What preamp should I build?

[Stuey]

Hi Guys,

Lurking here reading this thread as I'm thinking of building an Aikido line stage...

Nothing to add, but, Mike, a month ago you must've suffered when it was 45 degrees (celcius) in Port Hedland....?

It was bad enough down here at 42.5...

Cheers

Stuey

 

[OzMikeH]

Oil and gas worker?

I'll be working in the mines as soon as my sparky licence comes through. Gonna go where the money is.
I stayed in WA for a while in the early 90's and regret not buying a property there when I had the opportunity.

Yep. If you get the opportunity try to get hazardous area training for Ex rated stuff. even more money, safer than underground work too.
Great after-hours lifestyle in the right town. plenty of social sports, fishing, camping etc. Would be tough for a single bloke though. A lot of companies provide housing which makes thing easy. There is a real shortage and they are sticking everyone they can on FIFO which is pushing up the price in Perth even higher.

........
Nothing to add, but, Mike, a month ago you must've suffered when it was 45 degrees (celcius) in Port Hedland....?

It was bad enough down here at 42.5...

Cheers

Stuey

You get used to the heat pretty quickly. It's not too bad if you drink about a litre of water per hour and get a feel for how to balance exertion against your body's cooling capacity. Trying to work at 100% is where it gets very uncomfortable (and dangerous).
and in this climate I'm considering one of these... I must be insane.

 

[Stuey]

Mike, stick a steel plate on top and use it for a barbie!

 

[KP11520]

Hi Mike,

That's the beast.... what do you feed it? Do you live close to the "Power Station? Your Air Conditioning bills will double!

What does weather like that do to your equipment?

I wonder how this Transcendent Pre compares to other Tube kits and some of the other SS DIY Preamps like the Pumpkin Preamp that Magura suggested to me?

I just want to make the right choice be my first choice!

Thanks!

Regards//Keith

 

[OzMikeH]

Mike, stick a steel plate on top and use it for a barbie!

It isn't big enough.



Keith,
The room is just over 100 cubic metres so heat isn't a problem.
It couldn't be more than a couple of hundred watts. You see all of those tubes and think it must be very hot, but a plasma TV dissipates about 300W and people don't even blink.
I dont know a lot about these, I've just been doing some research. I haven't even sought approval from the domestic finance department yet. I cant offer any advice.
I've used various solid state, class t and push-pull EL34 tubes and the T16 looks like it combines the things I like about all three. It's also about 3 times the price of any of the amps I've tried before.

 

[Brett]

Power supply complexity: It needs to be very, very clean because of poor PSRR. Lots of filtering at a couple of hundred volts can't be cheap.

Perhaps the people who wrote about their build of it went overboard with the power supply.

Performance is important, Particularly low noise and high detail.
If performance isn't excellent then I may as well spend a few hundred bucks on super-duper op-amps. I'd rather not go down that path though.

Dragging this old post back up, as for low PSRR and noise, I was using 104+dB/W speakers and I heard no noise. Use a CCS as anode load for the best PSRR.

 

[OzMikeH]

Thanks for bringing it back to something useful Brett, are you talking about the 12B4? (if you think theres a lot of nattering ad-nauseum on there you should see the TA10.1 thread)

things have changed a bit since I started the thread. I'm looking at power amps too. The T amps don't have quite enough grunt for me.
I'm using fe207E in a big room - with heavier music they need more power. there isn't any headroom left with the T amps.
I'm starting to realise half measures and little steps can waste a lot of money and time. On the other hand jumping into a big tube Pre and power amp project when I'm still not sure about what I'm doing could be an even bigger waste.

I bought some instructional dvds off a guy on Ebay and I'm working my way through those. A bit too basic for me to begin with, I'm interested in getting a feel for bias voltage, typical current etc. Hopefully the latter parts will give me what I'm looking for.

 

[Brett]

I'm using fe207E in a big room

That's your problem. Two of those and an old belt make a nice set of headphones.

 

[KP11520]

Hi Mike,

So what are you showing off? Your Barbie or the Meat? LOL

Hopefully, all the other members can help us to shape which Pre would be best for our likes and needs!

As far as the "Beast" goes, It looks interesting. Expensive, so I can see why approval would be necessary! But I like some extra watts!

There is another thread in the "Chip Amp" section about Preamp kits as well and one guy recommended the Grounded Grid Preamp. I will ask about his experience with it! http://www.diyaudio.com/forums/showthread.php?postid=1418080#post1418080

Regards//Keith

 

[OzMikeH]

That's your problem. Two of those and an old belt make a nice set of headphones.

??? they are a 95dB/W/m 8 incher in a cabinet flat to 50Hz. I listen from 9 feet away. What do you suggest instead?

Hi Mike,
As far as the "Beast" goes, It looks interesting. Expensive, so I can see why approval would be necessary! But I like some extra watts!

Regards//Keith

It was actually a roast I was searing before putting in the oven. I'll take a picture of anything now I have a digital. with film everything had to be considered first.
I'm looking at the T16, The Beast is a much bigger animal.
The exchange rate at the moment is pretty good (for me) one US dollar buys 1.10 AUD. Just over two thousand for a semi-high end 15 watt amp and preamp with some fruity bits isn't too bad.

 

[KP11520]

Mike,

Let me know what you decide for a Pre/Line stage. Especially the reason why you chose the one you buy!

Have you looked into the Pumpkin, Zen Mod sells? It isn't Tube but gets the same kind of reviews the Transcendent gets (and unfortunately most of the them, that offers a lot of help for guys like you and me).

I wonder if you can get a remote, many step attenuator for the Transcendent or any of the kits. It is a nice feature.

Regards//Keith

 

[OzMikeH]

the transcendent has a 24 step for $119 as an option.
as for a remote, there is a thread in electronics and parts where someone is using a stepper motor and a PIC to turn the knob. Not worth the effort in my case. If you really wanted to I'm sure you could cobble together a ratchet which uses a solenoid to advance a click with each pulse. one solenoid for up, one for down.
for music: straight off a DAC into the preamp, then set and leave the volume.
for TV: pre-out from an AV receiver with integrated remote volume so it can be adjusted for advertisements, the quality doesn't matter so much there.
For DVD: digital out of the DVD player then into the DAC then same as for music.

I might keep my old amp for use with tv. It seems a waste to burn up hours on tubes while watching garbage.

Will go look at the pumpkin later.

 

[Brett]

??? they are a 95dB/W/m 8 incher in a cabinet flat to 50Hz. I listen from 9 feet away. What do you suggest instead?

Meh. I'll soon be using 2x12, 2x10 JBL's and an Altec (or B&C or BMS, I'll decide later) on a flare in a 14'x15'x10' room. And there'll be a tapped horn sub/channel underneath them. Don't play loud all the time.

 

[OzMikeH]

There is no replacement for displacement hey Brett. If you play a bass I should have expected something huge, If you were a drummer it would be truly massive.

 

[kvk]

Hah, got it figured out.  Thank you Netfirms.

In the interests of file and image size, the parts information is a bit terse. If you have questions, ask. Everyt'ing stay bestest kine.

   

Yes, the power transformer is wired unconventionally. I'm burning about ¼ its VA rating, no winding is overvolted, it doesn't even get warm.

Aloha,

Poinz

May I ask questions?

The components just labelled Rdrop, are they to adjust the voltage to the heaters to proper level and values have to be determined by testing?

I don't get the wire to the center tap on the filament transformer labeled 24V. Can you explain what this is and why the filament circuit is attached to the HV cricuit? Is that just a common ground?

 

[kvk]

I think I may have found the answer to my own in another thread-- "All these posts and no mention of DC biasing AC heaters? For shame! The technique eliminates nearly all the residual LF coupling between heater and cathode at the expense of two resistors."

So that 24 Vdc DC biases the heater but doesn't effect the voltage across the filament.

Still not sure about the Rdrop though. If the filament iron is outputting 6.3vac, what are they for and how do you determine values?

 

[Brett]

The Rdrop resistors are to tweak the voltage at the filaments to exactly 6.3V in use when warm. The power Tx will vary a bit depending upon size and it's inherent regulation as well as variations in local mains supply voltage.

 

[kvk]

The Rdrop resistors are to tweak the voltage at the filaments to exactly 6.3V in use when warm. The power Tx will vary a bit depending upon size and it's inherent regulation as well as variations in local mains supply voltage.

So you have to plug tube in, let them get hot, then measure the V across the heaters and if it's high add ad-hoc R values to get them in line?

 

[SY]

You can calculate the resistor values after measurement to make them a little less ad hoc. If a heater winding is run below its max, it will have too high of a voltage otherwise.

 

[Brett]

So you have to plug tube in, let them get hot, then measure the V across the heaters and if it's high add ad-hoc R values to get them in line?

Yes, or measure the filament winding without lod, try it with some resistors calced to get it correct with the expected load of the filaments, then try it with tubes in situ and measure. It's how I'd do it.

You can calculate the resistor values after measurement to make them a little less ad hoc. If a heater winding is run below its max, it will have too high of a voltage otherwise.