how would i go about making a new passive preamp design

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hi my name is diederick kavelaars.

I have been interested in making amps for a long time and have desided to build the leach poweramp (double barreled) at 300 w. Now since I do not own a tapedeck or a phonograph I will only be using this amp with my computer. Having said this I think this would provide me with enough power to blow the windows out of my room using the speakers I have, bang & olafsen (4-8 ohm,87db,20-120W) the only thing I am still looking for is a good passive preamp. I do not like the zen family because in conjunction with the leach low tim amp and thus the double barreled one as well create a slight hum. This is something I want to avoid. therefore I was wondering how I would go about designing the following.

A passive preamp, incorporating hte following:
-Volume control
-source selector 4x (aux)
-outports 4

Bass treble in a 5 or 7 band equaliser (in case of 5 band 100hz 300hz 1khz 3khz 10khz)in case of 7 band I don't know.

The only other requierments are that it should not create a buz hum thumb click at trun on/off, that it should be as fast as a ferrari and it should be compliant with the double barreled leach amp.

about which I have some questions as well. following here.
i would like to hook up some 8 speakers 2 subwoofers and 6 4way's. i understand this is somewhat ambisious but can i do this or would i be advisable to build two amps and biamp or build two and run subs and 4way's separate.

I have some electronics qualifications but when it comes to designing this new preamp i am feeling in the dark and about the speeker setup, one or two amps i am curious about your oppinion.

I realise this is a lot of questions all at once but i am dying for information as i have a lot of free time on my hands now. love to hear from you and what you think of my project.
You say you want a passive preamp, but it sounds like you want an active one. You need to sit down and think that one through.
I'm not clear on how you got the idea that any of the Pass designs hum as an inherent part of their design. It boils down to one of two possibilities: Either the preamp wasn't built properly (in particular, I'd suspect the power supply of passing ripple through to the gain stages), or there's a ground loop. Ground loops can happen in any system, regardless of what design you use for the preamp.
Tone controls won't be common because they tend to have deleterious effects on the sound; most people leave them out. That said, there are a few designs out there on the web--you'll just have to hunt for them. Another option would be to add tone controls (probably Baxandall) to a pre-existing preamp circuit. Not too dificult.
Depending on your intentions, meaning whether volume or sound quality is more important to you, you might consider different speakers. B&O aren't exactly top of the heap as far as sound quality goes. If it's quality you're after, you'll get more bang for your buck with new speakers. If it's volume you're seeking, ask yourself if the B&Os play loud enough to suit you, then proceed from there. As a general rule, PCs aren't regarded as the best sources for high fidelity sound, but it may be adequate if you're wanting volume or simply don't have enough room for a CD player.

grey, you are right i should have been more spesific.

what i mean about hum is when using a BOZ preamp in conjunction with the double barreled leach it creates a hum, as i read elsewere on this board that's why i wanted to go for a passive preamp. and i am not particularly fond of the BOZ circuit wise.

I want to go for quality so want to avoid any hum. do you think i could do without a preamp alltogether? and incorporate a digital volume dail in my leach amp?
furthermore what do you think about putting a 5 band graphic equaliser in it as well, one i suggested in my first message.

The b&o speakers suit me just fine, the power they supply is too much for the people i am living with right now so increasing them would be kind of useless even if i wanted to. i can only put my current amp up to 2 otherwise it becomes to loud. (current amp technics SA 202)

Diederick said:
when using a BOZ preamp in conjunction with the double barreled leach it creates a hum, as i read elsewere on this board

I'm not sure where you read this but as Grey said there is nothing inherent about this combination that will cause hum.

There are a few other flaws in your requirements:
- inputs for 4, but you'll only be using your computer as a source?
- building a 300W amp for speakers that can only handle 120 watts?
- passive preamp with tone controls? You'll lose too much gain, won't work.
- 2 subwoofers and 6 4-way speakers? Running from one stereo amp?
Why don't you just use the volume control on your sound card, controlled from the computer, and drive the Leach amp directly? No preamp necessary. Maybe your sound card can support a digital graphic equalizer too.
I think you're being too ambitious here. Start slowly and simply and refine your requirements as you go along.
you are absolutely right paul, i have just come to the same conclusion from the email i got from geoff

that was what i was thinking to discarding the preamp alltogether.

i wanted to build a 4 in/output because i might someday have cash to hook up other devices other than my computer. same goes for the leach amp, someday i hope to have enough cash to buy or build some better higher watt that case i would have to build a new amp for my new speakers, and you are right that is too much speakers for one amp thats why my question was if i build two should i biamp or run separate amp for four speakers each, what do you think about that. biamp or separate?

thanks for the feedback, much appreciated. if you have any other insights i would love to hear hem.

The more specific you become, the murkier things get. I'm not sure I understand why you want such a large amp when you can't play 'beyond 2' because of the people you live with. My comments about the B&O speakers weren't because of 'the power they put out,' but because of the (lack of) quality of the sound. It sounds as though you need a smallish amp and better quality speakers, possibly with a new front end. You won't notice much (if any) improvement from the Leach amp with your current setup.
Assuming that I've understood what you're saying, I believe you'll be disappointed if you follow your current course.


hmm ok so you say the b&o speakers are not up to scratch. i guess that could be true, what would you reccomend for speakers if i desided to build the leach. and as you suggessted the other one then 120W low tim one.

i want to build the leach because i am not going to live here forever and because i blew up my other amp sucked too much out of it i guess to many speakers connected or something that was a 360W amp or at least that is what it sais. the reason i want a strong amp is that I slach we enjoy a good house party here now and which get rather loud. but that is not what i am going for, quality

so to sum up the stuff
smaller amp w if staying with current speakers if not better speakers with higher w so to use amp to full potential, what kind of speakers would go well (quality) with leach double?

kind regards diederick

you have to excusse me for the bad english sorry
Just for refference this is the thin about a leach and a BOZ creating ahum took me a while to find it again.

Questions about Leach Amp & Preamp
DIYaudio Acolyte

Registered: Oct 2001
Posts: 13


Exactly what I am using now, ie Leach + BoZ. Can say without hesitation, they sound great together. A bit of hum/buzz though, if you place your ears within a foot or so from your loudspeaker. At normal listening distances (> 3 feet), even in a quiet room, no noises can be heard. The Leach is completely silent by itself.

I also have the opportunity to listen to the NAD 3020i extensively. It's a nice integrated, but lacks the muscle. The Leach has more than enough power, and can drive even highly capacitive loads. BoZ, what can I say? Simple is BEAUTIFUL! I build the BoZ in 2 hours (minus etching the board which was done the day before). Look into my posting in the Bride of Zen thread for further info.

Have fun!
House parties carry an entirely different set of expectations from a system set up for good listening. Yes, you'll need lots of power, I suppose, but whether the Leach is the right amp for that application is open to question. One thing you'll need to keep in mind--you'll need plenty of heatsinking regardless of what circuit you use.
If you're going for party mode, don't put money into good speakers. You might even consider pro sound gear, meaning PA speakers. Something that's going to put out a lot of sound and (hopefully) be reliable. Good speakers are far too delicate to use for parties.
You're going to need to make a decision. It's either party or serious listening. If you have even an occasional party, you're going to need to go a different route. It might be cheaper to buy a used PA amp and speakers than to go the DIY route, the majority of which is dedicated to good sound quality. I'm sure there are pro-style DIY amps out there somewhere, but I don't know where to point you as I've never had any interest in building one.
Good luck.

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.