hi carlos, the original lt1056 op amps were class a biased to 2ma. using the j555 crds along with the lt1010 buffers. the lt1010s had a 50 ohm resistor from the bias pin to the v+ pin for bw or current bias? i'm not sure of the purpose of the resistor but, of course the resistor is not being used now with the buf634s in the circuit which are in wide band mode. i replaced the j555 crds with 2sk170 cascode current sources but, maybe i should try removing the cascodes since i'm running the buf634ts in wide band and the lt1010s had the 50 ohm biasing resistors? i was sure surprised at having less than 1mv. dc offset at preamps bypass outputs which is direct coupled especially, with the buf634s. thanks again for your advice, crippledchicken 
crippledchicken said:
This is what happens with this good stuff.
I have 0.2~0.3mv, direct coupled.
Oh, remove all the biasing circuitry and give it a listen.
On the BUF634 datasheet, page 8:
"Bandwidth can be extended to approximately 180MHz by connecting the bandwidth control pin to V–. This increases the quiescent current to approximately 15ma."
No biasing needed.
hi carlos, that's the way i've been running the buf634s and, sounds great but, i think i'll remove the biasing cascoded jfets now, and give that a try with out them and see what the difference is and btw the buffers are on heatsinks and hardly even get warm so, i guess i'm alright there. one thing that did concern me though is, according to data, max +/- v. for buffers is 18 and my supplys are fed from a discrete regulator setup and the rails are at about 17.5 v. +/- as are all four of the 627s is that cutting it to close? like i say, nothing runs hot though. thanks again drippledchicken
carlosfm said:
If you are just comparing with the NJM, it should sound fabulous indeed.
Are you?
Yes, I am. I going to try some other OPAs later.
You recommended LM6172. They are being sold by RS. There are two models LM6172IN and LM6172IM. I suppose that LM6172IM is the right model for this application?
I have to check my AD8065 temperature some day. The PS voltage is 12.3 V.
carlosfm said:
Hmm... I'm not that good with abbreviations (can't tell what the difference is between these two). I suppose that DIP is the correct version?
http://kotiweb.kotiportti.fi/audiovideo/DIY/cdout/
EDIt: there are bypass caps in the original configuration (0.1 uF and 0.47 uF) but should I add new bypass caps (value, brand?). There are Silver mica bypass caps in the AD8065 PCB.
An externally hosted image should be here but it was not working when we last tested it.
The original configuration looks like this:
http://kotiweb.kotiportti.fi/audiovideo/DIY/cdout/kaavio.png
The AD8065 module is simply installed to the same pin holes without any modification. It doesn't seem probable that the caps are connected to power supply pins.
http://kotiweb.kotiportti.fi/audiovideo/DIY/cdout/kaavio.png
The AD8065 module is simply installed to the same pin holes without any modification. It doesn't seem probable that the caps are connected to power supply pins.
Have you heard about swenson mod?
If I've understood correctly, the idea is to pass the whole analog output stage by taking the signal straight from DAC output (needs a small coupling cap). They do it to cheap Toshiba players with great results. Do you think that it would be ok to try this mod with other players? What disadvantages and risks are there with this mod. I would think that there's no way that a DAC would be able to drive a preamp...
If I've understood correctly, the idea is to pass the whole analog output stage by taking the signal straight from DAC output (needs a small coupling cap). They do it to cheap Toshiba players with great results. Do you think that it would be ok to try this mod with other players? What disadvantages and risks are there with this mod. I would think that there's no way that a DAC would be able to drive a preamp...
SO8 - DIL8 adapter
Earlier I stated that SO - DIL adapters where available in Sweden from Elfa. This is not the case. They have either discontinued this product or I was mistaken and mixed it up with an experimental adapter for up to 28-pin SO. This adapter is not very practical.
Sorry for any inconvenience this may have caused.
I found a source in the USA:
http://cimarrontechnology.com/
They specialize in component adaptors.
Check the Audio Upgrade adaptors.
Earlier I stated that SO - DIL adapters where available in Sweden from Elfa. This is not the case. They have either discontinued this product or I was mistaken and mixed it up with an experimental adapter for up to 28-pin SO. This adapter is not very practical.
Sorry for any inconvenience this may have caused.
I found a source in the USA:
http://cimarrontechnology.com/
They specialize in component adaptors.
Check the Audio Upgrade adaptors.
- Status
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