i ve been building guitar amps since around 08 as a hobby. I’m wanting to expand my horizons and do some hi fi stereo . Any advice on the differences in guitar to hi-fi would be appreciated.Any insight to 12bh7’s would be helpful also. Thanks
OK, this might not be new information, but anyway:
IMHO, one of the biggest differences between guitar and Hifi amps is the power supply.
In a guitar amp, you want poor regulation, so that there is voltage sag. Interaction of stages is often wanted (while avoiding motorboating of course). In Hifi, you obviously want a stiff power supply and ideally no interaction of stages.
Another big difference is in the output transformer. In guitar amps, these are ridiculously under-sized. Transformer saturation at high power output is not a bug but a feature of guitar amps (at least in the British school of amps). Again, nothing you want to get near in a HiFi amp.
Furthermore, the compromise between power and distortion is obviously shifted towards low THD in Hifi when you look at load lines of tubes.
These are just the most obvious differences. Sorry, if these were too obvious and I misunderstood your question.
Best,
Martin
IMHO, one of the biggest differences between guitar and Hifi amps is the power supply.
In a guitar amp, you want poor regulation, so that there is voltage sag. Interaction of stages is often wanted (while avoiding motorboating of course). In Hifi, you obviously want a stiff power supply and ideally no interaction of stages.
Another big difference is in the output transformer. In guitar amps, these are ridiculously under-sized. Transformer saturation at high power output is not a bug but a feature of guitar amps (at least in the British school of amps). Again, nothing you want to get near in a HiFi amp.
Furthermore, the compromise between power and distortion is obviously shifted towards low THD in Hifi when you look at load lines of tubes.
These are just the most obvious differences. Sorry, if these were too obvious and I misunderstood your question.
Best,
Martin
Have a read of this Mullard Audio Design booklet. https://vdocuments.mx/mullard-circuits-for-audio-amplifiers.html
Very useful and you will see the differences between Guitar and HiFi.
TheWilliamson is the flagship of the 50s and still is along with the Quad II.
Very useful and you will see the differences between Guitar and HiFi.
TheWilliamson is the flagship of the 50s and still is along with the Quad II.
I'm a bass player and I started teaching myself about tube amps on my stage amp. So hello there!
Like Martin says you need to improve the power supply. The basics of transformer > tube rectifier > cap+choke+cap is fine but you would add a dropper resistor to input stages or a second choke and some good caps like DC Link caps which are excellent.
You are probably used to a typical guitar format - high gain input tube like 12AX7, phase splitter stage like 12ax7 or some other 9 pin tube, and then a couple of 6L6 types in push pull output. This will give you a pretty boring amp, though it's still a typical circuit.
Start to think out of the box here. Will your speakers allow you to use a single ended SE amp? If so, start with an output like 300b or 2a3. Get a good single ended output transformer (OPT) rated for 70mA input or more. Then read threads about 300b and 2a3 amps and you will pretty soon see that while the output stage is pretty simple to calculate, you have multiple choices for the input stage. This will introduce you to a lot of new tubes like D3a, C3g and plenty of pentodes in triodes all of which can be used as a 2 stage amp. Or indeed use a pentode. Then consider an interstage or a plate choke and a good coupling cap like Russian FT-2 or FT-3 teflon. Again, use a DC Link cap as the cathode bypass, like 40uF or more if you like.
In a really good SE amp most of the devices are audible - caps, tubes and sometimes even resistors can change the tone and timbre. As a musician I'm assuming timbre is important to you. It's everything to me!!! That and clarity/transparency, of course. And I'm sure vocals are important to you. A SE amp will really bring out the vocals. SE amps can be magic when you get everything right.
Good luck!
Like Martin says you need to improve the power supply. The basics of transformer > tube rectifier > cap+choke+cap is fine but you would add a dropper resistor to input stages or a second choke and some good caps like DC Link caps which are excellent.
You are probably used to a typical guitar format - high gain input tube like 12AX7, phase splitter stage like 12ax7 or some other 9 pin tube, and then a couple of 6L6 types in push pull output. This will give you a pretty boring amp, though it's still a typical circuit.
Start to think out of the box here. Will your speakers allow you to use a single ended SE amp? If so, start with an output like 300b or 2a3. Get a good single ended output transformer (OPT) rated for 70mA input or more. Then read threads about 300b and 2a3 amps and you will pretty soon see that while the output stage is pretty simple to calculate, you have multiple choices for the input stage. This will introduce you to a lot of new tubes like D3a, C3g and plenty of pentodes in triodes all of which can be used as a 2 stage amp. Or indeed use a pentode. Then consider an interstage or a plate choke and a good coupling cap like Russian FT-2 or FT-3 teflon. Again, use a DC Link cap as the cathode bypass, like 40uF or more if you like.
In a really good SE amp most of the devices are audible - caps, tubes and sometimes even resistors can change the tone and timbre. As a musician I'm assuming timbre is important to you. It's everything to me!!! That and clarity/transparency, of course. And I'm sure vocals are important to you. A SE amp will really bring out the vocals. SE amps can be magic when you get everything right.
Good luck!
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You will also need to understand negative feedback. Guitar amps don't have it. Hi-fi amps do.
Cheers
Ian
Cheers
Ian
Well, some amps have negative feedback, mostly the push-pull ones with pentode output stages. Others don't.
When you use triode output stages - which you are free to do when you don't need to shake the walls - you will typically have no global negative feedback. You also would not want it in a standard triode based circuit.
It could help if you start thinking about single ended amps and triode output stages as opposed to pentode push pull amps with negative feedback. It's your choice here, and a lot of it depends on the power you need for the speakers you have in mind. It may be that you want to go with a push-pull amp which is fine. Could have either a triode output stage (2a3, 300b or whatever or just EL34 in triode etc) or a pentode output stage. The advice you get will then be more matched to what your intentions are. If you don't know yet, consider all options and start with an open book!
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I have made the same transition a year ago. I had read tons of information about guitar amps. Built two (JTM45 and JCM800). Participated in a forum on guitar amps for several years. And despite all that I found the transition hard. A whole new world, with it own mix of science, art, components and snake oil...
I tried to prepare myself by asking stuff here, reading posts, searching the intenet, reading some books.
Some threads from that time:
https://www.diyaudio.com/community/threads/first-stereo-tube-amp-build-advice.362926/https://www.diyaudio.com/community/threads/european-el-cheapo-ish-build.367296/
On the bright side, after a lot of preparation, my amp turned out great and the build and test process went very smooth.
I tried to prepare myself by asking stuff here, reading posts, searching the intenet, reading some books.
Some threads from that time:
https://www.diyaudio.com/community/threads/first-stereo-tube-amp-build-advice.362926/https://www.diyaudio.com/community/threads/european-el-cheapo-ish-build.367296/
On the bright side, after a lot of preparation, my amp turned out great and the build and test process went very smooth.
It is true that some amps have NFB and some do not. I am not sure your generalisation about push pull is true but that does not matter.
There is no reason not to use NFB in triode amps. A lot of so called 'purists' abhor negative feedback for real reason.
It would help if you did not limit yourself to any single topology. Explore and examine them all.
Cheers
Ian
You just get a good Audio amplifier project, well documented, with parts that can reasonably be found, and follow it.
I understand you want to build, not design (possible but takes years).
I understand you want to build, not design (possible but takes years).
As many have said, errors and mistakes (even mistakes of economy - like small power supplies), can contribute to a great sounding guitar amp. It can add character, a tonal imprint, distortion and compression. All things that guitarists and music lovers seem to love. But generally in a hi-fidelity amplifier to reproduce music on full frequency, high resolution speakers, you don't want any of that. So much more care must be made to circuit topology, component selection and quality. You can build a guitar amp easily with just a digital multi-meter. For a hi-fi amp, to get the best performance, you really need to add an oscilloscope for testing and refining it (unless you are building a kit amp to exact tested specs).
On the 12BH7, it is similar to a 12AU7 and swappable for it in some circuits. Mainly, it is a bigger tube, with a slightly higher plate dissipation, so it can be run a little harder. However, it was not nearly as popular and is harder to find NOS examples. If you find that an amp you like calls for a low gain tube like these, I'd make sure to keep the specs in line for the smaller tube (except for the heater current of the 12BH7) so that you could use either one. Then you can tube roll, and if some time in the future you can't get a 12BH7, you probably could still find a 12AU7.
On the 12BH7, it is similar to a 12AU7 and swappable for it in some circuits. Mainly, it is a bigger tube, with a slightly higher plate dissipation, so it can be run a little harder. However, it was not nearly as popular and is harder to find NOS examples. If you find that an amp you like calls for a low gain tube like these, I'd make sure to keep the specs in line for the smaller tube (except for the heater current of the 12BH7) so that you could use either one. Then you can tube roll, and if some time in the future you can't get a 12BH7, you probably could still find a 12AU7.
As said before, PSU, OPT. But there's no generalisation, as there are many tube guitar amps with SS rectification, hence stiff voltages, as well as some (not that many!) with excellent and big OPT's that would also be good for HiFi service. Think about Fender and Hiwatt for the latter ones.
In my experience the main difference is the tone stack, which is responsible for »the« sound of a geetaar amp. For HiFi purpose you want frequency response as linear as possible, which simply is impossible with the usual guitar tone stacks.
Best regards!
In my experience the main difference is the tone stack, which is responsible for »the« sound of a geetaar amp. For HiFi purpose you want frequency response as linear as possible, which simply is impossible with the usual guitar tone stacks.
Best regards!
For hi-fi I tend to prefer the Baxandall tone controls because they are implemented with linear taper pots which are easier to get right. Passive versions require audio taper, and whether or not it’s flat at the middle setting is dependent on the actual (not the target) pot taper and ratio of capacitors. Can’t use the Bax if you’re allergic to feedback, though. I’m not.
Power supply stiffness is a matter of how much you are willing to SPEND on it. The best class AB I’ve built had 88% regulation full load to no load. Two ways to get it better - either a choke that can take the current swing (in this case 120 mA to almost an amp $$$$$) or oversize the trafo by 4 or 5X so it just doesn’t drop (Just as much $$$$$). Is 88% regulation good? Depends who you ask. The amp still has an “iron fist” bass - owing to a very low AC impedance in the power supply (470 uF), more than 25 dB of NFB, and 3 pair of output tubes. Is that even a hi-fi technique? Depends who you ask. I like the sound better than triode-strapped EL34’s (with a regulated supply but no feedback) and it will play at club levels.
OTOH, the triode strapped EL34 amp was started and working in the same day.
Power supply stiffness is a matter of how much you are willing to SPEND on it. The best class AB I’ve built had 88% regulation full load to no load. Two ways to get it better - either a choke that can take the current swing (in this case 120 mA to almost an amp $$$$$) or oversize the trafo by 4 or 5X so it just doesn’t drop (Just as much $$$$$). Is 88% regulation good? Depends who you ask. The amp still has an “iron fist” bass - owing to a very low AC impedance in the power supply (470 uF), more than 25 dB of NFB, and 3 pair of output tubes. Is that even a hi-fi technique? Depends who you ask. I like the sound better than triode-strapped EL34’s (with a regulated supply but no feedback) and it will play at club levels.
OTOH, the triode strapped EL34 amp was started and working in the same day.
Yes. Anyway, prominent guitar amps with »the« sound don't feature Baxandall tone stacks nor their passive relatives, but the well-known ones instead with three pots in series and three capacitors. There's just no linear setting possible with those.
Best regatds!
Best regatds!
I'm not clear on what the first project would be.
A power amp?
If so, how much power is needed?
What are the speakers to be used?
If the speakers are contemporary bookshelf types, then you'll probably want a power amp that has low output impedance and at least 10W per channel. That does suggest push-pull with NFB. I think a good first hi-fi project would be a classic PP Ultralinear EL84 or 6V6 amp. There are several good designs to choose from including...
All the above are relatively simple, well thought out, and all have their fans. I can't say which one is 'best', only that they all look like competent designs that would be a great way to build a useful power amp as your first hi-fi project.
IMO, YMMV, etc.
PS - 12BH7 is a twin-triode with mu similar to a 6SN7 or 12AU7 but higher gm and thus lower rp. Usually run with about 5 to 8mA of plate current. It's a good tube.
PPS - A push-pull EL34-triode or 6550A-triode amp can work pretty well too, if you're going for that triode with no NFB type of sound. You can get 10W/channel from PP EL34-triode, mostly class A. These would be quite a simple build too.
A power amp?
If so, how much power is needed?
What are the speakers to be used?
If the speakers are contemporary bookshelf types, then you'll probably want a power amp that has low output impedance and at least 10W per channel. That does suggest push-pull with NFB. I think a good first hi-fi project would be a classic PP Ultralinear EL84 or 6V6 amp. There are several good designs to choose from including...
- Morgan Jones Bevois Valley
- Tubelab Simple Push-Pull (SPP) (PCB available)
- Broskie "Surprisingly Good" PP EL84 design (it's in a thread here on diyAudio, somewhere)
- Eli Duttman El Cheapo (PP 12AQ5, but that's a 6V6 so you could use those instead, if you like)
- Poindexter's Musical Machine
All the above are relatively simple, well thought out, and all have their fans. I can't say which one is 'best', only that they all look like competent designs that would be a great way to build a useful power amp as your first hi-fi project.
IMO, YMMV, etc.
PS - 12BH7 is a twin-triode with mu similar to a 6SN7 or 12AU7 but higher gm and thus lower rp. Usually run with about 5 to 8mA of plate current. It's a good tube.
PPS - A push-pull EL34-triode or 6550A-triode amp can work pretty well too, if you're going for that triode with no NFB type of sound. You can get 10W/channel from PP EL34-triode, mostly class A. These would be quite a simple build too.
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Another simple one featuring EL84's is the Mullard 10-5. It is advisable to strap it's EF86 as a triode, though, to accomodate with today's predominant input signal levels.
Best regards!
Best regards!
Or reduce the value of the feedback resistor to reduce the gain and lower distortion at the same time.
Cheers
ian
Simply reducing the feedback resistor (increasing the level of negative feedback) invites instability so would likely require additional stabilization measures, and we're talking about an introductory project here.
I was thinking a PP EL84 amp would be a good transition from guitar amps to hi-fi, because it's basically taking the power amp circuit of a Fender Princeton Reverb (concertina) or Fender Deluxe Reverb (LTP) and reworking it for hi-fi. You can see what's similar, and what's different. That should be instructive, no?
I was thinking a PP EL84 amp would be a good transition from guitar amps to hi-fi, because it's basically taking the power amp circuit of a Fender Princeton Reverb (concertina) or Fender Deluxe Reverb (LTP) and reworking it for hi-fi. You can see what's similar, and what's different. That should be instructive, no?
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Indeed, I just offered it as an alternative to someone else's suggestion of strapping the EF86 for triode mode.
Agreed. If it is too sensitive, just turn down the input pot.
Cheers
Ian
Links to the PP EL84 amps...
Morgan Jones 'Bevois Valley' amplifier is in his book "Valve Amplifiers 3rd Edition", which is available in PDF form if you google around.
Tubelab 'Simple PP' - http://tubelab.com/designs/tubelab-spp/
Broskie/Tube CAD Journal 'Unexpectedly Good' PP EL84 - https://www.diyaudio.com/community/threads/unexpectedly-good-el84-amp.185823/
Eli Duttman 'El Cheapo' - https://www.diyaudio.com/community/threads/el-cheapo-builders-thread.169914/
Poindexter's 'Musical Machine' - http://ekingsbu.users4.50megs.com/blurb2.html
More complex, but well-liked - Baby Huey PP EL84-UL
https://www.diyaudio.com/community/threads/recommendations-for-pp-el84-circuits.376189/#post-6766161
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Morgan Jones 'Bevois Valley' amplifier is in his book "Valve Amplifiers 3rd Edition", which is available in PDF form if you google around.
Tubelab 'Simple PP' - http://tubelab.com/designs/tubelab-spp/
Broskie/Tube CAD Journal 'Unexpectedly Good' PP EL84 - https://www.diyaudio.com/community/threads/unexpectedly-good-el84-amp.185823/
Eli Duttman 'El Cheapo' - https://www.diyaudio.com/community/threads/el-cheapo-builders-thread.169914/
Poindexter's 'Musical Machine' - http://ekingsbu.users4.50megs.com/blurb2.html
More complex, but well-liked - Baby Huey PP EL84-UL
https://www.diyaudio.com/community/threads/recommendations-for-pp-el84-circuits.376189/#post-6766161
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I think the "Surprisingly good EL84" thread might be a good place to start. I haven't built one yet but it looks to be a pretty forgiving project.