhythm 2" channel into the ODS overdrive channel should be pretty easy as well

• Adding the new lead channel is the big quandary. Any ideas on this?

Thanks for your help. I'll post my progress as it progresses.

IMHO Modding this amp to your specs will be more difficult than gutting it and starting from scratch. I'd go from scratch myself.

Best of luck.

[KGW]

Thanks. I am gutting the amp. I did a number of mods using the existing PCB and decided that it was not getting to where I wanted it. So, I'm saving the old PCBs and doing a mostly scratch build using DIY turret boards.

I would sell it, but I like the cabinet and speaker (Eminence Delta Pro 12 LF). Also, These amps don't sell for much.

It's not so much about the amount of gain but the structure. Dumble gets the tone you're describing by driving a narrower frequency through the gain structure. Boogie pretty much goes full bandwidth through all the gain stages.

Good. That's how I understood it as well.

First off, the Dumble only has one real channel, but adds 2 additional gain stages between the clean side and the output for the ODS.

It looks to me (on the ODS) as if V1 is used for the clean channel and V2 is used for the overdrive channel. So V2 is switched in between V1 and the PI. Point "A" on the ODS 101 schematic. Is this incorrect?

It's do-able but you'll be pretty much on your own on this one. I'd bet you'll need a true 2 channel amp, 2 12AX7's per channel. You could design it as Dumble on one side, Boogie on the other.

Yeah maybe. So V1 and V2 could be the same as the ODS. V3 & V4 would be the same as V2 and V3 in the Mesa. So channel 1 is V1, channel 2 is V1 and V2 and channel 3 is V1, V3 & V4.

The switching of course is up to you. We tend to use relays because that's how the big man did it, and because there's 0 resistance or impedance when latched. An LDR can have some resistance that can couple with the tube's miller capacitance and change the tone. I've noticed quite a bit of this on the SLO I built.

LDRs were popular when the ODS was first built, but they do bleed. I am going to experiment with the switching techniques in O'Conners first TUT book before I commit to anything.

Glaswerks has a nice single tube reverb schematic, I drew up and breadboarded a single tube parallel effect loop using a feedback amp mixer. The concern is for real estate is starting to show up.

I'll check that one out. The FX loop would take 1 tube. The reverb would take 1 or 2 tubes. I'll have to add more tubes no matter what.

IMHO Modding this amp to your specs will be more difficult than gutting it and starting from scratch. I'd go from scratch myself.

Best of luck.

Thanks.

I agree (as stated above). I realise that I'm mostly on my own here, but you guys can help with the ODS part. I've built quite a few amps by now, but this one should prove to be the most challenging.

[Bob-I]

.... Also, These amps don't sell for much.

I'll give you $10

It looks to me (on the ODS) as if V1 is used for the clean channel and V2 is used for the overdrive channel. So V2 is switched in between V1 and the PI. Point "A" on the ODS 101 schematic. Is this incorrect?

No that's correct.

Yeah maybe. So V1 and V2 could be the same as the ODS. V3 & V4 would be the same as V2 and V3 in the Mesa. So channel 1 is V1, channel 2 is V1 and V2 and channel 3 is V1, V3 & V4.

I guess that's possible, as long as V1 has what you need to drive V3 and V4. I didnt' realize Boogie used that many gain stages in that amp.

LDRs were popular when the ODS was first built, but they do bleed. I am going to experiment with the switching techniques in O'Conners first TUT book before I commit to anything.

It's not so much about the bleed as the resistance. A small change in a series resistance makes a big difference in tone.

Glaswerks has a nice single tube reverb schematic, I drew up and breadboarded a single tube parallel effect loop using a feedback amp mixer. The concern is for real estate is starting to show up.

I'll check that one out. The FX loop would take 1 tube. The reverb would take 1 or 2 tubes. I'll have to add more tubes no matter what.

Be careful that the PT can supply the heater current required.

BTW, Mesa usually uses a very similar single tube reverb, why not stick to that. For the effects loop why not use an SS loop? Somewhere I saw a post where there's one available on a single board, can't remember where though.

[pdrie]

The SS loop is available from Ironsounds. There are good reports about it on the D Lite forum. I have one on order for my DLite kit. I can post some details when I receive it.

Paul

[KGW]

Be careful that the PT can supply the heater current required.

BTW, Mesa usually uses a very similar single tube reverb, why not stick to that. For the effects loop why not use an SS loop? Somewhere I saw a post where there's one available on a single board, can't remember where though.

The MkIII has 5 12AX7s and 4 6L6s. I could always stick in another filament tranny.

The MkIII's one tube reverb is weak. A SS FX loop may be fine.

I was originally trying to think of a "clever" way to make an amp that could sound both like both an ODS and a Boogie. Of course my DIY Champ, 50W Plexi and TW Express all sound completely different, so maybe I'm dreaming.

[Bob-I]

The MkIII's one tube reverb is weak.

Then check out the ECL86 reverb I used in my Peavey transplant, I think the schematic is posted on the files forum. Very good depth with a single tube but you have to get a few NOS tubes as no one makes them anymore.

[KGW]

OK, I just heard the lead clip here:

http://ampgarage.com/forum/viewtopic.php?t=2684

That's way better than the MkIII lead channel. So that makes things much easier. I can do an ODS/HRM and a 2 tube reverb without adding any more tubes. I'll just have to tweak the PSU a bit to get the correct voltages.

I'll start the preamp board tonight.

[Bob-I]

OK, I just heard the lead clip here:

http://ampgarage.com/forum/viewtopic.php?t=2684

Just in case you need more convincing that these amps are awesome.....

http://www.patmedia.net/bob-ingram/Rock ... hieKoo.mp3

All recorded with my D-Lite type amp (Built before the D-Lite existed) and a 24 fret PRS Standard. Hybrid type ckt in a Princeton chassis.

[pamaz67]

FWIW I have made a conversion to dumble circuit of a SOB mesa and have to say that the output transformer was excellent and a good part in the incredible dynamic capability of the amp. At least better than the usual fender bassman iron for sure.
Again, if you have a SOB on hand, you' ll find that the circuit is very easy to be transformed to dumble specs if you don't care too much of the rock jazz switch .

The most complicated thing has been to rebuild the pwr amp section.
Ciao

Paolo

[KGW]

FWIW I have made a conversion to dumble circuit of a SOB mesa and have to say that the output transformer was excellent and a good part in the incredible dynamic capability of the amp. At least better than the usual fender bassman iron for sure.
Again, if you have a SOB on hand, you' ll find that the circuit is very easy to be transformed to dumble specs if you don't care too much of the rock jazz switch .

The most complicated thing has been to rebuild the pwr amp section.
Ciao

Paolo

"SOB?" are you being derogatory (perfectly understandable) or do you mean something else? Sorry if I'm being dense.

I've about got the amp gutted. Did you need to alter the PSU much to get the voltages within tolerance?

[mlp-mx6]

"SOB?" are you being derogatory (perfectly understandable) or do you mean something else? Sorry if I'm being dense.

Uh, that would be "Son of Boogie" - an early reissue-ish amp from Mesa. I'm CERTAIN he meant no harm...

[heisthl]

The SOB had a strange PI set up using a tunnel diode as a constant current source that could be varied with a 1 Meg pot(called LIMIT) capable of amazing sweet sustain - really not usable because there was no way to manipulate the varaiation between solo and non solo tones. The other drawback was all that great sustain was a function of the PI and could not be harnessed to send to an FX loop short of using a separate power amp. Having said all that, I used to use one and had added a footswitch to get 2 LIMIT choice with a corresponding volume boost and for FX I stuck a separate power amp in the bottom of the combo cab to drive the main speaker while the SOB drove a hacksawed PV scorpion (spider VC and magnet only) with a voltage divider on it for a line out. It really did sound good, had a nice presence that really projected. It was as close to the majic sound of a Dumble as you could get at the time and probably explains my fascination with the clone sound.

Sorry about Hijacking the thread..