James Burgess 2A3 Monoblocks

[easymac77]

Hello all, I picked up a pair of James Burgess 2A3 SE monoblocks and as a newbie to DIY, I thought I'd use everyone's expertise on potential customizations.

First is the output transformers, the existing ones are 'Handwound' from David Lucas. I have read the numerous horror stories regarding his/their customer service, shipping etc., but I've read both positive and negative things about the transformers, if and when you receive them. With all that said, I'm thinking about changing to Hashimotos, but again with my lack of experience in this arena, I'm not quite sure which ones I need (primary impedance, etc.):

Hashimoto Products

Any suggestions or alternatives would be greatly appreciated.

The other thing I wanted to do was put in gain control so I can cut out the pre-amp. Suggestions on high quality stuff would also be appreciated.

As a side note, I won't be installing this stuff myself, I acknowledge my electrical ignorance and like being alive.

Thanks guys!

 

[SemperFi]

I'm sure those expencive Japanese OTs will look great, but is there something wrong with the amp as is? I've not heard of 'Davis Lucas OTs', but if they have a bad rep b/c of poor customer service, why do u care if the OTs are allready there?
Not to ruin your plan, and nothing wrong with upgrading something to the better, but perhaps a thorough testbench set of measurements, and ditto listening test, will reveal what mods if any should be looked at.
Just my nickle.

 

[easymac77]

As far as the OT's go, I had read ALL bad things about customer service, but both good and bad regarding the performance. I spoke with James about these particular amps and it sounds like he was quite pleased with the OT's; which I should have assumed in the first place as I doubt he would have even entertained the idea of using a less than stellar component. So with that said, I completely agree on bench and listening tests before I go crazy with modifications.

However, I would still like to install volume pots. James said he prefers TKD's... Thoughts?

Also, is 3 - 3.5 watts enough to drive 100dB speakers off a turntable source, or will a phono stage more than likely be needed?

 

[Sheldon]

Also, is 3 - 3.5 watts enough to drive 100dB speakers off a turntable source, or will a phono stage more than likely be needed?

You have enough power to drive speakers like that to reasonable levels for most listening. However, a phono stage is necessary for two reasons. One, the signal from a phono cartridge is around 0.5mV at 1kHz for an MC cartridge, and around 5mV for a typical MM cartridge. If your amp has a sensitivity of 1V full scale, for instance, you need to boost the signal for an MM cartridge by 10 fold, or 20dB (40dB for MC). Second, the treble is boosted and the bass is attenuated when the record is cut. So the phono stage also has to equalize for that. In short, yes you need a phono stage.

Sheldon

 

[easymac77]

Sheldon, thanks for all the info! I tried to see if my turntable had the RIAA correction, but I highly doubt it, given it's simplicity (Rega).

I guess the next question is: what is a good all-tube pre-amp/phono circuit? I hear '26' quite a bit, but I also know they are a huge pain to build...

 

[Allen Wright]

One, the signal from a phono cartridge is around 0.5mV at 1kHz for an MC cartridge, and around 5mV for a typical MM cartridge. If your amp has a sensitivity of 1V full scale, for instance, you need to boost the signal for an MM cartridge by 10 fold, or 20dB

Sorry, 5mV to one V is 200x, not 10x. And for a typical MC, you will need 2000x...

>>In short, yes you need a phono stage.

Yes, and a very good phonostage at that, as most phonostages are expecting a line stage's worth of gain before the poweramps.

REgards, Allen

Regards, Allen

 

[brady]

does anyone have James Burgess email add? I found a tel number in his jewelry business, but I thought an email to discuss an amplifier build might be more suitable.