I noticed I have all the parts to make this Zen Decware EL84/6BQ5/6P15P amp. I have a few quick questions about some possible improvements, opinions welcome. I want to make this a fast-build project so I'm not looking to depart too much or start all over from first-principles. Just what would be some good tweaks, if anyone wants to chime in. Schematic attached. Here are my questions:
1) Both the L/R output tubes are biased on the same cathode resistor, I assume its probably better for me to use two 75 ohom resistors instead of the single 150 ohm.
2) There doesnt seem to be a whole lot of capacitance in the reservoir and smoothing caps (only 33uf per). I have some 60uf motor run caps that I was thinking of using instead, go all-film since the designer didnt call for much capacitance in this design.
3) There seems to be a weird voltage divider dual capacitor decoupler (3.3 uf caps) for the 6N1P plates. What is that all about? I'll keep it I guess and I have some 5 uf motor run caps for these too.
4) The tranny voltage is 300-0-300 volts is this about right? does the operating point look ok overall at this voltage?
I'll be using this low-watts amp with a pair of Klipsch RP600M speakers (96db at 2.83V / 1m) and an 8 inch powered sub woofer coming off the speakers.
https://f072605def1c9a5ef179-a0bc3f...product-specsheets/RP-600M_Spec-Sheet_v01.pdf
1) Both the L/R output tubes are biased on the same cathode resistor, I assume its probably better for me to use two 75 ohom resistors instead of the single 150 ohm.
2) There doesnt seem to be a whole lot of capacitance in the reservoir and smoothing caps (only 33uf per). I have some 60uf motor run caps that I was thinking of using instead, go all-film since the designer didnt call for much capacitance in this design.
3) There seems to be a weird voltage divider dual capacitor decoupler (3.3 uf caps) for the 6N1P plates. What is that all about? I'll keep it I guess and I have some 5 uf motor run caps for these too.
4) The tranny voltage is 300-0-300 volts is this about right? does the operating point look ok overall at this voltage?
I'll be using this low-watts amp with a pair of Klipsch RP600M speakers (96db at 2.83V / 1m) and an 8 inch powered sub woofer coming off the speakers.
https://f072605def1c9a5ef179-a0bc3f...product-specsheets/RP-600M_Spec-Sheet_v01.pdf
Last edited:
There are literally tons of mistakes in this schematics (I'm not even mentioning some dubious engineering choices).
There should be a jumper between the connection point of two 20uF 250V caps and the connection point of two adjacent 220k resistors.
The top ends of the 6N1P plate resistors should each be connected to the other ends of those 10k resistors (and that answers your third question).
Output stage grid leak resistors definitely shouldn't be 1k - 330-470k rather.
As for your other questions:
1) Yes, I'd go for separate L/R resistors, but they should be 300 Ohm, not 75.
2) Worth trying.
3) More or less. A bit too high for my taste, but it should work.
There should be a jumper between the connection point of two 20uF 250V caps and the connection point of two adjacent 220k resistors.
The top ends of the 6N1P plate resistors should each be connected to the other ends of those 10k resistors (and that answers your third question).
Output stage grid leak resistors definitely shouldn't be 1k - 330-470k rather.
As for your other questions:
1) Yes, I'd go for separate L/R resistors, but they should be 300 Ohm, not 75.
2) Worth trying.
3) More or less. A bit too high for my taste, but it should work.
Wow those are some serious mistakes for a company doing this commercially!
As for the series connected low voltage smoothing caps I didnt see the point in those anyway, I was going to use a third motor run capacitor that can easily handle the voltage.
The 300-0-300 V did seem high to me, it would be the highest voltage amp I've tried so far.
Oops my bad yes 300 ohms, thanks.
The two biggest errors are the 6N1P plate connection and and the low ohms grid leak, wow.
Thanks a bunch, someday I'll be good enough to spot errors this bad, this fast. This would make a good pop quiz for anyone hosting a tube school.
Overall its making me lose some confidence in what I thought would be a quick build of a commercial proven kit. I'm going to cut out a top plate for it anyway using these parts and move forward. But even the weird way the schematic is drawn makes me leery now. I'll have to redraw it with the corrections and go to first principles where I was just hoping for a "call it in" build.
Thanks again TG!
I extracted the schematic page for my post here. But it came from this full Decware assembly manual (see link). The schematic is referenced in this manual down a ways. Who knows maybe it is counterfeit? I'd like to get the real Decware Zen schematic if anyone has it? But this manual definitely came from the secure Decware web site!
https://www.decware.com/newsite/ZKITmanual2019.pdf
And I found the above link on this thread at Decware:
Forums - Updated schematic for 2019 ~ Anniversary Mods !
Last edited:
There is a cult-like following of this little ZKIT amp, audio nirvana apparently, all the typical audiophile jabber from its followers. This is what attracted me to such a simple build, already having all the parts, I was looking for a quick project to use with my 96db speakers in a spare room here. But the mistakes in the schematic leave me wondering. If anyone has a reliable schematic, that would be pretty cool.
Zen Triode SET kit amplifier model ZKIT1
Zen Triode SET kit amplifier model ZKIT1
The more I look at this amp, the more I dislike it.
Well, the amp section itself is okay (except for that common cathode resistor for both channels and the missing grid leak resistors for the first stage - one should never rely on the pot wiper itself for this job, it can and will fail) - nothing special, but it isn't bad either.
But the PSU makes me cringe. It is definitely designed for higher profit margin, not for the quality.
And I suspect there are some mistakes in this part of the schematics too. That 1k 5W resistor looks suspicious:1k resistor in this position will dissipate around 5W, so 5W rating is not nearly enough - it should be 20W or more. But the assembly photos show someting that looks like 5W resistor indeed, and there's "1k 5W" silkscreened on the PCB itself, so I don't know what to think (at least I'm not able to come up with something nice to think).
Well, the amp section itself is okay (except for that common cathode resistor for both channels and the missing grid leak resistors for the first stage - one should never rely on the pot wiper itself for this job, it can and will fail) - nothing special, but it isn't bad either.
But the PSU makes me cringe. It is definitely designed for higher profit margin, not for the quality.
And I suspect there are some mistakes in this part of the schematics too. That 1k 5W resistor looks suspicious:1k resistor in this position will dissipate around 5W, so 5W rating is not nearly enough - it should be 20W or more. But the assembly photos show someting that looks like 5W resistor indeed, and there's "1k 5W" silkscreened on the PCB itself, so I don't know what to think (at least I'm not able to come up with something nice to think).
I have seen a lot of schematics that use two parallel caps in the filter, one to actually filter and the other to eliminate noise. That makes sense I guess, but I also seen many use two resistors in parallel wired in reverse ie. 2x300 Ohm rather than a single 150 Ohm resistor. The claim is that this sounds better. I am not convinced. I think a better idea would be to use Caddock film resistors rather than just two carbon resistors wired reverse in parallel.
Perhaps somebody was trying to play tricks on those who would try and build the amplifier
from that schematic.
Perhaps someone tried to draw a schematic of the insides of their own Decware amp,
And made a lot of errors.
Perhaps Decware was trying to protect their intellectual property.
What ever the reason, the schematic is full of errors.
The web is full of erroneous information.
Use at your own risk.
TG in post # 2 is correct.
Just do not forget to put an individual bypass cap across each of the new individual 300 Ohm bias resistors.
And, Oh! Don't all Factory built Decware amplifiers use tube rectifiers.
I believe only the kits use any solid state B+ rectification.
Check it out.
That should be a clue about what you are building.
I hope you do not have the PCB. PCBs are not made to be able to easily do modifications, point to point is far better for that.
Take a PCB, remove parts, cut traces, connect parts, and pretty soon you have a bad PCB.
In any case, with the corrections, and careful work, you should be able to have a working amplifier.
Then sit back, listen, and enjoy.
from that schematic.
Perhaps someone tried to draw a schematic of the insides of their own Decware amp,
And made a lot of errors.
Perhaps Decware was trying to protect their intellectual property.
What ever the reason, the schematic is full of errors.
The web is full of erroneous information.
Use at your own risk.
TG in post # 2 is correct.
Just do not forget to put an individual bypass cap across each of the new individual 300 Ohm bias resistors.
And, Oh! Don't all Factory built Decware amplifiers use tube rectifiers.
I believe only the kits use any solid state B+ rectification.
Check it out.
That should be a clue about what you are building.
I hope you do not have the PCB. PCBs are not made to be able to easily do modifications, point to point is far better for that.
Take a PCB, remove parts, cut traces, connect parts, and pretty soon you have a bad PCB.
In any case, with the corrections, and careful work, you should be able to have a working amplifier.
Then sit back, listen, and enjoy.
Last edited:
Yeah I'm looking at other EL84 SE switchable to SET amps. I want to see what all the hub bub is with 2 watt 6BQ5 amps and a high efficiency speaker. Hoping for some nice late night listening with my wife. The RH84 has been mentioned here and in May another member was asking for a list of EL84 SE amps, all helpful. In any case even not knowing the exact amp I can machine my top plate because I'll use parts I have.
FYI, Klipsch RP600M is not 96dB, $tereophile measured it and estimated 89.6dB. I experienced the same prior to that article when I took home a pair from a local BestBuy to try with a 8watt 300B SET amp and found they required about the same gain as a pair of 88dB speakers with a minimal parts simple 1st order crosover and easy impedance that I had on hand.
Klipsch Reference Premiere RP-600M loudspeaker Measurements | Stereophile.com
More on Decware:
YouTube
YouTube
The scema in the 1st post references Edcor transformers. AFAIK Steve makes his own OPTs at least.
We did clone the amp, but then kept making it better. Start with somethign like the RH84 or one of the developments on it.
dave
We did clone the amp, but then kept making it better. Start with somethign like the RH84 or one of the developments on it.
dave
You should definitely *not* use the same cathode resistor for both channels. This will absolutely cause channel separation issues. In the last amp I had in for service that had a shared cathode resistor in the output stage, I saw only 40dB of channel separation. I was not Inspired.
Thanks,
I suspected that the RP600 probably wasnt really a 96db speaker, based on its size, but it does play considerably louder than my Golden Ear bookshelf speakers and those are truly rated at I think 86db. I was looking for a budget speaker for a 12 x 12 room we like to sit in and just relax and listen to music late with no TV on in the dark. The RP600 is a fun speaker, I'm not into laid back speakers, my wife and I attend AXPONA every year and I'm only satisfied by horns year after year. Maybe its my aging ears, but I'd rather have a speaker I have to tame rather than laid back one that is "theoretically" perfect in measurements. True the RP600 is small and its a wave guide not a true horn, but at $600 a pair it had the fun factor, and it works good with tubes in a small room. Frequency response flatness, impedance dips, etc mean less and less to me as I get older. The acoustics bother me more than speaker inaccuracies, I'm done with speakers that are "perfect" but dull, no fun.
I considered doing the RP600 crossover modification kit that GR-research sells, but I really don't think my listening will be improved, it will just be different. I've paired these with a small 8 inch Golden Ear subwoofer and am happy in this 12 x 12 foot room. So far I'm pretty confident the RP600's will do well with a 2 watt amp which is why I'm looking to do an EL84 SET.
As for the Zen videos, thanks. I see this Guttenberg guy at AXPONA every year on the elevators, walking around, everyone seems to know him there, I always wondered who he was! And I see this guy likes the RP600 and commented about wanting to pair them with a Zen Decware, mmmm.
Last edited:
Post # 12:
There are no B+ bleeder resistors.
Safety First!
Prevent "The Surviving Spouse Syndrome"!
There are no dividing resistors across the two stacked 20uF B+ caps.
If you already have the two 20uF caps, then use a pair of resistors to divide, and to act as a bleeder too.
Or, replace the two 20uF with a single 10uF @ 500V, and put a single bleeder resistor across it.
Done.
The 6N1P has about 2 times the plate resistance of the other 2 tube types.
The 6N1P has about 1/2 of the transconductance of the other 2 tube types.
The 6N1P has about 1.5 times the filament current of the other 2 tube types.
Other than that, the 6N1P is similar (only similar specs are the mu, and the pinout).
Caution:
The SV83 screen is only rated for 200V Maximum.
The EL84 and 6BQ5 screens are rated at 300V Maximum.
The black wires on the output transformers (Speaker Out Common), need to be grounded.
Safety First!
Prevent "The Surviving Spouse Syndrome"!
Someone else can find any remaining errors, if there are still some.
There are no B+ bleeder resistors.
Safety First!
Prevent "The Surviving Spouse Syndrome"!
There are no dividing resistors across the two stacked 20uF B+ caps.
If you already have the two 20uF caps, then use a pair of resistors to divide, and to act as a bleeder too.
Or, replace the two 20uF with a single 10uF @ 500V, and put a single bleeder resistor across it.
Done.
The 6N1P has about 2 times the plate resistance of the other 2 tube types.
The 6N1P has about 1/2 of the transconductance of the other 2 tube types.
The 6N1P has about 1.5 times the filament current of the other 2 tube types.
Other than that, the 6N1P is similar (only similar specs are the mu, and the pinout).
Caution:
The SV83 screen is only rated for 200V Maximum.
The EL84 and 6BQ5 screens are rated at 300V Maximum.
The black wires on the output transformers (Speaker Out Common), need to be grounded.
Safety First!
Prevent "The Surviving Spouse Syndrome"!
Someone else can find any remaining errors, if there are still some.
Last edited:
I know a lot of people use those speakers with low power setups so they must work well enough but keep in mind that, according to Stereophile magazine, their sensitivity is more in the range of 89 than 96. 89 isn't a terrible sensitivity but it is a number that is found in a lot of bookshelf speakers; making them less unique.
"The Klipsch's specified sensitivity is an extraordinarily high 96dB/2.83V/m. My estimate was much lower, at 89.6dB(B)/2.83V/m,"
Klipsch Reference Premiere RP-600M loudspeaker Measurements | Stereophile.com
Then again I'm using 85 db speakers on a 7 watt amp right now and am plenty happy with the output...
All those things yes. But Steve the owner of Decware writes specifically in his literature that the OPT isn't grounded and that is part of the sound, not sure what to make of that, I'll ground it. I was going to use all motor run caps polypropylene in vegetable oil, since all these values are so low, may as well take advantage of that, so no need to series up any caps. I was going to do all that cap paralleling with small caps, I know many say that doesn't matter, I don't know I'll respect the designer. I noticed this designer doesn't like grid leak resistors, rather than have none, maybe I'll just make those 1 meg as though they are still not there but still protect from electron build up. Not sure what schematic you're seeing but some I've looked at have no grid leaks.
The cult following is pretty strong around this little amp. If I like low watt listening with a small sub, them I'm going to look into building a pair of 8 cubic foot 15 inch full range speakers at 104db. I can do those for under $1400 a pair using the Audio Nirvana alnico classic 15 speakers. Then I'll be all set till I die, right. Full range because crossover making is something I have no desire to do.
Yeah they are a budget speaker, but they are fun regardless of the midrange dip. I've compared them a/b to a modded RP600 that omitted the midrange dip and I actually still liked the stock design better. I hope to build some 8 cubic foot 15 inch full range 104db speakers, maybe this fall.