I am just a musician, but usually with cathode biased amps you only see a resistor for the bias, not a trim pot. But this amp is similar to other cathode bias amps, i.e. 5 watts amps with a 12bh7 in the power amp. But it has a trim pot for the bias (page 2, on the right of schematic). Is that a cathode biased amp with a trim pot to get the cathode resistor into a wider range? Or is it fixed bias with a trim pot? I have this amp and on first guess it sounds like a cathode bias amp (the power amp distortion is spongier and sweeter than usually on fixed bias amps, which is harder. But I might be wrong, and maybe this amp is fixed bias and just sounds and feels the way it does.) Thanks.
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You mean the one that says 'set bias balance' ?
That appears for balancing the bias and making the Ia in both tubes the same, not for setting the bias as such.
Changing this trimmer will increase bias to one tube and decrease in the other and vice versa.
Jan
That appears for balancing the bias and making the Ia in both tubes the same, not for setting the bias as such.
Changing this trimmer will increase bias to one tube and decrease in the other and vice versa.
Jan
Thank you 🙂 . I had been wondering if in this kind of push-pull 12bh7 amps, but without the bias balance pot, if the manufacturer fits a balanced 12bh7, not just any 12bh7. Otherwise if there's just cathode resistors for the bias but no bias balance, and plugging in a 12bh7 with unbalanced triodes, that would be the same as plugging mismatched tubes in a push-pull amp, which usually requires matched tubes, right? Such as Marshall or Fender, etc. In other words, the bias balance allows one to match the triodes, right? (Or at least do that more easily than without the bias balance). Thanks. 🙂
It's a fixed adjustable bias. (I always find that a contradiction in terms, but there you go.)
Typically, to set the bias you'd centre the PR2 balance pot, adjust the bias to required value with PR1; then adjust PR2 for minimum hum.
For what it's worth: II don't hear spongier and sweeter distortion on my HT5-R. It's quite raspy in the filth channel, largely because it is pretty much an op-amp distortion box with a valve stage on the end to smooth it out a bit. I'm not over-sold on it, to be honest.
Anyone in the UK want to buy an HT5-R? 🙂
Cheers, and regards,
Ant.
Typically, to set the bias you'd centre the PR2 balance pot, adjust the bias to required value with PR1; then adjust PR2 for minimum hum.
For what it's worth: II don't hear spongier and sweeter distortion on my HT5-R. It's quite raspy in the filth channel, largely because it is pretty much an op-amp distortion box with a valve stage on the end to smooth it out a bit. I'm not over-sold on it, to be honest.
Anyone in the UK want to buy an HT5-R? 🙂
Cheers, and regards,
Ant.
If both tubes have the same Rk, they will carry the same Ia so are 'balanced'.
Assuming they have the same grid bias.
It's negative feedback.
Jan
Assuming they have the same grid bias.
It's negative feedback.
Jan
12BH7 is a dual-triode.
The two cathodes are tied together and "grounded" (well, via a common 4R7 resistor with a diode bypassing it). The 4R7 is just so the bias can be conveniently measured). The bias balance allows some leeway in how closely the two halves of the 12BH7 need to be matched.
Edit: This balance is mainly about the DC state of things - keep the currents in each half of the output transformer equal, to reduce hum.
Cheers, and regards,
Ant.
Sure, but I was talking about power amp distortion, not preamp distortion. No op amps in the power amp. I don't have a problem at all with op amps before preamp tubes stages: I am a rock and metal guitarist. We do the same thing with 'purist' preamps such as those found on Marshall plexi and other 'vintage' amps: we plug in solid state distortion pedals to get the gain we want. Because we don't want just killer tone, we need the gain too. I don't play Hank Marvin. So Blackstar achieved the same purpose, by building the whole pedal into the amp, which I and hundreds of thousands other guitarists welcome. 🙂
So it seems to me strange that so many whine and moan about solid state components to achieve gain in a guitar preamp, mixed with a tube or tubes, and then they go out and spend one third of what they spent on the amp, to buy a distortion pedal. Op amps and diodes in a tube amp aren't a fraud: they are a low cost mean to get a lot more gain, or to work the tone in particular ways.
And here's something even stranger, at least to you: the preamp distortion of the HT5 to me sounds and feels WAY spongier than the preamp distortion in my Engl amp, which has no op amps or diodes anywhere in the preamp. I have the older model, maybe you have the latest one, which I know nothing about.
Anyways, I absolutely love the sound of this amp: I'd buy it again if it were stolen. Another major plus of Blackstar amps is this: the amps are super quiet, which is very, very welcome in the rock and metal guitar world.
Sure, you might say a Vox AC30 sounds better than the Blackstar, but then I'd disagree 😉. There's nothing, nothing, nothing bad with op amps or diodes before tubes. They are there to get the gain people like me want.
I have been doing this for 30 years. I have been doing blind tests, comparing 'purist' all tube preamps with preamps mixed with op amps before tubes, and have never noticed any significant differencies, and certainly no negatives with op amps, probably because I use mountains of gain. I have had almost any guitar amp imaginable. And, I selected this amp against several others. It sounds great for my style, it's super quiet, and it's well built. Blackstar is A-OK 😉
I do hate the ISF knob, though. I think it's overrated by the company, and just leave the darn thing in the middle. But it seems to be a lot more effective the more the amp's volume is cranked, then it becomes more subtle and useful.
Have you tried the amp maxed out and boosted? It has a ton of power amp distortion, and it sounds and feels great. Anyways, put it for sale on ebay wherever you live, you won't have trouble selling it, I am sure many other guitarists will appreciate this product.
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Heh! Only 30 years? N00b! 😀
I'm 50+ years into this game now, and like yourself, primarily a rock guitarist. [Ant now waits for someone to come and call him a n00b....]
So I have a couple of high-gain 100W valve heads, some cool vintage valve stuff, and an extremely non-valve Quad Cortex modeler that I'm putting through its paces at the moment (now that is quiet!). And of course various pedals and FX units that I've .accumulated over the years. So like yourself, I have no problem at all with op-amps, digital voodoo, or sand in general in my signal chain. I guess I've just never grown to love the HT5-R as much as you evidently have - which is of course fine. Each to his own.
(Wanna go stereo? I have an HT5-R you could have.... just sayin'.... 😆)
Cheers, and regards,
,
Ant.
I'm 50+ years into this game now, and like yourself, primarily a rock guitarist. [Ant now waits for someone to come and call him a n00b....]
So I have a couple of high-gain 100W valve heads, some cool vintage valve stuff, and an extremely non-valve Quad Cortex modeler that I'm putting through its paces at the moment (now that is quiet!). And of course various pedals and FX units that I've .accumulated over the years. So like yourself, I have no problem at all with op-amps, digital voodoo, or sand in general in my signal chain. I guess I've just never grown to love the HT5-R as much as you evidently have - which is of course fine. Each to his own.
(Wanna go stereo? I have an HT5-R you could have.... just sayin'.... 😆)
Cheers, and regards,
,
Ant.
And this last thought is not directed necessarily at you, or only you, but I'll say this: most guitarists whine and moan way, way too much in regard to gear. The reality is that all this gear is too good, for them, me, and anyone else, not too bad: for most of them cannot read half a bar of music to save their lives.
I was like them, too: very, very choosy. Insanely choosy. Then I learned to read music fluently, and a lot more, realized I was full of it, and that 95 per cent of all these amps are all great: it just takes a little resourcefulness and imagination, for example, I never just use the amp. I have favourite boosters and settings, that they practically never fail: I can get good or even killer sound with almost any good amp. I make the amp work for me, rather than just snap my fingers and expect to get exactly the tone I want. So I don't understand all the whining, really. I have heard someone saying that 'they can't get a good tone' out of this very amp.
I don't know, maybe they are dumb? I can get great tone quite easily, with this and any good tube amp (you'll say hybrid, but for me it's the same). I mean, is it possible that a company like Blackstar is made of a few fools who design an amp incapable of getting even a good tone? I am really, really puzzled by this.
But hey, if you don't like it, sell it, but I must ask: why did you buy an amp you don't like? I only ever bought what I liked.
I can just imagine if Clapton or Page would have been able to buy this very amp, back in the days: I am sure they would have been over the moon. 🙂 I mean, didn't Clapton record with a Fender Champ? Compared with this Blackstar, the Champ is like comparing a cart with wheels, with a SUV. Yet the Champ, a simplistic, hobbyist tube amp, has always been highly prized, but this poor Blackstar amp, a pro guitar amp which I use to record professionally, (although it's not the only one I use) remained a lonely black sheep. This world has never been fair...
I was like them, too: very, very choosy. Insanely choosy. Then I learned to read music fluently, and a lot more, realized I was full of it, and that 95 per cent of all these amps are all great: it just takes a little resourcefulness and imagination, for example, I never just use the amp. I have favourite boosters and settings, that they practically never fail: I can get good or even killer sound with almost any good amp. I make the amp work for me, rather than just snap my fingers and expect to get exactly the tone I want. So I don't understand all the whining, really. I have heard someone saying that 'they can't get a good tone' out of this very amp.
I don't know, maybe they are dumb? I can get great tone quite easily, with this and any good tube amp (you'll say hybrid, but for me it's the same). I mean, is it possible that a company like Blackstar is made of a few fools who design an amp incapable of getting even a good tone? I am really, really puzzled by this.
But hey, if you don't like it, sell it, but I must ask: why did you buy an amp you don't like? I only ever bought what I liked.
I can just imagine if Clapton or Page would have been able to buy this very amp, back in the days: I am sure they would have been over the moon. 🙂 I mean, didn't Clapton record with a Fender Champ? Compared with this Blackstar, the Champ is like comparing a cart with wheels, with a SUV. Yet the Champ, a simplistic, hobbyist tube amp, has always been highly prized, but this poor Blackstar amp, a pro guitar amp which I use to record professionally, (although it's not the only one I use) remained a lonely black sheep. This world has never been fair...
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Not sure I agree with your sentiments regarding guitarists and gear. All guitarists that I have ever met are chasing "that" tone. But none of them - us - can define exactly what "that" tone is. And as tastes change - which they inevitably do - so does "that" tone. Some amps simply don't get there for some people. And for example, what you might think is "that" tone for you and your playing, is not likely to be "that" tone for me.
But we can agree to differ on that.
To answer your question - why did I buy the Blackstar?
The 100W monsters are not family or neighbour friendly. Nor are the 50W vintage non-master volume jobbies I have. And I couldn't get on with them through a PowerBrake; that started to get a bit thin and unpleasant if you whacked the attenuation much above 10dB. So I thought the Blackstar would be suitable for home / practicing. And for the most part, is is. Not great tone on it;s own, but convenient. Enough gain on the filth channel to get by with. And just about enough clean headroom on the clean channel (thought the EQ there is a bit sparse). And good enough for use as a guide amplifier during home recording. Though I DI the guitar directly as well, and take the recorded parts up to our rehearsal space to re-amp through "nicer" (to my ears) amps.
Then then Quad Cortex rocked up. The QC performs all of the above, and better.(and at that price you'd bloody well hope so too!) And at some point it will completely replace my stage rig, I guess.
So yeah. It's not that I dont like it as such; but I dont see me using it again now. So it will be heading off to eBay in the near future. They don't go for much, but it might s well go to someone who has more use for it than I do now.
Oh.... I'm with you on that ISF control. Mine just ended up wound hard right, and left there. Blackstar do seem pretty proud of it, but i dont feel it is the route to sonic nirvana that they big it up to be.
Cheers, and regards,
Ant
But we can agree to differ on that.
To answer your question - why did I buy the Blackstar?
The 100W monsters are not family or neighbour friendly. Nor are the 50W vintage non-master volume jobbies I have. And I couldn't get on with them through a PowerBrake; that started to get a bit thin and unpleasant if you whacked the attenuation much above 10dB. So I thought the Blackstar would be suitable for home / practicing. And for the most part, is is. Not great tone on it;s own, but convenient. Enough gain on the filth channel to get by with. And just about enough clean headroom on the clean channel (thought the EQ there is a bit sparse). And good enough for use as a guide amplifier during home recording. Though I DI the guitar directly as well, and take the recorded parts up to our rehearsal space to re-amp through "nicer" (to my ears) amps.
Then then Quad Cortex rocked up. The QC performs all of the above, and better.(and at that price you'd bloody well hope so too!) And at some point it will completely replace my stage rig, I guess.
So yeah. It's not that I dont like it as such; but I dont see me using it again now. So it will be heading off to eBay in the near future. They don't go for much, but it might s well go to someone who has more use for it than I do now.
Oh.... I'm with you on that ISF control. Mine just ended up wound hard right, and left there. Blackstar do seem pretty proud of it, but i dont feel it is the route to sonic nirvana that they big it up to be.
Cheers, and regards,
Ant
There's another thing, though: perhaps you have the combo version, which has a 'good enough' speaker. I never use stock speakers, which is probably why I am happy with most amps. Anyways, sell it. I'll keep mine. 😉
Welcome to the Tubes / Valves threads; primarily for Hi Fi Stereo 'nuts' like me.
Different opinions on what sounds good exist on these threads.
There are also the Instruments and Amps threads, lots of Guitar amps there.
Different opinions on what sounds good exist on these threads.
But what sounds good is often most different when comparing Tubes / Valves, Versus Instruments and Amps.
The reason to make the push and pull plate currents the same is to prevent . . . Early Lamination Saturation; a very bad thing.
It sounds bad on Hi Fi Stereo.
Well, sounds good for Guitar amplifiers, if you want that distorted sound for effect.
Fixed Adjustable Bias
First you Adjust the bias for the tube current you want; after that, it is Fixed.
Fixed, until the pot wiper makes a bad contact with the resistive element, a really bad contact may result in letting the smoke out; it is real hard to stuff all the smoke back in.
Different opinions on what sounds good exist on these threads.
There are also the Instruments and Amps threads, lots of Guitar amps there.
Different opinions on what sounds good exist on these threads.
But what sounds good is often most different when comparing Tubes / Valves, Versus Instruments and Amps.
The reason to make the push and pull plate currents the same is to prevent . . . Early Lamination Saturation; a very bad thing.
It sounds bad on Hi Fi Stereo.
Well, sounds good for Guitar amplifiers, if you want that distorted sound for effect.
Fixed Adjustable Bias
First you Adjust the bias for the tube current you want; after that, it is Fixed.
Fixed, until the pot wiper makes a bad contact with the resistive element, a really bad contact may result in letting the smoke out; it is real hard to stuff all the smoke back in.
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