3W amps - options: SS which sounds as good as DHT’s

What people are working on at the moment
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#16 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by vinylnvalves »

Interesting, that’s the price in Singapore, get them in the uk, they are £40 each, from element 14. Bad timing, my son arrives back from Singapore today.. not paying those prices. Looks as if there are only 73 off these opamps in farnells worldwide.
User avatar
rowuk
Old Hand
Posts: 453
Joined: Sun Jun 01, 2014 2:50 pm
Location: Germany

#17 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by rowuk »

I built some large speakers using Carver mid/hi ribbons and a 12" acoustic suspension woofer. The B&O ice amps ended up being the amplification of choice. 2x 90 Watts with BALLS and FINESSE. I would have had to build at least 50W valve amps for the ribbons - with the compromise of PP. The Ice amplifiers sound SENSATIONAL.
Whenever I feel blue, I start breathing again.
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#18 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by vinylnvalves »

Over the weekend I have been auditioning some Pass Amp Camp Amplifiers in place of the the B&O ice amps. I am suprised how nice they sound, in there basic form ( feeding output through some 47000uf electrolytic caps). Even with the compression drivers they are quiet ( unless I stick my head in the horn). A detailed open sound, good 3D imaging, and a “thick” midrange. Seem to lack a bit of top end sparkle but that could be my hearing impaired due to a cold.
Quite frightening for something running off 19v computer smps with £20 worth of bits in them.
Obviously as I am running active I can change the size of the output DC blocking capacitors, I estimate I can get away with 50uf and 20uf ones for the midrange and HF, which might bring the top end sparkle back. Which is tin foil capacitors territory, if paralleled up.

Now for the advice, someone had suggested pass F5 amps sound nice. To my uneducated eye the F5 seems to be push pull amp using n and p devices to omit to DC blocking capacitor. However for my application where I can get way with foil caps on the output, is the simplicity of the ACA being SE is going to win out against the F5. ( the extra 800 watts of heat is also another consideration)

Or is there another first watt design which I should also consider, or one of Yorkshire’s answer to Nelson, Nicks, designs. I must admit those semisouth devices look interesting.
As I am currently thinking of making and populating some new versions running at the allegedly better 24v operating point, with better passive components (might cost me £20 extra - excepting the foil caps) Unless someone suggests something else.
User avatar
Nick
Site Admin
Posts: 15706
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#19 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by Nick »

This is very much a measuring string sort of thing, but to my ears the f5 (at least the one I built) lack a little in clarity compared to the mosfets I have been building lately. The clarity is to me the difference between a typical solid state amp and a SET, but it doesn’t of course have the "love" of the set sound, for better or worst.

The amps I have been building are far from simple things, partly because they are designed to drive the honking big output mosfets. To be honest I am unsure if the clarity is the result of the single pair of mosfets or the fact the driver stage has got a lot of cascodes in it, so hopefully avoiding any thermally induced memory type distortion. I suspect the former. One day I will find the time to try the same driver stage with a more conventional output stage and see what that sounds like, but time is in very short supply around here ATM.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#20 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by vinylnvalves »

Thanks Nick, food for thought.

I know that when Pete and Guy ( other forum) built the higara le monstre, they said it was about as good as their benchmark, an el84 pp. So I know one mans nectar is another’s marmite. With your Mosfet amps do they have to driven hard to get lots of watts out of them or could they be biased down to something more akin to what I am after?
User avatar
Nick
Site Admin
Posts: 15706
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#21 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by Nick »

Well the original point of the amps were to use the big single die mosfets, I use them here with 94dB speakers so probably overkill. I was not trying to push what I make, just saying that to my ears there are good and bad amps, and my metrics may not be yours.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#22 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by pre65 »

The single ended Mosfet amp monoblocks I built with the hockey puck mosfets were supposedly rated at 50 WPC. It was (is) a Nelson Pass design.

I understand that there were versions with a lower HT built that were lower powered.

There is a thread on here and also DIY audio.
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#23 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by vinylnvalves »

Nick. I know you would not puss, push I assume, your products. I think I may try hooking up some smaller film caps to see if the 47000uf cap is the weak link for the top end. What would people recommend for say 60 uf. I was thinking 3 off 20 uf mkt film caps in parallel, Vishay perhaps or Panasonic. Or are there some sonically superior motor run caps I don’t know about.

I don’t need more power, I am using 9db of attenuation in the DSP to pad the horns down to match the other 100db eff drivers.

I was thinking of looking at headphone amps, but haven’t got my head around what happens if you put 16 ohms onto something that wants to see 64 ohms, other than more power.
User avatar
Nick
Site Admin
Posts: 15706
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#24 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by Nick »

With your Mosfet amps do they have to driven hard to get lots of watts out of them or could they be biased down to something more akin to what I am after
Generally I think you need to bias mosfets at higher current than bipolar.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#25 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by vinylnvalves »

Sort of related to topic thread...

Does anyone know where I can get some thick (2oz - 4oz) copper clad pcb, double sided. I am going to machine a couple of circuit boards on my cnc router. I am thinking a thicker copper layer may be easier to machine. I can get 1oz stuff easily, the thicker copper, as used for power engineering applications, seems to be eluding me
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#26 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by vinylnvalves »

Spent last Saturday listening to various amps, from ncores to an Elliott 3a ( I think) and a headphone amp as well as the pass camp amps. The headphone amp and the pass amps had the best soundstage, the ncore sounded clinical and closed in, I do wonder if the amount of padding down (24 dB) of the ncore effected it.

So I have decided I am going to build one of the LPUHP amps or a variant of it. I have a question I have ( maybe stupid). For the attached schematic could I remove the lme49990 from the front end, as I can output upto 6v out of my Nadja DSP. The lme49600’s are current buffers so my logic I could get 6 x ( 8 x 250ma) = 12watts. Or do I need more voltage swing?
Attachments
TW LPUHP.pdf
(67.22 KiB) Downloaded 205 times
User avatar
Nick
Site Admin
Posts: 15706
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#27 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by Nick »

The first pair of lme49990 is working as a differential input buffer input , the second one is working as the feedback and driver for the output stage. You could input a single ended signal to H9 and H8 but its only got a 1k input impedance at that point.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
jack
Thermionic Monk Status
Posts: 5493
Joined: Wed Dec 29, 2010 8:58 pm
Location: ɐılɐɹʇsnɐ oʇ ƃuıʌoɯ ƃuıɹǝpısuoɔ
Contact:

#28 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by jack »

This input is simply a standard instrumentation amplifier with the output differential amplifier, U3, configured with global rather than local feedback. R25 and R26 set the input impedance to 10k and also stop the amp picking up noise when no input is connected, i.e stops the inputs floating and acting as aerials.

The gain of the front end is governed solely by R3 - as it stands, the gain is (1 + 2,000/R3), i.e. very close to x8 or 18dB. The normal complete gain equation for an instrumentation amplifier is simplified here by making R8 = R9 = R10 = R21. Note that it's very important to use 0.1% resistors (from the E192 series) as really close matching values are vital with instrumentation amps.

So, by increasing R3, you can lower the gain accordingly. Many instrumentation amps make this value switched to enable quick adjustment of the gain.

I would recommend changing R3 only and not otherwise messing with the input topology. The driver stage needs about 10.5v for full power, i.e. about 1.3VRMS in, so rather than a buffer gain of x8, you need x1.73 for 6V in full power, so R3 needs to be 2k74 which just happens to be an E192-series value.

Adding a non-inverting LME49990 with x8 (for 1.3V) or x1.73 (for 6V) gain to H9 with a 10k to gnd on its input would solve the single-ended low input impedance issue.
Vivitur ingenio, caetera mortis erunt
User avatar
jack
Thermionic Monk Status
Posts: 5493
Joined: Wed Dec 29, 2010 8:58 pm
Location: ɐılɐɹʇsnɐ oʇ ƃuıʌoɯ ƃuıɹǝpısuoɔ
Contact:

#29 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by jack »

vinylnvalves wrote: Mon Mar 05, 2018 10:40 pmThe lme49600’s are current buffers so my logic I could get 6 x ( 8 x 250ma) = 12watts. Or do I need more voltage swing?
Apologies - I missed that bit.

Yes, the maximum deliverable current is around 4A total, so a theoretical 32W (the PSU transformer is only rated at 25W) into nominal 8 ohms given a big enough voltage swing...

However, we're aiming for around 12W, which would only be 1.5A into 8 ohms which is where the approx 10V driver stage output requirement comes from - 10V into 8 ohms gives 12.5W with a 1.5A drive requirement. Note that I stated 10.4V in the previous post yet am only using a 10V value here - that's because the LME49600 has slightly less than unity gain, and anyway, these things aren't precise!!

So, with +/-18V rails and only driving the output at under 50% of it's capabilities with a 1.3VRMS (+18dB gain) or 6VRMS (+4.8dB gain) drive, we end up with a decent amp.

My only concern with this design is the lack of a DC servo in the global feedback loop to compensate for any DC offset at the output of the driver stage - this would be easy and cheap to do and would not impact signal quality whilst protecting any output device. The design is fully DC coupled end-to-end, so care should be taken wrt. DC levels.

Note also that the transformer is wired for 115VAC in by default, and though the pictures aren't clear, it doesn't look like there are jumper options for 230VAC - make sure you change that!

EDIT: Aha! There is a new thread and a V2 amp where the transformer is moved off-board and other changes: see http://www.diyaudio.com/forums/vendor-s ... ost3516741
Vivitur ingenio, caetera mortis erunt
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#30 Re: 3W amps - options: SS which sounds as good as DHT’s

Post by vinylnvalves »

I think I may not have expressed to question well. The output stage in the DSP is an Opamp gain stage(in mine I am using OPA627’s), why do I need to add another Opamp stage before the current buffer output stage If I can live with 6V ? The DSP and power amps won’t be in the same box but are close, so was ignoring any cable length effects.
Post Reply