5W Single Ended Class A Power Amp From Mark Houston - Page 6 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 19th April 2011, 03:52 AM   #51
diyAudio Member
 
chlorofille's Avatar
 
Join Date: Jul 2008
Location: Malaysia
Quote:
Originally Posted by SSDIY View Post
Hi everyone,

I use two 19000uF Mallory Capacitors and a choke as the PS. I got some hum noise. What can be done to solve it? Please advice.

Thanks
Got a pic of the choke? It may be saturating. I used a Mundorf 10mH ferrite core audio grade choke and it worked fine.
  Reply With Quote
Old 19th April 2011, 06:01 AM   #52
diyAudio Member
 
mhouston's Avatar
 
Join Date: Jan 2006
Location: Victoria, Australia
Yes the choke must be over-rated for the current draw.
  Reply With Quote
Old 4th May 2011, 12:11 AM   #53
diyAudio Member
 
Join Date: Mar 2011
Hi,
just got ready with a ZCA. I use 30000 µF per channel and 2 tiny chokes, too tiny.... I had to use a capacitance multiplier (one per channel) to reduce the hum to zero. Now running with ~ 19.5 Volts. I use 12 V 20 watts halogen bulbs instead of the resistors. So far nice warm sound, I like it.
Another user wrote, the ZCA is the most sensitive amp in matter of the input cap. I started with older russion paper in oil condensators resulting in nice natural mids but little dull highs. An Audyn A4 MKP cap was very transparent, but also with a little bit to offensive highs. I just ordered some russian teflons now....

The point is, I found some interesting facts about coupling caps and their behavier. It seems, the higher the output impedance the cap sees, the more the DF and DA of the cap is doing audible distortion and colouration.

Walter G. Jung wrote:
"In a single blind listening test using such various capacitor dielectric types as mica, polyester, tantalum, and polypropylene, it was found that a simple coupling capacitor can degrade sound quality quite strongly if the load impedance is high." ...." The other dielectrics mentioned followed similar patterns: Poor performance into the higher impedance, improvement in clarity with the lower impedance. However, even the best dielectric on hand in a usable size sounded much better into a lower impedance load."
"This factor can very logically explain points of disagreement on whether or not capacitors really do sound bad, as it tends to say they sound bad (within a given dielectric type) to the degree that the DA is allowed to manifest itself. Minimizing load resistance tends to optimize the circuit in terms of suppressing the DA."
http://classic-web.archive.org/web/2...tm#performance

In the ZCA, I guess the input cap works into a pretty high impedance of ~ 1 Mega Ohm, resulting in the need for a VERY good audiophil cap. So it could be a good idea to reduce the impedance down to at least 50-100k or even better to ~ 20k or so, to reduce the effects described by Walter Jung. This would result in a larger input cap, but every good MKP should do the job now with ease.
Could be done by changing the trimmer and gateresistor to lower numbers.

Michael
  Reply With Quote
Old 4th May 2011, 12:19 PM   #54
diyAudio Member
 
Join Date: Mar 2011
I just soldered a 150k over the 1M Resistor..., I´m really not shure but may be there`s more transparancy and less annoying highs with the Audyn caps. If I`m not wrong, it should no prob to reduce the 1M down to ~ 68k without any changes, the resulting highpass should be still under 20Hz. This would reduce the impedance at 1/15. Could be a good idea either to parallel the 33µ Cap with a Foil, cause I guess it`s more visible at a ground now. Maybe someone else likes to test if there is an improvement in sound and/or a less strong dependence in choosing caps. For the output cap I now ordered ELNA silmic II electros, should be the best choice (and cheaper...) next to BLACK GATES.

My ZCA, chaos again..., improvised red Audyn caps, the long silver ones are russian PIO, the darlingtons for the gyrator are on the main coolers. Getting tighter inside as I thought...
Click the image to open in full size.Click the image to open in full size.
  Reply With Quote
Old 4th May 2011, 01:38 PM   #55
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
I agree with you.
No need for so high value resistor 1M.
1uF input cap and 100k resistor, if I had done the amplifier.

Nice amplifier construction. You have a heavy filtered power supply.
This is what this amp needs.
__________________
lineup
  Reply With Quote
Old 10th July 2011, 11:14 AM   #56
diyAudio Member
 
Join Date: Mar 2011
What was starting as a toy (and it really looks like that at first….) and cause I wanted just to look into the singleended stuff/sound after some reading, is becoming more and more a serious highend thing for me….

It plays the most musical and transparent, compared to any amp I own, and to others at friends I know, in already a little pricey region. Some weeks in the “tweaking” phase every visitor had to listen to the new amp and I had often fun quickly change to a yamaha a380, a consumerprice amp, “natural sound stereo amplifier” written on it`s front, with “cd direct” switch for “best” cd sound…..

The difference is very clear, the non technical/hifi visitors all stated the yamaha is not sounding nice, but very flat and grey in comparison to the zca. I take the yamaha as example how a consumerpriced push/pull GNF amp sounds in general….

The decision about the input cap
was unexpected difficult and took 3 weeks of intense changing/hearing.

I had different mkp`s, tinnfoil, russian teflon, glimmer, styrene…but not very high priced v-caps or mundorf gold/silver etc.

The favourit, a audyn reference cap did not win, the winner was 6 paralled 47nF styrene 630V caps. I found every other cap was colouring the sound, every mkp even the “reference” did something in the treble region, making some hard “plastic” sound, tried also bypassing with 1837/1832 10nF, didn`t like it, better treble, but not homogen. The russian t3 teflon sounds very spacious, transparent at first, but had some “whiteness”, a kind of texture in the treble either.

With the styrene(s) I can not recognise any colouring, sounds very natural and transparent.

To the use of lamps (what I did)
instead of resistors….I have no glue what nonlinearity it adds. I would imagine some kind of very soft compression effect with a medium to slow time constant. On the other hand you will not find any uncompressed music at all…..Even the cleanest acustical recording is running in a compressor/loudnessmaximizer/brickwall-limiter in the upper 3 dB`s. We have a loudness war getting worser every year. I guess it was metallica rewarding something like the “siver citrus” for the most compressed and most unhearable cd of the year (~ 2004).

I did a lot of homerecording myself and worked with compressors, I did need them and I hate them. I´m pretty allergic against any audible compression artefacts, and I can not hear anything in a zca with 12v lamps.

The output cap:

I ordered Elna silmic II, cause should be good audio elkos….mysteriously they sound ugly, very veil sound, every transparency gone…built back to the cheap sanhwa(?) standarts, excellent! I have no glue why…….

Speakercable:

Years ago I bought any xx….streamline 5 something cable, pretty thick ~ 6mm/2 or so, to unhandy for tweaking around, so I bought the cheapest 2.5 mm/2 to play, nice so far…after finishing my testing I get back to my “good” cable and it sounded nasty….flat, grey treble, bad space. I was pretty surprised, I never took this cable thing serious (voodoo). After again some extended googling I ordered some coaxial speakercable, a very fair priced one, and I find it perfect now. May be I will try a twisted solid core thing with teflonisolation in the future.

May be a non NFB amp is more sensitiv to speakercables?

Will take some distortion measures with ARTA soon, just for my technical interest.

Michael
  Reply With Quote
Old 10th July 2011, 05:57 PM   #57
diyAudio Member
 
digits's Avatar
 
Join Date: Apr 2011
Sometimes you need to leave a cap in position a while to start doing its magic, takeing it out after a short evaluation can be a mistake.
  Reply With Quote
Old 10th July 2011, 09:11 PM   #58
diyAudio Member
 
Join Date: Mar 2011
@digits
you mean the Elna`s ? The difference was so hefty, I did not even thought about any burnin. On the other hand the standard cap worked fine from the first minute. Regarding the russian teflons I had in mind that teflon`s need 400h to burnin (so said for V-caps...), I waver between voodoo and can be...some guys burn in caps with 100 -200 Volts for 36 hours. The styrene caps did sound fine from the first minute, could not find any burnin effect. I tend to the opinion that if there is any burnin effect, it is pretty subtle. If there is a real flaw the first half hour it will not change in a relevant way over time.

Michael
  Reply With Quote
Old 10th July 2011, 10:00 PM   #59
diyAudio Member
 
Join Date: Jan 2011
Location: Shropshire
I note the comments describing this design as "pure Class A".
The amplifier output stage is half resistive load, using a constant current source is just as pure and using an active other half, ie. push pull is also just as pure.

There are several comments which quite rightly identify the quiescent disspation ( about 20 watts per channel) and the limited power output ( a watt or 2 ). BUT more importantly they identify the need for a very chunky power supply. Big transformer and very big electrolytic smoothing to reduce the inevitable supply hum in the output.

The initial post was looking for a mirror image cicruit to use the spare complementary devices he had purchased, and in the process was likely to incur a vastly greater cost in power supply circuitry and heatsinks to build another example.

Dare I suggest that the effective use of the complementaries would be to build a more efficient push pull class A circuit at lower dissipation, and then buy two more pairs of similar transistors and build the two more amps the gentleman requires.

The overall cost will be less! The existing supply will suffice, the existing heatsinks will still do the job because the dissipation will be very much reduced from each of the four amplifiers. All four channels will probably fit into the same casework. No high power resistors needed and since the amplifier is single supply the only other significant cost will be another two output caps of 4700uF.

Personally I have always been a big fan of negative feedback, for at least 40 years, and I know some people are not keen but I would look out a slightly more elaborate circuit with better performance. An input level shifting transistor stage, a voltage amplifier stage and buffer to the output transistors. One would ideally like a higher supply voltage ( more than 24V. ) to the driver stage to obtain a good output swing from the very modest main supply voltage. One neat alternative way to do this might be to bootstrap the driver stage with capacitors from the output. This is an ancient technique often used in days of yore with bjt's but especially useful also with FET circuits that operate with quite a large different gate to source voltage. This would further improve efficiency.
  Reply With Quote
Old 16th May 2013, 12:44 AM   #60
diyAudio Member
 
mhouston's Avatar
 
Join Date: Jan 2006
Location: Victoria, Australia
Quote:
Originally Posted by Celeron View Post
I just soldered a 150k over the 1M Resistor..., I´m really not shure but may be there`s more transparancy and less annoying highs with the Audyn caps. If I`m not wrong, it should no prob to reduce the 1M down to ~ 68k without any changes, the resulting highpass should be still under 20Hz. This would reduce the impedance at 1/15. Could be a good idea either to parallel the 33µ Cap with a Foil, cause I guess it`s more visible at a ground now. Maybe someone else likes to test if there is an improvement in sound and/or a less strong dependence in choosing caps. For the output cap I now ordered ELNA silmic II electros, should be the best choice (and cheaper...) next to BLACK GATES.

My ZCA, chaos again..., improvised red Audyn caps, the long silver ones are russian PIO, the darlingtons for the gyrator are on the main coolers. Getting tighter inside as I thought...
Click the image to open in full size.Click the image to open in full size.
Somehow I missed this post. What great looking amp. A bit steampunk.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
GERMANIUM Single ended Class A Headphone Amp. Mooly Headphone Systems 74 18th January 2014 10:19 AM
push pull Vs single ended class A amp space2000 Solid State 25 23rd August 2008 03:31 PM
Single ended amp from class A push-pull Wavebourn Tubes / Valves 2 12th October 2007 09:14 PM
Proposal On Single Ended Class-D Subwoofer Amp Workhorse Class D 8 27th January 2004 09:11 AM


New To Site? Need Help?

All times are GMT. The time now is 09:21 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2