Search found 122 matches
- 10 Mar 2024, 21:14
- Forum: Modern Stompbox Effects (1975 - ...)
- Topic: Wah Wah pedal switching
- Replies: 3
- Views: 507
Re: Wah Wah pedal switching
Thanks to you both. I was considering removing the footswitch and using a loop box to switch it in and out.
- 27 Feb 2024, 21:08
- Forum: Modern Stompbox Effects (1975 - ...)
- Topic: Wah Wah pedal switching
- Replies: 3
- Views: 507
Wah Wah pedal switching
The thing I really don't like with Wah Wah pedals is the on/off switch under the treadle, the way you can't avoid contact with it when you are working the treadle. I remember seeing a Wah Wah pedal with a slightly different design where the switch is under the treadle but there is a hole immediately...
- 24 Feb 2024, 19:15
- Forum: Amplifiers
- Topic: Mend-It Mark's cap discharger [schematic]
- Replies: 3
- Views: 14218
Re: Mend-It Mark's cap discharger [schematic]
He really knows his stuff. In a tape deck repair he actually rewound the motor. There is not much seems to stump him, taking on very complicated gear right across the spectrum. He repaired a chorus pedal with a faulty Reticon chip and was not amused when the chips he had all turned out to be fake. H...
- 18 Jan 2024, 20:53
- Forum: Pedal Debugging & Troubleshooting Support
- Topic: Rat - high pitched squeal
- Replies: 4
- Views: 686
Re: Rat - high pitched squeal
Try increasing the value of C12, 30pf. I recently repaired a Rat clone which had the same problem. I ended up using around 100pf and this solved the problem.
- 30 Dec 2023, 21:05
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
I’ve finally (almost) finished. Over Christmas I put an 8 ohm speaker I already had into a diy cabinet made out of an old melamine cupboard door. I’ve set this up with another speaker so I can sit in the middle and I am very pleased with the sound. It doesn’t need any extra pedals or even reverb and...
- 19 Dec 2023, 23:44
- Forum: Amplifiers
- Topic: Voltage Doubler for tube preamp
- Replies: 10
- Views: 3453
Re: Voltage Doubler for tube preamp
I have used back-to-back transformers a few times in the UK, using transformers with 12V secondaries to power the heaters in series. The problem is that with 240V, you end up with less than 200V under load for the HT supply, not enough for something like a Fender Champ. This is where a voltage doubl...
- 16 Dec 2023, 13:40
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
Sorry it didn’t work out for you. I can only guess that they selected specific MN3207s to work in the existing circuit. I don’t understand why they didn’t put in a bias adjuster. I must have spent nearly 2 weeks on that when I breadboarded it before I gave up and grafted in a different chorus design...
- 12 Dec 2023, 20:44
- Forum: Amplifiers
- Topic: Voltage Doubler for tube preamp
- Replies: 10
- Views: 3453
Re: Voltage Doubler for tube preamp
I also saw the Uncle Doug video and used the doubler in a Fender Champ build. It worked fine.
- 08 Dec 2023, 21:13
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
I have got it up and running now. I replaced the TDA2030s and both channels are working with chorus on one channel and the straight signal on the other. I changed the capacitor values C22 and C46 which connect to the 1K5 resistors on pin 2 of the TDA2030s to 22uf (from 4.7uf on the schematic). This ...
- 06 Dec 2023, 19:07
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
I connected the board up to the full transformer, a 2 x 15V toroidal and the voltage was too high, about +20v/-20V. I think I’ve cooked the TDA2030s in the process. I have changed over to a 2 x 10v transformer I already had and the voltages are lower, still too high for the MN3207. To sort this out,...
- 01 Dec 2023, 15:28
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
I have assembled the main board without the power chips for the moment. I tested it without the BBD chips to make sure the voltages were OK and I’m glad I did. I used a 12V bipolar power supply I had and while the other chips are getting about 9.3 volts, the sockets for the MN3207 and MN3102 are mea...
- 11 Nov 2023, 13:27
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
Would you like the Kicad files sent to you?
- 03 Nov 2023, 20:54
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
Excellent, this really helps.
- 03 Nov 2023, 11:08
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
Thanks. Are there any other pictures for the rest of the potentiometers? It would be good to confirm them as well. I’ve looked at the schematics for the JC-120, trying to make a comparison, and they are very different.
- 02 Nov 2023, 18:32
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
I’ve updating my Kicad schematic with the new chorus. I’ll start laying out the pcb next. Looking at the photos you provided, I noticed the distortion potentiometer, like the volume potentiometer, is marked “104B” which must mean 100k linear. The schematic gives the distortion pot as 25kA. You said ...
- 29 Oct 2023, 12:29
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
Thanks, I’ll change that resistor value. I’ve ordered in some TDA2030s which are supposed to be good substitutes for the upc1238s so the power amp is the next stage to try out.
- 28 Oct 2023, 13:17
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
OK, I’ve breadboarded the preamplifier section - it just about did my nut in, but it’s worth it when it finally works. I had real problems with the chorus and I spent literally days getting it working. I couldn’t get the original LFO to play nice with the MN3207 and in desperation I grafted the chor...
- 26 Oct 2023, 09:18
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
Thanks!
- 25 Oct 2023, 23:52
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
I’m making progress. I’ve breadboarded from the input up to “A” of the preamp. This has thrown up more queries though, R6 on IC 1 section 1 is listed as 68 ohms but the feedback resistor R8 is 68K. If I have got this right, this would give an amplification of 1000! I’m wondering whether R6 should be...
- 19 Oct 2023, 23:35
- Forum: Amplifiers
- Topic: Roland Jazz Chorus JC-20
- Replies: 38
- Views: 9595
Re: Roland Jazz Chorus JC-20
I’ve decided to try breadboarding the chorus section from C52 to point B. I’ll get back to you when I’ve done this.