Interesting schematic, a lot of gain. What's the bias voltage of the input stage?
Seems one set of diodes on the power supply are drawn reversed, unless you heard an initial pop when you first powered it on ;-)
Regards, KM
The amp only very occasionally pops when switched on (metal toggle switch), it is not that much of a pop really. I do not know the bias voltage of the input stages. I am reluctant to start checking thinks like that on a live circuit as I have no electrical training at all. Upgrading caps is one thing, but a live circuit is something only the trained should "mess" with. I have visited hospital enough over the past 3 years. I have learnt a bit from reading and trying to figure it out and replaced a few caps and a couple of resistors but i am not trained. In the actual amp there is only one diode on the power circuit. This is what I mean in my earlier post, the schematic and what the amp looks like in real life and not exactly the same.
What is the physical/audible effect of the amp having a lot of gain on the input stage?
What is the physical/audible effect of the amp having a lot of gain on the input stage?
It means it will overdrive the output stage before reaching full volume, giving you the illusion that the amp sounds bad above a certain point. In reality the amp is at full output at a lower volume setting. Typically, you would design the amp to start clipping at full, "line level" input. Sometimes it is not convenient to do this or the original designer had different goals.
This is all a lot of guesswork, so some measurements are in order. At the risk of commenting on a problem that has already been solved:
With that circuit (SE KT88) and even with the small Klipsch speakers, decent sound levels for rock/metal should be possible before significant distortion is noticed. For comparison: I have speakers that are comparable in sensitivity but that are also badly worn, with their paper drivers being partly consumed by many generations of silverfish, and I witness the same sort of distortion phenomena as outlined in this topic. However, this is with a badly dimensioned amplifier that is capable of producing about 1.5 wpc when it's running at maybe 0.5 wpc max. The speakers are not the bottleneck in my case; I know the amp will start to distort badly at the cited power level due to bad design of all stages.
It seems to me something's not in order in the case of bottletop, and the amp is the first thing I'd suspect. Incidentally, it's also the easiest thing to take measurements of, so it'd be the place to start. Bottletop, if you feel unqualified measuring this amp, please follow the advice that others have already given and either take the amp to someone nearby who has a pair of speakers of known and proven quality, or (better yet) take the amp to a qualified technician or repairman and have them evaluate it. Preferably pick someone with experience with vacuum tubes. If you decide to do measurements yourself nonetheless, be aware that for this problem, a scope as well as a sine wave generator would be very nice to have around.
With that circuit (SE KT88) and even with the small Klipsch speakers, decent sound levels for rock/metal should be possible before significant distortion is noticed. For comparison: I have speakers that are comparable in sensitivity but that are also badly worn, with their paper drivers being partly consumed by many generations of silverfish, and I witness the same sort of distortion phenomena as outlined in this topic. However, this is with a badly dimensioned amplifier that is capable of producing about 1.5 wpc when it's running at maybe 0.5 wpc max. The speakers are not the bottleneck in my case; I know the amp will start to distort badly at the cited power level due to bad design of all stages.
It seems to me something's not in order in the case of bottletop, and the amp is the first thing I'd suspect. Incidentally, it's also the easiest thing to take measurements of, so it'd be the place to start. Bottletop, if you feel unqualified measuring this amp, please follow the advice that others have already given and either take the amp to someone nearby who has a pair of speakers of known and proven quality, or (better yet) take the amp to a qualified technician or repairman and have them evaluate it. Preferably pick someone with experience with vacuum tubes. If you decide to do measurements yourself nonetheless, be aware that for this problem, a scope as well as a sine wave generator would be very nice to have around.
Mastodon, Yes much guess work. If I could be more helpful then I would. I agree with you and have been thinking the same thing during lunch. I am starting to get well out of my depth here as can be seen from the questions I am asking. There is an engineer in Mansfield who has a scope, is a sound engineer and repair/upgrades tube amps. I think I will take it to him to get a better idea. As regards to friends with speakers. This is tricky as no one I know as is into tube gear or even knows what a capacitor is or a valve. My friends use ipobs and docking stations or listen to music via their PC. Not that is wrong or anything. Need to take my amp to a professional.
So far....
It could be too much gain on the output stage.
It could be that the speakers are not full range drivers only.
It could be the horn loaded tweeters.
It could be speaker sensitivity.
It could be the diode.
It could be bad modern CD recordings (older cd do not end to make the amp distort until about 2/3-3/4 volume.
So I do think I need to get the amp to an engineer or just buy a hi end amp. Need less to say I am very grateful for all the points of advice and suggestions everyone have given me. Greatly appreciated, Thank you.
So far....
It could be too much gain on the output stage.
It could be that the speakers are not full range drivers only.
It could be the horn loaded tweeters.
It could be speaker sensitivity.
It could be the diode.
It could be bad modern CD recordings (older cd do not end to make the amp distort until about 2/3-3/4 volume.
So I do think I need to get the amp to an engineer or just buy a hi end amp. Need less to say I am very grateful for all the points of advice and suggestions everyone have given me. Greatly appreciated, Thank you.
No problem, I will let you know the outcome. Out of interest do you know of any manufacturers who make a integrated SET amp based on either KT88 or 300B tubes and for a reasonable price (circa £1500). I am looking for P2P wiring and audio grade caps like mundorf silver foil in oil or Jensen and decent transformers. I have looked at Raysonic, Prima Luna, MEG, and Melody. Some brands out there seem to look very like Chinese brands with different tube configurations and logo. Some are part pcb and P2P, Some have negative feedback and some do not. Not sure which is better. The list of variations seems endless as does the variation of price.
You can probably take the diode out of your list. If it wasn't installed correctly, bad things would have happened. As far as only having one instead of two, they probably just used an uprated part to eliminate the need for two.
Personally, based on what you've said and how it related to my experience, I think your amp is clipping and it is really coming out harshly from those horns. I don't think I came out and said that clearly in my original post.
I feel like maybe you are moving to the next level and need to build your own amp.
This DIY Audio, afterall...
Personally, based on what you've said and how it related to my experience, I think your amp is clipping and it is really coming out harshly from those horns. I don't think I came out and said that clearly in my original post.
I feel like maybe you are moving to the next level and need to build your own amp.
This DIY Audio, afterall...
I would also agree (w/Russ) that you probably have some amplifier issues. The input amp is pretty much a carbon-copy of the values used in the SP3 phono stage. High gain and in your case driving a 12AU7. I would guesstimate you have ~60dB of voltage gain before the KT88. You also have a low biasing (voltage and current) of the input stage and lot of feedback. I would probably replace the input/driver stage entirely.
Regards, KM
Regards, KM
KM, thank you; very helpful of you. I will take this on board. If I was going to replace the input stage, what would you recommend replacing it with? Something with no negative feedback? I have got my amp booked in with the engineer in Mansfield (next Thursday). He said he would be able to pin point the problem but fixing the problem is something else as he is snowed under with work.
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Lots of designs for zero-feedback, but would not go that way with a pentode or beam power tube. You'll need some feedback to clean it up. Perhaps time for a DHT-based SET...
Your amp has a lot of parts underneath... reworking it is time consuming, would recommend putting the effort and funding towards a nice DIY build and move forward.
Regards, KM
Your amp has a lot of parts underneath... reworking it is time consuming, would recommend putting the effort and funding towards a nice DIY build and move forward.
Regards, KM
Thank you for the pointer Jeff. Nice amp but I would like to make an amp that is all P2P.
KM- Yes, I have often thought there is quite a number of parts in my amp when I have seem other amps wiring. I don't mind spending time re-working my amp. But the question is will I end up with am amp that hums. The power tx seems quiet. IE you have to have your ear on it to hear any hum. Again showing my lack of knowledge, does negative feedback stop the tx from humming or does it dampen/stop the hum being "picked up" in the circuit? I had a look at the MEG amps. I like the lay out and the simple looking design. They have gone from eBay, but here is an image of the 300b se model. I would like to perhaps makes something like this but I am not sure about using 300b tubs as they are well pricy and there is not that much option for tube rolling due to the rarity/price of these nos tubes. I think a kt88 based amp is a bit more flexible.
KM- Yes, I have often thought there is quite a number of parts in my amp when I have seem other amps wiring. I don't mind spending time re-working my amp. But the question is will I end up with am amp that hums. The power tx seems quiet. IE you have to have your ear on it to hear any hum. Again showing my lack of knowledge, does negative feedback stop the tx from humming or does it dampen/stop the hum being "picked up" in the circuit? I had a look at the MEG amps. I like the lay out and the simple looking design. They have gone from eBay, but here is an image of the 300b se model. I would like to perhaps makes something like this but I am not sure about using 300b tubs as they are well pricy and there is not that much option for tube rolling due to the rarity/price of these nos tubes. I think a kt88 based amp is a bit more flexible.
Not sure where you got the idea that there was "not much option for tube rolling" wrt to the 300B, expensive yes, but plenty of manufacturers.
Here are some current suppliers of 300B:
Svetlana SPb made several iterations of the 300B, based on experience I would probably avoid these.
Some AVVT and VAIC NOS tubes stlll available but these have been out of production for a decade or more depending on brand.
Good 300B tend to be very long lived, and IMHO offer a level of audible performance in a properly designed SE amplifier that very few if any beam tubes can match. (My quartet of JJ 300B are all now over 10yrs old with >5K hrs use with no issues.)
Due diligence required before purchasing any of these tubes, and of course YMMV..
Here are some current suppliers of 300B:
- Electro-Harmonix (reasonably priced, quality mixed)
- Electro-Harmonix Gold
- Gold Lion PX300B (New Sensor, new version)
- JJ (Rugged and very good sounding, moderately expensive)
- TJ (Tian Jian) Mesh and solid plates (Good quality, sound nice, moderately expensive) AKA Full Music in the past
- Shuguang (Moderately expensive current production only)
- Western Electric (Very expensive)
- Sophia (Good sound quasi mesh plates, very expensive)
- Emission Labs (Very expensive)
- Valve Arts
Svetlana SPb made several iterations of the 300B, based on experience I would probably avoid these.
Some AVVT and VAIC NOS tubes stlll available but these have been out of production for a decade or more depending on brand.
Good 300B tend to be very long lived, and IMHO offer a level of audible performance in a properly designed SE amplifier that very few if any beam tubes can match. (My quartet of JJ 300B are all now over 10yrs old with >5K hrs use with no issues.)
Due diligence required before purchasing any of these tubes, and of course YMMV..
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Sorry I should have said NOS tube rolling. There is a US dealer listing WE 300b tubes at $1200. That is serious $. I have like 2 pair of matched nos GE6550 and one pair of GL kt88. I agree with what you are saying about modern tube rolling. There seems to be different points of view about 300b or KT88. Some say the 300b is the best and has the best mids and top end, though the bottom end can be a bit soft except in exceptionally well design amps. Others say about the same for the KT88 or something similar but the KT88 has more punch. This is the thing, there are always different points of view as there is people and their preferences. Yes the 300b is an excellent tube I have no doubt so I am undecided. Do I build my own amp or buy one. Stick with my 6550/kt88 tubes or sell the lot and go 300b. Tricky question to answer. I have emailed MEG audio like 3 times now with no response. It would be great if I could find a schematic to build an amp like in the above images using the same tube configuration for the 300se or 6550se amps.
Fortunately in my somewhat limited experience there are a number of current production 300B which perform very similarly or in some cases better than vintage WE 300B which incidentally are in any event excellent.
The performance of the 300B vs KT88 really comes down to amplifier design. My current 300B amp can deliver full power down to about 10Hz and has very good LF performance as well as all of the virtues 300B are noted for in the upper registers. Things IMHO to look for in a good 300B design are a capable driver design, fixed bias output stage design (not cathode bias which is both inefficient and interposes an additional and possibly suspect cathode bypass cap in the signal path) and a good low impedance power supply design.
You might want to take a look at building a p2p version of George's (tubelab) Tubelab SE (not the simple SE) for the 300B. The schematics I believe you will find on the tubelab site or somewhere here.
The MEG amp does look nicely made, but like so many I suspect they are no longer around. You might try Twins Audio here at diyaudio, they make some interesting amps, and I can attest that their OPTs are quite good. (I've used one of their inexpensive OPTS in a recent amp design and they perform far beyond the level I expected considering what they cost.) Nicely built stuff and I am sure they would be happy to build you an amp. I think their designs are quite good too.
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This is the KT88 amp I was going to build before stumbling onto this forum and finding out about Tubelab:
KT88 Single Ended (SE) Tube Amplifier
I decided to build a Tubelab SE amp, but also ordered a Simple SE PCB. I ended up waiting a while for iron for the Tubelab SE and so I actually built the Simple SE first. In a somewhat unusual move for me, I took the Simple SE build all the way to completion and the Tubelab SE is still living on a breadboard. These two amps are the first SE amps I have ever owned.
The 300B is probably the "ultimate" DHT for building SE amps. But the tubes are expensive. You can buy several pairs of EL34/6L6/6550/KT88 types for one pair of decent 300Bs. You also need to look at power output. A 300B amp won't make more than 8WPC...about the same as the EL34/KT88 amp in triode. If you want to kick it up and get more like 14W, you can go UL with some feedback. This flexibility is where designs like the Simple SE really shine.
This is completely a matter of personal opinion, but I find the EL34 strapped as triode in the Simple SE comes pretty close to how the Tubelab SE sounds with 300Bs. The difference is subtle and only shows itself to my ears during "critical listening" (lower volume levels, in a chair, in the "sweet spot"). When I want to rock and roll, I usually flip it to UL mode (with cathode feedback) and let it rip. Other people will probably strongly disagree and that's because, like the music we listen to, it is completely a matter of personal taste!
KT88 Single Ended (SE) Tube Amplifier
I decided to build a Tubelab SE amp, but also ordered a Simple SE PCB. I ended up waiting a while for iron for the Tubelab SE and so I actually built the Simple SE first. In a somewhat unusual move for me, I took the Simple SE build all the way to completion and the Tubelab SE is still living on a breadboard. These two amps are the first SE amps I have ever owned.
The 300B is probably the "ultimate" DHT for building SE amps. But the tubes are expensive. You can buy several pairs of EL34/6L6/6550/KT88 types for one pair of decent 300Bs. You also need to look at power output. A 300B amp won't make more than 8WPC...about the same as the EL34/KT88 amp in triode. If you want to kick it up and get more like 14W, you can go UL with some feedback. This flexibility is where designs like the Simple SE really shine.
This is completely a matter of personal opinion, but I find the EL34 strapped as triode in the Simple SE comes pretty close to how the Tubelab SE sounds with 300Bs. The difference is subtle and only shows itself to my ears during "critical listening" (lower volume levels, in a chair, in the "sweet spot"). When I want to rock and roll, I usually flip it to UL mode (with cathode feedback) and let it rip. Other people will probably strongly disagree and that's because, like the music we listen to, it is completely a matter of personal taste!
Kevinkr & Russ, I have had a look at the twins audio amps, they look pretty good. I have also has a look at Trafomatic amps. I am just not sure if I should have a go at DIY or just buy an amp. I can read schematic reasonably well, the issue I have is how to put the amp together. Please do not forget that I have no training. Reading a schematic is a bit like a process flow diagram but how the machinery goes together in the actual factory is a different matter. I have found a couple of amps which seem to fit the bill, then when I start digging I find they are part PCB or some have decent caps like nichicon or mundorf , then I find that there is half a dozen lower grade caps in there as well, but the price is like hi end. Then there seems to be amps with hi end tags but are actually not that hi end in components. Still not sure on KT88 or 300b I have even looked a 2A3. I will see what Thursday brings at the engineers. Are magnepans any good for tube amps or are they not sensitive enough? I ask this as they are ribbon speakers; is it a case of sensitivity is sensitivity end of story. I quite like the look of the Decware 6wpc zen triode. Not sure what is in it. Might email them to find out what components they use in their amps. Thank you again of you suggestions. All the best, Richard.
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