Blackstar Ht-20mkII - "balance" control/ variable resistor on PCB? :o

[Erlend_G]

Hello again,

Sorry for making so many threads lately.

I just had a sneek-peak inside the cooling "holes" on the back of my Blackstar HT-20mkII, and I can see two components on the PCB; which I think are variable resistors.

Square metal things, with a plastic "phillips" screwhead on top. One is marked "Bias", and I guess I think what that's for-

but the other one says "Balance". :o

(The amp also says there are no user serviceable parts inside, and I don't think I even got a schematic). Blackstar also has no! contact e-mail, just a "FAQ" solution :/.

What do you reckon the "Balance" pot is used for?

just curious

-Erlend

[Erlend_G]

Can it be something like this?

https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Balanced_Bias_With_Single_Balance_Pot

"This mod uses a bias adjust trim pot and a balance pot so you can adjust the bias and balance the bias between the power tubes. This allows you to use unmatched tubes but bias them evenly."

[Erlend_G]

I won't ever try to bias my amp myself, unless I've studied real hard on the subject; and am 110% sure and confident in what I'm doing.

Right now it's rockin n rolling with the stock tubes. I don't know what brand of tubes are in it- they are hidden behind the back plate, so I'll need to unscrew like 6/8 screws just to have a look.

thanks.

[FuseG4]

Yes, I believe that is the bias balance variable resistor! that guy's site, Rob Robinette, has a ton of great stuff, and is explained pretty well.
reading about how amps work is useful! You can learn how to pull the most out of an amp most easily if you know what it was designed to do, I think.

That guy's site makes me want to build an amp!

[Erlend_G]

My Blackstar is full of tiny, surface mounted components and chips XD. If one of those ever break, I'd need to put the print under a microscope to fix it .

I was saving up for something a'la a PTP Princeton Reverb, but the gosh-darn meth head neighbors stole all my savings. (Don't ask how. :/ )

But the Blackstar does an amazing job, for such a budget price! :o I just wish it had a real spring reverb. I'm gonna put a Danelectro "spring king" in the effects loop, just to give the reverb some life. .

I'm gonna keep it until I win the lottery, or i for some reason have to replace it.

-Erl

[FuseG4]

My bugera v22 also looks like I would not ever try to fix anything that breaks
Hopefully these things last until we can afford better amps lol

[Erlend_G]

My bugera v22 also looks like I would not ever try to fix anything that breaks
Hopefully these things last until we can afford better amps lol

Yeah, I like this little "budget" booger . If it had a real spring reverb.- it'd be twice the value...

I don't want to call it a poor amp at all- it has tubes; a dynamic OD channel- and even an USB port, lol! .

[idsnowdog]

Printed Circuit Boards are cheap to produce so that's why manufacturers use them. However, the problem is the heat producing components and pots often fail rendering the amp useless. Manufacturers could save a lot of money and make their amps a lot more reliable and serviceable by mounting the pots, transformers and tube sockets on the chassis and connect them to the circuit boards via Molex connectors like a desktop PC. If something breaks unscrew the board from the chassis standoffs, unplug the color coded connectors and replace the board. If they did that they could make amps a lot more modular, scalable, reliable, easy to service and economical. Designing and producing a different circuit board, and chassis for each amplifier in your line is wasteful and modularity could make it easier.

[FuseG4]

Printed Circuit Boards are cheap to produce so that's why manufacturers use them. However, the problem is the heat producing components and pots often fail rendering the amp useless. Manufacturers could save a lot of money and make their amps a lot more reliable and serviceable by mounting the pots, transformers and tube sockets on the chassis and connect them to the circuit boards via Molex connectors like a desktop PC. If something breaks unscrew the board from the chassis standoffs, unplug the color coded connectors and replace the board. If they did that they could make amps a lot more modular, scalable, reliable, easy to service and economical. Designing and producing a different circuit board, and chassis for each amplifier in your line is wasteful and modularity could make it easier.

You'd think as Homo Sapiens we would have gotten past board-mounted tube sockets etc by now but I guess there will always be a whole class of buyers not concerned about reliability (or who don't know that they need to be concerned so much, or what affects reliability).

I AM glad they make these things affordable! But looking forward to something that doesn't scare me to play it for 4 hours straight a few times a week
I have a feeling it wasn't meant for that lol xD

[DavidWard]

Printed Circuit Boards are cheap to produce so that's why manufacturers use them. However, the problem is the heat producing components and pots often fail rendering the amp useless. Manufacturers could save a lot of money and make their amps a lot more reliable and serviceable by mounting the pots, transformers and tube sockets on the chassis and connect them to the circuit boards via Molex connectors like a desktop PC. If something breaks unscrew the board from the chassis standoffs, unplug the color coded connectors and replace the board. If they did that they could make amps a lot more modular, scalable, reliable, easy to service and economical. Designing and producing a different circuit board, and chassis for each amplifier in your line is wasteful and modularity could make it easier.

I was reading somewhere on the internet, most common choice of flame retardant for PCB is FR4. Is it because they are less expensive? or it is because FR4 is easy to place between conductive layers in the PCB.

Source: https://en.wikipedia.org/wiki/Printed_circuit_board
Article I was reading can be found here: https://www.derf.com/printed-circuit...d-explanation/

[AlexR]

You'd think as Homo Sapiens we would have gotten past board-mounted tube sockets etc by now but I guess there will always be a whole class of buyers not concerned about reliability (or who don't know that they need to be concerned so much, or what affects reliability).

I AM glad they make these things affordable! But looking forward to something that doesn't scare me to play it for 4 hours straight a few times a week
I have a feeling it wasn't meant for that lol xD

Gotten past.......the whole manufacturing movement has been moving inexorably toward that more and more.

Its never the playing that is the issue.....its the transport and the associated jolting. I mean tubes themselves are much more prone to issue than the sockets.....and most people have no issue with treating PTP or turretboard tubed gear with the required respect just based on that aspect.
The crystal like fragility of these things is the myth that refuses to die.

[ehdwuld]

Printed Circuit Boards are cheap to produce so that's why manufacturers use them. However, the problem is the heat producing components and pots often fail rendering the amp useless. Manufacturers could save a lot of money and make their amps a lot more reliable and serviceable by mounting the pots, transformers and tube sockets on the chassis and connect them to the circuit boards via Molex connectors like a desktop PC. If something breaks unscrew the board from the chassis standoffs, unplug the color coded connectors and replace the board. If they did that they could make amps a lot more modular, scalable, reliable, easy to service and economical. Designing and producing a different circuit board, and chassis for each amplifier in your line is wasteful and modularity could make it easier.

but then why would folks buy new amps
its a business of amp making not repairing

[FuseG4]

Gotten past.......the whole manufacturing movement has been moving inexorably toward that more and more.

Its never the playing that is the issue.....its the transport and the associated jolting. I mean tubes themselves are much more prone to issue than the sockets.....and most people have no issue with treating PTP or turretboard tubed gear with the required respect just based on that aspect.
The crystal like fragility of these things is the myth that refuses to die.

I'm talking about board mounting being a problem because of heat from the tube dissipating through the rest of the board instead of the chassis
I'm talking heat related failure modes that's all I care about with board mounting the sockets.

[Erlend_G]

This amplifier, being so cheap it actually is- I actually think it will break down and become un-repairable at some time. :/

But, it sounds allright. A spring reverb would increase the tonal quality and value LOADS; (if you ask me)- also it's very bassy, with no "mid spike"- so it's not very loud either.

(unless you put an EQ in the effects loop, remove the bass, and give it some high mids).

I'll have to live with it, until the day I win the lottery . Main concern these days, is the onboard reverb; that sounds dead and lifeless.

I've got a pedal, (EHX Allied Overdrive) with 3-band EQ, and dial in more mids for OD sounds.


It's called a "20 watt" amp- but it has only 2xEL84's. AFAIK it's most likely to output around 15 watts. Still- it's too loud cranked (or getting power amp compression), for apartment use. Even with the "2-watt" switch in. And the amp sounds completely different when turned up, like "Dr. Jekyll and Mr. Hyde"-

one of the best sounds I've ever had, was on the clean channel, master volume cranked, no reverb.... it was "the" sound . A relevation for me, who never owned a tube amp before.

...

I've looked at real, outboard spring reverb tanks, but they cost the same as a used Fender tube combo. I wonder if the TC Electronics Hall of Fame reverb, though digital, will improve my sound enough, that it's worth buying. I play alot of ambient, calm music- ballads and so on...

I also need a new pair of preamp, and maybe output tubes. I've noticed tube microphonics, at the same time I've lost like 25% of my preamp gain. I guess one of the preamp tubes are faulty.

Great amp for the buck; but I wish it had a real spring reverb. And more mids on tap.

My next amp is gonna be a Vox MIni5 Rhythm, the small battery powered thing, you can carry in a backpack. I'll use it both as a practice amp, a headphone device, and amp/reverb simulation for recording.

Rock on! ♪

Erlend

[JamesPaul]

...


It's called a "20 watt" amp- but it has only 2xEL84's. AFAIK it's most likely to output around 15 watts. Still- it's too loud cranked (or getting power amp compression), for apartment use. Even with the "2-watt" switch in. And the amp sounds completely different when turned up, like "Dr. Jekyll and Mr. Hyde"-


...



I also need a new pair of preamp, and maybe output tubes. I've noticed tube microphonics, at the same time I've lost like 25% of my preamp gain. I guess one of the preamp tubes are faulty.

...

Rock on! ♪

Erlend

Maximum power dissipation for an EL84 is ~12.5 watts.

I have several amps which push that limit and they are definitely hard on their EL84's. When I was rehearsing and gigging weekly, EL84's were by far my most frequently replaced tubes.

So one positive, you are saving some money by not cranking that amp up.