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Hi all, I am building a new input switching board for my DIY preamp (using a couple of CMOS and relays). I made it so that I could connect each input direct or through a voltage divider. I did it so that I could use it as a passive attenuator for too hot sources. The input board is going to be...

They sound great, not fabulous but great. What I like best is the look and the omnidirectional qualities.

I think I got it now. This thread and this page gave me what I needed to figure it out. And this thread is giving me what I need to move forward. Ps. Still interested to know how to interpret the markings on the coils though.

Ps. I have learnt that the tweeter is a piezo and that it would explain the lack of a cap but I still don't get the coil for the tweeter?

I got a pair of BIC SoundSpan TPR-600 that I got from a friend (who bought them new in the 70s). I was considering an XO upgrade or to go active, so I took a look at the original XO. But I can't wrap my head around it! Please take a look at the attached image. Red wire to woofer, green to mid...

Thanks everyone, you really kept me going. It is now calibrated (trimpots worked perfectly but a bit finicky) and I have made some initial testing through AUX-1 and the phone jack. Sounds perfect apart from a faint hum (earth related?) on max volume. Feels great to have it up and running again! :)

OK, found the "error"... Feels almost ashamed to tell you... I traced E IN to the back plane thanks to friendly forum users on the Swedish www.faktiskt.io board. This is where it got really weird, my board seemed to have the 9P CIS connector at the wrong place, in the middle instead of to the...

Power Circuit Board seems to contain more than power though, phone jack, speaker selector, speaker protection (is that what relay MX2PO does?) etc. Not the exact same problem but Power Circuit Board apparently could affect one of the main amp boards as in this post...

I swapped sides of main amp board and the problem did not follow. So I guess the root cause is not on the amp board but somewhere downstream. DC rails seems OK (equal in voltage). Next stop Power Circuit Board I guess...

It has been in the "off" position all the time. Could it be further downstream? I will swap position with the main amp boards just to see if the problem follows the whole boards or not...

R607 = 389Ω R605 = 149.9Ω

I got some new measurements. Initially measuring the zener-diodes I measured between E (OUT), when measuring between E (IN) I get 12V and 0V on D601 and D603. Some further measurements against E (IN): Left side Tr601 base = 0.631V and right side Tr602 base = 0.163V Left side R611 towards VR601...

I have now swapped TR601/603 and TR602/604, the problem did not follow, it persisted on the left side (same midpoint voltage as before on both sides, about 0.5V on left side, 4mV on right side). Any other ideas?

No still the same problem with the midpoint, will work on it this weekend...

Ps. I was initially planning to use a pair of UKW1J472MRD (4700µF, 63V, D22, L50, P10) instead of the two MAL205158472E3 (4700µF, 63V, D30, L40, P17.5) I had to make adapters for. UKW1J472MRD would also need some type of support I guess...

You are right, it must be a cut-and-paste typo. I ended up buying everything from Digi-Key, here is the updated BOM (without Mouser No.): Filter Board ============ C505 & C506 (1µF, 35V, P3, tant); UFG1H010MDM (1µF, 50V, D5, L11, P2) C509 & C510 (100µF, 6.3V, D8, P4); UFG1E101MPM...

I have not made the swap yet but I made the following measurements: Main amp voltage: Left +B = 36.2V Left -B = -36.1V Right +B = 36.2V Right -B = -36.1V Left offset = -0.56V Right offset = -2.6mV Zener diodes: Left D601: cathode = 11.36V, anode = -1.79V Left D603: cathode = -1.09V, anode...

OMG you are right, I found it on the overall schematics diagram, RTFM... Thanks you so much. I will order some (and probably some new trimpots too) to be on the safe side. This will take some time since I am going skiing next week. I will post progress as soon as I get back working on it. To...

You said "swap 602/604 with 601/603". I can not find any 602/604 in the CA-600 service manual. Main amp boards are the same on both left and right side (only one schematic of "Main Amp Board) in the service manual. The main amp board got a Tr601 and a Tr603. Should I swap the Tr601 and a Tr603...

Yes off course, it should have been: 0.588V :oops:

OK, I took new measurements for both right and left side: Right side midpoint voltage started out at 30mV and slowly dropped to around 13mV after 3 minutes (service manual state 3 to 4 minutes warmup before measurement). The trimpots are really finicky and values jumps around as soon as I touch...

Thanks a lot for your help zaibatsu, the relay click on. I took measurement a while ago, it was quite tough, I got the feeling it was drifting a lot on both sides but blamed my meter (it is auto sensing). I have only replaced two transistors Tr607 (C458) on each Main Amp Board. Pinout should be...

Bump: Does anyone know what could be the cause of a high midpoint voltage in the CA-600? I have no idea where to start. Could Tr607 cause it? I should have, but I did not check the new pair of KSC1815YTA before I soldered them to the boards. I will order new trimpots and replace the old ones...

OK, all electrolytics replaced with new ones and both Tr607 (C458) replaced with two new KSC1815YTA. I put it together started it up, no smoke, great start. Amp coupler switch off, no speaker load, waited 3 minutes to set mid point voltage and bias current. This is where things got a bit...

Hi again everyone, here is a quick status update. I have tried to source the BOM for month in EU but there was always something on back order so I finally ordered from US. Digi-Key had everything in stock and delivered to my door in less than 3 days! Thanks Digi-Key you are just fabulous! I was...