Dynahi Questions: Integrate with Gainclone and some other questions.

[bg4533]

All of this started off that I wanted to build a Dynahi and also needed a decent poweramp. I looked into using the Dynahi as a poweramp, but just decided I would build a Gainclone. On a limited budget I don't have much money to build both amps seperately to high standards, so I started thinking that it might be a good idea to integrate them. This would save both space and money.

It seems I could use the same case, pot, heatsinks, PSU, inputs, etc. All that really differs is the amplifier area and the outputs. So, below are a lot of my questions related to my project.

First, my plan is to have a nice case for the amp sections and a seperate one for the PSU.

1. What would be a good gauge wire to connect the PSU and amps?

2. What is the best way to switch between the Dynahi and the Gainclone? Is it ok to just switch the power lines or do signal lines also need to be switched? If both need to be switched is it easily possible to do with just one switch?

3. Would the PSU of the Dynahi work as intended powering the Gainclone? I think I need a bigger transformer than normal. Does anything else need to be changed? Can anyone recommend a transformer?

4. In the amp case is there any disadvantage to having just 1 very large HS shared between everything or should I use seperate ones?

5. I am planning on rewiring my HD650s. After the Dynahi is finished I will likely only use the Senns with it. Should I terminate the HD650s to dual mono? What would the advantage to this be? What is the difference between a Dynahi created for dual mono and not? Can I just make an adaptor to use the dual mono Dynahi with regular stereo headphones if I want?

Anything else I should consider before taking on this project?

Thanks for all the help!

[Garbz]

1. Any old wire will do generally for the dynahi. I use 18AWG wire here. Gainclone will need considerbaly larger wire.

2. Its probably a good idea to switch the signal lines too. There are some pretty big switches out there. A 6pdt switch would do the trick. Just check to see if it can switch the gainclone psu.

3. No it will not. The gainclone draws a lot of power. You can try running it from a dynahi psu but you'll find that it'll clip at very low volume. (educated guess considering wer're talking about a poweramp)

4. No. Just make sure each part is electrically isolated and the heatsink is big enough.

5. Dual mono cables only makes sense if you build a Dynamite (balanced dynahi).

[bg4533]

If the same PSU can't be used then I am not sure I want to combine the amps. I got the idea of using the Dynahi PSU for the gainclone in a post by MisterX. I really know nothing about transformers or power supplies. It seems what I need is a power supply with the correct secondaries and then I need to pick up one with enough VA. I looked around and someone suggested a 160VA transformer for the Dynahi. A few sites mentioned a minimum transformer size of 120VA for the gainclone, but said it responds better to bigger transformers. Seems to me like it would work. Does anything else need to change as I go to a transformer with more VA?

As for the switch I would ideally like a rotary switch with 3 settings. Off (center position), Dynahi and Gainclone. Is there anything wrong with having the signal and power lines use the same switch?

Isn't dual mono supposed to give the amp more power and better control of the headphones or something? Wouldn't it help channel seperation a bit too?

[bg4533]

I did a bit looking for transformers and found a Plitron 300VA with dual 35V RMS secondaries, part #077018201. The cost is $62.95, a bit much, but not all that much more than the smaller units. Would this work well for both amps? Would a bigger transformer be better? The cost is about $10 more per 100VA.

[Garbz]

Sorry i didn't fully read the Qs because I was late for a date.

The dual mono would make a difference. Having separate PSUs would indeed reduce crosstalk, and the grounds can be completely separated as well. In this case the headphones may benefit from being re-wired too.

The powersupplies are still a problem though. Firslty the dynahi uses +-25v I think. IIRC the gainclone psu delivers about double that, correct me if i'm wrong. The other problem is the current output of the psu. A gainclone would require considerable current. Current is not only limited by the transformer, but by the opamps, the regulators, resistors etc. I made the educated guess because while I haven't checked the current requirements in detail, the dynahi being a headphone amp will probably use much less current then the Gainclone.

The use of current isn't a problem as far as I understand, the dynahi could probably run off the gainclone psu (providing voltages are correct), but I doubt it would work visaversa.

Anyway i appologise if any of this is wrong. I just bought an espresso machine and i'm on a coffee high.

/EDIT:
Regarding the last post if you get a 35VA transformer remember the dynahi runs of 25v. You amp will turn into a small heater dropping that voltage.

[bg4533]

The Dynahi uses a +-30V PSU. Transformer secondaries of 30V-40V have been mentioned and KG mentioned 36V. The Gainclone is flexible in the voltage it will take. It is roughly +-20V-38V, with the amount of voltage affecting power and sound qualities. I have no clue how much current it draws.

I will probably build a Dynahi either way, but the difference will be how nicely I finish it. The amp parts of the gainclone are pretty cheap. I might just build it and hook it up to the Dynahi PSU before I plan out the integrated case and other stuff.

The other issue I came across is that the LM3875 that the gainclone uses does not like large amounts of capacitance across it, but there are ways around this. The Dynahi PSU has almost 30,000uF of capacitance. I have no idea if it will work. I am going to try to ask on a gainclone forum.

[Garbz]

Capacitance wouldn't be a problem with the Dynahi PSU. The capacitance after the Opamp looks like 4700uf per rail, everything before it won't make a difference to the load.

The only problem you might encounter is the current draw. The output current of the OPA541 is 10A. Ask that on the gainclone forum.