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DIY TUBE PREAMP HELP PLEASE

C

Califmike33

Well-Known Member
I want to build a tube preamp, dont know where to start. I do have a few vintage 80s stereo recaps under my belt.

I have seen some interesting DIY clone kits on ebay that you build yourself they come with all the parts. I figured i could replace some of those cheap caps and things with better quality ones. Im looking for someone who has built some of these diy kits. If not just steer me in the right direction, thank you.

https://www.ebay.com/itm/1930703534...rentrq:9ea6afbf1860a9d91fde9b90fffff61a|iid:1

Michael
 
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I bought a SE 6l6 tube amp kits, ended up using the transformers and case and that was about it, but I would say it depends on the kit. The one you listed looks okay, as you said I would probably change the caps. If you search 6sn7 preamp build on youtube, there is one close to the same circuit as that kit that could be built for less but point to point wiring which is not a bad thing. Also 6sn7's are not that hard to find, good used ones can be had for cheap, check findatube, no affiliation.
 
Yes as a speaker amp, but the headphone output has issues as i have watched reviews. I guess with 300ohm and up its very good, but under that on ohms, it has several issues going on, but as far as a speaker amp its really good.
 
Are the headphones just driven off some resistors? Maybe changing the value would work forever impedance headphones.
 
Yes driven off some resistors, video review i watched him changed the resistors and it changed that you could use low-impedance headphones, but then he went on to change the power supplies also, at that point it got too costly and i wasn't liking it anymore. Check out review.

 
I found out there is an upgrade kit for the Elekit 8200r that includes new transformers for $300, now you're talking it's a $1000 diy kit. It does get really good reviews, i think at some point I'm going to build it.
 
Califmike33 said:
I want to build a tube preamp, dont know where to start. I do have a few vintage 80s stereo recaps under my belt.

I have seen some interesting DIY clone kits on ebay that you build yourself they come with all the parts. I figured i could replace some of those cheap caps and things with better quality ones. Im looking for someone who has built some of these diy kits. If not just steer me in the right direction, thank you.
Click to expand...
Preamp or amp? First post is about preamp but most of the ones after are about ampIifier kits.

I have no experience with kits and I'm not a fan of circuit boards. If non-kit DIY is an option, I built this a while back after going through a lengthy breadboarding process during which I auditioned about 10 or 12 different types of tubes:

https://www.audiokarma.org/forums/index.php?threads/1626-preamp-build.931276/

Simple circuit, inexpensive and easy to build. Additional features, such as multiple inputs and even remote volume control could be added if desired.

I've also gotten good results with another preamp recently but it is not a kit and not DIY.

It's a super basic, no frills, Chi-Fi cheapie that uses directly heated tubes. I picked it up because one of the tube types I liked during my breadboard adventure was the Russian 2P29L, which is very similar to the tube this uses. Perhaps too basic for you, though.

https://www.audiokarma.org/forums/i...e6-preamp-uses-directly-heated-tubes.1009865/

One thing about the "clone kits" is that they are almost never actually clones. That doesn't mean they might not sound OK but "inspired by" is typically more accurate. You really need to compare schematics to see how closely they follow the original. Some are much closer than others. I recall seeing one where the only resemblance is that they used the same type of tubes, the circuit was not even remotely similar.

And, yes, you can count on them coming with cheap parts. Even if the parts carry "name brand" labels they are often counterfeits if the kit is Chinese. If you're going to replace them, why buy them in the first place. Start with quality parts from a major distributor.

If you're limited to building a kit using a circuit board, you might want to check out one of the Glassware offerings. Much higher quality than a Chinese kit from eBay. Maybe even cheaper? If you end up using just the board from the eBay kit a board from Broskie / Glassware is definitely cheaper. https://glass-ware.stores.yahoo.net/newhardware.html

StepheK's YT channel is a great resource for DIY building. She compared some popular preamps, some of which are available as kits, a while back. Here's the summary, search her channel for the build videos. At least one was built from a kit (??):

She also did a four part series on how to add headphone capability to an amp:

As for the amp you linked, I read the description and they claim that it puts out 4wpc when running the 6L6GCs in triode mode. The 6L6GC data sheet says SE triode produces only 1.4w at 5% distortion so Elekit's claim (despite their good reputation) is obviously a fantasy. Either that or the distortion must be through the roof, more suited to a guitar amp.

In pentode their claim of 8.2wpc is reasonable. Pentodes require negative feedback to operate linearly. When I see amps that are switchable between pentode and triode I wonder if switching also eliminates the feedback or if they run feedback regardless of the mode of operation. I suspect that the cheapest kits just ignore this aspect but perhaps Elekit deals with it properly. You might want to ask if you're considering buying it.
 

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Thank you for your post I'm reading over it briefly lot of information I think I want to preamplifier. And he left a lot of good links when I get off of work I'm going to have to look over all of this information you've given me thank you.
 
FlaCharlie said:
Preamp or amp? First post is about preamp but most of the ones after are about ampIifier kits.

I have no experience with kits and I'm not a fan of circuit boards. If non-kit DIY is an option, I built this a while back after going through a lengthy breadboarding process during which I auditioned about 10 or 12 different types of tubes:

https://www.audiokarma.org/forums/index.php?threads/1626-preamp-build.931276/

Simple circuit, inexpensive and easy to build. Additional features, such as multiple inputs and even remote volume control could be added if desired.

I've also gotten good results with another preamp recently but it is not a kit and not DIY.

It's a super basic, no frills, Chi-Fi cheapie that uses directly heated tubes. I picked it up because one of the tube types I liked during my breadboard adventure was the Russian 2P29L, which is very similar to the tube this uses. Perhaps too basic for you, though.

https://www.audiokarma.org/forums/i...e6-preamp-uses-directly-heated-tubes.1009865/

One thing about the "clone kits" is that they are almost never actually clones. That doesn't mean they might not sound OK but "inspired by" is typically more accurate. You really need to compare schematics to see how closely they follow the original. Some are much closer than others. I recall seeing one where the only resemblance is that they used the same type of tubes, the circuit was not even remotely similar.

And, yes, you can count on them coming with cheap parts. Even if the parts carry "name brand" labels they are often counterfeits if the kit is Chinese. If you're going to replace them, why buy them in the first place. Start with quality parts from a major distributor.

If you're limited to building a kit using a circuit board, you might want to check out one of the Glassware offerings. Much higher quality than a Chinese kit from eBay. Maybe even cheaper? If you end up using just the board from the eBay kit a board from Broskie / Glassware is definitely cheaper. https://glass-ware.stores.yahoo.net/newhardware.html

StepheK's YT channel is a great resource for DIY building. She compared some popular preamps, some of which are available as kits, a while back. Here's the summary, search her channel for the build videos. At least one was built from a kit (??):

She also did a four part series on how to add headphone capability to an amp:

As for the amp you linked, I read the description and they claim that it puts out 4wpc when running the 6L6GCs in triode mode. The 6L6GC data sheet says SE triode produces only 1.4w at 5% distortion so Elekit's claim (despite their good reputation) is obviously a fantasy. Either that or the distortion must be through the roof, more suited to a guitar amp.

In pentode their claim of 8.2wpc is reasonable. Pentodes require negative feedback to operate linearly. When I see amps that are switchable between pentode and triode I wonder if switching also eliminates the feedback or if they run feedback regardless of the mode of operation. I suspect that the cheapest kits just ignore this aspect but perhaps Elekit deals with it properly. You might want to ask if you're considering buying it.
Click to expand...

I want a pre amp, so that first link looks like a nice build. Boggie factor sounds great. Now there is no follow along video, i dont have alot of experience building tube amps, i have done a few vintage stereo recaps and thats it. Do you think i could build it ? im very interested to try.
 
Califmike33 said:
I want a pre amp, so that first link looks like a nice build. Boggie factor sounds great. Now there is no follow along video, i dont have alot of experience building tube amps, i have done a few vintage stereo recaps and thats it. Do you think i could build it ? im very interested to try.
Click to expand...
Sure, the circuit is simple. One person who built it posted a parts list and pics of their build on the thread.

If you haven't built anything from scratch you might want to watch some of the DIY build videos on StepheK's YouTube channel, which are excellent and very detailed. Even though she is building other projects, the process of building something is pretty much the same regardless of exactly what you're building.
 
Got to get better at reading a schematic and I have watched some of her videos I'm probably going to take a crack at it.
 
Califmike33 said:
So you think all these capacitors are fake in this amp? its a clone from China
Click to expand...
:dunno:
Having read comments by people who work with various brands of caps in their jobs I'd say it's a distinct possibility. Flip a coin. These folks are very very familiar with the issue of counterfeit parts because the products they build, and their company's reputation and sales are affected.

I recall a thread in which someone pointed out some of the tell tale signs when they saw pics of some name brand electrolytic caps in a cheap Chinese tube amp. I've even read where someone cut open an expensive cap that was marketed to guitar players as some high end PIO "tone cap". They found that it wasn't paper in oil construction at all. Inside was a super cheap unbranded polyester cap.

The Chinese are notorious for selling counterfeits of all sorts.

Other times the parts are just poorly made. StepheK recently did a video series on the popular Willsenton R8 amp and found new resistors whose coating was flaking off. And that's a $1500 amp.

That's not to say the counterfeits don't work but don't count on them meeting the specs, or being as reliable, as the real ones.

An equally, or perhaps even bigger problem, is that they sometimes use parts that are not specced correctly.

In another post I recall, a Chinese amp burned a 1w metal film resistor. When I did the math, based on the voltages shown in a schematic, I found that it was dissipating about .9w. Standard engineering practice is to de-rate resistors by a factor of 3x, so they should have used a 3w part. It was likely dissipating over 1w since the power transformer was designed for a 110v primary and wall voltages in the US are typically over 120v, sometimes close to 125v. The transformer issue is very common and they often also run very hot.

This affects voltages throughout the amp but it's the tube heater voltages that are the most concerning because the higher voltage reduces tube life considerably. People often find the stock Chinese tubes to be sonically poor so they replace (aka tube rolling) them with tubes that are sometimes very expensive. Then they, unknowingly, run those expensive tubes at elevated heater voltages.

So, if you have anything Chinese that runs tubes you should always measure the heater voltages. While data sheets generally suggest that +/- 10% is acceptable, once you go over 5% tube life is drastically reduced. Best is to run them at spec or slightly under for long life. Many tubes types are not cheap and prices have increased significantly recently.

Many of the cheap Chi-Fi tube amps also use first caps after a tube rectifier that are much much too large in value. Apparently the "designers" have never thought to read tube data sheet, which specifies a much lower value cap. While some situations allow the use of a somewhat larger value, the ones they use go far beyond this. No doubt they do this to reduce hum but the result is that the rectifier tubes arc and die. In extreme cases this can also destroy transformers.

End of rant. :rolleyes:
 
Thank you for that rant I like it and I agree they definitely counterfeit stuff. I think if you were to get that kit and just put quality parts from digikey or somewhere like that and just basically use the board it might be okay.

There's another one that I found on there it's a headphone amplifier that it looks interesting again I don't know a whole lot about this stuff I'm trying to learn but this too you can also order without the Caps or resistors and just use your own parts you're just using the board and the design.

https://www.ebay.com/itm/2645080757...ar=564215758613&widget_ver=artemis&media=COPY
 
FlaCharlie said:
:dunno:
Having read comments by people who work with various brands of caps in their jobs I'd say it's a distinct possibility. Flip a coin. These folks are very very familiar with the issue of counterfeit parts because the products they build, and their company's reputation and sales are affected.

I recall a thread in which someone pointed out some of the tell tale signs when they saw pics of some name brand electrolytic caps in a cheap Chinese tube amp. I've even read where someone cut open an expensive cap that was marketed to guitar players as some high end PIO "tone cap". They found that it wasn't paper in oil construction at all. Inside was a super cheap unbranded polyester cap.

The Chinese are notorious for selling counterfeits of all sorts.

Other times the parts are just poorly made. StepheK recently did a video series on the popular Willsenton R8 amp and found new resistors whose coating was flaking off. And that's a $1500 amp.

That's not to say the counterfeits don't work but don't count on them meeting the specs, or being as reliable, as the real ones.

An equally, or perhaps even bigger problem, is that they sometimes use parts that are not specced correctly.

In another post I recall, a Chinese amp burned a 1w metal film resistor. When I did the math, based on the voltages shown in a schematic, I found that it was dissipating about .9w. Standard engineering practice is to de-rate resistors by a factor of 3x, so they should have used a 3w part. It was likely dissipating over 1w since the power transformer was designed for a 110v primary and wall voltages in the US are typically over 120v, sometimes close to 125v. The transformer issue is very common and they often also run very hot.

This affects voltages throughout the amp but it's the tube heater voltages that are the most concerning because the higher voltage reduces tube life considerably. People often find the stock Chinese tubes to be sonically poor so they replace (aka tube rolling) them with tubes that are sometimes very expensive. Then they, unknowingly, run those expensive tubes at elevated heater voltages.

So, if you have anything Chinese that runs tubes you should always measure the heater voltages. While data sheets generally suggest that +/- 10% is acceptable, once you go over 5% tube life is drastically reduced. Best is to run them at spec or slightly under for long life. Many tubes types are not cheap and prices have increased significantly recently.

Many of the cheap Chi-Fi tube amps also use first caps after a tube rectifier that are much much too large in value. Apparently the "designers" have never thought to read tube data sheet, which specifies a much lower value cap. While some situations allow the use of a somewhat larger value, the ones they use go far beyond this. No doubt they do this to reduce hum but the result is that the rectifier tubes arc and die. In extreme cases this can also destroy transformers.

End of rant. :rolleyes:
Click to expand...
I agree. I've run into counterfeit caps myself. Poor silk screening on supposed name brand caps, loose guts, etc. It amazes me why they counterfeit small very cheap signal transistors though. Tbeybals9 like to use cheap motor run film caps for things like coupling caps. The kind of caps you find in ceiling fans and such.
 
Other parts as well. Fake Alps Blue Velvet volume controls, STK power packs, the list goes on.
 
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