# Little Side Project



## BoomerangJ (Nov 25, 2012)

I thought I would seek some advice on a fun little project that I am about to undertake.

Way back in the late 70's I did what I could to have as good a stereo as I could afford. After college I picked up a Nakamichi BX 125 Cassette deck and Technics Turntable-powered by an A1000 Yamaha amp. I also kept all my albums. I played the albums once-made cassettes on the Nakamichi and only played them on the cassettes. Stored them correctly-so the albums should be good to go. The speakers were Cerwin-Vega 312's. (never cared a lot for the speakers)-but they did play loud!

Here's my little project:

-My home office has just been re-modeled and it has an industrial tech look. There is a big iron credenza that I can set the amp, take deck, and turntable on.

-I will need to get a new drive belt on the Nakamichi-but expect it will work well. Of course I need a new cartridge for the turntable.

-I just ordered Infinity Primus 363 speakers. This is an indicator of the budget I'm trying to spend-> Small. But the reviews that I have read on these speakers are really good. Paid $400 for the pair.

-The main missing piece is the Amp. I kind of wish that I had the old Yamaha A1000 back. But at the same time I've always lusted for a tube amp. I see that there are all kinds of companies out there that have re-engineered tube amps-but the reviews are a real mixed bag. I'd love a Marantz tube amp-but those are priced a little too collectible for me. I'm not trying to be a collector-but if I fond one-that was reasonable I'd be all over it as well. Not sure what reasonable is. And their might be better solutions out there. Part of the motivation is that an exposed tube amp would look cool with the decor. (I'm speaking for my wife-I'd be happy with a black box amp! but she surprised me with this office and I must say she blew me away with it-so I need to respect her decor choices and when I showed her a picture of a tube amp-her response was Wow! that would look cool in there!). 

My questions are two fold:

1.) This is probably too much sentimental-as in dusting off the old equipment that was never really that high end. Am I wasting money? Back in the day I wanted the Nakamichi Dragon-but could only afford the BX125-you get the picture.

2.) Amps-any recommendations on something that would pair up nicely with these components?

Again this is intended to be a fun system in my office to occasionally play the vinyl, make some cassette tapes (can you even buy cassette tape anymore?). But sound as nice as it can.

Any comments, various emoticons, ideas, links to products are welcome!


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## dgmartin (Oct 29, 2011)

I consider this Primus line of speakers to be amongst the few listenable ones in their price/size range. 

However, these speakers are not as sensitive as they claim and the impedance reaches just below 4Ohms - likely results from the two bass drivers in parallel. Generally speaking, the huge impedance swings does not make it a tube-friendly speaker due to the amplifier's output impedance (the speaker impedance peaks will be reflected into increased speaker's response at those frequencies). Without getting specific, there are tube amp designs that are better at alleviating this issue. If you go the tube amp route, try to select the lowest internal output impedance and make sure you have 4-Ohm binding posts - also often called output impedance (i.e. multiple output TX secondaries). 

Hope I'm not confusing things or steering you away from tubes, this is not my intention.

http://www.audioholics.com/tower-speaker-reviews/primus-p363/primus-p363-measurements


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## BoomerangJ (Nov 25, 2012)

dgmartin said:


> I consider this Primus line of speakers to be amongst the few listenable ones in their price/size range.
> 
> However, these speakers are not as sensitive as they claim and the impedance reaches just below 4Ohms - likely results from the two bass drivers in parallel. Generally speaking, the huge impedance swings does not make it a tube-friendly speaker due to the amplifier's output impedance (the speaker impedance peaks will be reflected into increased speaker's response at those frequencies). Without getting specific, there are tube amp designs that are better at alleviating this issue. If you go the tube amp route, try to select the lowest internal output impedance and make sure you have 4-Ohm binding posts - also often called output impedance (i.e. multiple output TX secondaries).
> 
> ...



I really appreciate your reply. I probably pulled the trigger too soon on the speakers. I had read a review on absolute sound that raved on them and then a few other good reviews and thought why not. The review you linked me too explains the "inner workings" and I did understand most of it. Sounds like the issue is the quality/consistency of the components leading to a bit of variability in the measurements. Thus the price.

Just before I saw your reply to my thread I was following a thread in this site on the Rogue Audio Cronus Magnum. That tube amp sounds like a good target to go after. I've been away from this hobby so long that it's going to take some time to learn. That's why I love this site. The You Tube video review 



 taught me a few things. Setting bias on a tube amp was a little confusing to me before this video. 

Sounds like you might know a thing or two about tube amps. What are your thoughts/recommendations? The Cronus Magnum is at the upper limit of what I would want to spend. This amp can set up to support 4 Ohm speakers-it was one of the reviewers cons as you have to go inside the cabinet and change out the tap wires-but I can do that.

What do you think about going the route of a tube amp with the old turntable and the Nakamichi? I might upgrade the turntable as well over time. What about any of the tub amp kits out there? I think skill wise I could tackle it-but only if the time spent on building will get me something that is of value.


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## dgmartin (Oct 29, 2011)

About the impedance, I was not really pointing out at the differences between the two speakers but the fact it is not flat. One fun thing you could do is get 8x 1Ohm, 10W resistors and put them between a solid-state amp and the 363 to see how the sound is affected by different output impedances.

I won't comment the review. I would never spend that kind of money on any amplifier. One thing strange is the two OTX are aligned and in close proximity, which is a no-go in theory. Tube amps are interesting/rewarding as a hobby but you don't get a lot of sound for your money buying finished products. Building it you find out that a lot of the money goes into the chassis and aluminum faceplate/remote. 

Kits are a good option since you only do the fun part (i.e. no part procurement from different suppliers). There are tons of kits available, a ST-70 kit would cost you about 1/3 the price and is a classic/proven design. The RCA Radiotron Designer's handbook is a good place to understand the basics. You can find it at Pete Millett's DIY audio page.


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## BoomerangJ (Nov 25, 2012)

Another great and helpful post. What kind of money would you spend on a kit? I'm having a lot of fun researching. Been reading about the Chinese/Japanese amps. Shocked/stunned at the prices of vintage McIntosh and Marantz stuff, Intrigued with the McIntosh used MC240's.

I will look into the kits. I browsed a couple on EBay-but I think I would prefer a US based kit manufacturer. I'd like to make sure the directions make sense to me.

Didn't KEF speakers come as kits way back in the day? It seems one of my college room mates had built some great KEF speakers? Maybe they were just knock offs-it's a 1980's memory. so over 35 years ago.


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## dgmartin (Oct 29, 2011)

I've not looked into amp kits since 5 years... bottlehead are great to deal with but offers only single-ended amps which may not be a good match for your speakers (they have nice preamp, though). Triodeelectronics offers ST-70 kits and tubedepot has some kits as well. 

A good combination for your objectives (likes the look of tubes but difficult load speakers) would be to have a tube preamp (visible) and use a (used) solid-state power amp under the desk. You could probably get that combo for less than 600$. Of course the small preamp valves does not make the same impression...


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## BoomerangJ (Nov 25, 2012)

Last night I hooked up the turntable, used an old A/V amp and played some old vinyl!!!! Wow! It was great to listen to this music. Really like the Infinity speakers. As the reviewers have said these speakers are a nice little buy. 

This little project has caused me to learn a lot. I am committed to buying a tube amp and pretty much settled on one of the Rogue Audio products. The old Technics DD turntable is working great. 

Now to get a belt for the Nakamichi and fix it up. 

I'm sure over time I will keep upgrading stuff.

The one thing I learned from the very helpful people at Acoustic Sounds and the other vendors I've been buying stuff from. 

I had forgotten that for some stupid reason I gave my CD player away a few years ago!!! I guess the right thing to do is to burn my CD's to my Apple MacBook Pro and get a DAC for re-playing my CD's.

Anyway fun stuff!


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## TheGimp (Jan 27, 2015)

The two output transformers are placed far from the power transformer to reduce 60Hz pickup. The close proximity of the two OPTs to each other may reduce channel to channel isolation. If noticeable, it will most likely at low frequency where magnetic coupling will be the strongest.


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## BoomerangJ (Nov 25, 2012)

Did you mean to post in this thread? or are you writing about the Cronus Magnum amplifier?


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## TheGimp (Jan 27, 2015)

I am writing about the Chronus Magnum Amplifier with respect to dqmartins comment about the transformers in close proximity.

I wouldn't design an amp that way, but having the two OPTs in close proximity is not as bad as having them close to the power transformer.


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## BoomerangJ (Nov 25, 2012)

Got it. Dq martin posted to this thread talked about the RCA Radiotron Designers guide. I actually downloaded and read a few chapters. Interesting stuff. Brings back fond memories of engineering school! One of the things I remember reading was the trade-off on wire length/proximity to key components and shielding. I looked hard at the kits-but really want to go the integrated amp route. There are aesthetics and shelf space to consider with what I am doing. By the time I added up the kits: Power amp, pre-amp, phono amp-it no longer made sense to me to go this route. With the Chronus I get what I need. Is it the optimum for the money? For me it's a start. I did not intend to jump in this way-but it's still fun. 

For the next piece of the puzzle: I have a whole box of CD's-and no CD player. It was mentioned to me that instead of getting a CD player get a DAC and playback using that. More homework to do!


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## dgmartin (Oct 29, 2011)

TheGimp has got the right info about the transformers. The Chronus I still in my eyes a big investment for what I consider an ordinary amplifier. Have you looked into used amps? 

For my part I still like to be able to take a CD and put it into the player and flip through the booklet. The problem those days is that most players are Blu-Ray's intended to be connected into receivers via HDMI and, hence, RCA outputs are only found in the higher end (say 200+). OPPO makes nice universal players from about 500$ there is a volume control on the analog outputs which you might find convenient.


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## BoomerangJ (Nov 25, 2012)

DG-I hear ya! I was following your advice, actually read several chapters of the RCA Radiotron designers guide. Interesting document. I looked at kits and looked at used on EBAy/web. I was really trying to stay around $1500 (or under) and there was used stuff in that ballpark such as Fisher and kit built systems. None of them grabbed me. The nice stuff was way out of my league. Do I now want some McIntosh block amps? ya! But will never pay that kind of money. I was all in on the kits-but by the time I built the 3 kits I needed (pre, power, phono) I was over the $2k mark and I just don't have the space for the 3 foot prints. I'm still intrigued with building one. I think I have one son that would be interested in taking on this project and that would be fun. 

The stuff I read about the Chronus was for the most part positive. The dealer and the Rogue Audio people are really good folks to deal with. Honest and upfront. The clincher was the remote. I think the remote is the most under rated piece of gear out there. It will be nice to be in the listening position and control volume.


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## dgmartin (Oct 29, 2011)

Sound like your did your homework. If you go for it you will be happy for a while. I agree with your line of thought if you also factor the phono and want all these items at (and for) once. I'm not aware of Kits with all those features; you would need combine a couple into one chassis and manage the layout and procurement yourself. The integrated route is not as upgradable. p.s. A LM3886 kit could be a nicer/safer project for your son. It is cheap, simple and involves Voltages below the mains.


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## BoomerangJ (Nov 25, 2012)

Update on my little project. The Rogue Audio Cronus Magnum arrived a couple of weeks ago. I'm stunned at what a difference the tube amp makes. 

This was supposed to be an inexpensive revival of my old turntable to play my old records and getting my old Nakamichi tape deck serviced. These old components needed a new amp to drive them and I began looking for tube amps: used, kit, etc. Ran across Rogue Audio and their integrated amp-Cronus Magnum and pulled the trigger. 

In the beginning of this project I was motivated by a review on cheap speakers-Infinity Primus 363's. And I initially hooked them up to a 110W old Yamaha AV amp that I had. As the review indicated the mid range on these speakers was a bit on the bright side. To the point that after 2-3 weeks of listening-they were getting on my nerves a little. 

Hooked up the Rogue Audio amp and the system just sounds great-big step up for me. I'm not an audiophile like a lot of folks on this forum-but I now see why folks chase that last upgrade to get a little closer to perfection. (I realize I'm light years away from that-but sure am happy with what I now have). 

I did upgrade my speaker cables-nothing real fancy-large guage monster cut to minimum length and equal length. 

I've also decided to put my house on a whole house power conditioner/Surge protection and then add a plug in power conditioner/surge protection for my stereo. Looking at Furman and/or Panamax.

Sent my Nakamichi off to Willy Hermann in California for a tune up. Hope to get it back soon.


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## dgmartin (Oct 29, 2011)

Congratulations on your new setup!


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## JBrax (Oct 13, 2011)

We love pics!


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## BoomerangJ (Nov 25, 2012)

*Re: Little Side Project-Picture*

Here's the pic! We are re-modeling (thus the cardboard boxes). My wife surprised me with a new office. It's a Heavy industrial look. I love it. Desk is huge cast base with large planked/stressed top. My desk chair is in a really good listening position between the speakers. I'm sure the room arrangement leaves more to be desired for acoustics. But as you may be able to deduce-we are going for looks as well! 

I plan to build a metal platform for the turntable. Flat steel with 4 round rubber feet to isolate it. The turntable would be above the Nakamichi tape deck. More pics when that happens.


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## BoomerangJ (Nov 25, 2012)

*Re: Little Side Project-Picture*

The gramaphone is a decoration from my wife. I like it though. It's supposed to play music via USB-but pretty worthless!


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