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Old 24th June 2013, 03:48 PM   #21
Vostro is offline Vostro  South Africa
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Search for Apex B500

Maybe you can make it suit your needs

Last edited by Vostro; 24th June 2013 at 03:51 PM.
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Old 24th June 2013, 03:59 PM   #22
brlmat is offline brlmat  Romania
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Yeah, I saw it, tho haven't heard much about it.
The idea is that I am pretty new to amps. I have actually built 3 so far (10, 15 and 50 watt). I know I need more power but I am not experienced enough to make a decision.

Any info abiut the amp and sound quality is taken into account and thanked for.
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Old 24th June 2013, 04:55 PM   #23
Struth is offline Struth  Canada
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Hi Guys

If forced to build a single amplifier per channel, I would choose either the low-TIM Leach - not the Double-Barrel - or the Blameless (Doug Self's refined circuit) version of the Lin, and just increase the rails and use modern output devices and drivers - but more of them.

Both topologies are well-proven and easy to build. Mosfet amps that are as simple in form as these do not provide as good performance. There is a lot of performance information available for both of these circuits, not just anecdotal evidence that "it sounds okay".

If your speakers are truly power hungry, you might consider expanding the project to bi-amp them. In this way, you can use a solid high-power amp for the woofer and a better quality unit for mids and treble. Doing this also allows you to exercise an option for the woofer amp inasmuch as it can be built as a bridge amp running from lower rails. Where the 250Wrms requires a peak signal of 64V at 8R, requiring +/-80V rails, as a bridge amp you achieve this output with +/-40V rails. That same supply level provides about 60Wrms or so for the mid-treble range, where you need a lot less power.

Bridge amps can be built in a dedicated fashion with one input and balanced outputs, or simply as two identical single-ended amps with an inverter between the inputs. The latter format is more popular and easier to fix if there are problems. Bridging eliminates the need for very high voltages although the output devices may end up being the same types as the ones people gravitate to are a small group.

The mid-treble range can be passively crossed over within itself, or further split to be separate amplifiers. The two-way active crossover between the woofer and mid-treble range would become a three-way active with separate, woofer, mid and treble outputs.

Have fun
Kevin O'Connor
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Old 24th June 2013, 05:18 PM   #24
brlmat is offline brlmat  Romania
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I already have a 2x 50 vac transformer so I'll to with a single amp per channel and my woofers are just woofer, not subwoofer. I will build a pair of subwoofers later on anyway. I need a 200-250w amp in 8 ohms which sound very good. I'll be driving a pair of 80-20000 hz speakers. Subs will go 15-150-200hz.

Please elighten me. Which topology is better and which ine is better implemented?
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Old 24th June 2013, 06:12 PM   #25
Struth is offline Struth  Canada
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Hi Guys

Note that most "sub" woofers are in fact just woofers in a separate box to allow the satellites to be small. The use of a single bass box is a major design flaw.

Bi-amping has nothing to do with sub-frequencies, rather it allows a substantial decrease of system distortion by replacing the passive crossover in the speaker box with an electronic crossover working in the small-signal domain. The necessity of requiring extra amplifiers is balanced by the fact that the largest of those can be low quality.

Bi-amping itself is a generic term that originally meant using two amplifiers for the low frequency range and for the high frequency range. Where the crossover occurred changed over the years, and the "bi-amp" term has come to mean using an active crossover and separate power amps for any number of ways. So, you can separately amplify your sub, then electrically split the main cabinet into two or three ranges itself.

The Blameless designs have more data to support their performance ability and are based upon the use of unmatched devices. Easily expanded in voltage and output pair numbers for any power required.

Have fun
Kevin O'Connor
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Old 24th June 2013, 06:21 PM   #26
brlmat is offline brlmat  Romania
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Look, I have two 80L satelites with eminence alpha ( or beta, I can't remember) 12 woofers, jbl selenium 6w4p midwoofers and jbl selenium st200 tweeters. The eminence speakers don't go so low in frequency but I have 2 other subwoofers ( 15mm xmax) for which I am going to build active enclosures. For the satelites I already have passive diy crossovers. So I am just looking for an amp to drive the two satelites. No bi-amping, just a single amp per channel. I have everything except the actual amp modules.
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Old 24th June 2013, 06:41 PM   #27
Struth is offline Struth  Canada
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Hi Guys

Brlmat, try re-reading the last paragraph of post-25.

Have fun
Kevin O'Connor
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Old 24th June 2013, 06:47 PM   #28
brlmat is offline brlmat  Romania
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Please be more specific. I do not know anything about this "blameless" design you are talking about.
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Old 24th June 2013, 07:40 PM   #29
Struth is offline Struth  Canada
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Hi Guys

If you search the term "blameless" here, or on the web for "blameless amp" you'll see references to Douglas Self's fine tuning and explorations of the modified Lin amp - the essence of most amps on the market.

All BJTs: diff-amp with emitter degeneration, with tail current source and current mirror load, feeding buffer then VAS which is current-source loaded, then into EF or CFP output stage. EF can can be Locanthi-T style for best performance, made further into a triple.

For your needs, two output pairs as a minimum, preferably three or four pairs to assure low stress of the outputs. Use MJL1302A/3281A or MJL21193/94 pairs or similar for outputs. Use 2SA1837/2SC4793 or MJE13034/35 drivers or similar. The MJEs could be used as drivers with the 2SA/2SC as predriver.

Small signal BJTs have to handle 100V+ for the diff stage, mirror, diff current source, buffer, and 200V+ for VAS, VAS current source, and predrivers. MPSA42/92 will work in all of these positions, but the diff-amp can be improved if it is cascoded. This in itself will reduce common-mode distortion, and also allows higher-beta devices for the actual inputs.

Built a similar 250W/ch amp in the early '90s, using MPSA42/92s, and power devices of the day running from +/-85V. Added SOA protection and DC protection for the speaker. There was basically zero offset voltage with no parts matching.

Back in the day, built my own speakers and wound the coils for the crossover. Dumped that as soon as I heard the benefits of bi-amping.

Have fun
Kevin O'Connor
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Last edited by Struth; 24th June 2013 at 07:42 PM.
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Old 24th June 2013, 09:35 PM   #30
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I have built the Leach Low TIM and am just finishing the Leach Superamp (Double Barreled). Good thing about them is they use easily available parts and not much matching needed. Drawback is there are no PCB boards available. You will either have to etch your own of have them made. I have been looking at the DX Blame and similar but from what I can tell there are no boards available for them either except from ebay which I am told are pirated. The Low TIM is a very good sounding amp, and from what I can tell, so is the Superamp though I have only played it through jumper wires so far. I will know better in about a week when I hope to have my case built. I am running the Superamp on a 55-0-55 800VA transformer which is giving me about +/-90VDC rails. They sag to about +/-88V when playing. The Low TIM is running +/-65 rails.s It can get quite loud though.

Look at the DX Blame thread for a lot of detail about that amp. I hear they are trying to get some boards available for folks outside Brazil.
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