[edit] forgot to mention that the red lines are jumpers that are ontop of the board.

[edit2] i forgot to mark the orientation of the diodes, but thats pretty straight forward]

schem

layout

[Edited by pho_boi on 11-03-2005 at 03:39 AM.]

Those polypropylene caps are way too big physically. Are you sure you can't get any VISHAY BC or EPCOS radial caps ?
Remember what the SOHA is about and thus its overall performance.
In your shoes I'd be happy to try using polyester caps for the 22nF and 100nF bass boost in this amp (if I thought bass boost is needed that is). Can you get these ? ... it'd help with your layout, but, of course, the caps you use is your choice.

[Edited by mains_hum on 11-03-2005 at 01:59 PM.]

link

link2

Are these caps suitable for this amp? Polyester are easily obtainable in the values required, but I was told that polypropylene caps are much better?! Is there a huge difference in performance between the two types?

[Edited by pho_boi on 11-04-2005 at 07:41 AM.]

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quote:

[By skyskraper] ill speculate that the value of that cap is hardly critical. you could probably use a 0.1uF cap quite easily. *ss awaits confirmation or discreditation of his theory*

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Second .. the polypropylene caps you show in the link will work just fine. The spec is pretty similar to the same style I used in the prototype.

You can use larger values with impunity, but don't go smaller than 100nF otherwise bass will suffer ... if this helps you choose.
Oh!, I see runeight has said the same thing while I was busy replying. It must be true then.

[Edited by mains_hum on 11-04-2005 at 09:23 AM.]

Changing out the buffer in the SOHA needs some thought because the OPA2134 in unity gain mode has little or no DC offset. Other buffer types, with no output cap, might put significant DC offset into the headphones.

Here are two schematics for adding a diamond buffer to the SOHA. The first one uses a simple adjustment pot to set the DC offset to zero. The second uses an opamp servo. Obviously, either of these changes significantly increases the parts count of the original design.

Basic Stoopid with Diamond Buffer

This is a simple way to adjust the offset and it will work, but it may have substantial temperature drift problems. If it does, then the alternative is this opamp servo that will keep the output to within a 1mV or so.

Basic Stoopid with DB and Servo

As I recommened in the YAHA thread, I think it is best to first build the SOHA as originally designed because the quality of the sound comes mostly from the tube with higher B+. The output stage probably contributes little to the overall sound of the amp. I believe that mains and batman would agree with this based on the tweaking process that they went through as we finalized the design.

[Edited by runeight on 11-06-2005 at 04:11 PM.]

The point that runeight and mains_hum are making is that, in both YAHA and SOHA, the biggest contributor to the sound is the valve and trying to improve the sound by changing other parts of the circuit is not likely to offer as much improvement as increasing the plate voltage. As I mentioned earlier, when I first powered up the prototype, the plate voltage was only 17V and the amp sounded decidedly unpleaseant. As we raised the plate voltage the sound became much more pleasing, perhaps as the tube became more linear.

One of the attractive features of these circuits (YAHA ansd SOHA) is their simplicity and low cost.

[Edited by Batman on 11-06-2005 at 09:45 AM.]

Sorry to ask for this again, but could someone 'proof-read' my layout for the power supply section?

http://users.tpg...lmnlo/psu01.jpg

thank you

Are you still going to use the transformers that you showed us before? If so, we'll need to change the value of the heater resistors for the 12AU7. The resistors in the diagram are selected for a 200mA trafo with about 25% regulation. My first calculation says that you'll need about 60R on either side of the heater for your trafos. The 100||220 combination in the diagram gives about 69R.

You can get 60R by with 100||150. 2W resistors.

[Edited by runeight on 11-10-2005 at 11:09 PM.]

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quote:

[By runeight] Looks correct to me.

Are you still going to use the transformers that you showed us before? If so, we'll need to change the value of the heater resistors for the 12AU7. The resistors in the diagram are selected for a 200mA trafo with about 25% regulation. My first calculation says that you'll need about 60R on either side of the heater for your trafos. The 100||220 combination in the diagram gives about 69R.

You can get 60R by with 100||150. 2W resistors.

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At the moment I think I will be using those two tranfos. I was also wondering if I could use this transformer:

transformer

And I'll just wire the secondaries together like how you showed me earlier. That transfo has two 0-115v primaries, could I wire them in series so that I can use it with Australia's 230vac? If I do wires the primaries in series, how will this affect the secondaries? Sorry for all these questions about transformers

Thanks

If you use this trafo you should use the 100||220 resistor combination for the heaters. If you use your two big trafos, use the 100||150 combination first.

[Edited by runeight on 11-10-2005 at 11:38 PM.]

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quote:

[By skyskraper] for future reference, RS links time out pretty quickly so you can't link directly, a RS catalog number would be much better coz its universal across all RS organisations.

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But, the 201-7038 is what I drew the picture for.

Why don't we just say that all 100uF are 100V rating ?
Any PCB mount 0-15-0-15 transformer will then work and not be a problem no matter what the transformer regulation, also, caps are often supplied in packs of 5, so it helps in component type count too.

Just a hint to you builders out there.... while I put together the parts for my "Cool Stoopid" ... coming soon ....

[Edited by mains_hum on 11-12-2005 at 11:29 AM.]