Help needed understanding component values.

[cbj591]

Good evening,

Since my design skills are limited, I was wondering if someone could help explain what effects changing values of several components in my amp would do.

-1k gridstoppers - Why 1k, what happens if the value is changed lower or higher?

-100k input resistor - what are the effects of raising and lowering the value?

-.1uf coupling cap - From what I have read, the higher the value, the lower -3db is at the bottom end. Also the value is tied to the input resistor. Since the original input resistor was 470k, the coupling cap should be around .1uf. Since the input resistor was changed to 100k, the value of the caps should now be around .40-.50uf. This is based on several calculators that I have found. Is this correct?

-1k resistor and 16v 100uf cap on the 6SL7. What is their function and what effect does changing the values have?

- 250R 5W and 50v 47uF capacitor between the output tubes - What is this section/combo called? What happens when you change the value up or down.

I am trying to get an understanding what the various sections of the amp do and how tweeking them affects the sound. This will help me see why certian values are chosen and help me understand the overall design.

It is amazing how much info can be learned in a small amount of time....

Thanks
Brian

[aardvarkash10]

Originally Posted by cbj591

Good evening,

Since my design skills are limited, I was wondering if someone could help explain what effects changing values of several components in my amp would do.

-1k gridstoppers - Why 1k, what happens if the value is changed lower or higher?

as long as you don't move far (say, 560 to 1.5k), not a lot. Make sure they are carbon though. Cheap as you can get...

Originally Posted by cbj591

-100k input resistor - what are the effects of raising and lowering the value?

changes the loading on your preceding stage - in this case probably your source - CD or tuner or whatever. Modern devices will be happy down to as low as 50k, but 100k is a happy medium

Originally Posted by cbj591

-.1uf coupling cap - From what I have read, the higher the value, the lower -3db is at the bottom end. Also the value is tied to the input resistor. Since the original input resistor was 470k, the coupling cap should be around .1uf. Since the input resistor was changed to 100k, the value of the caps should now be around .40-.50uf. This is based on several calculators that I have found. Is this correct?

Largely. Don't forget the parallel and series values and the capacitance of the grid circuit.

Originally Posted by cbj591

-1k resistor and 16v 100uf cap on the 6SL7. What is their function and what effect does changing the values have?

the resistor sets the DC bias voltage for the SL7. The cap bypasses the resistor for AC purposes.

Originally Posted by cbj591

- 250R 5W and 50v 47uF capacitor between the output tubes - What is this section/combo called? What happens when you change the value up or down.

As above. Strongly advise you to read through this to get the idea!

I am trying to get an understanding what the various sections of the amp do and how tweeking them affects the sound. This will help me see why certian values are chosen and help me understand the overall design.

It is amazing how much info can be learned in a small amount of time....

Thanks
Brian[/QUOTE]

[Eli Duttman]

Modern devices will be happy down to as low as 50k, but 100k is a happy medium

The IHF "standard" calls for "line" level units to drive a 10 KOhm load. Commercial CDPs do that easily enough. IMO, any DIY design offered to other folks should comply too.

[cbj591]

Thanks for the all info, it is greatly appreciated.

If you think anything else that may help please let me know.

Thanks again
Brian

[cbj591]

Originally Posted by aardvarkash10

as long as you don't move far (say, 560 to 1.5k), not a lot. Make sure they are carbon though. Cheap as you can get...

Just curious, why carbon and cheap as I can get for the grid stoppers?

I am using Kiwame now, but when I finish the new pc boards, I was going to install Takman resistors.

Are cheaper better for this, or do the more expensive resistors just not function any better for this application.

Thanks

[aardvarkash10]

Originally Posted by Eli Duttman

The IHF "standard" calls for "line" level units to drive a 10 KOhm load. Commercial CDPs do that easily enough. IMO, any DIY design offered to other folks should comply too.

Fair enough too Eli - but often we are unsure what is going to be in front of a device. I tend to err on the side of caution (100k) but don't go stratospheric (250-500k).

Carbon because of the purpose of a grid stopper - to stop oscillations. Cheap is just a reasonably sure way of ensuring you are getting a carbon resistor. Also, since the tolerance is irrelevant in this location, no point paying for 1% pieces.

Others will argue the relative sonic merits of their favourite brands. Meh. Whatever.

[megaohmz]

Get a good book on the math behind all of the electronic components. Go to borders or order online.The basic components are resistors , capacitors and inductors. This is all you can do in a circuit by the way! It is just as simple as math! "You can only add to a number and subtract from a number and nothing else". Electronics are simple to a point, and then it becomes art when you start using components made from different materials and configuring them in unique ways. The sound quality can change just by changing the material the wires are made of, copper, silver, aluminum, gold. Good luck bro!

[Arnulf]

Originally Posted by cbj591

Just curious, why carbon and cheap as I can get for the grid stoppers?

Because carbon ones are non-inductive. More expensive high precision types are usually metal foil.

Expensive resistors are right up there with transformers with solid silver wire and few other audiophool gimmicks: something for gullible suckers to waste their money on, rather than investing it in better parts build-quality or design wise. Opting for transformer of same design but with more iron in the core and consequently larger primary inductance and lower bass response, or using only film capacitors in place of electrolytics for durability reasons etc. would make more sense as an investment than "brand name" $10 a pop resistors do.

[DF96]

Are carbon ones non-inductive? Carbon composition, maybe, but they are difficult to find nowadays. Carbon film uses a spiral cut to adjust the value so is slightly inductive, although the inductance can be ignored up to VHF frequencies. I'm not convinced that they are much better than metal film as grid stoppers, although they are cheaper. A bit of inductance doesn't matter as long as the resistance dominates at the potential parasitic frequency. In many cases the lead inductance is greater than the resistor body inductance anyway.

[Arnulf]

Now that you mentioned it, it is sometimes very ironic to see long lengths of wires running throughout the chassis to keep with the "old" look, with all the parasitic inductance that brings, only to have to damp it later with a suitable stopper. I rarely do old-style (rat's nest) wiring, mostly PCB, but I use stoppers anyway jkuist to be on the safe side. They don't hurt anything (when reasonably sized) and there is absolutely no need to squander money on luxury brands - that money will be better spent on larger capacitors, a filtering choke, better OPT, more robust switches etc. This is just like LEDs for voltage reference - one can buy incorrectly when going solely by the price (high brightness types have higher Vf than the old, cheapest run of the mill kind of same color, green for example).

Since grid stoppers are meant to dampen VHF/UHF nasties that's precisely where I'd be concerned about potentially inductive nature of said resistors. They should have zero effect in the audio band (I size mine so that Fc is 1/2 to 1 decade above the higherst frequency of interest - this way they cut below MW radio yet well above audio).