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Old 26th February 2010, 07:43 PM   #1
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Question Gainclone preamp

I've searched around a bit on the message boards to find some solid information, but mostly I got pointers to dead links, etc., so I'll post a question here which may have been answered many times over.

I'm new to building hi-fi amps, although I've built a few guitar amps, and I'd like to build a gainclone amp with a preamp housed in the same enclosure so I can switch between phono and CD. It would also be nice to have the option of tone/balance controls and maybe even a tape input, but those are not necessary.

Do you guys have any pointers as to where I could find out about how to implement this? I've already found some great sources about building the gainclone amp itself, but it's the preamp and how to integrate it I'd need help with.

Thanks!
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Old 27th February 2010, 01:16 AM   #2
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What IC are you going to use?. I build the LM3875/LM3886 and in the LM3875 (AudioSector)I just add a 25k potentiometer and an input selector and I got an integrated amp that rocked.
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Old 27th February 2010, 01:18 AM   #3
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I too am looking for designs\boards for a good tone circuit.
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Old 27th February 2010, 02:30 AM   #4
mikje is offline mikje  United States
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A Velleman K8084 will give you volume, bass, and treble, but no balance. It's a nice addition to an amp. I built a Velleman amp and added this preamp and am very happy with it. As far as a selector switch, I believe a simple DPST switch will work. The CDP on one pole and the phono on the other, with the "throw" connected to the input of the amp.
You can find the preamp here: www.tequipment.net
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Old 27th February 2010, 08:06 AM   #5
Nuuk is offline Nuuk  United Kingdom
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Building a pre amp for a Gainclone chip amp.
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Old 27th February 2010, 05:25 PM   #6
dukep is offline dukep  United States
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Default some tone ideas

In research for my tone circuit in the Stereo 80, I came across some interesting ones.

Audio Tone Controls
The James-Baxandall Passive Tone-Control Network

***very cool program for tone circuits, passive type
Duncan's Amp Pages
Software


I rather much like the passive types for simplicity. I chose the active type, but intend to have a easy configure option in rev 2 of my board for passive. (doable now, but components must be adjusted).

Active types can turn into oscillators if not careful. I had to add 100pf, Cf, from output to (-) in on the op-amp, ne5532a. Appears true with the high end lm4562 also, but not so with tl072 or lf353.
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Last edited by dukep; 27th February 2010 at 05:28 PM.
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Old 27th February 2010, 07:29 PM   #7
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So: I will purchase the Audio Sector LM3875 amp kit and something like the Velleman k8084 preamp kit. Now, I'm guessing I would need to integrate a phono preamp as well in order to play records.

How would I work it so that regardless of what input is selected (CD or Phono), the volume, treble, and bass controls on the Velleman preamp work properly? It seems like the DPDT switch would flop between the two preamps. Is that right?

Again, I'm a bit of a noob, so forgive me if this is the kind of question that makes you slap your forehead.
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Old 28th February 2010, 02:34 AM   #8
dukep is offline dukep  United States
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Default preamp

Look at the config's on some of the Rod Elliot stuff. His well of information is infinite.

Check out my stereo 80 schematic, perhaps the circuits here can help. info at dukecreations.com

This kit may do what you want with the 2 input paths that are gain adjustable. It also has a 2 op-amp phono stage on the preamp board (yet most don't really use it). And of coarse, treble and bass tone control, etc. and,, biamp,,, with 40w/ch stereo out on the other side.
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