Sjöström Audio DIY forum

Thank you once again for the valuable comment! I think I will stick to the BC5xx transistors, and will leave the supply voltage not very high, say +- 24V. I hope the stage will be able to handle 5-10V of output amplitude (this is actually much more than necessary)...

heaveno,

I am looking for a good design of a line level preamplifier, gain 15..20 dB. I have built the QSXM2 phono preamplifier and I am very pleased with it's sound. I like symmetrical designs, I like discrete designs. So I was thinking of using the first stage of the QSXM2 as a line level preamplifier.

Is this a good idea? What should be considered if doing this? Any changes to the schematics you wold recommend?

I guess the preamplifier should be able to work with higher level signals, so I was thinking of running it at a higher supply voltage. Is this ok? I guess the servo cannot be powered from, say, +- 30V, so it should have a separate supply. Would it still be working?

I will be glad to read any advise about the idea!
Thanks in advance!

Best Regards,
Angel Sinigersky

another two pictures come...


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heaveno Everybody,

a month ago I have built a QSXM2 phono preamplifier and I am testing it now at my stay in Bulgaria while converting my favorite old LP to digital. My implementation of the amp is as follows:

- single Analog Devices SSM2220 / SSM2210 input pairs of transistors
- toroidal transformer, soft recovery diodes and a single Jung Super Regulator as power supply (the spec's for the best pickups say that channel separation is approx. 25 dB so I've decided not building separate regulators)
- aluminum casing from an old LAN switch
- Neutrik connectors

I am using an Ortofon OM 20 Super pickup (loaded with 440 pF) and a TOSHIBA turntable. For digital conversion, a M-AUDIO Audiphile USB is used in 24 bit / 48 kHz mode.

First listening impressions are that the preamp is absolutely superior over the original preamp integrated in the stereo. Far better mid-range, very, very clean sound! The bass is also very pleasant, I think a big improvement came from the new pickup, too. I was pleased to hear my favorite LPs with this new system!

The M-AUDIO measures 96 dB S/N ration with Right Mark audio analyzer. The idle background noise shown / recorded by CoolEdit Pro 2.1 stays about -81...-84 dBFS (dB relative to the sample's Full Scale). I noticed that when connecting the QSXM2 preamp only (without anything connected at it's input), a noise floor of -60 dBFS was detected. I then tried removing the chopper stabilized op-amps at the input (I am using TLC 2652 from Texas Instruments, which require a small PCB modification), and the noise level fell back to the sound card's -81 dBFS! The DC offset did not become worse, or at least I was not able to notice such an effect. I think this input servo ruins the noise performance, which is otherwise extreme! Here is a question about the amp. I don't quite understand why this input servo is implemented in that way. After removing the op-amps, the LEDs in the RIAA stages began to illuminate weaker! Is this ok, or should I adjust something when omitting the input servoes? I would be glad to read some comments!

Thanks to the Author for this superb project!!!

Here are some pictures of the preamp:



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