Marshall AFD100 owners

[jerrydyer]

Auto bias is a pretty simple concept actually. I have some buddies of mine who have actually made these circuits. You have a small Integrated circuit with firmware that measures the tube current and plate voltage of each tube, the circuit simply adjusts the -grid voltage to each tube based on current. According to Marshall, their circuit also keeps the tubes from max plate dissipation when the amp is dimed.

An adjustment on the back sets the bias threshold based on desired taste. Basically at lower volumes the amp will be biased much hotter but still not exceed plate dissipation and at louder volumes biased colder.

This is no more complicated that the Integrated circuits for MIDI control, mapping etc.

But in tube amps, it adds too much expense for the cheaper mass produced amps. But could be a good thing to prevent amp failure from tube meltdowns.

screw that crap... to much junk just to bias an amp..

 

[LP Freak]

Regarding mixing tubes i read this hear:
http://marshallroadhouse.com/viewtopic. ... 2&start=15

I think, we need to ask the man himself: Santiago Alvarez.

Btw, i run this set (3xEl34 and 1x6550), since a couple of months and the sound is great and none of the tubes failed till now.

That quote says mix tubes but we knew that. The question is what youre doing ok? Now you say a tube failed?

 

[Santiall]

Any of you AFD owners screwed around with other combinations of tubes? I was wondering if I should try some winged C el34 and some gold lion KT88 in together.

What kinda preamp tubes has anyone gotten great results with?

Not sure if its just me but I found the stock tubes kinda lifeless in that amp, amp doesn't breathe or have mojo

I just got this question through the service deparment and googling around I found it here... the answer is yes, you can mix tube types and won't harm anything. Other issue is how they sound.

Auto bias is a pretty simple concept actually. I have some buddies of mine who have actually made these circuits. You have a small Integrated circuit with firmware that measures the tube current and plate voltage of each tube, the circuit simply adjusts the -grid voltage to each tube based on current. According to Marshall, their circuit also keeps the tubes from max plate dissipation when the amp is dimed.

An adjustment on the back sets the bias threshold based on desired taste. Basically at lower volumes the amp will be biased much hotter but still not exceed plate dissipation and at louder volumes biased colder.

This is no more complicated that the Integrated circuits for MIDI control, mapping etc.

But in tube amps, it adds too much expense for the cheaper mass produced amps. But could be a good thing to prevent amp failure from tube meltdowns.

don't know where this come from but this is not the case. The autobias doesn't do anything like that. It is just a system that bias the amplifier exactly like you would do but instead of you turning the trim pots, the amp does it for you. If you bias out of max dissipation or very cold it is your problem, you select the bias current and set the amplifier to bias itself, the amp does it for you and keeps the settings same way as a traditional trim pot would be set with a multimeter measuring tube currents.

The amplifier doesn't bias it hotter at lower volumes neither there is any bias threshold. The trimmer just selects the bias current, the same number as you would read on the multimeter and that the user can decide with the graphs included in the handbook. After the amp is biased there is no difference between the autobias or the traditional trim pots, the system is completely transparent and is engaged only when the user wants to bias the amp.

Protection for overcurrent is a completely different feature and nothing to do with the biasing.

 

[LP Freak]

Any of you AFD owners screwed around with other combinations of tubes? I was wondering if I should try some winged C el34 and some gold lion KT88 in together.

What kinda preamp tubes has anyone gotten great results with?

Not sure if its just me but I found the stock tubes kinda lifeless in that amp, amp doesn't breathe or have mojo

I just got this question through the service deparment and googling around I found it here... the answer is yes, you can mix tube types and won't harm anything. Other issue is how they sound.

Auto bias is a pretty simple concept actually. I have some buddies of mine who have actually made these circuits. You have a small Integrated circuit with firmware that measures the tube current and plate voltage of each tube, the circuit simply adjusts the -grid voltage to each tube based on current. According to Marshall, their circuit also keeps the tubes from max plate dissipation when the amp is dimed.

An adjustment on the back sets the bias threshold based on desired taste. Basically at lower volumes the amp will be biased much hotter but still not exceed plate dissipation and at louder volumes biased colder.

This is no more complicated that the Integrated circuits for MIDI control, mapping etc.

But in tube amps, it adds too much expense for the cheaper mass produced amps. But could be a good thing to prevent amp failure from tube meltdowns.

don't know where this come from but this is not the case. The autobias doesn't do anything like that. It is just a system that bias the amplifier exactly like you would do but instead of you turning the trim pots, the amp does it for you. If you bias out of max dissipation or very cold it is your problem, you select the bias current and set the amplifier to bias itself, the amp does it for you and keeps the settings same way as a traditional trim pot would be set with a multimeter measuring tube currents.

The amplifier doesn't bias it hotter at lower volumes neither there is any bias threshold. The trimmer just selects the bias current, the same number as you would read on the multimeter and that the user can decide with the graphs included in the handbook. After the amp is biased there is no difference between the autobias or the traditional trim pots, the system is completely transparent and is engaged only when the user wants to bias the amp.

Protection for overcurrent is a completely different feature and nothing to do with the biasing.

That's a very cool option then. It's always good to hear it straight from the guy who designed it.

 

[Ventura]

Keep going, you guys are killing any remaining GAS I still had left for an AFD100.

On my Silver Jubilee, the =C= EL34's sound awesome in it.

I'll say this much about the AFD. I test drove it a few months back and did so in a portion of a warehouse that was nicely sound damped; basically an alcove that was about 30' x 40' and soft-walled. I got to crank the piss out of that amp and it was one of the first times I was totally drooling over what I was hearing. No stomps up front, no boosts, ODs, or the like. Just axe, cable, amp. Was great sounding.

Fact is? I'd play that amp in that style at that volume MAYBE 5% of the time I had it. So it was a no dice scene for me. Cat that was letting me do the run through even said it - unless it's cranked up, it's a "bit brittle and thin" (I believe his words were). I tried knocking the volume back, but honestly by that time, I was already ringing in my ears.

Just sayin, I think it's a great stage volume amp - but not so much a bedroom brawler. And that's my review of an amp I spent maybe 25 minutes with.

 

[blackba]

Keep going, you guys are killing any remaining GAS I still had left for an AFD100.

On my Silver Jubilee, the =C= EL34's sound awesome in it.

I'll say this much about the AFD. I test drove it a few months back and did so in a portion of a warehouse that was nicely sound damped; basically an alcove that was about 30' x 40' and soft-walled. I got to crank the piss out of that amp and it was one of the first times I was totally drooling over what I was hearing. No stomps up front, no boosts, ODs, or the like. Just axe, cable, amp. Was great sounding.

Fact is? I'd play that amp in that style at that volume MAYBE 5% of the time I had it. So it was a no dice scene for me. Cat that was letting me do the run through even said it - unless it's cranked up, it's a "bit brittle and thin" (I believe his words were). I tried knocking the volume back, but honestly by that time, I was already ringing in my ears.

Just sayin, I think it's a great stage volume amp - but not so much a bedroom brawler. And that's my review of an amp I spent maybe 25 minutes with.

Thanks for the review, not surprised it sounds good cranked, I mean that is what Marshalls are known for. My Silver Jubilee sounds better cranked too, enough so that I am shopping for an attenuator.

I am also considering the new Marshall SL-5 that is coming out, just wish it came in a head.