Says it all?
http://www.diyaudio.com/forums/tubes-valves/72699-diy-something-like-impamp.html
Regards
John
http://www.diyaudio.com/forums/tubes-valves/72699-diy-something-like-impamp.html
Regards
John
Agreed, this is a low powered example, but the basic topology is similar.
I would personally use the DRV134. that can output approximately 30V pk-pk each leg. more than adequate for PP EL84.
For higher drive swing you will have to go to higher voltage rated OpAmps or fabricate one from discrete components, with all the problems etc.
Regards
John
I would personally use the DRV134. that can output approximately 30V pk-pk each leg. more than adequate for PP EL84.
For higher drive swing you will have to go to higher voltage rated OpAmps or fabricate one from discrete components, with all the problems etc.
Regards
John
Oh dear, I should not have asked
You may well be right Miniwatt
Jeff Macaulay at Electronics World + Wireless World in October 1995?
2 x TL072 + 2 x EL34 (PP)
That would be this one here?
http://www.diyaudio.com/forums/solid-state/88723-nishiki-hybrid-amp-5.html#post1061973
Some more discussion:
http://www.diyaudio.com/forums/tubes-valves/55909-opamp-driving-tubes.html
Figure 17 of the OP275 datasheet has some possibilities.
The DRV134 certainly looks useful and has high drive current too, it would be almost like having a "powerdrive" built-in. This and the fact we get rid of the coupling caps may help swing the deal, maybe...it still needs a gain stage in front of it unfortunately.
Thanks for the tips people. Would this work?
Attachments
As far as obliterating any sonic advantage a tube amp may have it will do wonders. I would not consider using a DRV134 even ahead of a chip amp as it sounds really bad but my priorities are obviously different.
These parameters appear extremely modest for high quality audio. Did you notice the full power bandwidth? Or the overshoot? This chip is not likely to attract much attention if one is designing a good sounding opamp pre but should be ok for a tube amp? Those tubes can make anything sound great
ADA's "Ampulator" had an OpAmp driver/phase splitter. Very basic setup similar to one used in Music Man and Peavey guitar amps but ADA eliminated the cascode-style BJT+pentode output and drove the output tube grids directly with OpAmps. This also allowed them a very easy bias setup: Simply make the OpAmps' DC offset to correspond the required output tube bias. Ampulator was a low power setup, though, driving just two 12AX7 as output devices, current-boosted with BJTs. All in all, it's a kinda clever hybrid.
Schematics can be found from here:
adadepot.com
Schematics can be found from here:
adadepot.com
I was curious so gave it a go. Even with a couple of 4558's, the only pair of audio IC's in my junk box, I hear deeper bass and much more detail. The idea has a lot of promise, but unfortunately its an unpalatable one for tube and SS enthusiasts alike, since the amp becomes a hybrid. I used the Rod Elliott P87B cct with some gain in the first amp stage. There are no caps in the signal path.
Hello All,
This is DIY. What source are we using for our amplifiers anyway? Most likely there is a DAC and many Op-Amps in the chain already. One more is so bad? I say give it a try.
BTW there were a pair of cool steam punk copper 8 sided PA speakers at Burning Amp last October.
DT
All just for fun!
This is DIY. What source are we using for our amplifiers anyway? Most likely there is a DAC and many Op-Amps in the chain already. One more is so bad? I say give it a try.
BTW there were a pair of cool steam punk copper 8 sided PA speakers at Burning Amp last October.
DT
All just for fun!
Ironically, when you replace a somewhat non-linear circuit with a highly linear one it tends to have an effect of improving the overall sound quality. Next step: Get rid of that tube output and replace that with solid-state as well.
I think you are basically discovering the same thing that many designers discovered already in the early 1960's when transistors made tubes obsolote in almost every application.
Ok, waiting for the hell break loose now.
What exact degree of non-linearity are we talking about? It's easy to design and build a NFB free tube circuit capable of at least opamp rail output with mostly low harmonics and a thd <0.05% Would better thd achieved from an opamp at the expense of lots more potential and audible problems be worth it?
Ian444's experiment is interesting but generally predictable. For a number of reasons like better psrr, lower output impedance, lower microphony, etc it is easier to achieve better sounding bass with opamps. As for the "much more detail" i am more inclined to attibute it to high nfb and the subsequent issues with overshoots. And some clipping here and there
And that 11th harmonic which brings detail forward like nothing else.
Last edited:
Ironically, when you replace a somewhat non-linear circuit with a highly linear one it tends to have an effect of improving the overall sound quality. Next step: Get rid of that tube output and replace that with solid-state as well.
I think you are basically discovering the same thing that many designers discovered already in the early 1960's when transistors made tubes obsolote in almost every application.
Ok, waiting for the hell break loose now.
I very much doubt that the opamp is better than a well setup tube, depends a lot on the opamp. As analog_sa says above - do not mistake detail for better, harmonics sound like detail but are fatiging over long periods and at higher levels.
In the 1960s opamps were slow and dreadful for audio so it was transistors. Here again they were not very good, and only used correctly by the japanese, but still giving rise to a wall of upper harmonics mistakenly taken as extra detail and necessitating a redesign to deliberately dull speakers.
Linearity itself was a stranger to transistors and has only re-appeared with high voltage parts in my view. The great progress of the transistor really bought one important aspect to hi-fi: affordability. Then during the 70s the UK/US hi-fi industry ripped itself apart with unstable transistor amps while the japanese mastered the circuits and took over almost completely.
What you get with a single simple tube that you fail to get with an modern opamp is voltage swing and linearity without correction. An op-amp at full swing has no headroom for feedback correction whereas a tube will effortlessly swing past it. For instance my SRPP driver section can swing 2-300V without breaking sweat whereas an op-amp would be giving up at 45V
. This usage of high voltages is I consider a fundamental part of a good sound: headroom is king and aids linearity.The 'detail' of transistor amps (with equivalent frequency responses to their 'smoother' tube cousins) has long been mistaken for a good thing even at the same time ones hand reaches to turn the level down but it isn't - it's just a tiring form of chronic distortion typical to the type. In fact all modern transistor amps sound the same (and like this) now, magazine reviews and the power of advertising and money has headed the hi-fi industry off the tracks and into a cul-de-sac of inoffensive blandness and uniform polite dullness as exemplified by the Naim stuff, a mastery of marketing over sound.
I am a bit disturbed by the result. I was not expecting the IC's to sound good.
The amp in the linked pic is a Simple PP and is my best/favourite amp, it has Hashimoto OT's and I love the sound.
I have found from other experiments that better bass and more detail is also achievable with mosfet source followers driving the output tubes, so some part of the improvement could be attributed to the low output impedance of the IC's I believe. Also the cap-less signal path may help.
I ordered a few different IC's to try, but where this may go tits up, is the available output voltage swing of most of the common opamps, which seems to be limited to around 10 to 11V peak before distortion skyrockets, according to the datasheets.
When I said "much more detail" it is because I can hear subtle sound sources (instruments or percussion or effects in the background) in familiar recordings that I could not hear before, or did not notice before. "Clarity" may be a better word.
teemuk, maybe the SS guys would be able to hear the differences between their various opamps better if they had a tube output stage to audition them, as I have
This project will keep me busy for a while I think.
The amp in the linked pic is a Simple PP and is my best/favourite amp, it has Hashimoto OT's and I love the sound.
I have found from other experiments that better bass and more detail is also achievable with mosfet source followers driving the output tubes, so some part of the improvement could be attributed to the low output impedance of the IC's I believe. Also the cap-less signal path may help.
I ordered a few different IC's to try, but where this may go tits up, is the available output voltage swing of most of the common opamps, which seems to be limited to around 10 to 11V peak before distortion skyrockets, according to the datasheets.
When I said "much more detail" it is because I can hear subtle sound sources (instruments or percussion or effects in the background) in familiar recordings that I could not hear before, or did not notice before. "Clarity" may be a better word.
teemuk, maybe the SS guys would be able to hear the differences between their various opamps better if they had a tube output stage to audition them, as I have
This project will keep me busy for a while I think.
I'm still listening to this setup. I tried a few IC's I didn't like, TL072, NE5532, LM833, LF353. RC4558 is decent and the OP275 is very nice. I have on hand DRV134 and LF412 but haven't tried them yet. In hindsight I should have got some OPA2134 to try as well. This is the schematic I'm using. I am not very good with opamps or opamp schematics so if anyone has any design tips I would be grateful for any advice. I really like the sound, no fatigue so far.
Interesting differences between opamps, it just shows how the open loop character of even fast modern opamps is very important.
I am puzzled by the schematic - is the signal for the lower tube really travelling through both opamps?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.