I just received this little JLH beauty. Already really impressed with it, but would like to try swapping the output caps for something of better quality.
My JLH is supposed to be "2017 model" with MJ15025 & MJ15024. Looking at schematics online, I was expecting the output cap to be 2200 uF. However - mine seems to be 1500 uF. Would that be a mistake?
Any suggestions as to what to replace i with? Should I go with another 1500 uF or replace it with 2200uF? Any particular brands to look for?
TIA
My JLH is supposed to be "2017 model" with MJ15025 & MJ15024. Looking at schematics online, I was expecting the output cap to be 2200 uF. However - mine seems to be 1500 uF. Would that be a mistake?
Any suggestions as to what to replace i with? Should I go with another 1500 uF or replace it with 2200uF? Any particular brands to look for?
TIA
hi rallen
everything is documented on the jlh
uF vs supply voltage vs speaker impedance
what i can advise you is to ask the questions in the thread dedicated to jlh and to start from the pincipe that what you bought is a base, but which can be so much better.
this circuit is very simple and requires to understand it a little to be able to put the right components in the right place and in the right way.
after, the capacitor capacity is not very important in itself, I mean by that you can try "by ear" 2.2k 3.3 4.7 and even 10k if you want, as long as it is higher than 40v operating voltage.
you can also try to bypass with mkt, mkp, pio according to a multiple of 1/100 or 1/10 or even both, it will allow you to get an idea and find out how it reacts.
have fun, it's the main thing
everything is documented on the jlh
uF vs supply voltage vs speaker impedance
what i can advise you is to ask the questions in the thread dedicated to jlh and to start from the pincipe that what you bought is a base, but which can be so much better.
this circuit is very simple and requires to understand it a little to be able to put the right components in the right place and in the right way.
after, the capacitor capacity is not very important in itself, I mean by that you can try "by ear" 2.2k 3.3 4.7 and even 10k if you want, as long as it is higher than 40v operating voltage.
you can also try to bypass with mkt, mkp, pio according to a multiple of 1/100 or 1/10 or even both, it will allow you to get an idea and find out how it reacts.
have fun, it's the main thing
Thanks. Should i just read the mentioned thread from end to end, or where is the best place to go for the mentioned documentation?
Since that model/style JLH amp was introduced a few years ago, the price has been falling and what might we expect to have happened to parts quality? That's right, it drops in size and spec too, in order to maintain some profit margin.
I'd say that there are other reductions too. For example, judging by the crooked print on the power transistors, there is also something not quite right about those MJ15024 transistors.
I bought one of these (branded Krell 🙄) for a friend, about 3 years ago and indeed it looked very classy but inside yours, you may want to consider whether any of the electrolytics and semis are as good as you may have hoped for. At least when you read 1500uF, you are not being fooled that its 2200uF. By replacing with the specified value, the difference won't be dramatic but you need to be conservative with bass from any low power amplifiers - don't oversize the cap when you only have 10W or so to share over the whole audio spectrum since bass is the most power hungry part of audio spectrum by far. If you need more of it, consider a much bigger amp.
Otherwise, It still amazes me how the Chinese manufacturers have apparently limitless quantities of shiny, new 2N1613 or 2N1711 transistors that are unobtanium elsewhere and have been for many years
.
I'd say that there are other reductions too. For example, judging by the crooked print on the power transistors, there is also something not quite right about those MJ15024 transistors.
I bought one of these (branded Krell 🙄) for a friend, about 3 years ago and indeed it looked very classy but inside yours, you may want to consider whether any of the electrolytics and semis are as good as you may have hoped for. At least when you read 1500uF, you are not being fooled that its 2200uF. By replacing with the specified value, the difference won't be dramatic but you need to be conservative with bass from any low power amplifiers - don't oversize the cap when you only have 10W or so to share over the whole audio spectrum since bass is the most power hungry part of audio spectrum by far. If you need more of it, consider a much bigger amp.
Otherwise, It still amazes me how the Chinese manufacturers have apparently limitless quantities of shiny, new 2N1613 or 2N1711 transistors that are unobtanium elsewhere and have been for many years
.
I made a typo, though - I should have referred to the MJ15025 in pic 2. Even so, that could be bad lens aberration, given that some pics are taken with phones that have only simple optics.
no doubt that all of the transistors are most likely counterfeits.
these boards are sold $ 46 / pair on aliexpress and fully assembled and debugged.
just the 6 mj 15024 or 15025 exceed the price of the boards.
it always leaves me dreaming when I see NOS usa or EU for sale on aliexpress.
and you know like me that this chassis is very limited to dissipate heat properly, but for the price, it's still a great playground.
you just have to empty the cards of its transistors and capacitors, check the resistance values and then repopulate with real parts
these boards are sold $ 46 / pair on aliexpress and fully assembled and debugged.
just the 6 mj 15024 or 15025 exceed the price of the boards.
it always leaves me dreaming when I see NOS usa or EU for sale on aliexpress.
and you know like me that this chassis is very limited to dissipate heat properly, but for the price, it's still a great playground.
you just have to empty the cards of its transistors and capacitors, check the resistance values and then repopulate with real parts
ps and off topic, I just received a nytech cta 252 xd mk1 to repair.
this thing is really funny.
it is one of the very first model with exotic transistors 😀
this thing is really funny.
it is one of the very first model with exotic transistors 😀
Thanks for your inputs. I am not a naive optimist in the sense that I believe to have gotten gold for the price that I paid.
That being said; it does sound really good - for my one pair of speakers, it even sounded better than the Yaqin MC-13S I normally use. If I can make it even better by swapping out parts, I am more than prepared to do so - also simply because I like the process.
Reading through your various posts, I guess I should:
1. Replace the capacitors (all 12? I guess the output caps are the most important?)
2. Replace the 4xMJ15025G & 2x4xMJ15025G
What really puzzles me based on your answers, is whether I should replace the caps with others of the same value as the current, or with the values I can look up from schematics? I.e - would I replace the 1500uF caps with new 1500uFs or 2200ufs?
That being said; it does sound really good - for my one pair of speakers, it even sounded better than the Yaqin MC-13S I normally use. If I can make it even better by swapping out parts, I am more than prepared to do so - also simply because I like the process.
Reading through your various posts, I guess I should:
1. Replace the capacitors (all 12? I guess the output caps are the most important?)
2. Replace the 4xMJ15025G & 2x4xMJ15025G
What really puzzles me based on your answers, is whether I should replace the caps with others of the same value as the current, or with the values I can look up from schematics? I.e - would I replace the 1500uF caps with new 1500uFs or 2200ufs?
Thanks. Do I understand things correctly, if im reading from the table on page 3 that suggested value for 8Ω speakers is 2500 uF?
Electrolytic capacitors are not particularly accurate in value (perhaps +/- 20% at best) so the marked values of new capacitors can be quite different to reality anyway. The values assigned to cap. values are nominal and widely spaced, which you see when you read their datasheets. Not only that, sellers only carry a part of the manufacturer's range, typically only 1 value per decade.
Capacitors are sometimes produced to the order of electronics manufacturers, so we also find unusual values in some Japanese models that were engineered to a price point. A current series of stock values would probably be: 1000, 1500, 2200, 3300, 4700 uF etc. but in 1969 when JLH published his design, the series was different. IIRC, it was probably more like 1000, 1500, 2000, 2500, 3000 as you see in the table.
I suggest you just choose the closest available values. 3300uF would be plenty, 2700uF is sometimes available and 2200uF would still be fine since you know that 1500uF is acceptable. Bear in mind that speaker impedances are also nominal - some 8 ohm speakers fall even as low as 3 ohms at low frequencies along their impedance curve but you can't avoid that with affordable speakers. Those marked with impedances like 6 or 4 ohms may not be much different to others marked 8 ohms, nowadays.
Capacitors are sometimes produced to the order of electronics manufacturers, so we also find unusual values in some Japanese models that were engineered to a price point. A current series of stock values would probably be: 1000, 1500, 2200, 3300, 4700 uF etc. but in 1969 when JLH published his design, the series was different. IIRC, it was probably more like 1000, 1500, 2000, 2500, 3000 as you see in the table.
I suggest you just choose the closest available values. 3300uF would be plenty, 2700uF is sometimes available and 2200uF would still be fine since you know that 1500uF is acceptable. Bear in mind that speaker impedances are also nominal - some 8 ohm speakers fall even as low as 3 ohms at low frequencies along their impedance curve but you can't avoid that with affordable speakers. Those marked with impedances like 6 or 4 ohms may not be much different to others marked 8 ohms, nowadays.