|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
76.24.78.116
I've been this hobby for quite some time. About a year ago, started investigating use of a low mu tube design for preamp usage. I've tried a LOT of designs over the years, and there has always been a trade off. In order to get the tonal bliss of tubes, one had to compromise by tolerating a high noise floor. This is especially true with 12AX7 designs for line stage usage. The high gain comes with a price, and that price is higher noise floor. And, for a line stage, high gain is not really necessary. IMHO, one is better off providing sufficient current to drive the power amp stage, while maintaining the lowest possible noise floor.So, started playing around with low mu tube designs. Tried a 12B4 design, and that was definitely a step in the right direction. However, when I stumbled across the Thomas Meyer design using a 6AH4 and transformer coupling, I knew that was the way to go.
After using the 6AH4 preamp for several months, I'm convinced that this is the way to go for line stages. It is several orders of magnitude better than any other preamp I've ever heard, be it tube or solid state, commercially made or DIY. The advantages of this design are many, but a few of the biggest are as follows: 1) VERY low noise floor (Seems as good or better than even the quietest SS units 2) Outstanding drive, dynamics, and 3-D presentation 3) Reference quality mico detail pretension: extremely linear
4) Transformer coupled: No caps in audio stage. This will make it seem like your tube power amp has undergone a upgrade, as it makes it sound better. 5) No listener fatigue like you get with with SS. Even if one uses a higher powered pentode design like I do, there is still no fatigue.I get why the commercial guys don't make this type of preamp. The iron alone is quite a bit, but my counter to that is that one can get someone like Heyboer to make the iron for reasonable cost. Folks pay as much just to get Mundorf coupling caps. What is puzzling is why more DIY guys don't try this route. I can state with a high degree of confidence that if they did, they would very likely stick with it. It's THAT good!
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Edits: 09/27/14Follow Ups:
I get why the commercial guys don't make this type of preamp. The iron alone is quite a bit, but my counter to that is that one can get someone like Heyboer to make the iron for reasonable cost. Folks pay as much just to get Mundorf coupling caps.
It's cost effective as well as being 'Chic'. Manufacturers(marketing) prefer to tout the amount of Joules they've implemented.
Tubes can't have enough iron!
Lytic caps are cheap and compact compared to iron. Quite the reverse from fifty years past.
Nice looking build.
Not wanting to jack this thread, but I'm curious - what do you think of the Khozmo stepped attenuator? I'm about to plunk $500 for 3 of them, so your input would really help me out.
Thanks!
Very happy with their performance. Very well made, and as neutral as any attenuator I've ever used. Khozmo stepped attenuators are as good as it gets.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
there are many diy'ers who are "going this route". Mine also uses an output transformer.
Also something like a 801A/10Y/10 (DHT). (Which is a work in progress)
To infinity and beyond!!!
26 is a very popular tube for a low mu preamp. There's a huge thread on DIY Audio. Transformer coupled with LL1660, or active load and teflon Russian caps, different options. Try that one one day.
It is a myth (especially on this forum for some reason) that transformer coupling has no capacitors in the signal path. Is there a cap at the B+ connection of the interstage transformer? If so, that's in the signal path.
There are some commercial preamps that use low mu triodes, and some are designed to not need the interstage iron at all.
Here is the schematic to the unit. Mine is slightly modified, in that I put a stepped attenuator in the front of the unit. I would argue that the B+ cap has much less impact than a typical RC network.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: