The most effective Gainclone upgrades - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 10th June 2007, 07:06 AM   #1
diyAudio Member
 
uncle_leon's Avatar
 
Join Date: Jun 2007
Location: Czyżeminek, near Łódź
Question The most effective Gainclone upgrades

Hi,
This is my first post on this forum, so hi to everyone out there I used to be quite deep into overclocking processors, but recently I became hooked into making a Gainclone amp. I didn't have much experience (none, to be honest, at least not with audio stuff), so I decided to make it easy for myself, and ordered Peter Daniel's basic LM3875 kit. The amp isn't finished yet, but I already started thinking about possible ways of making it better. If anyone can make some suggestions as to what has the biggest impact on amp's sonics, I'll be very grateful.

First, let me tell you where I am now:
- Nuvotem Talema trafo, 225VA, 2x18V (20.8V real), encapsulated.
- MUR680 diodes, ordinary resistors, Panasonic FC caps. No Zobel, snubber etc., just simple basic Peter's NI design.
- mains cable and plug from gutted computer PSU
- for internal power wiring - 2x0.75mm stranded copper cable in nice, thick&flexible insulation.
- for internal signal wiring - cable i made myself, cutting 3 leads off computer hard disk ATA ribbon, braiding them together and wrapping in insulating tape.
- a rather pathethic 10K pot, that I took off some old PC speakers
- heatsinks taken off broken PCs, they seem more than adequate for LM3875s.
- ordinary, nickel plated RCA sockets
- plastic 3A terminal block connectors as speaker binding posts.

As you can see, the config is a rather cheapskate/scavenger one. So, I started to think what could make an audible difference without terminally harming my wallet. I came up with a list of all possible points to upgrade:

- resistors (4 per amp board, 8 in total)
Upgrade to Caddock/Riken would cost 31-35$, and should bring significant improvement in noise level and overall clarity. I consider this a good option.

- small caps (4.7 or 10uF/50V, 2 on rectifier board)
Upgrade to Black Gate N would cost 7$. Probably not much to be gained here, but it's not expesive so I'd give it a try.

- big caps (1000 or 1500uF/50V, 2 on each amp board, 4 in total)
Upgrade to Black Gate STD would cost almost 70$ - ouch!... Quite possibly an audible improvement, but since Panasonic FC are really good, and the cost of upgrade is so high, I'd rather invest my money elsewhere, for now. (I don't event take into consideration an option of Black Gate 'N' series, they simply CAN'T be that good to be worth that kind of money)

- transformer
I've heard opinions that higher rail voltages tend to give better sound, but I was afraid I could run into problems if I changed speakers to some low impedance ones. I also read that 300VA isn't too much for a GC. So I might give some 2x25V 300VA trafo a try. But I'm going to do it later, as it would cost me around 90$... Yes, much later.

- power wire
Well, I can't honestly think what could I upgrade it to? It seems thick enough, and is easy to work with.

- signal wire
Since so little of it is needed, I was seriously considering upgrading to pure silver, teflon insulated wire (not that I honestly believe it would bring astonishing improvement, but it would be a nice thing to impress friends with . The thing is, I don't know which one to choose... Jupiter from PartsconneXion (silver solid core/cotton wrapped) looks nice and is inexpensive, but I don't know if it is thick enough - 28awg.

- signal sockets, speaker binding posts, mains cable&plugs
I'm not much of a 'cable believer', so if I upgrade connectors or mains wiring, it will be purely because of esthetic reasons. Or am I wrong?

Thanks in advance for any comments and suggestions.
  Reply With Quote
Old 10th June 2007, 08:30 AM   #2
Nuuk is offline Nuuk  United Kingdom
diyAudio Member
 
Nuuk's Avatar
 
Join Date: Feb 2003
Location: Somerset, SW England
IMHO, and after trying most things, a simple GC is still the best GC!

Don't bother with BGs in a GC. Panasonic FCs and MUR 860's work well in a GC (although not necessarily elsewhere)

Solid core wiring for signal is fine (you don't need silver etc for those short lengths). Just keep it short and tidy.

Dual mono PSU is best with 37 volt rails (if you have 6-8 ohm speakers).

I prefer the PSU in a separate enclosure. I also prefer a non metallic enclosure for the amp.

Resistors - won't cost much so try what you fancy.

Zobel - won't cost much so try with and without.

:attn: One of the biggest improvments I got with GCing was to build a four channel amp and bi-amp the speakers.

Finally, remember that a lot depends on what goes before the GC! ie you may need an active pre or buffer stage.
__________________
The truth need not be veiled, for it veils itself from the eyes of the ignorant.
  Reply With Quote
Old 10th June 2007, 08:33 PM   #3
diyAudio Member
 
uncle_leon's Avatar
 
Join Date: Jun 2007
Location: Czyżeminek, near Łódź
Thanks for the response, Nuuk.

I forgot to mention 'preamp section' - I'm going to upgrade it to a simple Noble potentiometer - and probably leave it this way, until I'm stinkin' rich and can afford one of those fancy hi-end preamps

As to biamping - I was actually thinking about that, inspired by this crossover project. But for now, I think it's a bit too advanced for me :P Simple biamping is an interesting option though, especially that you say it brings significant improvement.

With signal wires - correct me if I'm wrong, but logically reasoning, a perfect signal cable should:
- have no capacitance (very important)
- have low resistance (quite important too)
- shield out any interference coming from higher voltaged wires/RF.
The first is achieved by insulating the core, with teflon being probably the best material to use.
The second is achieved by use of the best conductive material (i.e. silver); its thickness doesn't matter much as currents flowing in it are very low.
And the last can be done with braiding wires and/or shielding them.

With internal power wires, things change by 180 deg.:
- capacitance doesn't really matter much
- low resistance is prefferred, but not crucial
- fairly high current capability is important
- shielding is irrelevant as voltages are quite high
So, basically any copper cable of diameter, say, 0.75mm or more will do just fine.

This is how I thing wires work. Only thing I have no clue about is how does compare braided wire vs solid core one.
I know that braided are generally more flexible, they don't snap, and are easier to solder. But what is the trade-off? Is there any? I guess, there should be, and my bet was that they have higher capacitance than comparable solidcore. Can someone experienced shed some light on this, please?
  Reply With Quote
Old 10th June 2007, 10:05 PM   #4
Hartono is offline Hartono  Indonesia
diyAudio Member
 
Join Date: Nov 2002
Location: currently in China
Hi,

without active pre-amp the high frequency could be rolled off.

"shielding is irrelevant as voltages are quite high"

actually, the high voltage signal can cause interference with the small signal on the pcb and adjacent wire, but shielding is not very effective at low frequency.


"I know that braided are generally more flexible, they don't snap, and are easier to solder. But what is the trade-off? Is there any? I guess, there should be, and my bet was that they have higher capacitance than comparable solidcore. Can someone experienced shed some light on this, please?"

This one is tougher to answer and subject to some controversy, so I'll try to explain minimally .

Capacitance is practically the same with solid core, it's governed by cable geometry and insulation material. cable that's not paired (figure 8, twisted pair) have lower capacitance but higher inductance.
Extreme example is : ribbon wire (Goertz) have higher capacitance and very low inductance.

the problem with cheap cable is, in some condition (humidity) the insulation material can attack the surface of the conductor, causing oxidation and corrosion. PVC / PVDC is known to be very bad in this regard. with stranded cable, the corrosion will be terrible, much worse than solid core. Solution : don't use PVC/PVDC

http://ecmweb.com/ops_maintenance/el...ocating_swine/



Hartono
  Reply With Quote
Old 10th June 2007, 10:42 PM   #5
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
Default The most effective Gainclone upgrades

Some new music, and a bottle of something nice to drink whilst you listen.
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 10th June 2007, 10:42 PM   #6
diyAudio Member
 
uncle_leon's Avatar
 
Join Date: Jun 2007
Location: Czyżeminek, near Łódź
Thanks for a good point, Hartono. I actually forgot about inductance completely (it was one of the things about electricity, that I had trouble understanding, to be honest).

I've just read a bit about it on Wikipedia, and it seems to me, that, basically, inductance derives from resistance (i.e. higher resistance -> higher inductance), length and diameter of the conductor. But why then, coaxial wires have so high inductance (which makes them useless for audio signals, from what I heard)? I initially thought they would make very nice signal wires - shielded and all...
Ahh... I wish I had paid more attention to physics back then, at school :P

As to "actually, the high voltage signal can cause interference with the small signal on the pcb and adjacent wire", you are of course absolutely right. I felt it, sort of intuitively, and kept power wires separated from signal ones, while designing casing for my GC.
  Reply With Quote
Old 10th June 2007, 10:52 PM   #7
Hartono is offline Hartono  Indonesia
diyAudio Member
 
Join Date: Nov 2002
Location: currently in China
Hi,

tin plated cable might be ok with PVC/PVDC since tin is acid resistant. but the pvc/pvdc still can release gases and might affect other metal inside the equipment. Tin plating is the cheap solution.

inductance is the inverse of capacitance , coaxial cable has high capacitance, and relatively low inductance, not the other way around. some coax inner conductor is made from copper clad steel , steel is not good for audio (magnetic) and add distortion.

Inductance in cable is usually more benign in audio frequency, unless a "single" conductor/cable is coiled (inductor,coil, the name is self explanatory). if one of the conductor carry + signal and the other - signal(or ground) the inductance is lowered (example: speaker cable).

I notice you used nickel plated connector , some nickel plating contain iron (magnetic).


Cheers,
Hartono
  Reply With Quote
Old 10th June 2007, 11:11 PM   #8
Arx is offline Arx  Canada
diyAudio Member
 
Join Date: Aug 2003
Location: North Vancouver, B.C.
Quote:
Originally posted by uncle_leon
I've just read a bit about it on Wikipedia, and it seems to me, that, basically, inductance derives from resistance (
Nope, they're not tied together.

If you think of capacitance as being a resistance(impedance is a better word) to a change in voltage, you could think of inductance as a resistance(impedance) to change of current.

So, as a rule of thumb, capacitance is going to be more of a problem for low level (voltage based) signals, since a certain amount of the signal energy is going towards discharging and recharging the capacitance. Inductance doesn't really matter, since the current flow is so small.

For high level (current based) signals like speaker outputs, inductance will be more of a problem, since a lot of energy is taken trying to reverse the high current flow back and forth. Reasonable amounts of capacitance are easily swamped by the high current output.

There are, of course, exceptions. This is a very simplified description.

-Nick
  Reply With Quote
Old 11th June 2007, 12:10 AM   #9
diyAudio Member
 
uncle_leon's Avatar
 
Join Date: Jun 2007
Location: Czyżeminek, near Łódź
So, what you mean is that braiding the signal wire - like I did - in Litz fashion is no use for signal wire? And that it would be actually better idea to use single, widely spaced wires, in order to get the least capacitance possible?
  Reply With Quote
Old 11th June 2007, 12:57 AM   #10
diyAudio Member
 
uncle_leon's Avatar
 
Join Date: Jun 2007
Location: Czyżeminek, near Łódź
Sorry for double posting, but why 'edit' feature on this forum is limited to 30mins after posting?...

Anyway, I was thinking about what Hartono said, regarding possible hi-freqency roll-off with passive preamp. And I think I found the perfect solution - a stepped attenuator. I found one, based on Vishay 1% resistors, for as little as 50AUD (yes, it is in Australian dollars and no, I have no clue as to how much would it cost to post it from there). I think this kind of solution will be quite hard to beat, even for good quality active preamps.
  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
Effective mass?? dario54 Analogue Source 6 6th August 2008 07:40 PM
effective mass IZHAKKATZ Analogue Source 6 6th August 2007 08:48 AM
What's the effective delay ? Will Multi-Way 8 26th March 2006 06:45 AM
Cost effective upgrades Pan Solid State 4 9th April 2003 12:09 AM


New To Site? Need Help?

All times are GMT. The time now is 08:32 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