High-end preamp for my GC

[tbla]

we parallel 10 BUF634s

its not unusual to use 2, 3 or even 4 buf 634 in parallel - especially when talking headphoneamps powering grados........btw you should try it carlos.

 

[protos]

My experience is that it sounds better even when driving pwer amps.I am currently using the PPA headphone amp with four paralleled buffers per channel as my preamp.I thought that one buffer would be enough for preamp duty (250ma per buffer) but when I started adding buffers the dynamics went thru the roof - huge difference.Made the gainclone sound like a kilowatt hi-end amp with no smearing or lack of finesse.

 

[miguel2]

Ok, maybe its tooo odd, but I was thinking if the parallel buffers couldn't drive a normal speaker. As a power amp.

Miguel

 

[protos]

In theory why not.10 buffers would have 2.5A capability so you could lets ay swing about 12v into 8ohm speakers (assuming about +- 15v supply) that would work out to about 11w rms I think and about twice that into 4 ohms.
But why would you really want to do that?

 

[mikelm]

My experience is that it sounds better even when driving pwer amps.I am currently using the PPA headphone amp with four paralleled buffers per channel as my preamp.I thought that one buffer would be enough for preamp duty (250ma per buffer) but when I started adding buffers the dynamics went thru the roof - huge difference.Made the gainclone sound like a kilowatt hi-end amp with no smearing or lack of finesse.

Would that be inverting or non-inverting GC ?

 

[protos]

IGC but I used it balanced or pseudo balanced as some would say usually with a PASS BLS.Now the PPA is a little strange in that it has a buffered ground channel so it is not really balanced but I am using this ground channel as reference for one input with a three wire "balanced" connection with separate normal ground connection on the third wire. Sounds better this way.

 

[Dr.H]

Finally built the second channel and applied the mods-

All I can say is that if the GC was a great DIY discovery, this pre is equal in impact! Soundstage is amazing-This is the best I have heard and considering the small outlay, this is the best bang for buck DIY can provide. Music is simply delicious...You actually listen to a musician communicating now-not just information but emotion.
Carlosfm was right on the 200pF cap-it cures some edginess-Seems it may be worth playing around with.

A strongly recommended upgrade to the GC! Thanks to Pavel Macura and Carlosfm for introducing the delights of this beautiful device.


Rest of system: Proceed PDT3, Theta DAC, NIGC, Royd doublet speakers

Ryan

 

[protos]

You are ready for batteries then!

 

[matjans]

i've just hacked together a pcb layout for this preamp. I'm working on a better version. In this version the caps are not bypassed and i've left out a few resistors (which i will probably include in the next version too).

Eagle file:

 

[PMA]

Finally built the second channel and applied the mods-

All I can say is that if the GC was a great DIY discovery, this pre is equal in impact! Soundstage is amazing-This is the best I have heard and considering the small outlay, this is the best bang for buck DIY can provide. Music is simply delicious...You actually listen to a musician communicating now-not just information but emotion.
Carlosfm was right on the 200pF cap-it cures some edginess-Seems it may be worth playing around with.

A strongly recommended upgrade to the GC! Thanks to Pavel Macura and Carlosfm for introducing the delights of this beautiful device.


Rest of system: Proceed PDT3, Theta DAC, NIGC, Royd doublet speakers

Ryan

You are right .

Glad to bring enjoyment .

Pavel

 

[king30]

Could someone post the Power Supply schematic for this pre. I am very interested in building one, but am finding it hard to piece together from the descriptions.

Thanks Lee

 

[Nuuk]

.

Could someone post the Power Supply schematic for this pre. I am very interested in building one, but am finding it hard to piece together from the descriptions.

You could try this Lee. It will work very well and I have used it for preamps, active crossovers and a sub woofer control circuit.

Please note that on the diagram showing the second stage of voltage regulation (shown in the crossovers section), the resistor values are transposed, ie the blue ones are 240R and the lilac ones are 2K7's

Alternatively, any PSU producing a +/- 15 volt supply will do.

 

[king30]

Nuuk,
Thanks for the info...Lee

 

[Nuuk]

Thanks for the info...Lee

Pleased to be of service

 

[Alcaid]

Any comments on my PCB?

I've made a PCB for a this preamp with the BUF634T at the end of the PCB so I can attach it to the cabinet which has heatsink-walls.
Any comments about the layout? Is the decoupling/coupling ok? I Intend to use 100nF ceramic and 100uF electrolytics (Panasonic FC). The red traces will be wire links.

 

[PMA]

Nice job, Alcaid.

I would like to comment a little bit. Keep the shortest distance between the BUF and the OpAmp. Probably you would like to use a groundplane.
The power dissipation of the BUF is not critical.

Regards,
Pavel

 

[Alcaid]

I managed to shrink the distance a bit. Are they close enough? Will I get any problems like oscillation? (hard to answer, I know)

 

[Alcaid]

The board size is 1.175 x 2.350 inch

 

[Nuuk]

Just a suggestion and I may be wrong here, but if you use a cap across the supply pins of both IC's, you should be OK with just one set of electrolytics for both chips.

You could then remove the caps between the two IC's and move them even closer together.

 

[PMA]

I managed to shrink the distance a bit. Are they close enough? Will I get any problems like oscillation? (hard to answer, I know)

As Nuuk has said, you can move electrolytes. For bypassing reasons, the ceramics are important. I do not suppose the oscillation problem, but it is customary to keep the shortest distance between the BUF and the OA, just to minimalize signal and feedback tracks. Then you'll get lowest distortion, best RFI imunity and low stray capacitances.

Regards,
Pavel