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Beginner DIY Amp
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Old 26th August 2015, 06:46 PM   #1
blizznasty is offline blizznasty  United States
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Default Beginner DIY Amp

Hey all,

First disclaimer: I'm aware there are other "Beginner" threads. However, many of these are years out of date. While that may not seem significant, sometimes website links changes, designs and kits no longer supported, or new designs come along. Additionally, the needs/wants of the builder, as well as their budget, can vary dramatically.

So without further ado... what would be a recommendation for a good DIY amplifier for a beginner?

For the "Why," I have never heard the "tube magic" in my system and I think I would find it desirable. Qualities I've heard imparted to tube systems are the natural timbre of instruments, the "air" and spacing of instruments, excellent soundstaging and "musicality."

For the "What," My speakers are of moderate efficiency (92 dB), my listening space is large, 25x15x10, volume levels are low to moderate, and music style varies from indie folk to classic rock to pop to electronica to hip hop.

Regarding "How," well, it gets a little convoluted. I have a SS integrated 50 wpc amplifier which has ample power to drive my speakers. What I feel is lacking is clarity, cohesiveness, realism and engagement of the listening experience. I was considering a tube preamp to my integrated SS as a power amp. Alternatively, I've considered a tube integrated amp. However, I would estimate I need at least 8W, perhaps more, to power my system to listening levels I am accustomed to.

As far as price is concerned, the target would be $250. The maximum budget would be $500. My ability to read circuit diagrams is well above average, although my soldering skills are about 10 years rusty. My access to tools (such as a lathe) is limited, so my capability/desire to punch holes in an aluminum chassis is low.

Thanks.
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Old 26th August 2015, 06:57 PM   #2
vinylkid58 is offline vinylkid58  Canada
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Have a look a Pete Millett's DCPP amp board. There's also a big thread here on diyaudio, you just have to search for it. You'll need a preamp with some gain to drive it, whether it's SS or tube.

jeff
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Old 27th August 2015, 12:43 AM   #3
Eli Duttman is offline Eli Duttman  United States
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An "El Cheapo" wired ultra-linear (UL), instead of triode, will yield approx. 12 WPC. Any 6V6 family tube works with parts values shown. Nice 6V6s are being produced currently. The 6CM6 is a low cost NOS type, but you have to lay stock away.

Magnetics have never been truly inexpensive and the run up in the cost of copper, etc., over the last few years has made the situation worse. To stay "close" to a $250 total cash outlay, use Edcor's CXPP25-MS-8K O/P transformer. A complete set of power "iron" can be ordered from Allied, for under $100.

No preamp is necessary, if a "standard" CDP is the signal source.

Jim McShane sells kits of parts suited to execution of the project.

BTW, I suggest that triode/UL mode switches be part of the build. Triode is "more refined" and 6 WPC is enough for stuff like a small Jazz combo or a string quartet.
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Old 27th August 2015, 07:25 AM   #4
petertub is offline petertub  Sweden
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Beginner DIY Amp
Have a look at "dynakitparts.com" where modern replicas of dynaco amps are avail.

The only integrated dynaco is SCA35, which may be built as kit , or found at places like ebay. If you go pre-amp/power amp route your choices are larger.
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Old 27th August 2015, 08:46 PM   #5
blizznasty is offline blizznasty  United States
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Thanks for the suggestions. Is there any calculator or rule of thumb for predicting listening levels, based on speaker sensitivity, output wattages, and room size? I have heard that tube watts are bigger than SS watts. I would hate to build an amp that is too low powered for my needs. (I would rather not also build/purchase high efficiency speakers... I need to stick to one project at a time).
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Old 27th August 2015, 09:24 PM   #6
Eli Duttman is offline Eli Duttman  United States
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Quote:
Originally Posted by blizznasty View Post
Thanks for the suggestions. Is there any calculator or rule of thumb for predicting listening levels, based on speaker sensitivity, output wattages, and room size? I have heard that tube watts are bigger than SS watts. I would hate to build an amp that is too low powered for my needs. (I would rather not also build/purchase high efficiency speakers... I need to stick to one project at a time).
A watt is a watt, regardless of the technology used to obtain it. What is different between tubes and SS is that you can safely take a tube amp up right to the point of clipping. SS amps clip hard. Hard clipping damages tweeters. Tube amps compress, before hard clipping sets in.

Paul Joppa has provided us with a useful rule of thumb for mating amps to speakers. Joppa's Rule states that in listening room of "typical" volume, each channel of an amp/speaker combo should be capable of producing 102 dB. SPL peaks at a 1 M. distance. Adjust up or down, depending on room volume and listening habits.

You stated your speakers are 92 dB. sensitive. What is their nominal impedance? Can you provide a link to the impedance curve of the speakers?

Speaker manufacturers provide specifications that make them look good. Remember, 2.83 V. into 4 ohms is 2 W., not 1 W. and such a claimed sensitivity has to be derated by 3 dB. Another reason for derating speaker sensitivity is large dips in the impedance curve, particularly in the deep bass region. A tube amp's power O/P does not "double", when switched from 8 ohms to 4 ohms.
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Old 27th August 2015, 09:55 PM   #7
blizznasty is offline blizznasty  United States
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Eli,

I have requested the impedance curve from the manufacturer. If they furnish this, I will provide it. Based on the limited information currently available on their website (https://www.aperionaudio.com/manuals...GrandTower.pdf), they are 6 ohm nominal impedance. And prior to looking it up, I would have sworn they were 8 ohm.
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Old 27th August 2015, 10:15 PM   #8
petertub is offline petertub  Sweden
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Quote:
Originally Posted by blizznasty View Post
Eli,

I have requested the impedance curve from the manufacturer. If they furnish this, I will provide it. Based on the limited information currently available on their website (https://www.aperionaudio.com/manuals...GrandTower.pdf), they are 6 ohm nominal impedance. And prior to looking it up, I would have sworn they were 8 ohm.
A tube amp, an sca-35 for instance, has several taps on the
output transformer where one can select the best matching impedance.
If your speakers are 8 ohm, choose the 8 ohm tap and let the amp deliver
it's full capacity.

Transistor amps on the other hand are designed to drive 4 ohm, when used with 8 ohm speakers you loose power.
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Old 27th August 2015, 11:40 PM   #9
blizznasty is offline blizznasty  United States
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Default Impedance Curve

Found an impedance curve for my speakers. (Source: Aperion Verus Grand Tower Overview and Measurements | Audioholics)

Looks to be a 4 ohm dip in the ~100 Hz range.
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Old 28th August 2015, 02:17 AM   #10
blizznasty is offline blizznasty  United States
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Quote:
Originally Posted by Eli Duttman View Post
A complete set of power "iron" can be ordered from Allied, for under $100.
I'm assuming this refers to a soldering iron? Are you suggesting my $20 RadioShack soldering iron (which I lost in my recent move) isn't adequate?

My concern for any build is the enclosure. Either woodwork or metalwork sounds somewhere between difficult and untenable in my current situation.
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