MikeW said:Do you need the $ to get the boards?
G'day
No, I’ll recoup that later when I sell them.
I'm still waiting on a quote to come from one mob, but it looks like the boards will come in at about AU$10 each if I have 50 made.
This is for 1.6mm FRP, 1oz copper, green solder mask and a white component overlay.
Production will be slow over the Easter period also, unfortunately.
Cheers,
Glen
Re: ProJet Preamp Module
Thanks!
That’s a rather professional looking board you’ve designed there.
😎
Cheers,
Glen
Lazy Cat said:
Thanks!
That’s a rather professional looking board you’ve designed there.
😎
Cheers,
Glen
G.Kleinschmidt said:
OK goddit.
I didn't look at the design very carefully + lack of R values caught
me.
I thought you were from the ultra low measured distortion camp?
What is the motivation to use a tube in dif pair?
I suppose one advantage would be zero thermal related distortion
in the dif pair.
Terry
Hi Glen
Interesting idea of designing an amp with both new and old school technology. Don't get me wrong, tubes are great it's just they have been around for much longer. I like this circuit for that reason of using more parts than it is "perceived" by some as necessary....but you left out the cascode VAS, cascode drivers, and all the output error correction circuitry.😛
Heh Heh, seriously though, I think this circuit will work much better than the one in post 43. I like your way of preventing the VAS transistor from saturation via the current limiting transistor at the top. The way I see it, current from that transistor flows through the left side of the differential, making the right side and mirror source that much less current back to the left side, thus keeping the input differential balanced during the time when the VAS is being limited. This leads me to believe it would not cause an audiable effect. Such a simple and neat idea, I will have to try it out.🙂
Although there wouldn't be any difference if SS was used except bias voltage, but the mix of SS and tube has such a cool 'retro' look to it.😎 Worth the extra complexity for a DIY project IMO.
Good luck to you
.
The beautiful linearity of a triode I'm sure has nothing to do with it....
Interesting idea of designing an amp with both new and old school technology. Don't get me wrong, tubes are great it's just they have been around for much longer. I like this circuit for that reason of using more parts than it is "perceived" by some as necessary....but you left out the cascode VAS, cascode drivers, and all the output error correction circuitry.😛
Heh Heh, seriously though, I think this circuit will work much better than the one in post 43. I like your way of preventing the VAS transistor from saturation via the current limiting transistor at the top. The way I see it, current from that transistor flows through the left side of the differential, making the right side and mirror source that much less current back to the left side, thus keeping the input differential balanced during the time when the VAS is being limited. This leads me to believe it would not cause an audiable effect. Such a simple and neat idea, I will have to try it out.🙂 Although there wouldn't be any difference if SS was used except bias voltage, but the mix of SS and tube has such a cool 'retro' look to it.😎 Worth the extra complexity for a DIY project IMO.
Good luck to you
.
Terry Demol said:
The beautiful linearity of a triode I'm sure has nothing to do with it....
Terry Demol said:
This amp actually has reasonably low distortion. I have designed amplifiers with much lower distortion, but this is just for fun. I’m not under the delusion that 0.0001% THD "sounds" better than 0.001% THD or 0.01% THD.
I was motivated to incorporate the 12AX7 for the LTP for the same reason that someone might be motivated to house their amplifier in marine varnished carved oak box. It looks different and pretty and if the style doesn’t adversely compromise the performance, then why not do something different?
Also, 12AX7’s can be sourced from numerous present day manufacturers for prices below that of many exotic and endangered dual JFET pairs, so perhaps this will be the next big thing! 🙂 😀
Incorporating the 12AX7 into the well proven unipolar amplifier presents a few technical challenges, which, despite a dismissive claim of unoriginality*, I think I’ve overcome with a minimal of extra complication and the use of common-as-muck components.
These are:
1) Providing an adequate plate voltage for the 12AX7
2) working around the output stage / speaker poofing DC offset problem as the tube warms up (or if it ever gets knocked from its socket)
3) Interfacing the VAS referenced to the 12AX7 plate voltage to the low voltage output stage.
Number one was solved with a simple voltage doubler circuit requiring the addition of two 1N4007 diodes, two 470uF electrolytic capacitors and a readily available, small and cheap 24V or 12V+12V secondary transformer.
Two was addressed simply by using a unipolar supply rail and capacitively coupling the load. This is a compromise between performance (coupling capacitor non-linearity) and complexity on more of an objective level that a subjective on, IMHO.
A DC coupled design would require a power up timer combined with an output-DC protection circuit, which either disconnects the speaker with a relay or interrupts power to the output stage during the heater warm up interval / valve wobbled from it’s socket scenario.
For this simple little amp, I didn’t want to resort to this added complexity.
Issue three was resolved with the previously mentioned anti-saturation clamp for the NPN driver transistor combined with the standard VAS current limiter. This increased the parts count by four 1N914’s, one BC557 transistor, one BD140 transistor and one 1k resistor.
Cheers,
Glen
* Although I won’t bother confirming it, the schematic provided for the original “Italian” hybrid amplifier cited looks like it was lifted straight from John Broskie's Tube Cad Journal, presumably after a frantic websearch.
CBS240 said:
Thanks for the compliments! Yes, there is no electronic component at is quite as cool as the vacuum tube. I’ll see how this design pans out in terms of success, depending on which I may present in the same manner another, but more elaborate and powerful hybrid design under my hat, specifically aimed at simple DIY construction 😎
Cheers,
Glen
Hi, Glen,
To extract the tube characteristic over transistor deeper, how about eliminating VAS and use folded cascode? You use classA output stage, the gain will be sufficient?
To extract the tube characteristic over transistor deeper, how about eliminating VAS and use folded cascode? You use classA output stage, the gain will be sufficient?
Such realitivily small differences in THD has not near the audiable influence as per say, the noise floor. That being said, how is the noise floor?
lumanauw said:
A folded cascode VAS can provide ample gain, provided that the VAS sees a rather high impedance load. A triple emitter follower output stage or something similar would therefore be required. Also, the drive capability of a folded cascode VAS is governed by the tail current of the LTP, practical operating values of which aren’t as high for a high mu twin triode such as the 12AX7, as for a pair of BJT’s, for example.
These are just ponderings from the top of my head, and I really haven’t considered a tube LTP + folded cascode VAS much beyond that.
Cheers,
Glen
CBS240 said:
Can't give a exact figure because I didn't measure it on the prototype. It won't be something to be worried about though. VAS noise is pretty much out of the picture, due to the high gain of the LTP, ensured by the light loading of the current mirror and the emitter follower buffered VAS, so it's all pretty much down to the 12AX7, a part that has been put to use in many phono amplifiers over the decades. There are less noisy types, better suited to phono amp service, but the point is moot with respect to a power amplfier (even if it's only rated at 10W 🙂 )
Cheers,
Glen
Geeh, no selected 12AX7WA/6681/E83CC hunting,..bummer.
(put me down for 6 boards, maybe i can get kids into soldering tube sockets and Phily 139/140)
(put me down for 6 boards, maybe i can get kids into soldering tube sockets and Phily 139/140)
Telefunken E803s ?
I recently bought 5 pieces of NOS Telefunken E803S. Maybe I could use some for this project? I got them for 2 Euro each ... Was it a nice buy or was it a nice buy... 😀
Yes such business is still available at the right place with people that doesn't know to well which tubes is a go and which one is for old TV sets.
I recently bought 5 pieces of NOS Telefunken E803S. Maybe I could use some for this project? I got them for 2 Euro each ... Was it a nice buy or was it a nice buy... 😀
Yes such business is still available at the right place with people that doesn't know to well which tubes is a go and which one is for old TV sets.
Sorry I have to pester.
I also bought 5 NOS Philips SQ E84L at the same auction for the same price. 10 Euro for all. 😀 he he. Offtopic sorry
Sorry about my bragging but today I'm celebrating with some beer 
I have just got my new Sennheiser HD650 today and are going trough some of my collections.
Recently listened to with pleasure:
James Ingram (Quincey Jones production)
Little Feet ( an old Vinyl Live album and the tune " Time loves a hero"
Bach "Toccata D Major" Michael Murray on the "Telarc" label CD
Yes "Drama" and the tune Does it really happen?" vinyl
Brenda Russel ... CD
Patty Smith (Quincy Jones) vinyl
Earth wind and Fire.... some old nice recording also vinyl
The rest of my Hifi equipment isn't anything fancy but this headphone's really did the trick 🙂 Allthough I had Sennheiser HD200 before, this phones are definately "more" 🙂
I also bought 5 NOS Philips SQ E84L at the same auction for the same price. 10 Euro for all. 😀 he he. Offtopic sorry
Sorry about my bragging but today I'm celebrating with some beer I have just got my new Sennheiser HD650 today and are going trough some of my collections.
Recently listened to with pleasure:
James Ingram (Quincey Jones production)
Little Feet ( an old Vinyl Live album and the tune " Time loves a hero"
Bach "Toccata D Major" Michael Murray on the "Telarc" label CD
Yes "Drama" and the tune Does it really happen?" vinyl
Brenda Russel ... CD
Patty Smith (Quincy Jones) vinyl
Earth wind and Fire.... some old nice recording also vinyl
The rest of my Hifi equipment isn't anything fancy but this headphone's really did the trick 🙂 Allthough I had Sennheiser HD200 before, this phones are definately "more" 🙂
jacco vermeulen said:
What do you do with all these amps that you build?I'm about to give the PCB mob a ring. Boards will arrive in 7-10 working days.
Re: Telefunken E803s ?
Dude, the EL803S is a pentode, definately not a substitute for the 12AX7 🙁
Cheers,
Glen
Radioman62 said:I recently bought 5 pieces of NOS Telefunken E803S. Maybe I could use some for this project? I got them for 2 Euro each ... Was it a nice buy or was it a nice buy... 😀
Yes such business is still available at the right place with people that doesn't know to well which tubes is a go and which one is for old TV sets.
Dude, the EL803S is a pentode, definately not a substitute for the 12AX7 🙁
Cheers,
Glen
Hi Glen.
Interesting design, please put me down for 2 of these boards. Have many NOS 12AX7 /ECC83 to try in this circuit.
Keep us informed when boards are available. I will definitely take 2 off your hands, thanks.
Best Regards
Gary..
Interesting design, please put me down for 2 of these boards. Have many NOS 12AX7 /ECC83 to try in this circuit.
Keep us informed when boards are available. I will definitely take 2 off your hands, thanks.
Best Regards
Gary..
G.Kleinschmidt said:
The 3 stereo sets are for the 3 gents who reside on the top level in me brick house.
They're starting to get interested in music, range 10-13 year olds.
Your ten-incher looked like a nice contemporary piece of work with the right size to serve as a high-Q starter amp for youngsters.
Psych warfare, anything to get them away from the Nintendo-DS.
The regular outcomes from this hobby are becoming a bit of a storage issue, i have yet to throw/give away something i made myself.
Still nothing compared to my quarter century audio paper collection or my tools.
Storage is not a problem if you live in a 2m$ home, but i dread the day i'll turn a retirement home goner.
You rejuvenate a few more tube transmitters, come back in 10 years and we'll talk again.
PS : anyone familiar with the small French Triangle hybrid class A ampy ?
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