Here is my new preamp, it has the phono stage from Allen Wright's RTP5 and the line stage from Acoustic Research AR25. Both are hybrid stages, with the phono using bipolars and a 6922EH, the line stage using JFETs and 6H30.
This preamp also has an amplifier for electrostatic headphones and a few other things, probably the most complex preamp I ever built. Took me 8 years (with breaks)....
The whole thing is put into a salvaged Revox chassis which is barely enough to hold everything... hope you like it!
amazing perseverance and it looks superb.
How does it sound
A while back I posted a schematic for my amp using 6216 output tubes. The feedback was wired incorrectly and corrected. The 0A2 regulator tube is a new addition for the screen supply. I used to have an LR8 regulator with a pass transistor but wasn't happy with that design. As a safety feature the bias supply holds a b+ relay closed. The tubes run at 260v on the plate and have the idle current set for 27ma.
This chassis was used for a previous design that never went anywhere so it needs some touch up paint.
This chassis was used for a previous design that never went anywhere so it needs some touch up paint.
Attachments
Here is my new preamp, it has the phono stage from Allen Wright's RTP5 and the line stage from Acoustic Research AR25. Both are hybrid stages, with the phono using bipolars and a 6922EH, the line stage using JFETs and 6H30.
This preamp also has an amplifier for electrostatic headphones and a few other things, probably the most complex preamp I ever built. Took me 8 years (with breaks
The whole thing is put into a salvaged Revox chassis which is barely enough to hold everything... hope you like it!
Looks marvellous.
Very cool. Can you explain a little bit about the R Loading and C Loading options?
cheers, Derek
thanks a lot for the nice words! Not sure if I am happier or actually my wife, because that construction site is finally gone
Small correction, the line stage is a clone of Acoustic Research LS25.
Sound-wise, it was an interesting ride. First turn-on was horrible, this preamp took two weeks of frequent use to break in , and it takes at least an hour of turn-on before listening. It did sound like a cheap transistor radio first. Now there is a lot of details and very precise imaging, the best I have heard so far - but thats just me.....
The cartridge loading is done with rotary switches and resistors and caps, I always wanted to try if cap loading in addition to resistor loading is making a difference for MC cartridges, the results are still out though while I am fixing the phono stage gain. Phono balance is controlled through relays - as the phono stage expects constant 50Kohm loading on its output for proper RIAA equalization , it took a lot of head scratching and calculations to come up with the proper values.
My main goal was to be able to drive STAX headphones directly, its working but not yet fully up to speed as I am still modding a few details. This one is using semiconductors though
Small correction, the line stage is a clone of Acoustic Research LS25.
Sound-wise, it was an interesting ride. First turn-on was horrible, this preamp took two weeks of frequent use to break in , and it takes at least an hour of turn-on before listening. It did sound like a cheap transistor radio first. Now there is a lot of details and very precise imaging, the best I have heard so far - but thats just me.....
The cartridge loading is done with rotary switches and resistors and caps, I always wanted to try if cap loading in addition to resistor loading is making a difference for MC cartridges, the results are still out though while I am fixing the phono stage gain. Phono balance is controlled through relays - as the phono stage expects constant 50Kohm loading on its output for proper RIAA equalization , it took a lot of head scratching and calculations to come up with the proper values.
My main goal was to be able to drive STAX headphones directly, its working but not yet fully up to speed as I am still modding a few details. This one is using semiconductors though
Or do you mean Audio Research Corporation LS25? Acoustic Research made mostly loudspeakers and turntables, although they had few amps in their repertoire.
Acoustic Research - Wikipedia
It wasn't the LR8 itself but something popped on powerup during bench testing. The pass transistor was salvaged from a monitor and rated for 1200vdc. I rebuilt it slightly different using a found schematic but something wasn't quite right. With a 20 turn trim pot there was a lot of "dead space" so to speak with the pot and when it got into the adjustable range it was very narrow. You can't beat the simplicity of an 0A2.
Hi Folks,
Another project which is worth to be shown here is the "KlarTon 604" with the famous German triode Telefunken RE604, RE134 driver and (4x) rectifier RGN1054. Special open vertical chassis design (on rollers), and, well, further specials regarding the circuit design...
A detailed report can be found here:
2A3 Maniac strikes back!: Single-ended power amplifier with the tube RE604
Another project which is worth to be shown here is the "KlarTon 604" with the famous German triode Telefunken RE604, RE134 driver and (4x) rectifier RGN1054. Special open vertical chassis design (on rollers), and, well, further specials regarding the circuit design...
A detailed report can be found here:
2A3 Maniac strikes back!: Single-ended power amplifier with the tube RE604
Very nice build 2A3 Maniac a clear opposite to those who build as small as they can with all components tightly packed with the risk of interference.
With all the iron you have there, what does it weigh?
On closer inspection, it is the mdf you have used as the chassis material, it will be a thumbs up for what I like wood in the chassis.
With all the iron you have there, what does it weigh?
On closer inspection, it is the mdf you have used as the chassis material, it will be a thumbs up for what I like wood in the chassis.
Overall weight of the amp is about 40 kg. You can find (almost) all technical details in the report.
Just to point it out here again in order to avoid misunderstandings: This is the work of a friend of mine (Roland Kraft). He is well known in the German tube scene and also working as hifi editor.
Just to point it out here again in order to avoid misunderstandings: This is the work of a friend of mine (Roland Kraft). He is well known in the German tube scene and also working as hifi editor.
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