Suppo Audio -- New Chinese EL84 PP amp for CHEAP.

[Jaap]

Originally Posted by bigjppop

Suppo Audio was kind enough to send the schematic for this amp and is most open to hearing what the DIY community has to say on ways to improve its design. I can't figure out a way to edit/attach it to my first post, but here it is. They also have some hi-res pictures on there website of the interior of this amp.

I would try a small mosfetregulator at the front tubes. I suppose the PSU can be made better. You can simulate on Duncan PSU designer.
Bij the way 6N1P is not the same as ecc88. Check the current through the powertubes, Russian tubes are more rugged than el84.

If it doesnot sound good you can always build a Baby Huey in this enclosure. But as said before all depends on the OPT.

[drongo]

Like some other posters, I find the price difficult to believe, even buying this and replacing the output transformers with something familiar (Hammonds or whatever) would still be a pretty good deal. Love to hear some first hand reports of this little beauty.

[jrenkin]

Very nice at that price. Too bad shipping to the US is as expensive (almost) as the amp. It might be worth $120 just for the nice box...

I am doing something similar, but with an older beat up Sophia Electric EL34. I posted the schematic if anyone is interested (looking for advice, of course...).

I think that with the schematic, you could basically rip it apart, put in better components where needed and rebuild in the same box point to point. Probably with a new set of OPTs if you can find something suitable.

What are it's operating points?

[Michael Koster]

I enjoyed looking at the pictures of their workshop. They're already in the hobby business and obviously have adjusted their overhead appropriately, with plywood workbenches, $100 worth of used test gear, etc. A skilled electronics worker could probably build and test several of these in one workday. There are plenty of skilled electronics workers around.

The parts cost is what amazes me. They must have less than $40 in parts cost even with super low overhead and people costs. What do EL34s cost in China by the flat?

The openness and free communication is refreshing! They are well suited to the hobby business

[Fenris]

Interesting schematic, very conservative design. Almost exactly like the amp I'm building now. Interesting design choice on adding C1 / C13, almost ultrapath, probably done for PSRR. Current on the first triode (via high plate resistor) seems a bit small for a 6N1P, probably done to get it to DC couple with the second triode. That will hurt performance since the 6N1P likes current, but that's probably why there's feedback. Personally, I'm going to run a CCS with about 4x the current (5ma vs 1.3ma) on my 6N1P with a voltage divider/cap to couple the stages. There's alot of capacitance on the B+ as well, almost a scary amount, probably to make up for no choke. The poor power transformer is going to suffer from small conduction angle. It might be a good upgrade to throw a regulated PSU in there. The capacitor on the cathode of the drive tubes looks a little small as well - I'd double it and bypass with a good film cap as a minimum.

I'm guessing this amp will probably sound pretty decent, as long as the OTs are up to snuff.

[TheGimp]

Another consideration is that the output tubes are running off a single resistor per pair, so I hope they are matching the 6P1Ps.

They Are, I looked at their shop and they show the tube tester.

One can order 6P1P-EVs from the former Soviet Union for less than $2 each including shipping. I suspect they are paying less than $1 per tube and more likely 0.50/tube. Figure $7 per OPT (maybe less), and the same for the PT. Circuit board $3. Yes, $40 is probably reasonable for the BOM.

[bigjppop]

So the post man just paid me a visit and my new amp is sitting on my desk, glowing as we speak. 4 days from when I sent my paypal, the amp is here safe and sound. The packing job is EXCELLENT (Joe and Suppo told me about the amp that was destroyed enroute to Australia and said he was beefing up the packing). Amp arrived double boxed with both the inner box and the amp itself totally encased in hard foam blocks. Absolutely no shipping damage.

The fit and finish on the amp is a little rough. The panels don't all fit together completely perfect when it comes to the chassis and it looks like some things had to be forced a little to make them fit; ie the bottom plate is a little bent to make room for the OPTs. There was also a screw rolling around inside that is one of the four holding the front plate on. There is no way to put that screw back in without totally taking apart the amp so the front plate will just have to make due with three screws.

Unfortunately I am completely out of anything that could even be construed as speaker cable (don't even have enough cat5 laying around!) so I can't listen yet. I wasn't expecting this thing to get here so fast but I've got a new spool of speaker cable coming from monoprice that should be here tomorrow.

That being said, I fired it up and everything lit up like it was supposed to and no smoke or foul orders came from underneath. I'm going to be running this with a brand new pair of Omega 3i's that have been sitting in my closet for a couple of months waiting for me to finish my Simple SE.

Anyway, so far so good. Everything looks pretty great and arrived safe and sound and VERY fast. Hopefully more to post soon (I might have to go steal speaker cable from the neighbor!).

[rhing]

bigjppop,

Congratulations on the delivery. Hopefully, the amp works fine. I purchased one too, and USPS attempted to deliver the amp to my home, but no one was home at the time, so I'll get mine later today.

Thanks for posting the schematic that Suppo provided to you. This will help a lot with future mods, and I'm looking forward to what other buyers of this amp plan to do with theirs.

I'll post my listening impressions once I have time later tonight to listen to the amp. I have an Anthem Integrated One, another EL84 P-P amp on hand for comparisons.

[Fenris]

Wow. I was finally able to see the pictures after I got home last night. It looks better than I thought it would, although a little messy in the interior. At $120, that's some serious bang for the buck. The toroid looks a little small - 80va means it's nearly maxed out with 24 watts of heaters and 45 watts of tubes. I like to have at least 50-100% margin on my power transformers, but that's just me. It also leads to needing LOTS of capacitance to keep the B+ up, but that leads to a harder working transformer. That case is compact, but there might be room for a PSU regulator in there (series, feedback shunt, feedforward shunt, take your pick). It may not be a problem, but I personally like to use DC heaters. Again, personal preference, but I understand the cost saving measures in this design. I'm not wild about the cheap looking volume pot - I'd probably bypass it and use a good preamp anyway, or replace with something better. I'd also see if it sounds better with or without feedback. It's probably better with it if it was designed that way, but you never know. It would be interesting to see just how good the OPTs are and whether cheap Edcors or toroids would fit and would be an improvement.

What would be really interesting to see is if they would sell the amp without any transformers. Since those are fairly heavy, it would make sense to source those locally and not have to ship heavy iron around the planet. If it halved shipping costs ($35 to the US) and dropped materials costs (let's say $20), it could be worth it for the DIYer to source transformers from Antek and Edcor for a possible upgrade at minimal extra cost.

bigjppop - could you tell us the size of the OPTs in the amp (or at least the overall dimensions of the amp? It looks pretty small for a tube amp)? And please don't turn it on without a load on the outputs - that's really bad for a tube amp. The load helps control the tubes, without it they can oscilate and do very bad things.

[vdi_nenna]

Have you guy seen these? Ssaw some at an audio swap meet. Reseller was offering them. Nice build and the price...disposible.

YARLAND AUDIO