Soldered a Vf=1.8V led and feeding the preamp with 44V DC i measure 41V after regulator. When feeding the preamp with 58V DC i measure 43-44V after regulator. Are these numbers ok?
Probably not. The idea of the regulator is to, ehh, regulate the output DC. 41V one time and 43-44 another time doesn't sound too regulated.
What probably happens is that with 44V input, there's not enough overhead to regulate down to 41V. I use a 48V wall-wart and have it rock-stable at 40V out. 58V might be a bit too much because that would require a lot of current to be absorbed by the regulator to make sure 18V is dropped over the series R, and that series R also will get quite hot.
To adjust it I would recommend going with 48V initially and adjusting the input att resistors to the LED you have to get 40V out. Your final input can then vary a bit like between 46 and 50V, but as I said 48V seemed pretty ideal to me.
Jan
My preamp îs working now. Adjusted RP2 to 23k în order to match the led Vf. Installes some temporar sockets for an easyer xhange of components.
An externally hosted image should be here but it was not working when we last tested it.
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Input att resistors. I meant 'adjusting the input att resistors to the LED voltage', not to the LED as such, my bad. These are the two resistors that divide down the output voltage of the regulator to the inverting input of the opamp. At the non-inverting input you have the reference voltage, which in this case is the LED. The opamp will drive its output to whatever it takes in an attempt to make the voltages at it's inverting and non-inverting inputs the same.
So if you know the LED voltage, say 2V, and you want an output voltage of 40V, you have to size the two resistors on the inverting input such that they give also 2V.
In this example, you could for instance use two resistors of 2k and 38k. That would divide down the 40V to the 2V of the LED and extablish equilibrium and thus regulation.
Jan
First time installed KSC1845 transistors and listened two days, today changed to BC550C. To my ears KSC sounded more rounded a bit more bass and BC550c seems to sound more open with little more details in the high freq but the bass seems a bit more shy. I will give them 2-3 days and swith back to KSC and "see". Overall i like the sound of this preamp even if i deviated from recommended BOm especially the polistirene caps in RIAA network as i had some nice Wima FKP2 2.5% already in my stash.
Mine should be here from China any time. They are most likely fakes, but they were cheap enough not to worry. We will see.
See posts #71 and #74
Russellc
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@2Bak - ordered some parts twice so i have some to offer 1xths4031, 1xSTP55NF06,2xDN2540. All of them from Mouser. Pm if you are interested.
@h_a : Hannes the case used to finish this nice preamp posted in the first posts is available somewhere or is custom made? Trying to find a suitable case.
Thanks,
Adrian
@h_a : Hannes the case used to finish this nice preamp posted in the first posts is available somewhere or is custom made? Trying to find a suitable case.
Thanks,
Adrian
I received the 2SC2547s from the Amazon vendor today. Unfortunately, the H.O. phono board sent by Hans hasn't arrived yet. Until recently, most small items from European countries items arrived in less than 10 days but lately our regular Post service seems to be in a disrupted condition ( as many other things State owned ). So, the parcel might be lost. Let's wait and see.
Out of curiosity I checked the HFE of these transistors ( my tester has a function for that) and I obtained a close rating of 185 to 190 for all of them. I wonder if this any indication of being fakes or not.. 190 seems a suspiciously low value.
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I know, I know.. that's why I said 'suspiciously' low value. My transistors are marked 'E'. Easy to draw the obvious conclusion -> It seemed too good to be true ..and it wasn't true.
Instead of that unreliable stuff I'll use BC550C. I have a bunch with HFE measuring 600-650, which seems O.K.
Instead of that unreliable stuff I'll use BC550C. I have a bunch with HFE measuring 600-650, which seems O.K.
Hi there,
sorry for lack of reply, but I've been away a few days!
Great to see the first finished preamps - great work Adrian!
Many thanks also to Jan for helping sorting out with the regulator questions!
@atupi: I'm sorry my prototype case is not a ready to buy unit. I gutted a commercial phono preamp which I didn't like much and used its case. The new boards will have mounting holes which will make mounting easier and these fit then also into standard Hammond-cases. I'm sorry that this doesn't help you with your original board.
@ Russellc, msdin, jvhb, Hdonly, tubesguy, arthur: many thanks for your interest! I'll contact you then when the new boards are ready!
@ 2Bak: many opamps will do the job, it's just that the THS4031 is an outstanding performer in this circuit.
You will want a low-noise, SOIC8, high speed opamp that is unity-gain stable and has a relatively high output current to drive the mosfet. Also please note that the opamp is driven from the unregulated rail voltage minus 18V, so it needs to cope with about 30V rail voltage.
EDIT: my pm-box jammed as I was away - sorry for that! In case somebody couldn't send me a message for this reason, it will work now again.
sorry for lack of reply, but I've been away a few days!
Great to see the first finished preamps - great work Adrian!
Many thanks also to Jan for helping sorting out with the regulator questions!
@atupi: I'm sorry my prototype case is not a ready to buy unit. I gutted a commercial phono preamp which I didn't like much and used its case. The new boards will have mounting holes which will make mounting easier and these fit then also into standard Hammond-cases. I'm sorry that this doesn't help you with your original board.
@ Russellc, msdin, jvhb, Hdonly, tubesguy, arthur: many thanks for your interest! I'll contact you then when the new boards are ready!
@ 2Bak: many opamps will do the job, it's just that the THS4031 is an outstanding performer in this circuit.
You will want a low-noise, SOIC8, high speed opamp that is unity-gain stable and has a relatively high output current to drive the mosfet. Also please note that the opamp is driven from the unregulated rail voltage minus 18V, so it needs to cope with about 30V rail voltage.
EDIT: my pm-box jammed as I was away - sorry for that! In case somebody couldn't send me a message for this reason, it will work now again.
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Another source for 2SC2547 I have had luck with in past for other discontinued pieces:
B+D Enterprises - Search results for: '2sc2547'
Russellc
B+D Enterprises - Search results for: '2sc2547'
Russellc
