World-Designs-Forum  

Go Back   World-Designs-Forum > World Designs > WD Amplifiers
Register FAQ Members List Calendar Gallery Today's Posts Mark Forums Read

WD Amplifiers For discusson of World Designs Amplifiers

Reply
 
Thread Tools Display Modes
  #1  
Old 20th August 2011, 09:21 PM
john & Jake the dog's Avatar
john & Jake the dog john & Jake the dog is offline
Senior Member
 
Join Date: Apr 2007
Location: Stockton on Tees North Ea
Posts: 750
Default 6000cdp and Kel84 - output, input, caps are everywhere

Hi,
Following on from my modding caps thread could anyone say if the Kel 84 has input caps as I have been advised to remove the cd player's output caps if this is the case.

cheers
__________________
john & who still runs rings round me
Reply With Quote
  #2  
Old 20th August 2011, 09:36 PM
Richard Richard is offline
Super Moderator
 
Join Date: Dec 2005
Location: Notts
Posts: 4,981
Default Re: output, input, caps are everywhere

Hi John, none on input of Kel84 so keep the output caps on the cdp incase there is any dc present which will turn on the first valve.
Reply With Quote
  #3  
Old 20th August 2011, 09:44 PM
john & Jake the dog's Avatar
john & Jake the dog john & Jake the dog is offline
Senior Member
 
Join Date: Apr 2007
Location: Stockton on Tees North Ea
Posts: 750
Default Re: output, input, caps are everywhere

Ok Richard will do. To be fair he also mentioned the dc problem.
__________________
john & who still runs rings round me
Reply With Quote
  #4  
Old 23rd August 2011, 05:04 PM
john & Jake the dog's Avatar
john & Jake the dog john & Jake the dog is offline
Senior Member
 
Join Date: Apr 2007
Location: Stockton on Tees North Ea
Posts: 750
Default Re: output, input, caps are everywhere

Hi,
if I need to protect the Kel84 from DC would some film caps of 0.22uf be enough.
Also does the value affect the sound, bass extension etc They are 220uf at the mo
__________________
john & who still runs rings round me
Reply With Quote
  #5  
Old 23rd August 2011, 06:12 PM
Richard Richard is offline
Super Moderator
 
Join Date: Dec 2005
Location: Notts
Posts: 4,981
Default Re: output, input, caps are everywhere

Hi John,

I could just give you figures but maybe it's better to explain some more

The blocking of DC is nowadays assumed to be on the output of the source device.

DC on the output of any source is naughty and most will have a cap before their output RCAs to block it. This includes opamp outputs as in your Marantz CDp and valve stage outputs such as I've just stuck on mine. Other sources such as WD Pre3 have a transformer output so no DC again.

Most amps these days (things were more varied years ago) assume they will not be fed DC and do not have any blocking on their inputs. This includes Kel84 and most of the WADs etc.

So, block the output of your CDp and you will ensure compatibility with Kel84 and all other gear.

Any series cap you use to do this will make a high pass filter with the following (amp input) shunt resistance. Different amps will have different input resistances.

Go here and look at the drawings first,

http://www.muzique.com/schem/filter.htm

On the High Pass drawing you see your series output cap that will be in the CDp and then the shunt resistance that is in the amp input.

Enter 50000 for the resistor as that is a common input resistance. Enter 220uF for the Cap as your player has at the moment. The calc will show a corner f of 0Hz. The signal will be transferred pretty much down to DC. Clear the boxes and enter 50000 and 0.22uF and you'll get 14.5Hz. That is the corner f, the roll off started higher remember and it will be 3dB down by then. So you will lose the lows with decent speakers and it will sound light.

Try 50000 and 2.2uF and you'll get 1.4Hz. That works pretty well and you can see why 2.2uF is often suggested for this app.

Why does Marantz use 100uF or 220uF? Well some ss amps have 10K input. 10K with 220uF gives 0.1Hz so it ensures the bass is not lost at this interface. Play with the calc values.

There is a small confusion to this sometimes when an amp maker might put a cap on the front end to deliberately make a high pass filter (to block very lows). WAD used to do this on some with 0.1uF followed by 220K gridleak gives 7.2Hz and might stop the power amp saturating its OPTXs with subsonics for example.
Reply With Quote
  #6  
Old 23rd August 2011, 06:52 PM
john & Jake the dog's Avatar
john & Jake the dog john & Jake the dog is offline
Senior Member
 
Join Date: Apr 2007
Location: Stockton on Tees North Ea
Posts: 750
Default Re: output, input, caps are everywhere

Hi Richard, thanks for the in depth explanation, I'll read it a couple of times but I think I get it.
Just a pity I can't use the 0.22 as I have some quality film caps.
__________________
john & who still runs rings round me
Reply With Quote
  #7  
Old 23rd August 2011, 07:39 PM
john & Jake the dog's Avatar
john & Jake the dog john & Jake the dog is offline
Senior Member
 
Join Date: Apr 2007
Location: Stockton on Tees North Ea
Posts: 750
Default Re: output, input, caps are everywhere

Hi, richard, played with that

is it possible for you to look at these at tell me which are the resistors in question , then I can get the exact value, please
surface mount resistors


component side
__________________
john & who still runs rings round me
Reply With Quote
  #8  
Old 24th August 2011, 10:35 AM
Richard Richard is offline
Super Moderator
 
Join Date: Dec 2005
Location: Notts
Posts: 4,981
Default Re: output, input, caps are everywhere

Hi John,

The resistors of the coupling I described are in Kel84.
The blocking caps are in the CDp.
Together they make a high pass filter as I explained.

Here are the input resistors in Kel84; VR1 and R2/R3.
Follow the input signal path to ground. It can only get there via the 100K of the pot with the 1M gridleak in parallel. So depending on vol position it is 100K at min vol to 91K at max vol.

You would then find the coupling caps in the CDp and replace them with better quality caps of a value which would not lose bass.


Reply With Quote
  #9  
Old 24th August 2011, 11:08 AM
john & Jake the dog's Avatar
john & Jake the dog john & Jake the dog is offline
Senior Member
 
Join Date: Apr 2007
Location: Stockton on Tees North Ea
Posts: 750
Default Re: output, input, caps are everywhere

Hi, righto richard, from what I'd read elswhere I thought that there was a 10k resistor formining a low or high pass filter with the caps.
I'm playing it safe I think and replaciing with Nichicon kz of the same value.

"Output stage
Output stage is based on three sub-stages:
A passive 2nd order RC low pass filter present in all CD6000 series.
An active low pass filter based on a NJM2114D op-amp, 12K, 1% tolerance, 0.1W film resistors and 120pF, 5% tolerance, 100V ceramic capacitors, following the design guidelines defined on SM5872BS DAC datasheet.
The HDAM sub-stage acting as line amplification." WIKhifi marantz cd6000

Probably getting wires crossed though. Out put impedance is 250ohms if that has a bearing.
__________________
john & who still runs rings round me
Reply With Quote
  #10  
Old 24th August 2011, 11:14 AM
Richard Richard is offline
Super Moderator
 
Join Date: Dec 2005
Location: Notts
Posts: 4,981
Default Re: output, input, caps are everywhere

Hi John,

Now the CDp.

See those pairs of series connected back to back 220uF 2219/2220/2221/2222. They are the DC blocking caps. However we see they are also followed by a 10K shunt resistor 3247/3248. (Assuming I'm using the same schematic as your pic is from!) This is why the caps are so large as they make a 110uF with 10K coupling even before the amplifier load is attached.

I can only think the 10K are present as the op stage may not like being open circuit (it may be that it would oscillate and fry if it was not connected to a load) so they fit one permanently. An attached amplifier load will then appear in parallel to the 10K so the caps must be large enough to make a low frequency coupling.

In short, Kel84 has 91K load at lowest. So do your player for a 50K attached load (as many pre's have a 50K pot) and it will be fairly universal. 10K already fitted // 50K = 8K. With present 110uF caps that makes 0.2Hz coupling. You could get away with much higher than this. Remove both 220uF caps (each channel) and replace with one 4.7uF film cap (using the "+" holes!) That would give a coupling of 4Hz with typical 50K to 100K amp loads and is probably about the highest you'd want to go if it is not to sound light. (10uF film caps would give 2Hz coupling)

So, tinker at your peril. I threw mine away, broke the tracks after the dac and fed the signal into a valve op stage but I do not know anything about your player. Perhaps others can help some more.


Reply With Quote
Reply

Thread Tools
Display Modes

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
Forum Jump


All times are GMT +1. The time now is 11:21 AM.


Powered by vBulletin® Version 3.7.3
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Copyright World Designs