A Very Compact Hybrid Amp

[Forte]

Looks great, Any idea on the cost of the BOM as it currently stands?

 

[m0b1liz3]

I thought he said around 125 USD previously. Too bad that will end up being 250 Aus at the rate the exchange is going! If anyone wants to come stay a few nights at my place I would accept the parts as the fee! I am right near Surfer's Paradise

 

[cfcubed]

Quote:

Originally Posted by wiatrob /img/forum/go_quote.gif < snip > Congrats on another unique design - that's a lot of little holes Looking forward to reports on the first builds. Great gents!

Thanks for the congrats... Unique & innovative things, based on proven/tested designs, had to happen to make this amp possible. And yes, there are about 160 (though-hole) parts going on this 3" x 5" (75mm x 120mm) PCB. But one does not get something for nothing... Or, in this case, one does not get everything for nothing

> cost of the BOM

m0b1liz3 is correct, complete build est. (incl A/C adapt, case, etc.) is $125 USD plus any shipping & taxes. My cost was only $70 Mouser + $11 Digikey orders plus shipping + taxes + cost of PCB, because I had a 1A 24VAC adapter, tube socket & 12AU7s around.

This is one heck of a lot of amp for that $$$, regardless of size. And can be lowered through groups buys/supply support down the road. Some bundling could help those overseas too.

 

[Forte]

Quote:

Originally Posted by cfcubed /img/forum/go_quote.gif My cost was only $70 Mouser + $11 Digikey orders plus shipping + taxes + cost of PCB, because I had a 1A 24VAC adapter, tube socket & 12AU7s around. This is one heck of a lot of amp for that $$$, regardless of size.

Sounds great.

I have just realised this uses the same 24VAC adapter as my MAX and I also have sockets, tubes and even an enclosure for a SOHA I never built. Could end up a very cheap project(as amps go) if I can pick up any parts locally and limit it to one international order.

Put me down for one of the extra boards if not already spoken for.

 

[dracoV]

Very interesting project, it caught my eye just before the headwize site went down. Now I'm following this thread.

BTW, Have I missed a post ? I wonder. How is the B+(voltage multiplier) schematic look like?

 

[runeight]

Hi dracoV. I haven't posted the PS because it is very straightforward and/or its design is explained in the SOHA II section of the Cavalli Audio website.

The LV supply is conventional, using a bridge, a pre-regulator filter section, and then a stock 24V fixed regulator.

The B+ supply comes from a 3X multiplier. 24V * 1.414 * 3 = 101. In reality it is lower because of diode drops and various losses. Let's say 95V would be typical from the multiplier.

The mulitplier feeds a primary filter cap which then splits to two capacitance multipliers. The cap multipliers use 22u caps whose effective value is then multiplied by the hfe of the MPSA42 transistors. The base resistors are very large. This reduces the ripple to almost negligible amounts.

In addition, because the tube stage uses a CCS at the plates and because the servo is referenced to the 24V rail, the input stage has very high PSRR. Between the excellent ripple rejection and the high PSRR the input stage should be clean of PS noise.

Does this help? If you guys really want to see the schematic, however, I can gin it up and post it.

BTW, for those of you who have been following the schematics, you've seen quite a few opamps. But, none of these opamps are in the primary signal path. The cathode servo opamps are bypassed by the cathode bypass caps and the buffer opamps control the current mirrors. The splitter opamp comes closest to being in the signal path because it does have to hold the VG constant during current swings from the O/P buffers. But in all cases the primary active devices are the triodes or the BJTs.

 

[cfcubed]

Quote:

Originally Posted by m0b1liz3 /img/forum/go_quote.gif < snip> If anyone wants to come stay a few nights at my place I would accept the parts as the fee! I am right near Surfer's Paradise

Always wanted more reasons to visit the land down under... Taste aside, still have those meter maids making the rounds in SP?
Ehh, it's half a world away from me (56 days by car according to google maps

)

 

[dracoV]

Thanks runeight, I see, this amp uses a similar PS to SOHA II,
so its power should be a clean one,

since SOHA II has filter stages.
Now I'm really want to hear it sing.

Quote:

Originally Posted by runeight /img/forum/go_quote.gif Does this help? If you guys really want to see the schematic, however, I can gin it up and post it.

That would be great; it seem this amp PS is a little bit different.
It use 24V and GND unlike SOHA II which are +15v, -15v,
and also cfcubed switching heater.

Well, a question (kinda off topic but somewhat related)
The buffer of this amp looks good, can I use it as an upgrade to SOHA?

Cheers,

 

[runeight]

OK. I'll get around to it.

I see that you're new to heafi. Welcome aboard.

Where are you located?

 

[dracoV]

Thanks for the welcome

I often lurk around head-fi, headwize, and some other DIY sites, but did not register

I register here to subscribe to this thread, and so I can ask some questions.
This forum teach me so many new things and techniques.

Oh, I live in Thailand. BTW.

Cheers,

 

[cfcubed]

Quote:

Originally Posted by dracoV /img/forum/go_quote.gif < snip > Well, a question (kinda off topic but somewhat related) The buffer of this amp looks good, can I use it as an upgrade to SOHA?

Although this rail/buffer would represent an upgrade for SOHA, the JISBOS buffer is the way to go to upgrade SOHAs. It's well-documented & better suited for that purpose.

> Learning from forum - YES & something I've been doing too

BTW, I've the PCB in hand & its a *perfect* fit for its target case, no surprise but nice to actually see this... Have most of the resistors in & if all goes well will post back w/more this weekend.

 

[adamus]

tight... just how i like it.

 

[MrSlim]

Hey boys, I've been thinking about this. I know its your new baby and you deserve the credit for bringing it to "term", so you get to name it, but if you need a suggestion, I think "CHamp" would be a fun as well as descriptive name..

I'd love to get a crack at one of the proto boards after cfcubed has done his due diligence.

 

[runeight]

Good idea. Thanks.

Let's see if cfcubed's proto deserves the name.

 

[nsx_23]

This looks very promising. Can't wait to see the completed build.

I'm sure the price will drop if the parts are purchased in bulk.