Need help on DIY Toccata Phono Preamp

bigpandahk · 10th June 2011, 02:55 PM

Recently, I DIY the Toccata Phono MKII preamp and found the amplificiation of the amp is far lower than expected. I am using Dynavector 17D3 MC phono and connect the Preamp to a headphone amplifier. I turn the volume to maximum and merely hear the music. I checked the voltages and found nothing adnormal. Attached the schematic with voltage shown. Please advise the possible cause of problem....many thanks.

bigpandahk · 11th June 2011, 05:30 AM

After several trail, I find the cause of problem, since I couldn't find 2SK147, I use Vishay J/SST201 instead. May be it is not compatible with 2SK147, it doesn't amplify the signal. what shall I use to replace the 2SK147?

Rod Coleman · 11th June 2011, 04:46 PM

Quote:

Originally Posted by bigpandahk

After several trail, I find the cause of problem, since I couldn't find 2SK147, I use Vishay J/SST201 instead. May be it is not compatible with 2SK147, it doesn't amplify the signal. what shall I use to replace the 2SK147?

Try 2SK369. Still available, though maybe not for long. The K369 has the largest Yfs, and gain, of any of the low-noise Toshibas - and they sound excellent in the MC first-stage position. IMO, you can ignore the popular demand for the BL or V grade of these, and use the easy-to-find GR version. 4 to 7mA is plenty low noise for most cartridges, and gain and sound quality excellent.

You can get even more gain, and better sound, if you connect them up as shunt-cascode - search in the Analogue Source forum for Werner's OP637 RIAA amp, with K369 first stage. This circuit gives an idea of what that JFET can really do. You can use passive RIAA eq, followed by a valve in the second stage.

Rod Coleman · 11th June 2011, 04:57 PM

I found Werner's circuit.

folded-cascode FET/opamp MC phono

Keep Q1 and all the parts to the LEFT of it. Throw out the op-amp.
Capacitor couple to the 6GK5 grid of the Toccata - you can delete the first stage Valve 5842.

This front end is lower noise, better sounding, and highly resistant to EMI and power line noise, compared to the original, IMHO.

bigpandahk · 12th June 2011, 06:33 AM

Thanks Rod

Will find some K369 and put in the Toccata first, and try your suggestion later to see which one sound better.

Rod Coleman · 12th June 2011, 07:52 AM

If you put the K369 in the Toccata, check that the 5842 Anode voltage appears as shown on Thorsten's drawing. This is very important - and it is also easy to adjust.

The 50 ohm resistor in the JFET source can be varied until the 8V drop across the 10K anode load resistor is correct.

bigpandahk · 12th June 2011, 08:03 AM

Hi Rod

You mentioned that voltages were shown on Thorsten's drawing, I can't find this drawing, can you show me the link? I would like to verify voltage on other stages.

Thanks

Rod Coleman · 12th June 2011, 08:08 AM

Hi, I am looking at the drawing you posted in post #1. Thunderstone is Thorsten's old Audio name.

The voltages I mean are 230V and 238V marked in the anode circuit of the 5842

bigpandahk · 12th June 2011, 08:12 AM

Oh,thanks

Those voltages are my measurement on my amp. I will check the voltage after replace the JFET.

Rod Coleman · 12th June 2011, 08:17 AM

If the values you measured are 230v and 238v, this means 0.8mA in the JFET. With a K369, try to get 4 to 6mA to flow (change the 50 ohm). The noise will reduce between 1 and 4mA and the sound will be better.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Diy Tube Phono Preamp	alexmoose	Tubes / Valves	39	11th December 2011 08:43 PM
What is the best DIY phono preamp projectY	Justinasia	Analogue Source	37	2nd December 2006 08:22 PM
Toccata Phono Preamp	Algar_emi	Tubes / Valves	19	11th November 2006 01:48 AM
Help for newbie building Toccata preamp	summilux	Tubes / Valves	3	26th November 2005 07:33 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

11th June 2011, 05:30 AM	#2
bigpandahk diyAudio Member Join Date: Jul 2009	After several trail, I find the cause of problem, since I couldn't find 2SK147, I use Vishay J/SST201 instead. May be it is not compatible with 2SK147, it doesn't amplify the signal. what shall I use to replace the 2SK147?

11th June 2011, 04:57 PM	#4
Rod Coleman работник diyAudio Member Join Date: Jul 2004 Location: Warwickshire UK	I found Werner's circuit. folded-cascode FET/opamp MC phono Keep Q1 and all the parts to the LEFT of it. Throw out the op-amp. Capacitor couple to the 6GK5 grid of the Toccata - you can delete the first stage Valve 5842. This front end is lower noise, better sounding, and highly resistant to EMI and power line noise, compared to the original, IMHO.

12th June 2011, 06:33 AM	#5
bigpandahk diyAudio Member Join Date: Jul 2009	Thanks Rod Will find some K369 and put in the Toccata first, and try your suggestion later to see which one sound better.

12th June 2011, 07:52 AM	#6
Rod Coleman работник diyAudio Member Join Date: Jul 2004 Location: Warwickshire UK	If you put the K369 in the Toccata, check that the 5842 Anode voltage appears as shown on Thorsten's drawing. This is very important - and it is also easy to adjust. The 50 ohm resistor in the JFET source can be varied until the 8V drop across the 10K anode load resistor is correct.

12th June 2011, 08:03 AM	#7
bigpandahk diyAudio Member Join Date: Jul 2009	Hi Rod You mentioned that voltages were shown on Thorsten's drawing, I can't find this drawing, can you show me the link? I would like to verify voltage on other stages. Thanks

12th June 2011, 08:08 AM	#8
Rod Coleman работник diyAudio Member Join Date: Jul 2004 Location: Warwickshire UK	Hi, I am looking at the drawing you posted in post #1. Thunderstone is Thorsten's old Audio name. The voltages I mean are 230V and 238V marked in the anode circuit of the 5842

12th June 2011, 08:12 AM	#9
bigpandahk diyAudio Member Join Date: Jul 2009	Oh,thanks Those voltages are my measurement on my amp. I will check the voltage after replace the JFET.

12th June 2011, 08:17 AM	#10
Rod Coleman работник diyAudio Member Join Date: Jul 2004 Location: Warwickshire UK	If the values you measured are 230v and 238v, this means 0.8mA in the JFET. With a K369, try to get 4 to 6mA to flow (change the 50 ohm). The noise will reduce between 1 and 4mA and the sound will be better.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)