Just a question regarding the amplifier section...
There are two capacitors (C205 and C233) almost smack in the middle of the left and right channels on the schematic. They are 4.7uF electrolytics and in my amp are non-polarised.
What do these caps actually do, and would it be worth swapping them out for, say better electros or even polypropylene etc?
Also, C214 and C239 on the input stage are ceramic caps, should I replace these with polypropylene / polystyrene etc. for better sound, or would this not have any noticeable effect, not being in the direct signal path?
There are two capacitors (C205 and C233) almost smack in the middle of the left and right channels on the schematic. They are 4.7uF electrolytics and in my amp are non-polarised.
What do these caps actually do, and would it be worth swapping them out for, say better electros or even polypropylene etc?
Also, C214 and C239 on the input stage are ceramic caps, should I replace these with polypropylene / polystyrene etc. for better sound, or would this not have any noticeable effect, not being in the direct signal path?
mystery amp
Hi, Xephon.
As a matter of fact, I have changed c205 and c223 for polypropylene. It´s a little messy, cause´there isn´t too much space in that position, but it´s possible. I don´t know exactly if they are in the signal path; but nonpolars usually are used for coupling.
A nice move would be to change the input caps c212/c240. Polypropylene is good there.
C239 and C214 are part of an input low pass filter. Silver mica, or some polyestyrene, would be better.
I have deleted the preamp section in my amp. The original is a little hissy, has too much gain and sounds slightly ¨metallic¨ to my taste.
I made a 15v psu and a very simple opa606 preamp that I´ve stucked inside. Is much more silent and good sounding than the original pre.
If you want to be frugal, the amp has sufficient gain to be used with only an attenuator at the input.
C213 and c238 were changed for some old stock silver-mica that I found by chance in an old radio components shop -an old part, labelled ¨Suzuki¨, with the code expressed in coloured dots-: the effect was very noticeable in that position. I think -maybe I´m in error, but for what I have read they appear to do so- that those caps form a ¨dominant pole¨ in the amp topology, contributing to the overall sound of the amp in a good measure.
I´m trying to get the basics on amplifier design, but for now I´m only an apprentice. But it´s fun, really.
I believe that Greg is more acquainted with the circuit and has much more experience with amp topologies.
Some other common ceramic caps that happen to be in the board were changed too, for more stable ceramic NP-zero types.
That amp is a mistery to me: good transformer, good output transistors, a decent PSU... I don´t understand how it´s priced so cheaply.
Cheers, and have fun.
Hi, Xephon.
As a matter of fact, I have changed c205 and c223 for polypropylene. It´s a little messy, cause´there isn´t too much space in that position, but it´s possible. I don´t know exactly if they are in the signal path; but nonpolars usually are used for coupling.
A nice move would be to change the input caps c212/c240. Polypropylene is good there.
C239 and C214 are part of an input low pass filter. Silver mica, or some polyestyrene, would be better.
I have deleted the preamp section in my amp. The original is a little hissy, has too much gain and sounds slightly ¨metallic¨ to my taste.
I made a 15v psu and a very simple opa606 preamp that I´ve stucked inside. Is much more silent and good sounding than the original pre.
If you want to be frugal, the amp has sufficient gain to be used with only an attenuator at the input.
C213 and c238 were changed for some old stock silver-mica that I found by chance in an old radio components shop -an old part, labelled ¨Suzuki¨, with the code expressed in coloured dots-: the effect was very noticeable in that position. I think -maybe I´m in error, but for what I have read they appear to do so- that those caps form a ¨dominant pole¨ in the amp topology, contributing to the overall sound of the amp in a good measure.
I´m trying to get the basics on amplifier design, but for now I´m only an apprentice. But it´s fun, really.
I believe that Greg is more acquainted with the circuit and has much more experience with amp topologies.
Some other common ceramic caps that happen to be in the board were changed too, for more stable ceramic NP-zero types.
That amp is a mistery to me: good transformer, good output transistors, a decent PSU... I don´t understand how it´s priced so cheaply.
Cheers, and have fun.
Wow, thanks for all that! I'll definately try those alternate caps.
I have already removed the preamp and used the 100k pot with a few resistors as a shunt for volume control (would this be more accurately described as gain comtrol??)
My brother has access to a company that makes panels and labels (for electrical switchboards and the like) so I am looking at getting them to CNC me up a new face panel minus the tone control holes using their laser cutters soon.
I am getting interested in this stuff (I am more knowledgeable in the area of robotics ATM) and thought this amp would be a good place to start learning.
I have already removed the preamp and used the 100k pot with a few resistors as a shunt for volume control (would this be more accurately described as gain comtrol??)
My brother has access to a company that makes panels and labels (for electrical switchboards and the like) so I am looking at getting them to CNC me up a new face panel minus the tone control holes using their laser cutters soon.
I am getting interested in this stuff (I am more knowledgeable in the area of robotics ATM) and thought this amp would be a good place to start learning.
posted by Xephon
Nice, it would be more exactly described as a ¨shunt attenuator¨, ¨shunted pot¨ or something like that. Some people refer to it as a ¨passive preamplifier¨. There are 3 or 4 different variations over the same theme.
Have you noticed a better sound with that arrangement?
And yes, the amp is rugged, and well suited to modifications. And is a good starting point to do some learning.
If you check out the schematics, you´ll note that the output transistors aren´t included in the global feedback scheme. Maybe for some issue related to the ¨less feedback is better¨school of thinking, I don´t know really. But I remember that in the manual that came with the amp, that issue was highlighted as a design point -in pidgin english, with not a lot of explanation-.
In some other thread, somebody suggested the inclusion of the output stage in the global feedback scheme, something that I haven´t done yet... I have my reserves
Cheers
Nice, it would be more exactly described as a ¨shunt attenuator¨, ¨shunted pot¨ or something like that. Some people refer to it as a ¨passive preamplifier¨. There are 3 or 4 different variations over the same theme.
Have you noticed a better sound with that arrangement?
And yes, the amp is rugged, and well suited to modifications. And is a good starting point to do some learning.
If you check out the schematics, you´ll note that the output transistors aren´t included in the global feedback scheme. Maybe for some issue related to the ¨less feedback is better¨school of thinking, I don´t know really. But I remember that in the manual that came with the amp, that issue was highlighted as a design point -in pidgin english, with not a lot of explanation-.
In some other thread, somebody suggested the inclusion of the output stage in the global feedback scheme, something that I haven´t done yet... I have my reserves
Cheers
Re: posted by Xephon
Yea, the sound is more 'natural' and there is less hiss present on quiet pieces (actually, none at all). I can turn the volume all the way up and I have no noticeable hiss. Better speakers may change this, but I'm happy at the moment, except for those caps...
I have found a supplier for Atco Pots (the black square one). I can get one from Farnell for around $58 Australian. Is this a good price?
I do seem to have a slight lack in bass though. Is there something I can do to fix this? I am running it from a modified souncard that has DC blocking caps of 47uF (nichicon fine gold) built in, so have removed the 4.7uF ones (C212 and C240) from the amp to see if that helps. It did a little, but my Panasonic stereo seems to have more bass when everything is set to flat. I am using the same set of speakers.
federico moreno said:
Yea, the sound is more 'natural' and there is less hiss present on quiet pieces (actually, none at all). I can turn the volume all the way up and I have no noticeable hiss. Better speakers may change this, but I'm happy at the moment, except for those caps...
I have found a supplier for Atco Pots (the black square one). I can get one from Farnell for around $58 Australian. Is this a good price?
I do seem to have a slight lack in bass though. Is there something I can do to fix this? I am running it from a modified souncard that has DC blocking caps of 47uF (nichicon fine gold) built in, so have removed the 4.7uF ones (C212 and C240) from the amp to see if that helps. It did a little, but my Panasonic stereo seems to have more bass when everything is set to flat. I am using the same set of speakers.
hi guys,
You've made me get my DSE amp back out. I reckon the changes you blokes have done would have more effect than what I've done.
I reduced the gain because using a CD player as a source, only a quarter of the volume control was usable. I don't know exactly the full implications of doing this, but its seems to work well for me. Removing the pre-amp is probably a better idea.
Original gain:
Gain = 1 + R231/R230
Gain = 1 + 47k/1k
Gain = 48
New gain:
Gain = 1 + R231/R230
Gain = 1 + 47k/2.2k
Gain = 22.36
R230 = 1.8k would probably be better.
I made the Vbias adjustable by replacing R209 with a 1k pot.
Having Vbias set correctly can reduce or eliminate crossover distortion. For EF output topology, the Vbias should be set by adjusting voltage across the 2 emitter resistors to 47mV to 55mV.
A good starting point is R209 equal to 160R. Vbias is temperature depend so it must be adjusted when the amp is at normal operating temperature.
Increasing Vbias will usually increase the heat generated by the output transistors. Watch out with these small heatsinks.
I can't really say it made an improvement, but it made me feel better.
DoomPixie,
I have a old 90's Yamaha AX550, it's not good.
I don't know why, because as you say, it is a quality product using very good components. I imagine the newer Yamahas are a lot better.
BTW: Sorry, this thread has nothing to do with chipamps, should it be moved?
regards
You've made me get my DSE amp back out. I reckon the changes you blokes have done would have more effect than what I've done.
I reduced the gain because using a CD player as a source, only a quarter of the volume control was usable. I don't know exactly the full implications of doing this, but its seems to work well for me. Removing the pre-amp is probably a better idea.
Original gain:
Gain = 1 + R231/R230
Gain = 1 + 47k/1k
Gain = 48
New gain:
Gain = 1 + R231/R230
Gain = 1 + 47k/2.2k
Gain = 22.36
R230 = 1.8k would probably be better.
I made the Vbias adjustable by replacing R209 with a 1k pot.
Having Vbias set correctly can reduce or eliminate crossover distortion. For EF output topology, the Vbias should be set by adjusting voltage across the 2 emitter resistors to 47mV to 55mV.
A good starting point is R209 equal to 160R. Vbias is temperature depend so it must be adjusted when the amp is at normal operating temperature.
Increasing Vbias will usually increase the heat generated by the output transistors. Watch out with these small heatsinks.
I can't really say it made an improvement, but it made me feel better.
DoomPixie,
I have a old 90's Yamaha AX550, it's not good.
I don't know why, because as you say, it is a quality product using very good components. I imagine the newer Yamahas are a lot better.BTW: Sorry, this thread has nothing to do with chipamps, should it be moved?
regards
Greg Erskine said:
Only Yamaha i heard that was any good was the B-6, maybe some day i get the chance to judge myself what the B-1 was like.
I've witnessed the 100 year Yamaha celebration model combo CX/HX/MX-10.000, cost like 25 k$ overhere ('88-'89).
They too gave me the impression a screw was overtorqued inside my head, the screaming highs of the AX-xxx series are still ringing.
An importer overhere stopped offering the KD-261 around 2003.
Conrad was into the Koda models, Conrad France still offered the 261 last time i visited their site. Priced at 160 Euro, so make that 270-275 AUD.
The kind of devices in the KD-261 schematic make it obvious that the thing is filled with China garbage copies.
The 2SA733/2SC945 and 2SA1013/2SC2383 Chinese copies have nothing in common with the original Toshiba and NEC devices.
The Koda is likely to have a 10MHz copycat device of a 100MHz original in the Vas position.
Me thinks that Erno Borbely and Me, Myself and I are among the few who still posess more than a single pair of genuine Toshiba 2SA1301/2SC3280 output devices.
The ones used in the Koda are bound to be the $1, guaranteed till you pop the switch, versions.
For those who are able to convert the amp boards to the real McCoy and have the parts, the KD-261 offers astonishing value for money imo.
People who have no intention to convert a KD-261 are better off with secondhand proven record items.
The PCB's in my amp have the 260 number in the code. For example, the preamp board has the number KD-260A then 7.820.043.
Here's hoping I got a decent one!....
Greg, can you clarify which resistors I should measure the votage across for the Vbias adjustment? I'm sorta new to this and am not exactly sure which ones to measure.
Oh, also, what is the RP201 for? It is a small trimmer pot.
Here's hoping I got a decent one!....
Greg, can you clarify which resistors I should measure the votage across for the Vbias adjustment? I'm sorta new to this and am not exactly sure which ones to measure.
Oh, also, what is the RP201 for? It is a small trimmer pot.
koda amp
posted by Greg
Nice question;
I´ve heard about reports of fake transistor failure, but I don´t know if that happens when stressed or in normal operation.
The ones in my amp -sc52007sa1943 - never failed...
And nicely stressed they were, a lot of times!
The little and not-so-efficient 6.5 inches Vifa woofers in my speakers bottomed just in the verging of audible clipping -clipping in this amp is relatively soft; I have heard some middle of the road Rotels or Arcams clipping in a more violent way-... so I believe that the 80w/ch is a real assertion...
But, as I have said, I don´t know what´s the real history with the pricing of this amp. Putting a good toroidal transformer, an anodized alu fascia, machined alu knobs and a lot of caps, and then throw in fake transistors sound like a nonsense to me.
It would be more logical to make some cheap plastic chassis and knobs -as in some Rotel integrated amps-, an undersized trafo, barely caps at all, and then, yes, a nice pair of fake transistors to gild the lilly...
By the way, the amp now sounds much better than my old Pioneer A400, or than a Rotel ¨audiophile¨ 30w/ch that I have loaned to a friend. Not a giant killer, but decent still...
posted by Greg
Nice question;
I´ve heard about reports of fake transistor failure, but I don´t know if that happens when stressed or in normal operation.
The ones in my amp -sc52007sa1943 - never failed...
And nicely stressed they were, a lot of times!
The little and not-so-efficient 6.5 inches Vifa woofers in my speakers bottomed just in the verging of audible clipping -clipping in this amp is relatively soft; I have heard some middle of the road Rotels or Arcams clipping in a more violent way-... so I believe that the 80w/ch is a real assertion...
But, as I have said, I don´t know what´s the real history with the pricing of this amp. Putting a good toroidal transformer, an anodized alu fascia, machined alu knobs and a lot of caps, and then throw in fake transistors sound like a nonsense to me.
It would be more logical to make some cheap plastic chassis and knobs -as in some Rotel integrated amps-, an undersized trafo, barely caps at all, and then, yes, a nice pair of fake transistors to gild the lilly...
By the way, the amp now sounds much better than my old Pioneer A400, or than a Rotel ¨audiophile¨ 30w/ch that I have loaned to a friend. Not a giant killer, but decent still...
xephon said:
Hi xephon,
Yeah, mine has the same identification markings.
Measure across R210||R211 in series with R213||R214, points A and B. Points A and B connect to the emitters of the output transistors. Note where I added the 1K pot for Vbias adjustment. 160 ohms is a good starting point.
My guess is RP201 is for adjusting the DC offset on the output. If the input transistors V216/V218 are not matched you'll get a DC offset. Also, ideally R238 and R231 are usually the same value. To measure DV offset, short the input RCA and measure across the output posts. It should be less than 100mV, but probably closer to 0mV.
On my better amps, the cap across the Vbias transistor is a good quality electro in the 47uF to 120uF range. Don't know if this is Ok in this design.
regards
Attachments
Okidoki,
you've convinced me, i'm grabbing me one of the remaining KD261s overhere.
The thing i really don't understand why your KD-260s have 2SA1943/2SC5200s and the KD-261 has 2SA1301/2SC3280s.
The latter should be utterly extinct, the first are (still) used in expensive gear.
The V-I limiter of the KD-261 grabs in at little over 6 amps, that checks out with the 10mS SOA limit of the Toshiba 120 watt 2SA1301/2SC3280 devices.
Shame nobody had an interior picture to share.
you've convinced me, i'm grabbing me one of the remaining KD261s overhere.
The thing i really don't understand why your KD-260s have 2SA1943/2SC5200s and the KD-261 has 2SA1301/2SC3280s.
The latter should be utterly extinct, the first are (still) used in expensive gear.
The V-I limiter of the KD-261 grabs in at little over 6 amps, that checks out with the 10mS SOA limit of the Toshiba 120 watt 2SA1301/2SC3280 devices.
Shame nobody had an interior picture to share.
photos
Jacco, I´d love to post some photo, but my camera is rubbish... no zoom, no definition, nada. I´ll ask a friend of mine to check if he got the time to take some good images.
But I believe that for the money you can´t go wrong. And in the event that you don´t like the amp, it´s a good source of spare, good standard quality parts.
When I first saw the thing, -exposed ¨at hand¨ in some shop- I resorted to the classical ¨materialist¨ audiophile expedients: I checked out the weight, and taking some look at the innards -through the ventilation holes in the lid-, said to myself...¨mmm, toroidal trafo, metalfilm resistors, four not-so-thin PSU caps, and 100 u$s... sold!¨ (by the way, that`s the price of a discman here in Argentina).
That was in 2001. And the damn thing is still working, impervious to all of my ´abuses´. Not so bad.
Luck!
Jacco, I´d love to post some photo, but my camera is rubbish... no zoom, no definition, nada. I´ll ask a friend of mine to check if he got the time to take some good images.
But I believe that for the money you can´t go wrong. And in the event that you don´t like the amp, it´s a good source of spare, good standard quality parts.
When I first saw the thing, -exposed ¨at hand¨ in some shop- I resorted to the classical ¨materialist¨ audiophile expedients: I checked out the weight, and taking some look at the innards -through the ventilation holes in the lid-, said to myself...¨mmm, toroidal trafo, metalfilm resistors, four not-so-thin PSU caps, and 100 u$s... sold!¨ (by the way, that`s the price of a discman here in Argentina).
That was in 2001. And the damn thing is still working, impervious to all of my ´abuses´. Not so bad.
Luck!
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