Jadis JP200 preamp or alternative?

[Ian Greenhalgh]

Hi folks

I want to built a valve preamp and the Jadis JP200 design seems very popular, I like this style of building, rather than a PCB:

Before I make a final decision though, I wonder if there are better designs I should look at as I noticed a few people making derogatory comments about the JP200.

 

[directdriver]

There's nothing special about its design. Using 6 high gain twin-triode tubes for a stereo line stage is a waste of tubes.

 

[famousmockingbird]

There's nothing special about its design. Using 6 high gain twin-triode tubes for a stereo line stage is a waste of tubes.

I am scratching my head thinking the same thing.

 

[Ian Greenhalgh]

What would be a better design? I read positive comments about the Aikido design but don't know enough about the subject to make any judgements myself.

 

[DF96]

A voltage gain of 11 seems inappropriate for almost any modern audio system. The 12AX7 is about the worst valve you could choose for a cathode follower. Hard to imagine what the designer thought he was doing.

 

[Eli Duttman]

I agree with the negative assessment of the Jadis design. The remark about 11X gain being wrong is spot on.

Getting end to end gain structure right is important. If a "standard" CDP is the signal source, line stage gain is frequently not needed. A passive or buffered control center is, all too often, a better choice. Please provide the drive level the power amp requires and the signal source(s) to be employed.

 

[Demonkleaner]

What would be a better design? I read positive comments about the Aikido design but don't know enough about the subject to make any judgements myself.

I built an all octal Aikido about a year ago and it does a great job. Lots of info and boards to build several versions on the glass-ware website. Folks have done point to point versions as well. There are also threads here that chronicle
building of the Aikido.


Heed DF96's advice. I've learned a lot by reading his posts.

 

[Ian Greenhalgh]

Thanks for the feedback guys. I wonder why this JP200 thing is popular with DIY builders if it's such a bad design - perhaps they have never heard a valve amp before and think it sounds good when really, it's not all that great at all?

So, what do people think - should I go for the Aikido or is there something else I should look at?

I favoured point to point because I was concerned at the quality of the Chinese PCBs, but I read that the Aikido boards are very high quality.

So, is there much, if any benefit to going point to point or should I just get a good quality PCB such as the Aikido?

 

[DF96]

I wonder why this JP200 thing is popular with DIY builders if it's such a bad design - perhaps they have never heard a valve amp before and think it sounds good when really, it's not all that great at all?

Popularity is a very weak indicator of quality; in audio the correlation can sometimes be negative. People who build stuff do not necessarily understand what they are building; if they could understand it they would probably prefer to design something themselves.

 

[Adolf Corkscrew]

Thanks for the feedback guys. I wonder why this JP200 thing is popular with DIY builders if it's such a bad design - perhaps they have never heard a valve amp before and think it sounds good when really, it's not all that great at all?

So, what do people think - should I go for the Aikido or is there something else I should look at?

I favoured point to point because I was concerned at the quality of the Chinese PCBs, but I read that the Aikido boards are very high quality.

So, is there much, if any benefit to going point to point or should I just get a good quality PCB such as the Aikido?

I've had a good number of board designs manufactured in China - in small numbers, though - and I've had no complaints about the production quality. If you don't cheap out the chinese companies are perfectly capable of producing perfectly good boards.

 

[Eli Duttman]

Getting the gain structure right remains key. Please provide the info. previously requested.

The "Aikido" is certainly a good design. As an alternative, I'm providing a somewhat simpler design intended for a point to point build. Gain is roughly 6X to 7X and that may be too much. The setup is non-inverting, extremely linear, and will drive very nasty loads, with great aplomb.

 

[45]

Why everyone is guessing and no one asking what such preamp is needed for?What's the source? What's the power amp?

Anyway I have used preamps with 15-16 dB gain to drive power amps with 0.5V rms sensitivity and it worked pretty well. Of course the original mated preamp had low gain (about 6 dB) but it wasn't better by any point of view.

Who cares if I can't turn the volume pot all the way up and have to stop at 2/3 or 3/4 of its full rotation? On the other end a low gain preamp will also have more limited application, including the use with phono preamps.

 

[Ian Greenhalgh]

Thanks for the help guys, is this what you need to know to guide me further?

Source: my desktop PC into a DAC via TOSlink then into the preamp

Power amp: a pair of Linn Roomamps bridged

Speakers: Mission 731s or Jamo Euro 7Bs, can't make my mind up which I prefer at the moment, both are 8ohm bookshelf types

 

[45]

Sorry Ian but I have no idea about the specs of your gear. Anyway it comes to my mind now that I also used to drive my 0.5 V rms solid state power amp with an ECC82 SRPP that had a gain of 24 dB (16x) and this was fine too! If you make it properly, especially the power supply, resulting in low noise figures there is no problem. The same power amp directly driven from the CD player that had an internal volume control sound really dull and muddy in comparison....

 

[DF96]

In order to find out the input sensitivity of your power amp we would need to Google it. It might be easier (for us) if you told us - presumably you have the manual?

In order for us to find out the output level of "a DAC" we would need a crystal ball, but unfortunately mine is away for maintenance at present.

Why not help us to help you?

 

[Ian Greenhalgh]

I'm afraid I don't have the Linn Roomamp manual, but I'll see if I can find one online.

I haven't finished building the DAC yet, so no concrete information there either, not least because I still haven't decided what form the output stage will take, whether valve or SS.

Sorry for the vague-ness, I didn't even realise these parameters were needed when considering the preamp which shows how much of a beginner I am.

 

[DF96]

OK. Nobody can tell you how much gain you need at present, although we could guess that unless your DAC turns out to be unusual and the power amp is unlike others you won't need any extra gain so you probably don't need a line stage. If you don't know about gain etc. then you may have some difficulty sorting out the DAC output stage.

 

[Ian Greenhalgh]

Well, my paltry understanding was that line level was a fairly narrow definition and as long as the output of the DAC was within the parameters of 'line level' then all would be fine.

So, are you saying that I need to work out the parameters of my DAC's output first, before considering the preamp as the DAC's output level will determine how much gain my preamp needs to have?

Sorry if this is a boneheaded question, I'm on the nursery slopes of the learning curve with a brain that is starting to hurt a bit from all the info I've been feeding into it.

 

[DF96]

'Line level' is very poorly defined in domestic audio, so yes you need to know the DAC output level and the power amp input level in order to determine whether you need any extra gain. As I said, in most cases the answer is no.

 

[Ian Greenhalgh]

Thanks for the clarification.

I'm having no luck finding the specs on the input level of the Linn Roomamp, so far I've only found this:

Knekt balanced interface levels

They are discussing the balanced line level input via an RJ-45 connector:

"the levels are consistent with normal line level signals"

I'm not using that input, I'm using the RCAs, so I'm not sure if this info applies to those input as well and besides, "normal line level" is pretty vague....

As for the DAC output level, well, that's upto me, as I'm building the thing, and I haven't decided what sort of output stage it will have yet.