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Old 21st November 2006, 04:47 AM   #21
Nordic is offline Nordic  South Africa
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I dissagree.. I believe more actual options/finer tuning can be done with just bass/treble adjustment as opposed to 3 tone controls.
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Old 21st November 2006, 05:01 AM   #22
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Nordic,

If you were to have a 3 way tone control, the mid having a sweep control as well, you can actually voice a system.

However, since the voicing and balance of bass/treble and the rest of the band has already been equalised in the studio, hi-end systems do not resort to such bells and whistles.

Yes, you would need a tone control for guitar cubes and other live music equipment.
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Old 5th March 2007, 03:52 AM   #23
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Quote:
Originally posted by Minion
The Power supply I use has a Regulated +/-15v and unregulated +/-24v useing the LM317/337 regulator chips.....

The supply was originally designed for Mic preamps but I changed the design so I could Run a LM3886 Chip amp and a Opamp Based +/-15v preamp from it, I just removed the Phantom power circuit and I modified it so I could have More PSU filter caps and just took the Power off the PSU before the regulators but after the Filter caps for the Unregulated 24v rails.....

I have a PCB and stuffing guide for this PSU if you want it?? Let me know and I"ll post it for you.....
Possibly stupid question- I'm building one of the BrianGT kits and was looking at adding one of these buffered preamps as well:

http://myweb.tiscali.co.uk/nuukspot/...nclonepre.html

Like the previous poster, I'm wondering if I can double-purpose the PSU for the Gainclone itself. The preamp calls for LM317/337 regulators and an 18V PSU, while I was going to use a 25V transformer for the amp. The amp's PSU looks like this I believe:

http://www.chipamp.com/images/ps-rev3-sch.gif

Without having to reengineer the whole thing, is it possible to just siphon power off the transformer at 25V and feed that to the preamp and have the 317/337 chips regulate it down?

The toroid I'm looking at is the Avel 250VA 25V+25V seen on Parts Express which has dual secondaries. If I was going to tap power off of this for the preamp, would I use one pair of the secondaries for that, and another for the power amp, or would I want to do something different?

Thanks in advance!
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Old 5th March 2007, 04:20 AM   #24
Minion is offline Minion  Canada
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Well the short answer is "Yes", (So is the long answer)......

You would probably have to add a Small PCB with the Regulator chips and a couple caps and resistors and just take a Lead from the Postive and negitive rails of your Gainclone PSU to the Regulator board and feed the Preamp from that.....

It would be a Bit too difficult to add the Regulators and related Parts to an allready existing PCB but you could build a seperate board for the regulators...

Or you could simply use a PSU that allready has Regulation for the Preamp....I could post the one I use for you if you wanted to etch your own PCB.....


Cheers
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Old 5th March 2007, 08:00 AM   #25
Nuuk is offline Nuuk  United Kingdom
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A 25 volt transformer will supply around 37 volts DC after the rectification. If you use the LM317/337 regs to drop that supply down to around 21 volts, you will need to use some pretty hefty heatsinks, and even then, those regs will get very hot!

The other consideration here is sound quality (we are presumably talking hi-fi and not lo-fi). The preamp supply will be modulated by the demands of the power amp section. How much you will notice that depends on how good your system is and how critical you are with your listening.

However, given the cost of a small transformer and rectifier bridge etc, I honestly suggest building a separate supply for the pre amp section.
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Old 5th March 2007, 10:15 AM   #26
owen is offline owen  United Kingdom
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Alternatively an interesting low current drawn op-amp buffer with a battery supply would do the trick - lots fewer componants, and easier to get 'right'. I've used OPA627, 637 and the venerable LF353 with great success in the past

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Old 5th March 2007, 06:21 PM   #27
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Quote:
Originally posted by owen
Alternatively an interesting low current drawn op-amp buffer with a battery supply would do the trick - lots fewer componants, and easier to get 'right'. I've used OPA627, 637 and the venerable LF353 with great success in the past
Owen- any recommended designs you'd point to? I'm all for simple, as I can always go back and build something more intricate after I become more comfortable.
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Old 5th March 2007, 09:06 PM   #28
owen is offline owen  United Kingdom
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My Gainclone/buffer

http://www.freewebs.com/gaincloner/images/1-picture.gif

left hand side - LF353 buffer, right side LM3875 gainclone. Both inverting net phase shift = 0.

Piccies of its guts

http://www.freewebs.com/gaincloner/page5.html

Now this site has big pics behind the little ones - just click through if you have ADSL...

Alternatively

http://www.freewebs.com/gaincloner/

This is my normal site for those whose line speed isnt great. You still get a flavour of what's what though.


Have fun, and check out the LCC (Low Cost Case) - you should be able to make a nice box for less than 5 if you're careful in your scrounging



Owen
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Old 7th March 2007, 11:34 PM   #29
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Owen, thanks for the link. A few more questions from the Stupid Club:

1. I'm building the gainclone dual-mono style. Do I need two preamp blocks, one for each channel?

2. Does it make any difference to the preamp if the gainclone is non-inverted? (OK, make that an *important* difference)

3. This page shows a bank of caps and a rectifier. I assume this is for use with a line PSU. If I do a pair of 9V batteries like you did, do I just wire the two batteries in series and feed the power straight to the op-amp chip?

4. Coming off a stereo plug (like an iPod or PC sound card), I have three outputs, right? Left, Right, and common. Which goes where on the schematci I linked above? Yeah, I know, DUH.

5. Any minimum recommendations for the resistors in terms of wattage?

6. The schematic is captioned, "Overall phase is non-inverting. Please remeber when wiring speaker outputs if whole circuit is used." It sounds slightly ominous, but aside from that I have no idea what it means.

Any answers greatly appreciated
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Old 8th March 2007, 06:47 PM   #30
Nordic is offline Nordic  South Africa
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A little capacitance won't hurt... I would still keep at least 10uf infront of the chip.. even with batery supply. You can get very good low esr caps in these low voltage ranges, for reasonably cheap (compared to larger values).

I experiment quite a lot with diffirent chipbased headphone amps, and in most cases I like at least 470uf to 1000uf at the battery, with 10uf closer to chip bypassed with 10nf at the pins themself. Any breakup in bass peaks will probably turn out to be too little capacitance on the big cap. However going too extreme on the value is also pointless and can have diffirent effects from makeing the opamp shrill to dull. With a good quality cap you fill see that less is more.
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