Regards to the forum, newcomer here, got some question...

[massygt6]

Hi to all of you,
I'm Massimiliano, and I've been redirected here by Mr.Gary "the glasman" Johnson, thank you again Gary for the help...
I've realized some amps before...
some 18watts like this one:
[img:320:239]http://img2.putfile.com/thumb/11/32915031281.jpg[/img]

or soldano slo based amps with some major tweaks:
[img:90:120]http://f10.putfile.com/7/18718301360-thumb.jpg[/img]

Now it's time to enter Dumble's territory but I've got some question, I hope you can forgive me if some of them have been discussed already, but I can't find a certain and univoque answer...so, here we go...

1- the difference between an HRM and a NON HRM ODS is the post OD ToneStack...from what I see in the schems and layout, engaging the OD channel took off the Clean tone stack, so basically, no control over the tone in a NON HRM...
The question is: has anyone tried to make the trimmers of the HRM add-pad adjustable from the outside, making a two EQs, two channel amp? Is it useless?

2- Some amps has a massive HV filtering section, with up to 10 filter caps... some amps no (for example, the overtone special)...what's the difference?

3- Different preamp stages CK, RK and RA are floating around...
there's really a fab one? 100k vs 200k on anode...someone tried 150k or 180k?

4- In one of the fantastics Normster's layouts, there a 4th preamp tube...it's the Dumbleator fx loop I guess...the stock loop is bad? accepts pedal's or rack's processing?

thanks for tha attention
Regards
Max

[Normster]

Welcome to the forum, Massimiliano. I'll try to answer a few of your questions and hopefully the real gurus will correct my mistakes.

1- has anyone tried to make the trimmers of the HRM add-pad adjustable from the outside, making a two EQs, two channel amp? Is it useless?

Several people have tried this and it works OK. The main reason the controls are inside is because there's a very narrow "sweet spot" and once you find it, you'll want to leave it alone.

2- Some amps has a massive HV filtering section, with up to 10 filter caps... some amps no (for example, the overtone special)...what's the difference?

The photos with 10 filter caps actually have the same number of B+ nodes. The "precision" power supply uses two 47uF caps in series instead of a single 22uF cap per node.

3- Different preamp stages CK, RK and RA are floating around...
there's really a fab one? 100k vs 200k on anode...someone tried 150k or 180k?

Gil just completed a build using 100K plate resistors instead of the 220K/150K/180K/120K values we've all come to know and love. Lot's of good discussion in that thread. ( http://ampgarage.com/forum/viewtopic.php?t=3839 )

4- In one of the fantastics Normster's layouts, there a 4th preamp tube...it's the Dumbleator fx loop I guess...the stock loop is bad? accepts pedal's or rack's processing?

The stock loop is passive so it will not drive long cables or rack effects. It works fine for adding delay or reverb pedals on short cables. For long cable runs or effects that require a low impedance signal, you'll need a booster pedal or buffered loop.

[massygt6]

thanks so much Normster...
I had the chance to appreciate your layouts and works, they're all awesome...
Got to study the discussion you've linked, there's a lot of very interesting points...
This amplifiers are a totally different world from what I'm used to build...
I've seen a lot of EVM speakers in the cabs, are really that good with the ODS?
Got a Mesa rectocab 2x12 with v30s, a great cab for certain type of sounds but for the ods:?: ...we will see

[odourboy]

Welcome Max.

Your amps look amazing!!!

Regarding the speaker question, the EVM 12L is an excellent choice for an ODS. It works very well in a TL-806 (Mesa Theile) type cab. Another choice that is very highly regarded by members of this forum is the Celestion Heritage G12-65. There are others that work well - a search through the threads will uncover many discussion on the topic.

Cheers!

[Fischerman]

Hi massygt6 and welcome to the forum. I'm relatively new here too and just finished my first ODS-type amp. I can't help with any of your questions except maybe the first one. That's the way I built mine...with the HRM tone stack controls on the front panel (using a Fender Bandmaster Reverb chassis).

My understanding (and someone please correct me if I'm wrong) is that with an HRM amp...the 'best' OD tone is with the PAB on (with Mid-Boost and Deep switches off). And since with PAB on the early tone stack is defeated...I thought having the HRM stack on the front panel would be necessary. I set my amp up such that it automatically switches the PAB on when you switch to the OD channel (this is selectable). But as Normster mentioned...once you get the HRM stack set it stays pretty much fixed. It also required some semi-long wire runs from the circuit board to the controls and I used shielded cable for them...with the typical mini-board inside the amp you have extremely short wire runs and no shielded cable capacitance which I'm sure makes some sort of difference. Something to keep in mind.

But I'm an incessant tweeker and if I didn't put those controls on the outside of the amp...the chassis may NEVER get to stay inside the cabinet for longer than a week! I'd constantly be going back in there to tweek the HRM stack (even if I ultimately left it exactly where it was...I'd still have to tweek it and listen). But that's just how it is for me...and it's entirely possible that I'd be better off if I didn't have those tone controls staring at me screaming to be tweeked.

[massygt6]

Welcome Max.

Your amps look amazing!!!

Regarding the speaker question, the EVM 12L is an excellent choice for an ODS. It works very well in a TL-806 (Mesa Theile) type cab. Another choice that is very highly regarded by members of this forum is the Celestion Heritage G12-65. There are others that work well - a search through the threads will uncover many discussion on the topic.

Cheers!

thanks Odourboy,
If I'm not wrong, you've realized a two Eqs version of the ODS...the brown tolex one...great work, and I want to come up to something similar...great speaker the G12-65...an UP for Celestion choosing to reissue that glorious speaker

[massygt6]

Hi massygt6 and welcome to the forum. I'm relatively new here too and just finished my first ODS-type amp. I can't help with any of your questions except maybe the first one. That's the way I built mine...with the HRM tone stack controls on the front panel (using a Fender Bandmaster Reverb chassis).

My understanding (and someone please correct me if I'm wrong) is that with an HRM amp...the 'best' OD tone is with the PAB on (with Mid-Boost and Deep switches off). And since with PAB on the early tone stack is defeated...I thought having the HRM stack on the front panel would be necessary. I set my amp up such that it automatically switches the PAB on when you switch to the OD channel (this is selectable). But as Normster mentioned...once you get the HRM stack set it stays pretty much fixed. It also required some semi-long wire runs from the circuit board to the controls and I used shielded cable for them...with the typical mini-board inside the amp you have extremely short wire runs and no shielded cable capacitance which I'm sure makes some sort of difference. Something to keep in mind.

But I'm an incessant tweeker and if I didn't put those controls on the outside of the amp...the chassis may NEVER get to stay inside the cabinet for longer than a week! I'd constantly be going back in there to tweek the HRM stack (even if I ultimately left it exactly where it was...I'd still have to tweek it and listen). But that's just how it is for me...and it's entirely possible that I'd be better off if I didn't have those tone controls staring at me screaming to be tweeked.

Thanks for the advice fischerman!
Yes, engaging the PBA effectively lift the ground of the tonestack, and the result is a bypass of the tone controls...I did something similar in the 18watt with the wood cabinet, the sound grews in volume and saturation, but man, the ODS drive is soooooo smooth, it's impressive...
As I said before, this is a really new design approach for me, so I'd like to experiment as much as possible, and maybe I'll find that an externa control for the hrm pad is useless as long as you "set and forget" it...but who knows...

[odourboy]

Welcome Max.

Your amps look amazing!!!

Regarding the speaker question, the EVM 12L is an excellent choice for an ODS. It works very well in a TL-806 (Mesa Theile) type cab. Another choice that is very highly regarded by members of this forum is the Celestion Heritage G12-65. There are others that work well - a search through the threads will uncover many discussion on the topic.

Cheers!

thanks Odourboy,
If I'm not wrong, you've realized a two Eqs version of the ODS...the brown tolex one...great work, and I want to come up to something similar...great speaker the G12-65...an UP for Celestion choosing to reissue that glorious speaker

You are correct regarding my brown tolex implementation. I take it that you've done a thorough scan of the existings threads - most appreciated! That was my first D-clone and I wasn't sure if myself if I'd need routine access to those controls, so I thought it would be prudent to expose them. But as Normster stated, I've found those controls to be pretty much 'set and forget' (after careful tweaking) so I save the complexity and clutter and stick with internal trimmers now.

[Fischerman]

...this is a really new design approach for me, so I'd like to experiment as much as possible...

Me too...my amp is sort of a prototype so I could learn a bit about these amps before I do a full-blown 100W amp. I think the main thing that I learned is that...I'd really like to have at least 3 different versions! A non-HRM, an HRM, and a Bluesmaster...and it probably doesn't stop there (for example, a 'low-plate non-HRM' and a 'high-plate non-HRM' like discussed in the thread posted above).

And FWIW, I still can't really get the medium gain smooth tones like dogears gets...or Richard Guth on the Fuchs site. Those dudes get some sweet tones! Still working on it.