#84 Sounds Really Really Sweet !!!

['67_Plexi]

I went over Pauls house today with my amp and checked out #84.
Anyone who didn't believe him about owning this amp should apologise.

Firstly Paul is the nicest guy you could wish to meet and was happy to let me play through this amp and check it out. It sounded lovely...very gainy and open. Even on cleanish settings using a Strat it would bloom in to feedback.

Bearing in mind that my amp is a 100W EL34 HRM inspired build, it's not easy or realistic to compare the two exactly (#84 is an early 80's 50W 6L6 transition model).

However.....there are some similarities in tone as would be expected, however the HRM on the lead channel has a more smooth compressed overdrive that's voiced more modern and is certainly a little more forgiving than that of #84.
#84 is a very raw and very touch sensitive, each note blooms to a sweet harmonic.
The 'clean' channel of #84 is very open and gainy too, but cleans up really well. I really liked this channel with boost with a Strat. The clean channel on mine was very tight and percussive, but not constipated.
A great tone in itself, just different from #84.
Both Paul and myself agreed that the feedback and power supply differences attributed a lot to the overall 'feel' difference we were experiencing, as well as the EL34 Vs 6L6. The 100W had to be physically louder before it started to get the nice note bloom. #84 wanted to tear your head off right out the gate....I loved that about it !!!
Here's something that you might find strange. With a HB guitar in the clean channel set with a high preamp gain, #84 really nailed the 'plexi' tone. That made me smile.
#84 was slightly smaller in physical size to mine, but the HRM's may be a little larger anyway, I don't know. The chassis on #84 was also a little narrower than mine, which helps the air circulation.

Again, thanks Paul for opening your home up for me to check out this very special amplifier and I hope you found mine interesting.

Alan.

[jaysg]

Transition era? Black chassis or brushed aluminum?

[makrisp]

Alan,

It was a pleasure meeting you this afternoon. Its great to meet someone who really understands tone, not just from an amp perspective, but your playing ability.

Your amp sounds and looks fantastic! The build quality is impeccable and the tone was Robben Ford all the way.

Let's meet up soon when you have more time so that we can put the amps through their paces.

Fantastic amp! Highly reccomended to the folks out there!

['67_Plexi]

Thanks Paul,

It's great to get a perspective from an actual owner. As I told you todayI'm not actually trying to 'clone', just create great sounding amps while gaining inspiration and knowledge from as many sources as possible. The Dumble amps are very fine examples of a highly tuned amplifier and are worthy of study by any amp builder. If you are looking to clone every part and wire type, you may just be missing the whole point. That goes for Trainwrecks and many other respected amps.

I'm definately looking at my feedback circuit again, I do want to loosen it up a little, not much, just a little. It's that tight at the moment that you can play Drop-D nu-metal and keep up with the high gain boys
No seriously, I agree that a little higher value fb resistor may just work wonders in my particular amp. However just because I may do that to my HRM type build, doesn't mean that it would work in every one.....and that's my whole point. There are some critical areas, but the exact recipe dynamically changes for every single amp.

['67_Plexi]

Transition era? Black chassis or brushed aluminum?

It's black....there's some pics in this thread http://ampgarage.com/forum/viewtopic.php?t=1807

[Normster]

I knew it! The NFB is a critical part of the equation. My little 22watt sounded like poo with a 4k7/390 NFB circuit. I was ready to scrap the iron. After doing a bit of reading on Aiken's site, it was pretty obvious why the amp sounded so congested. With a 6k/390 NFB circuit, this amp sings!!!

Great report! Somehow I had a sneaky suspician that Paul was the real deal. Damn I wish you guys lived in my area. (No way I'm moving to NJ. Too f'n cold.)

[Bob-I]

(No way I'm moving to NJ. Too f'n cold.)

Wouldn't help anyway, he lives near Boston.


Great to get a hands on report. I really have to experiment more with the NFB.

[tonelab2]

I knew it! The NFB is a critical part of the equation. My little 22watt sounded like poo with a 4k7/390 NFB circuit. I was ready to scrap the iron. After doing a bit of reading on Aiken's site, it was pretty obvious why the amp sounded so congested. With a 6k/390 NFB circuit, this amp sings!!!

Great report! Somehow I had a sneaky suspician that Paul was the real deal. Damn I wish you guys lived in my area. (No way I'm moving to NJ. Too f'n cold.)

I experienced a similar thing with NFB. The 6K/390 works well but I think it's deeper than that. I've built 2 amps now both hybridA's. One uses TR PT and BM OT with voltages same as #124, the other uses Xformer trans designed for a '64 tremoluxrevrb. The voltages on this amp are higher, round 475v on B+1. This amp loves the 6K NFB, not as nice at 4k7 and terrible without NFB. The other amp prefers the 4k7, too hi-fi with 6K and screams like a plexi on steriods in a good way without NFB. What gives I don't know but something says the 2 are related , NFB and B+ voltages . Maybe someone with experience could explain.

[makrisp]

I knew it! The NFB is a critical part of the equation. My little 22watt sounded like poo with a 4k7/390 NFB circuit. I was ready to scrap the iron. After doing a bit of reading on Aiken's site, it was pretty obvious why the amp sounded so congested. With a 6k/390 NFB circuit, this amp sings!!!

Great report! Somehow I had a sneaky suspician that Paul was the real deal. Damn I wish you guys lived in my area. (No way I'm moving to NJ. Too f'n cold.)

I experienced a similar thing with NFB. The 6K/390 works well but I think it's deeper than that. I've built 2 amps now both hybridA's. One uses TR PT and BM OT with voltages same as #124, the other uses Xformer trans designed for a '64 tremoluxrevrb. The voltages on this amp are higher, round 475v on B+1. This amp loves the 6K NFB, not as nice at 4k7 and terrible without NFB. The other amp prefers the 4k7, too hi-fi with 6K and screams like a plexi on steriods in a good way without NFB. What gives I don't know but something says the 2 are related , NFB and B+ voltages . Maybe someone with experience could explain.

I highly agree that the B+ voltages are critical to determine the correct NFB resistor, especially at the phase inverter. Ex: Changing the PI resistors can really "brown the sound" which will yield more room to increase the NFR and not allow much of the signal back to the circuit.
As you know if the amp is not designed properly, removing the NFR will sound too trebly or even harsh.
A great sounding amp will have almost no negative feedback and be smooth, articulate and sustain, again if all the earlier parts are designed properly.

[jaysg]

NFR ? Negative feedback resistor?

[makrisp]

NFR ? Negative feedback resistor?

Yes,
NFR = Negative Feedback Resistor

Paul

[Robert]

Due to your conversations in this thread I spent some time with my amp today and tweaked the NFR up to ~6.7K. It really increased the amps sensitivity and touch response. Now I have that wonderful singing bloom so characteristic of the Dumble amp at my finger tips like never before. This is really a sweet spot to tweak. Many thanks to you boys!!!!

['67_Plexi]

Glad we could help !

[heisthl]

I read a post from Gil that said all 50w Dumble's had 8,2K with 1K to ground instead of the 4.7k/390 of the 100 watters. Did you try the 8.2K value and then settle on 6.7K?

[Normster]

I read a post from Gil that said all 50w Dumble's had 8,2K with 1K to ground instead of the 4.7k/390 of the 100 watters. Did you try the 8.2K value and then settle on 6.7K?

Actually, it was Gil's post that motivated me to go back and Read Aiken's info. Scott and Gil had quite a few formulas bouncing back and forth, but the one thing that was consistent was the amount of dB decrease with 4k7/390 in the 100 watt and 8k/1k in the 50 watt. Both values calculated out to -8dB.

What was interesting though is that -8dB wasn't quite right for the iron I was using. In looking at a Deluxe Reverb, the NFB calculated to -4.7dB, quite a bit less than Dumble. So, in tuning the NFB circuit to the Deluxe iron, 6k8/390 worked out to -4.7dB which would be all wrong according to the Dumble formula, but sounds great with the Deluxe Reverb OPT.

Scott and I have had many discussions about tuning the amp to the iron. This is also pretty consistent with Paul's remarks about tuning the amp beginning with the output and working your way towards the input.